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Welding Inspector
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Duties and Responsibilities
Section 1
Main Responsibilities 1.1
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• Code compliance
• Workmanship control
• Documentation control
Personal Attributes 1.1
Important qualities that good Inspectors are expected to have are:
•Honesty
•Integrity
•Knowledge
•Good communicator
•Physical fitness
•Good eyesight
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Standard for Visual Inspection 1.1
Basic Requirements
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BS EN 970 - Non-destructive examination of fusion
welds - Visual examination
Welding Inspection Personnel should:
• be familiar with relevant standards, rules and specifications
applicable to the fabrication work to be undertaken
• be informed about the welding procedures to be used
• have good vision (which should be checked every 12
months)
Welding Inspection 1.2
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Conditions for Visual Inspection (to BS EN 970)
Illumination:
• 350 lux minimum required
• (recommends 500 lux - normal shop or office lighting)
Vision Access:
• eye should be within 600mm of the surface
• viewing angle (line from eye to surface) to be not less than
30°
30°
600mm
Welding Inspection 1.3
Aids to Visual Inspection (to BS EN 970)
When access is restricted may use: • a mirrored boroscope• a fibre optic viewing system
Other aids:• welding gauges (for checking bevel angles, weld profile, fillet
sizing, undercut depth)• dedicated weld-gap gauges and linear misalignment (high-low)
gauges• straight edges and measuring tapes• magnifying lens (if magnification lens used it should have
magnification between X2 to X5)
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usually by
agreement}
Welding Inspectors Equipment 1.3
Measuring devices:
• flexible tape, steel rule
• Temperature indicating crayons
• Welding gauges
• Voltmeter
• Ammeter
• Magnifying glass
• Torch / flash light
• Gas flow-meter
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Welding Inspectors Gauges 1.3
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TWI Multi-purpose Welding Gauge Misalignment Gauges
Hi-Lo Gauge
Fillet Weld Gauges
G.A.L.
S.T.D.
10mm
16mm
L
G.A.L.
S.T.D.
10mm
16mm
01/4 1/2 3/4
IN
HI-
LO
S
ing
le P
urp
os
e W
eld
ing
Ga
ug
e
1
2
3
4
5
6
Welding Inspectors Equipment 1.3
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Tong Tester
AmmeterVoltmeter
Welding Inspection 1.3
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Stages of Visual Inspection (to BS EN 970)
Extent of examination and when required should be defined in
the application standard or by agreement between the
contracting parties
For high integrity fabrications inspection required throughout
the fabrication process:
Before welding
(Before assemble & After assembly)
During welding
After welding
Typical Duties of a Welding Inspector 1.5
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Before Welding
Preparation:
Familiarisation with relevant „documents‟…
• Application Standard/Code - for visual acceptance
requirements
• Drawings - item details and positions/tolerances etc
• Quality Control Procedures - for activities such as material
handling, documentation control, storage & issue of
welding consumables
• Quality Plan/Inspection & Test Plan/Inspection Checklist -
details of inspection requirements, inspection procedures
& records required
Typical Duties of a Welding Inspector 1.5
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Before Welding
Welding Procedures:
• are applicable to joints to be welded & approved
• are available to welders & inspectors
Welder Qualifications:
• list of available qualified welders related to WPS‟s
• certificates are valid and ‘in-date’
Typical Duties of a Welding Inspector 1.5
Before Welding
Equipment:
• all inspection equipment is in good condition & calibrated as necessary
• all safety requirements are understood & necessary equipment available
Materials:
• can be identified & related to test certificates, traceability !
• are of correct dimensions
• are in suitable condition (no damage/contamination)
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Typical Duties of a Welding Inspector 1.5
Before Welding
Consumables:
• in accordance with WPS’s
• are being controlled in accordance with Procedure
Weld Preparations:
• comply with WPS/drawing
• free from defects & contamination
Welding Equipment:
• in good order & calibrated as required by Procedure
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Typical Duties of a Welding Inspector 1.5
Before Welding
Fit-up
• complies with WPS
• Number / size of tack welds to Code / good workmanship
Pre-heat
• if specified
• minimum temperature complies with WPS
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Typical Duties of a Welding Inspector 1.5
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During Welding
Weather conditions
• suitable if site / field welding
Welding Process(es)
• in accordance with WPS
Welder
• is approved to weld the joint
Pre-heat (if required)
• minimum temperature as specified by WPS
• maximum interpass temperature as WPS
Typical Duties of a Welding Inspector 1.6
During Welding
Welding consumables
• in accordance with WPS
• in suitable condition
• controlled issue and handling
Welding Parameters
• current, voltage & travel speed – as WPS
Root runs
• if possible, visually inspect root before single-sided welds are filled up
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Typical Duties of a Welding Inspector 1.6
During Welding
Inter-run cleaning
in accordance with an approved method (& back gouging) to good workmanship standard
Distortion control
• welding is balanced & over-welding is avoided
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Typical Duties of a Welding Inspector 1.6
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After Welding
Weld Identification
• identified/numbered as required
• is marked with welder‟s identity
Visual Inspection
• ensure weld is suitable for all NDT
• visually inspect & „sentence‟ to Code requirements
Dimensional Survey
• ensure dimensions comply with Code/drawing
Other NDT
• ensure all NDT is completed & reports available
Typical Duties of a Welding Inspector 1.6
After Welding
Repairs
• monitor repairs to ensure compliance with Procedure, ensure NDT after repairs is completed
• PWHT
• monitor for compliance with Procedure
• check chart records confirm Procedure compliance
Pressure / Load Test
• ensure test equipment is suitably calibrated
• monitor to ensure compliance with Procedure
• ensure all records are available
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Typical Duties of a Welding Inspector 1.6
After Welding
Documentation
• ensure any modifications are on ‘as-built’ drawings
• ensure all required documents are available
• Collate / file documents for manufacturing records
• Sign all documentation and forward it to QC department.
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Summary of Duties
A Welding Inspector must:
• ObserveTo observe all relevant actions related to weld quality throughout production.
• RecordTo record, or log all production inspection points relevant to quality, including a final report showing all identified imperfections
• CompareTo compare all recorded information with the acceptance criteria and any other relevant clauses in the applied application standard
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It is the duty of a Welding Inspector to ensure all the welding and
associated actions are carried out in accordance with the
specification and any applicable procedures.
Welding Inspector
Terms & Definitions
Section 2
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Welding Terminology & Definitions 2.1
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What is a Weld?
• A localised coalescence of metals or non-metals produced
either by heating the materials to the welding temperature,
with or without the application of pressure, or by the
application of pressure alone (AWS)
• A permanent union between materials caused by heat, and
or pressure (BS499)
• An Autogenous weld:
A weld made with out the use of a filler material and can
only be made by TIG or Oxy-Gas Welding
Welding Terminology & Definitions 2.1
What is a Joint?
• The junction of members or the edges of members that are to be joined or have been joined (AWS)
• A configuration of members (BS499)
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Joint Terminology 2.2
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Edge Open & Closed Corner Lap
Tee ButtCruciform
Welded Butt Joints 2.2
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A_________Welded butt jointButt
A_________Welded butt jointFillet
A____________Welded butt jointCompound
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Welded Tee Joints 2.2
A_________Welded T jointFillet
A_________Welded T jointButt
A____________Welded T jointCompound
Weld Terminology 2.3
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Compound weld
Fillet weldButt weld
Edge weld
Spot weld
Plug weld
Butt Preparations – Sizes 2.4
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Full Penetration Butt Weld
Partial Penetration Butt Weld
Design Throat
Thickness
Design Throat
Thickness
Actual Throat
Thickness
Actual Throat
Thickness
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Weld Zone Terminology 2.5
Weld Boundary
C
A B
D
Heat Affected Zone
Root
Weld metal
A, B, C & D = Weld Toes
Face
Weld Zone Terminology 2.5
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Excess Root Penetration
ExcessCap heightor Weld Reinforcement
Weld cap width
Design
Throat
Thickness
Actual Throat
Thickness
Heat Affected Zone (HAZ) 2.5
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tempered zone
grain growth zone
recrystallised zone
partially transformed zone
Maximum
Temperature
solid-liquid Boundarysolid
weld
metal
unaffected base
material
Joint Preparation Terminology 2.7
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Included angle
Root Gap
Root Face
Angle of
bevel
Root FaceRoot Gap
Included angle
Root
Radius
Single-V Butt Single-U Butt
Joint Preparation Terminology 2.8 & 2.9
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Root Gap
Root Face Root FaceRoot Gap
Root
Radius
Single Bevel Butt Single-J Butt
Angle of bevel Angle of bevel
Land
Single Sided Butt Preparations 2.10
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Single Bevel Single Vee
Single-J Single-U
Single sided preparations are normally made on thinner materials, or
when access form both sides is restricted
Double Sided Butt Preparations 2.11
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Double sided preparations are normally made on thicker materials, or
when access form both sides is unrestricted
-VeeDouble-BevelDouble
- JDouble - UDouble
Weld Preparation
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Terminology & Typical Dimensions: V-Joints
bevel angle
root face
root gap
included angle
Typical Dimensions
bevel angle 30 to 35°
root face ~1.5 to ~2.5mm
root gap ~2 to ~4mm
Butt Weld - Toe Blend
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6 mm
80
Poor Weld Toe Blend Angle
Improved Weld Toe Blend
Angle
20
3 mm
•Most codes quote the weld
toes shall blend smoothly
•This statement is not
quantitative and therefore
open to individual
interpretation
•The higher the toe blend
angle the greater the
amount of stress
concentration
•The toe blend angle ideally
should be between 20o-30o
Fillet Weld Features 2.13
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Design
Throat
Vertical
Leg
Length
Horizontal leg
Length
Excess
Weld
Metal
Fillet Weld Throat Thickness 2.13
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ba
b = Actual Throat Thickness
a = Design Throat Thickness
Deep Penetration Fillet Weld Features 2.13
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ba
b = Actual Throat Thickness
a = Design Throat Thickness
Fillet Weld Sizes 2.14
Calculating Throat Thickness from a known Leg Length:
Design Throat Thickness = Leg Length x 0.7
Question: The Leg length is 14mm.
What is the Design Throat?
Answer: 14mm x 0.7 = 10mm Throat Thickness
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Fillet Weld Sizes 2.14
Calculating Leg Length from a known Design ThroatThickness:
Leg Length = Design Throat Thickness x 1.4
Question: The Design Throat is 10mm.
What is the Leg length?
Answer: 10mm x 1.4 = 14mm Leg Length
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Features to Consider 2 2.14
Importance of Fillet Weld Leg Length Size
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Approximately the same weld volume in both Fillet
Welds, but the effective throat thickness has been
altered, reducing considerably the strength of weld B
2mm
(b)
4mm
8mm
(a)
4mm
Fillet Weld Sizes 2.14
Importance of Fillet weld leg length Size
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Area = 4 x 4 =
8mm2
2
Area = 6 x 6 =
18mm2
2
The c.s.a. of (b) is over double the area of (a) without the extra
excess weld metal being added
4mm 6mm
(a) (b)
4mm 6mm
(a) (b)
Excess
Excess
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Fillet Weld Profiles 2.15
Mitre Fillet Convex Fillet
Concave Fillet
A concave profile
is preferred for
joints subjected to
fatigue loading
Fillet welds - Shape
EFFECTIVE THROAT THICKNESS
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“s” = Effective throat thickness
sa
“a” = Nominal throat thickness
Deep penetration fillet welds from high heat
input welding process MAG, FCAW & SAW etc
Fillet Features to Consider 2.15
Welding Positions 2.17
PA 1G / 1F Flat / Downhand
PB 2F Horizontal-Vertical
PC 2G Horizontal
PD 4F Horizontal-Vertical (Overhead)
PE 4G Overhead
PF 3G / 5G Vertical-Up
PG 3G / 5G Vertical-Down
H-L045 6G Inclined Pipe (Upwards)
J-L045 6G Inclined Pipe (Downwards)
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Welding Positions 2.17
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ISO
Welding position designation 2.17
Butt welds in plate (see ISO 6947)
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Flat - PA Overhead - PE
Vertical
up - PF
Vertical
down - PG
Horizontal - PC
Welding position designation 2.17
Butt welds in pipe (see ISO 6947)
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Flat - PA
axis: horizontal
pipe: rotated
H-L045
axis: inclined at 45°
pipe: fixed
Horizontal - PC
axis: vertical
pipe: fixed
Vertical up - PF
axis: horizontal
pipe: fixed
Vertical down - PG
axis: horizontal
pipe: fixed
J-L045
axis: inclined at 45°
pipe: fixed
Welding position designation 2.17
Fillet welds on plate (see ISO 6947)
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Flat - PA Overhead - PD
Vertical up - PF Vertical down - PG
Horizontal - PB
Welding position designation 2.17
Fillet welds on pipe (see ISO 6947)
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Flat - PA axis: inclined at 45°
pipe: rotated
Overhead - PD axis: vertical
pipe: fixed
Vertical up - PF axis: horizontal
pipe: fixed
Vertical down - PG axis: horizontal
pipe: fixed
Horizontal - PB axis: vertical
pipe: fixed
Horizontal - PB axis: horizontal
pipe: rotated
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Plate/Fillet Weld Positions 2.17
PA / 1GPA / 1F
PC / 2GPB / 2F
PD / 4FPE / 4G PG / 3G
PF / 3G
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Pipe Welding Positions 2.17
Weld: Flat
Pipe: rotated
Axis: Horizontal
PA / 1G
Weld: Vertical Downwards
Pipe: Fixed
Axis: Horizontal
PG / 5G
Weld: Vertical upwards
Pipe: Fixed
Axis: Horizontal
PF / 5G
Weld: Upwards
Pipe: Fixed
Axis: Inclined
Weld: Horizontal
Pipe: Fixed
Axis: Vertical
PC / 2G
45o
Weld: Downwards
Pipe: Fixed
Axis: Inclined
J-LO 45 / 6G
45o
H-LO 45 / 6G
Travel Speed Measurement 2.18
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Definition: the rate of weld progression
measured in case of mechanised and automatic
welding processes
in case of MMA can be determined using ROL and arc
time
Welding Inspector
Welding Imperfections
Section 3
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Welding Imperfections 3.1
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All welds have imperfections
• Imperfections are classed as defects when they are of a
type, or size, not allowed by the Acceptance Standard
A defect is an unacceptable imperfection
• A weld imperfection may be allowed by one Acceptance
Standard but be classed as a defect by another Standard
and require removal/rectification
Welding Imperfections 3.1
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Standards for Welding Imperfections
BS EN ISO 6520-1(1998) Welding and allied processes –
Classification of geometric
imperfections in metallic materials -
Part 1: Fusion welding
Imperfections are classified into 6 groups, namely:
1 Cracks
2 Cavities
3 Solid inclusions
4 Lack of fusion and penetration
5 Imperfect shape and dimensions
6 Miscellaneous imperfections
Welding Imperfections 3.1
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Standards for Welding Imperfections
EN ISO 5817 (2003) Welding - Fusion-welded joints in steel,
nickel, titanium and their alloys (beam
welding excluded) - Quality levels for
imperfections
This main imperfections given in EN ISO 6520-1 are listed in
EN ISO 5817 with acceptance criteria at 3 levels, namely
Level B (highest)
Level C (intermediate)
Level D (general)
This Standard is „directly applicable to visual testing of welds‟
...(weld surfaces & macro examination)
Welding imperfections 3.1
classification
Cracks
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Cracks 3.1
Cracks that may occur in welded materials are caused generally by many factors and may be classified by shape and position.
Note: Cracks are classed as Planar Defects.
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Classified by Shape
•Longitudinal
•Transverse
•Chevron
•Lamellar Tear
Classified by Position
•HAZ
•Centerline
•Crater
•Fusion zone
•Parent metal
Cracks 3.1
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Longitudinal parent metal
Longitudinal weld metal
Lamellar tearing
Transverse weld metal
Cracks 3.1
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Transverse crack Longitudinal crack
Cracks 3.2
Main Crack Types
• Solidification Cracks
• Hydrogen Induced Cracks
• Lamellar Tearing
• Reheat cracks
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Cracks 3.2
Solidification Cracking
• Occurs during weld solidification process
• Steels with high sulphur impurities content (low ductility at elevated temperature)
• Requires high tensile stress
• Occur longitudinally down centre of weld
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Cracks 3.3
Hydrogen Induced Cold Cracking
• Requires susceptible hard grain structure, stress, low temperature and hydrogen
• Hydrogen enters weld via welding arc mainly as result of contaminated electrode or preparation
• Hydrogen diffuses out into parent metal on cooling
• Cracking developing most likely in HAZ
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Lamellar Tearing 3.5
• Location: Parent metal
• Steel Type: Any steel type possible
• Susceptible Microstructure: Poor through thickness ductility
• Lamellar tearing has a step like appearance due to the solid inclusions in the parent material (e.g. sulphides and silicates) linking up under the influence of welding stresses
• Low ductile materials in the short transverse direction containing high levels of impurities are very susceptible to lamellar tearing
• It forms when the welding stresses act in the short transverse direction of the material (through thickness direction)
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Gas Cavities 3.6
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Root piping
Cluster porosityGas pore
Blow hole
Herringbone porosity
Gas pore <1.5mm
Blow hole.>1.6mm
Causes:
•Loss of gas shield
•Damp electrodes
•Contamination
•Arc length too large
•Damaged electrode flux
•Moisture on parent material
•Welding current too low
Gas Cavities 3.7
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Root piping
Porosity
Gas Cavities 3.8
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Cluster porosity Herringbone porosity
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Crater pipe
Weld crater
Crater Pipe 3.9
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Crater pipe is a shrinkage defect and not a gas defect, it has
the appearance of a gas pore in the weld crater
Causes:
• Too fast a cooling
rate
• Deoxidization
reactions and
liquid to solid
volume change
• Contamination
Crater cracks
(Star cracks)
Crater pipe
Crater Pipe 3.9
Solid Inclusions 3.10
Slag inclusions are defined as a non-metallic inclusion caused by some welding process
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Causes:
•Slag originates from
welding flux
•MAG and TIG welding
process produce silica
inclusions
•Slag is caused by
inadequate cleaning
•Other inclusions include
tungsten and copper
inclusions from the TIG
and MAG welding process
Slag inclusions
Parallel slag lines
Lack of sidewall fusion with
associated slag
Lack of interun
fusion + slag
Solid Inclusions 3.11
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Elongated slag linesInterpass slag inclusions
Welding Imperfections 3.13
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Typical Causes of Lack of Fusion:
• welding current too low
• bevel angle too steep
• root face too large (single-sided weld)
• root gap too small (single-sided weld)
• incorrect electrode angle
• linear misalignment
• welding speed too high
• welding process related – particularly dip-transfer GMAW
• flooding the joint with too much weld metal (blocking Out)
Lack of Fusion 3.13
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Incomplete filled groove +
Lack of sidewall fusion
1
2
1. Lack of sidewall fusion
2. Lack of inter-run fusion
Causes:
•Poor welder skill
• Incorrect electrode
manipulation
• Arc blow
• Incorrect welding
current/voltage
• Incorrect travel speed
• Incorrect inter-run cleaning
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Lack of sidewall fusion + incomplete filled groove
Lack of Fusion 3.13
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Weld Root Imperfections 3.15
Lack of Root FusionLack of Root Penetration
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Cap Undercut 3.18
Intermittent Cap Undercut
Undercut 3.18
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Cap undercutRoot undercut
Surface and Profile 3.19
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Incomplete filled groove Poor cap profile
Excessive cap height
Poor cap profiles and
excessive cap reinforcements
may lead to stress
concentration points at the
weld toes and will also
contribute to overall poor toe
blend
Surface and Profile 3.19
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Incomplete filled grooveExcess cap reinforcement
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Excessive root
penetration
Weld Root Imperfections 3.20
Overlap 3.21
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An imperfection at the toe or root of a weld caused by metal
flowing on to the surface of the parent metal without fusing to it
Causes:
•Contamination
•Slow travel speed
•Incorrect welding
technique
•Current too low
Overlap 3.21
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Toe Overlap
Toe Overlap
Set-Up Irregularities 3.22
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Plate/pipe Linear Misalignment
(Hi-Lo)
Angular Misalignment
Linear misalignment is
measured from the lowest
plate to the highest point.
Angular misalignment is
measured in degrees
Set-Up Irregularities 3.22
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Linear Misalignment
Set-Up Irregularities 3.22
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Linear Misalignment
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Lack of sidewall fusion + incomplete filled groove
Incomplete Groove 3.23
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Concave Root
Causes:
• Excessive back purge
pressure during TIG welding
Excessive root bead grinding
before the application of the
second pass
welding current too high for
2nd pass overhead welding
root gap too large - excessive
„weaving‟
A shallow groove, which may occur in the root of a butt weld
Weld Root Imperfections 3.24
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Concave Root
Weld Root Imperfections 3.24
Weld Root Imperfections 3.24
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Concave root Excess root penetration
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Causes:
• High Amps/volts
• Small Root face
• Large Root Gap
• Slow Travel
SpeedBurn through
A localized collapse of the weld pool due to excessive
penetration resulting in a hole in the root run
Weld Root Imperfections 3.25
Weld Root Imperfections 3.25
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Burn Through
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Causes:
• Loss or insufficient
back purging gas (TIG)
• Most commonly occurs
when welding stainless
steels
• Purging gases include
argon, helium and
occasionally nitrogen
Oxidized Root (Root Coking)
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Miscellaneous Imperfections 3.26
Arc strike
Causes:
• Accidental striking of the
arc onto the parent
material
• Faulty electrode holder
• Poor cable insulation
• Poor return lead
clamping
Miscellaneous Imperfections 3.27
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Causes:
• Excessive current
• Damp electrodes
• Contamination
• Incorrect wire feed
speed when welding
with the MAG welding
process
• Arc blowSpatter
Mechanical Damage 3.28
Mechanical damage can be defined as any surface material
damage cause during the manufacturing process.
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• Grinding
• Hammering
• Chiselling
• Chipping
• Breaking off welded attachments
(torn surfaces)
• Using needle guns to compress
weld capping runs
Mechanical Damage 3.28
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Mechanical Damage/Grinding Mark
Chipping Marks
Welding Inspector
Destructive Testing
Section 4
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Qualitative and Quantitative Tests 4.1
The following mechanical tests have units and are termedquantitative tests to measure Mechanical Properties
• Tensile tests (Transverse Welded Joint, All Weld Metal)
• Toughness testing (Charpy, Izod, CTOD)
• Hardness tests (Brinell, Rockwell, Vickers)
The following mechanical tests have no units and are termed
qualitative tests for assessing joint quality
• Macro testing
• Bend testing
• Fillet weld fracture testing
• Butt weld nick-break testing
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Mechanical Test Samples 4.1
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Tensile Specimens
Fracture Fillet
Specimen
CTOD Specimen
Charpy Specimen
Bend Test
Specimen
Destructive Testing 4.1
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Typical Positions for Test
Pieces
Specimen Type Position
•Macro + Hardness 5
•Transverse Tensile 2, 4
•Bend Tests 2, 4
•Charpy Impact Tests 3
•Additional Tests 3
WELDING PROCEDURE QUALIFICATION TESTING
2
3
4
5
top of fixed pipe
Definitions
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• Malleability
• Ductility
• Toughness
• Hardness
• Tensile Strength
Ability of a material to
withstand deformation
under static compressive
loading without rupture
Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.
Definitions
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• Malleability
• Ductility
• Toughness
• Hardness
• Tensile Strength
Ability of a material
undergo plastic
deformation under static
tensile loading without
rupture. Measurable
elongation and reduction
in cross section area
Mechanical Properties of metals are related to the amount of
deformation which metals can withstand under different
circumstances of force application.
Definitions
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• Malleability
• Ductility
• Toughness
• Hardness
• Tensile Strength
Ability of a material to
withstand bending or the
application of shear
stresses by impact loading
without fracture.
Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.
Definitions
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• Malleability
• Ductility
• Toughness
• Hardness
• Tensile Strength
Measurement of a
materials surface
resistance to indentation
from another material by
static load
Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.
Definitions
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• Malleability
• Ductility
• Toughness
• Hardness
• Tensile Strength
Measurement of the
maximum force required to
fracture a materials bar of
unit cross-sectional area in
tension
Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.
Transverse Joint Tensile Test 4.2
Weld on plate
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Multiple cross joint
specimensWeld on pipe
Tensile Test 4.3
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All-Weld Metal Tensile
Specimen
Transverse Tensile
Specimen
STRA (Short Transverse Reduction Area)For materials that may be subject to Lamellar Tearing
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UTS Tensile test 4.4
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Charpy V-Notch Impact Test 4.5
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Objectives:
• measuring impact strength in different weld joint areas
• assessing resistance toward brittle fracture
Information to be supplied on the test report:
• Material type
• Notch type
• Specimen size
• Test temperature
• Notch location
• Impact Strength Value
Ductile / Brittle Transition Curve 4.6
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- 50 0- 20 - 10- 40 - 30
Ductile fracture
Ductile/Brittletransition point
47 Joules
28 Joules
Testing temperature - Degrees Centigrade
Temperature range
Transition range
Brittle fracture
Three specimens are normally tested at each temperature
Energy absorbed
Comparison Charpy Impact Test Results 4.6
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Impact Energy Joules
Room Temperature -20oC Temperature
1. 197 Joules
2. 191 Joules
3. 186 Joules
1. 49 Joules
2. 53 Joules
3. 51 Joules
Average = 191 Joules Average = 51 Joules
The test results show the specimens carried out at room
temperature absorb more energy than the specimens carried
out at -20oC
Charpy V-notch impact test specimen 4.7
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Specimen dimensions according ASTM E23
ASTM: American Society of Testing Materials
Charpy V-Notch Impact Test 4.8
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Specime
n
Pendulu
m
(striker)
Anvil (support)
Charpy Impact Test 4.9
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10 mm8 m
m2
mm
22.5o
Machined
notch
100% DuctileMachined
notch
Large reduction
in area, shear
lips
Fracture surface
100% bright
crystalline brittle
fracture
Randomly torn,
dull gray fracture
surface
100% Brittle
Hardness Testing 4.10
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Definition
Measurement of resistance of a material against
penetration of an indenter under a constant load
There is a direct correlation between UTS and
hardness
Hardness tests:
Brinell
Vickers
Rockwell
Hardness Testing 4.10
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Objectives:
• measuring hardness in different areas of a welded joint
• assessing resistance toward brittle fracture, cold cracking
and corrosion sensitivity within a H2S (Hydrogen Sulphide)
environment.
Information to be supplied on the test report:
• material type
• location of indentation
• type of hardness test and load applied on the indenter
• hardness value
Vickers Hardness Test 4.11
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Vickers hardness tests:
indentation body is a square based diamond pyramid
(136º included angle)
the average diagonal (d) of the impression is
converted to a hardness number from a table
it is measured in HV5, HV10 or HV025Adjustable shuttersIndentationDiamond
indentor
Vickers Hardness Test Machine 4.11
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Brinell Hardness Test 4.11
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• Hardened steel ball of given diameter is subjected for
a given time to a given load
• Load divided by area of indentation gives Brinell
hardness in kg/mm2
• More suitable for on site hardness testing
30KN
Ø=10mm
steel ball
Rockwell Hardness Test
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1KN
Ø=1.6mm
steel ball
Rockwell B Rockwell C
1.5KN
120 Diamond
Cone
Hardness Testing 4.12
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Hardness Test Methods Typical Designations
Vickers 240 HV10
Rockwell Rc 22
Brinell 200 BHN-W
usually the hardest region
1.5 to 3mm
HAZ
fusion line
or
fusion
boundary
Hardness specimens can also be used for CTOD samples
Crack Tip Opening Displacement testing 4.12
• Test is for fracture toughness
• Square bar machined with a notch placed in the centre.
• Tested below ambient temperature at a specified temperature.
• Load is applied at either end of the test specimen in an attempt to open a crack at the bottom of the notch
• Normally 3 samples
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Fatigue Fracture 4.13
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Location: Any stress concentration area
Steel Type: All steel types
Susceptible Microstructure: All grain structures
Test for Fracture Toughness is CTOD
(Crack Tip Opening Displacement)
Fatigue Fracture 4.13
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• Fatigue cracks occur under cyclic stress conditions
• Fracture normally occurs at a change in section, notch
and weld defects i.e stress concentration area
• All materials are susceptible to fatigue cracking
• Fatigue cracking starts at a specific point referred to as
a initiation point
• The fracture surface is smooth in appearance
sometimes displaying beach markings
• The final mode of failure may be brittle or ductile or a
combination of both
Fatigue Fracture
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• Toe grinding, profile grinding.
• The elimination of poor profiles
• The elimination of partial penetration welds and weld
defects
• Operating conditions under the materials endurance limits
• The elimination of notch effects e.g. mechanical damage
cap/root undercut
• The selection of the correct material for the service
conditions of the component
Precautions against Fatigue Cracks
Fatigue Fracture
Fatigue fracture occurs in structures subject to repeated application of tensile stress.
Crack growth is slow (in same cases, crack may grow into an area of low stress and stop without failure).
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Fatigue Fracture
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Initiation points / weld defects
Fatigue fracture surface
smooth in appearance
Secondary mode of failure
ductile fracture rough fibrous
appearance
Fatigue Fracture
• Crack growth is slow
• It initiate from stress concentration points
• load is considerably below the design or yield stress level
• The surface is smooth
• The surface is bounded by a curve
• Bands may sometimes be seen on the smooth surface –”beachmarks”. They show the progress of the crack front from the point of origin
• The surface is 90° to the load
• Final fracture will usually take the form of gross yielding (as the maximum stress in the remaining ligament increase!)
• Fatigue crack need initiation + propagation periods
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Fatigue fracture distinguish features:
Bend Tests 4.15
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Object of test:
• To determine the soundness of the weld zone. Bend
testing can also be used to give an assessment of
weld zone ductility.
• There are three ways to perform a bend test:
Root bend
Face bend
Side bend
Side bend tests are normally carried out on welds over 12mm in thickness
Bending test 4.16
Types of bend test for welds (acc. BS EN 910):
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Thickness of material - “t”
“t” up to 12 mm
“t” over 12 mm
Root / face
bend
Side bend
Fillet Weld Fracture Tests 4.17
Object of test:
• To break open the joint through the weld to permit examination of the fracture surfaces
• Specimens are cut to the required length
• A saw cut approximately 2mm in depth is applied along the fillet welds length
• Fracture is usually made by striking the specimen with a single hammer blow
• Visual inspection for defects
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Fillet Weld Fracture Tests 4.17
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Fracture should break weld saw cut to root
2mm
Notch
Hammer
Fillet Weld Fracture Tests 4.17
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This fracture indicates
lack of fusion
This fracture has
occurred saw cut to root
Lack of Penetration
Nick-Break Test 4.18
Object of test:
• To permit evaluation of any weld defects across the fracture surface of a butt weld.
•Specimens are cut transverse to the weld
•A saw cut approximately 2mm in depth is applied along the welds root and cap
•Fracture is usually made by striking the specimen with a single hammer blow
•Visual inspection for defects
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Nick-Break Test 4.18
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Approximately 230 mm
19 mm
2 mm
2 mm
Notch cut by hacksaw
Weld reinforcement
may or may not be
removed
Nick Break Test 4.18
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Inclusions on fracture
lineLack of root penetration
or fusion
Alternative nick-break test
specimen, notch applied all
way around the specimen
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We test welds to establish minimum levels of mechanical
properties, and soundness of the welded joint
We divide tests into Qualitative & Quantitative methods:
Qualitative: (Have no units/numbers)
For assessing joint quality
Macro tests
Bend tests
Fillet weld fracture tests
Butt Nick break tests
Quantitative: (Have units/numbers)
To measure mechanical properties
Hardness (VPN & BHN)
Toughness (Joules & ft.lbs)
Strength (N/mm2 & PSI, MPa)
Ductility / Elongation (E%)
Summary of Mechanical Testing 4.19
Welding Inspector
WPS – Welder Qualifications
Section 5
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Welding Procedure Qualification 5.1
Question:
What is the main reason for carrying out a Welding Procedure
Qualification Test ?
(What is the test trying to show ?)
Answer:
To show that the welded joint has the properties* that satisfy
the design requirements (fit for purpose)
* properties
•mechanical properties are the main interest - always strength but
toughness & hardness may be important for some applications
•test also demonstrates that the weld can be made without defects
Welding Procedures 5.1
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Producing a welding procedure involves:
• Planning the tasks
• Collecting the data
• Writing a procedure for use of for trial
• Making a test welds
• Evaluating the results
• Approving the procedure
• Preparing the documentation
Welding Procedures 5.2
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In most codes reference is made to how the procedure are to
be devised and whether approval of these procedures is
required.
The approach used for procedure approval depends on the
code:
Example codes:
• AWS D.1.1: Structural Steel Welding Code
• BS 2633: Class 1 welding of Steel Pipe Work
• API 1104: Welding of Pipelines
• BS 4515: Welding of Pipelines over 7 Bar
Other codes may not specifically deal with the requirement of
a procedure but may contain information that may be used in
writing a weld procedure
• EN 1011Process of Arc Welding Steels
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The welding engineer writes qualified Welding Procedure
Specifications (WPS) for production welding
Welding Procedure Qualification 5.3
Production welding conditions must remain within the range of
qualification allowed by the WPQR
(according to EN ISO 15614)
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Welding Procedure Qualification 5.3
(according to EN Standards)
welding conditions are called welding variables
welding variables are classified by the EN ISO Standard as:
•Essential variables
•Non-essential variables
•Additional variables
Note: additional variables = ASME supplementary essential
The range of qualification for production welding is based on
the limits that the EN ISO Standard specifies for essential
variables*
(* and when applicable - the additional variables)
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Welding Procedure Qualification 5.3
(according to EN Standards)
WELDING ESSENTIAL VARIABLES
Question:
Why are some welding variables classified as essential ?
Answer:
A variable, that if changed beyond certain limits (specified by
the Welding Standard) may have a significant effect on the
properties* of the joint
* particularly joint strength and ductility
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Welding Procedure Qualification 5.3
(according to EN Standards)
SOME TYPICAL ESSENTIAL VARIABLES
• Welding Process
• Post Weld Heat Treatment (PWHT)
• Material Type
• Electrode Type, Filler Wire Type (Classification)
• Material Thickness
• Polarity (AC, DC+ve / DC-ve)
• Pre-Heat Temperature
• Heat Input
• Welding Position
Welding Procedures 5.3
Components of a welding procedure
Parent material• Type (Grouping)
• Thickness
• Diameter (Pipes)
• Surface condition)
Welding process• Type of process (MMA, MAG, TIG, SAW etc)
• Equipment parameters
• Amps, Volts, Travel speed
Welding Consumables• Type of consumable/diameter of consumable
• Brand/classification
• Heat treatments/ storage
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Welding Procedures 5.3
Components of a welding procedure
Joint design•Edge preparation
•Root gap, root face
•Jigging and tacking
•Type of baking
Welding Position•Location, shop or site
•Welding position e.g. 1G, 2G, 3G etc
•Any weather precaution
Thermal heat treatments•Preheat, temps
•Post weld heat treatments e.g. stress relieving
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Welding Procedures 5.3
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Object of a welding procedure test
To give maximum confidence that the welds mechanical
and metallurgical properties meet the requirements of the
applicable code/specification.
Each welding procedure will show a range to which the
procedure is approved (extent of approval)
If a customer queries the approval evidence can be
supplied to prove its validity
Welding Procedures
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Summary of designations:
pWPS: Preliminary Welding Procedure Specification
(Before procedure approval)
WPAR (WPQR): Welding Procedure Approval Record
(Welding procedure Qualification record)
WPS: Welding Procedure Specification
(After procedure approval)
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Example:
Welding
Procedure
Specification
(WPS)
Welder Qualification 5.4
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Numerous codes and standards deal with welder qualification,
e.g. BS EN 287.
• Once the content of the procedure is approved the next
stage is to approve the welders to the approved procedure.
• A welders test know as a Welders Qualification Test (WQT).
Object of a welding qualification test:
• To give maximum confidence that the welder meets the
quality requirements of the approved procedure (WPS).
• The test weld should be carried out on the same material and
same conditions as for the production welds.
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Welder Qualification 5.4 & 5.5
(according to EN Standards)
Question:
What is the main reason for qualifying a welder ?
Answer:
To show that he has the skill to be able to make production
welds that are free from defects
Note: when welding in accordance with a Qualified WPS
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The welder is allowed to make production welds within the
range of qualification shown on the Certificate
The range of qualification allowed for production welding is
based on the limits that the EN Standard specifies for the
welder qualification essential variables
Welder Qualification 5.5
(according to EN 287 )
A Certificate may be withdrawn by the Employer if there is
reason to doubt the ability of the welder, for example
• a high repair rate
• not working in accordance with a qualified WPS
The qualification shall remain valid for 2 years provided there is certified
confirmation of welding to the WPS in that time.
A Welder‟s Qualification Certificate automatically expires if the welder has not
used the welding process for 6 months or longer.
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Welding Engineer writes a preliminary Welding Procedure
Specification (pWPS) for each test weld to be made
• A welder makes a test weld in accordance with the pWPS
• A welding inspector records all the welding conditions used
for the test weld (referred to as the „as-run‟ conditions)
An Independent Examiner/ Examining Body/ Third Party
inspector may be requested to monitor the qualification
process
Welding Procedure Qualification 5.7
(according to EN ISO 15614)
The finished test weld is subjected to NDT in accordance with
the methods specified by the EN ISO Standard - Visual, MT or
PT & RT or UT
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Welding Procedure Qualification 5.7
Test weld is subjected to destructive testing (tensile, bend,
macro)
The Application Standard, or Client, may require additional
tests such as impact tests, hardness tests (and for some
materials - corrosion tests)
(according to EN ISO 15614)
A Welding Procedure Qualification Record (WPQR) is prepared
giving details of: -
• The welding conditions used for the test weld
• Results of the NDT
• Results of the destructive tests
• The welding conditions that the test weld allows for
production welding
The Third Party may be requested to sign the WPQR as a true
record
Welder Qualification 5.9
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(according to EN 287 )
An approved WPS should be available covering the range of
qualification required for the welder approval.
• The welder qualifies in accordance with an approved WPS
• A welding inspector monitors the welding to make sure that the
welder uses the conditions specified by the WPS
EN Welding Standard states that an Independent Examiner,
Examining Body or Third Party Inspector may be required to
monitor the qualification process
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The finished test weld is subjected to NDT by the methods
specified by the EN Standard - Visual, MT or PT & RT or UT
The test weld may need to be destructively tested - for certain
materials and/or welding processes specified by the EN
Standard or the Client Specification
Welder Qualification 5.9
(according to EN 287 )
• A Welder‟s Qualification Certificate is prepared showing the
conditions used for the test weld and the range of qualification
allowed by the EN Standard for production welding
• The Qualification Certificate is usually endorsed by a Third
Party Inspector as a true record of the test
Welder Qualification 5.10
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Information that should be included on a welders test certificate are,
which the welder should have or have access to a copy of !
• Welders name and identification number
• Date of test and expiry date of certificate
• Standard/code e.g. BS EN 287
• Test piece details
• Welding process.
• Welding parameters, amps, volts
• Consumables, flux type and filler classification details
• Sketch of run sequence
• Welding positions
• Joint configuration details
• Material type qualified, pipe diameter etc
• Test results, remarks
• Test location and witnessed by
• Extent (range) of approval
Welding Inspector
Materials Inspection
Section 6
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Material InspectionOne of the most important items to consider is Traceability.
The materials are of little use if we can not, by use of an effective QA system trace them from specification and purchase order to final documentation package handed over to the Client.
All materials arriving on site should be inspected for:
• Size / dimensions
• Condition
• Type / specification
In addition other elements may need to be considered depending on the materials form or shape
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Pipe Inspection
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We inspect the condition(Corrosion, Damage, Wall thickness Ovality, Laminations & Seam)
Specification
Welded seam
Size
LP5
Other checks may need to be made such as: distortion tolerance, number of plates and storage.
Plate Inspection
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Size
We inspect the condition
(Corrosion, Mechanical damage, Laps, Bands & Laminations)
5L
Specification
Other checks may need to be made such as: distortion tolerance, number of plates and storage.
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Parent Material Imperfections
Lamination
Mechanical damage Lap
Segregation line
Laminations are caused in the parent plate by the steel making
process, originating from ingot casting defects.
Segregation bands occur in the centre of the plate and are low
melting point impurities such as sulphur and phosphorous.
Laps are caused during rolling when overlapping metal does not
fuse to the base material.
Lapping
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Lamination
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Laminations
Plate Lamination
Welding Inspector
Codes & Standards
Section 7
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Codes & Standards
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The 3 agencies generally identified in a code or standard:
The customer, or client
The manufacturer, or contractor
The 3rd party inspection, or clients representative
Codes often do not contain all relevant data, but may
refer to other standards
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Standard/Codes/Specifications
STANDARDS
SPECIFICATIONS CODES
Examples
plate, pipe
forgings, castings
valves
electrodes
Examples
pressure vessels
bridges
pipelines
tanks
Welding Inspector
Welding Symbols
Section 8
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Weld symbols on drawings
Advantages of symbolic representation:
• simple and quick plotting on the drawing
• does not over-burden the drawing
• no need for additional view
• gives all necessary indications regarding the specific joint to be obtained
Disadvantages of symbolic representation:
• used only for usual joints
• requires training for properly understanding of symbols
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Weld symbols on drawings
The symbolic representation includes:
• an arrow line
• a reference line
• an elementary symbol
The elementary symbol may be completed by:
• a supplementary symbol
• a means of showing dimensions
• some complementary indications
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Dimensions
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In most standards the cross sectional dimensions are given to
the left side of the symbol, and all linear dimensions are give on
the right side
Convention of dimensions
a = Design throat thickness
s = Depth of Penetration, Throat thickness
z = Leg length (min material thickness)
BS EN ISO 22553
AWS A2.4
•In a fillet weld, the size of the weld is the leg length
•In a butt weld, the size of the weld is based on the depth of the
joint preparation
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A method of transferring information from the
design office to the workshop is:
The above information does not tell us much about the wishes
of the designer. We obviously need some sort of code which
would be understood by everyone.
Most countries have their own standards for symbols.
Some of them are AWS A2.4 & BS EN 22553 (ISO 2553)
Please weld
here
Weld symbols on drawings
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Joints in drawings may be indicated:
•by detailed sketches, showing every dimension
•by symbolic representation
Weld symbols on drawings
Elementary Welding Symbols(BS EN ISO 22553 & AWS A2.4)
Convention of the elementary symbols:
Various categories of joints are characterised by an elementary symbol.
The vertical line in the symbols for a fillet weld, single/double bevel butts and a J-butt welds must always be on the left side.
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Square edge
butt weld
Weld type Sketch Symbol
Single-v
butt weld
Elementary Welding Symbols
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Single-V butt
weld with broad
root face
Weld type Sketch Symbol
Single
bevel butt
weldSingle bevel
butt weld with
broad root
face
Backing run
Elementary Welding Symbols
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Single-U
butt weld
Weld type Sketch Symbol
Single-J
butt weld
Fillet weld
Surfacing
ISO 2553 / BS EN 22553
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Plug weld
Resistance spot weld
Resistance seam weld
Square Butt weld
Steep flanked
Single-V Butt
Surfacing
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Arrow Line
(BS EN ISO 22553 & AWS A2.4):
Convention of the arrow line:
• Shall touch the joint intersection
• Shall not be parallel to the drawing
• Shall point towards a single plate preparation (when only
one plate has preparation)
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(AWS A2.4)
Convention of the reference line:
Shall touch the arrow line
Shall be parallel to the bottom of the drawing
Reference Line
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or
Reference Line
(BS EN ISO 22553)
Convention of the reference line:
• Shall touch the arrow line
• Shall be parallel to the bottom of the drawing
• There shall be a further broken identification line above or
beneath the reference line (Not necessary where the weld
is symmetrical!)
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(BS EN ISO 22553 & AWS A2.4)
Convention of the double side weld symbols:
Representation of welds done from both sides of the joint
intersection, touched by the arrow head
Fillet weld
Double V
Double bevel
Double U
Double J
Double side weld symbols
ISO 2553 / BS EN 22553
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Arrow line
Reference lines
Arrow side
Other side Arrow side
Other side
ISO 2553 / BS EN 22553
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Single-V Butt flush cap Single-U Butt with sealing run
Single-V Butt with
permanent backing strip
M
Single-U Butt with
removable backing strip
M R
ISO 2553 / BS EN 22553
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Single-bevel butt Double-bevel butt
Single-bevel butt Single-J butt
ISO 2553 / BS EN 22553
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Partial penetration single-V butt
„S‟ indicates the depth of penetration
s10
1015
ISO 2553 / BS EN 22553
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a = Design throat thickness
s = Depth of Penetration, Throat
thickness
z = Leg length(min material thickness)
a = (0.7 x z)
a 4
4mm Design throat
z 6
6mm leg
az s
s 6
6mm Actual throat
ISO 2553 / BS EN 22553
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Arrow side
Arrow side
ISO 2553 / BS EN 22553
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Other side
Other side
s6
s6
6mm fillet weld
ISO 2553 / BS EN 22553
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n = number of weld elements
l = length of each weld element
(e) = distance between each weld element
n x l (e)
Welds to be staggered
Process
2 x 40 (50)
3 x 40 (50)111
ISO 2553 / BS EN 22553
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80 80 80
909090
6
6
5
5
z5
z6
3 x 80 (90)
3 x 80 (90)
All dimensions in mm
ISO 2553 / BS EN 22553
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All dimensions in mm
8
8
6
680 80 80
909090
z8
z6
3 x 80 (90)
3 x 80 (90)
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Supplementary symbols
Concave or Convex
Toes to be ground smoothly
(BS EN only)Site Weld
Weld all round
(BS EN ISO 22553 & AWS A2.4)
Convention of supplementary symbols
Supplementary information such as welding process, weld
profile, NDT and any special instructions
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Supplementary symbols
Further supplementary information, such as WPS number, or
NDT may be placed in the fish tail
Ground flush
111
Welding process
numerical BS EN
MR
Removable
backing strip
Permanent
backing strip
M
(BS EN ISO 22553 & AWS A2.4)
Convention of supplementary symbols
Supplementary information such as welding process, weld profile,
NDT and any special instructions
ISO 2553 / BS EN 22553
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ba
dc
ISO 2553 / BS EN 22553
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ConvexMitre
Toes
shall be
blended
Concave
ISO 2553 / BS EN 22553
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a = Design throat thickness
s = Depth of Penetration, Throat
thickness
z = Leg length(min material thickness)
a = (0.7 x z)
a 4
4mm Design throat
z 6
6mm leg
az s
s 6
6mm Actual throat
ISO 2553 / BS EN 22553Complimentary Symbols
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Field weld (site weld)
The component requires
NDT inspection
WPS
Additional information,
the reference document
is included in the box
Welding to be carried out
all round component
(peripheral weld)
NDT
ISO 2553 / BS EN 22553
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Numerical Values for Welding Processes:
111: MMA welding with covered electrode
121: Sub-arc welding with wire electrode
131: MIG welding with inert gas shield
135: MAG welding with non-inert gas shield
136: Flux core arc welding
141: TIG welding
311: Oxy-acetylene welding
72: Electro-slag welding
15: Plasma arc welding
AWS A2.4 Welding Symbols
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AWS Welding Symbols
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1(1-1/8)
60o
1/8
Depth of
Bevel
Effective
Throat
Root Opening
Groove Angle
AWS Welding Symbols
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1(1-1/8)
60o
1/8
GSFCAW
Welding Process
GMAW
GTAW
SAW
AWS Welding Symbols
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3 – 10
3 – 10
Welds to be staggered
SMAW
Process
10
3 3
AWS Welding Symbols
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1(1-1/8)
60o
1/8
FCAW
Sequence of
Operations
1st Operation
2nd Operation
3rd Operation
AWS Welding Symbols
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1(1-1/8)
60o
1/8
FCAW
Sequence of
Operations
RT
MT
MT
AWS Welding Symbols
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Dimensions- Leg Length
6/8
6 leg on member A
8
6Member A
Member B
Welding Inspector
Intro To Welding Processes
Section 9
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Welding Processes
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Welding is regarded as a joining process in which the work
pieces are in atomic contact
Pressure welding
• Forge welding
• Friction welding
• Resistance Welding
Fusion welding
• Oxy-acetylene
• MMA (SMAW)
• MIG/MAG (GMAW)
• TIG (GTAW)
• Sub-arc (SAW)
• Electro-slag (ESW)
• Laser Beam (LBW)
• Electron-Beam (EBW)
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20 8040 60 130 140120100 180160 200
10
60
50
40
30
20
80
70
90
100
Normal Operating
Voltage Range
Large voltage variation, e.g. +
10v (due to changes in arc
length)
Small amperage change
resulting in virtually constant
current e.g. + 5A.
Vo
lta
ge
Amperage
Required for: MMA, TIG, Plasma
arc and SAW > 1000 AMPS
O.C.V. Striking voltage (typical) for
arc initiation
Constant Current Power Source
(Drooping Characteristic)
Monitoring Heat Input
• Heat Input:
The amount of heat generated in the
welding arc per unit length of weld.
Expressed in kilo Joules per millimetre
length of weld (kJ/mm).
Heat Input (kJ/mm)= Volts x Amps
Travel speed(mm/s) x 1000
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Monitoring Heat Input
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Weld and weld pool temperatures
Monitoring Heat Input
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Monitoring Heat Input
• Monitoring Heat Input As Required by
• BS EN ISO 15614-1:2004
• In accordance with EN 1011-1:1998
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When impact requirements and/or hardness requirements are
specified, impact test shall be taken from the weld in the highest
heat input position and hardness tests shall be taken from the
weld in the lowest heat input position in order to qualify for all
positions
Welding Inspector
MMA Welding
Section 10
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MMA - Principle of operation
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MMA welding
Main features:
• Shielding provided by decomposition of flux covering
• Electrode consumable
• Manual process
Welder controls:
• Arc length
• Angle of electrode
• Speed of travel
• Amperage settings
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Manual Metal Arc Basic Equipment
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Power source
Holding oven
Inverter power
source
Electrode holder
Power cablesWelding visor
filter glass
Return lead
Electrodes
Electrode
oven
Control panel
(amps, volts)
MMA Welding Plant
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Transformer:
• Changes mains supply voltage to a voltage suitable for welding.
Has no moving parts and is often termed static plant.
Rectifier:
• Changes a.c. to d.c., can be mechanically or statically achieved.
Generator:
• Produces welding current. The generator consists of an armature
rotating in a magnetic field, the armature must be rotated at a
constant speed either by a motor unit or, in the absence of
electrical power, by an internal combustion engine.
Inverter:
• An inverter changes d.c. to a.c. at a higher frequency.
MMA Welding Variables
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Voltage
• The arc voltage in the MMA process is measured as close to
the arc as possible. It is variable with a change in arc length
O.C.V.
• The open circuit voltage is the voltage required to initiate, or
re-ignite the electrical arc and will change with the type of
electrode being used e.g 70-90 volts
Current
• The current used will be determined by the choice of
electrode, electrode diameter and material type and
thickness. Current has the most effect on penetration.
Polarity
• Polarity is generally determined by operation and electrode
type e.g DC +ve, DC –ve or AC
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20 8040 60 130 140120100 180160 200
10
60
50
40
30
20
80
70
90
100
Normal Operating
Voltage Range
Large voltage variation, e.g. +
10v (due to changes in arc
length)
Small amperage change
resulting in virtually constant
current e.g. + 5A.
Vo
lta
ge
Amperage
O.C.V. Striking voltage (typical) for arc
initiation
Constant Current Power Source
(Drooping Characteristic)
MMA welding parameters
Travel speed
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Travel
speedToo highToo low
•wide weld bead contour
•lack of penetration
•burn-through
•lack of root fusion
•incomplete root
penetration
•undercut
•poor bead profile,
difficult slag removal
MMA welding parameters
Type of current:• voltage drop in welding cables is lower with AC
• inductive looses can appear with AC if cables are coiled
• cheaper power source for AC
• no problems with arc blow with AC
• DC provides a more stable and easy to strike arc, especially with low current, better positional weld, thin sheet applications
• welding with a short arc length (low arc voltage) is easier with DC, better mechanical properties
• DC provides a smoother metal transfer, less spatter
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MMA welding parameters
Welding current
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– approx. 35 A/mm of diameter
– governed by thickness, type of joint and welding
position
Welding
currentToo highToo low
•poor starting
•slag inclusions
•weld bead contour too
high
•lack of
fusion/penetration
•spatter
•excess
penetration
•undercut
•burn-through
MMA welding parameters
Arc length = arc voltage
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Arc
voltageToo highToo low
•arc can be extinguished
•“stubbing”
•spatter
•porosity
•excess
penetration
•undercut
•burn-through
Polarity: DCEP generally gives deeper penetration
MMA - Troubleshooting
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MMA quality (left to right)current, arc length and travel speed normal;
current too low;
current too high;
arc length too short;
arc length too long;
travel speed too slow;
travel speed too high
MMA electrode holder
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Collet or twist type“Tongs” type with
spring-loaded jaws
MMA Welding Consumables
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The three main electrode covering types used in MMA welding
• Cellulosic - deep penetration/fusion
• Rutile - general purpose
• Basic - low hydrogen
(Covered in more detail in Section 14)
MMA Covered Electrodes
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Most welding defects in MMA are caused by a lack of welder
skill (not an easily controlled process), the incorrect settings
of the equipment, or the incorrect use, and treatment of
electrodes
Typical Welding Defects:
•Slag inclusions
•Arc strikes
•Porosity
•Undercut
•Shape defects (overlap, excessive root penetration, etc.)
MMA welding typical defects
Manual Metal Arc Welding (MMA)
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Advantages:
• Field or shop use
• Range of consumables
• All positions
• Portable
• Simple equipment
Disadvantages:
• High welder skill required
• High levels of fume
• Hydrogen control (flux)
• Stop/start problems
• Comparatively uneconomic when compared with some
other processes i.e MAG, SAW and FCAW
Welding Inspector
TIG Welding
Section 11
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Tungsten Inert Gas Welding
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The TIG welding process was first developed in the USA
during the 2nd world war for the welding of aluminum alloys
• The process uses a non-consumable tungsten electrode
• The process requires a high level of welder skill
• The process produces very high quality welds.
• The TIG process is considered as a slow process compared
to other arc welding processes
• The arc may be initiated by a high frequency to avoid scratch
starting, which could cause contamination of the tungsten
and weld
TIG - Principle of operation
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TIG Welding Variables
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Voltage
The voltage of the TIG welding process is variable only by the
type of gas being used, and changes in the arc length
Current
The current is adjusted proportionally to the tungsten
electrodes diameter being used. The higher the current the
deeper the penetration and fusion
Polarity
The polarity used for steels is always DC –ve as most of the
heat is concentrated at the +ve pole, this is required to keep
the tungsten electrode at the cool end of the arc. When
welding aluminium and its alloys AC current is used
Types of current
• can be DCEN or DCEP
• DCEN gives deep penetration
• requires special power source
• low frequency - up to 20 pulses/sec (thermal pulsing)
• better weld pool control
• weld pool partially solidifies between pulses4/23/2007 256 of 691
Type of
welding
current
can be sine or square wave
requires a HF current (continuos
or periodical)
provide cleaning action
DC
AC
Pulsed
current
Choosing the proper electrode
Current type influence
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++
+
++
+
++
+
--
-
--
-
--
-
Electrode capacity
Current type & polarity
Heat balance
Oxide cleaning action
Penetration
DCEN DCEPAC (balanced)
70% at work
30% at electrode
50% at work
50% at electrode
35% at work
65% at electrode
Deep, narrow Medium Shallow, wide
No Yes - every half cycle Yes
Excellent
(e.g. 3,2 mm/400A)
Good
(e.g. 3,2 mm/225A)
Poor
(e.g. 6,4 mm/120A)
ARC CHARACTERISTICS
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Volts
Amps
OCV
Constant Current/Amperage Characteristic
Large change in voltage =
Smaller change in amperage
Welding Voltage
Large arc gap
Small arc
gap
TIG - arc initiation methods
• simple method• tungsten electrode is in contact
with the workpiece!• high initial arc current due to the
short circuit• impractical to set arc length in
advance• electrode should tap the
workpiece - no scratch!• ineffective in case of AC• used when a high quality is not
essential
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Arc initiation
method
Lift arc HF start
need a HF generator (spark-
gap oscillator) that generates a
high voltage AC output (radio
frequency) costly
reliable method required on
both DC (for start) and AC (to
re-ignite the arc)
can be used remotely
HF produce interference
requires superior insulation
Pulsed current
• usually peak current is 2-10 times background current
• useful on metals sensitive to high heat input
• reduced distortions
• in case of dissimilar thicknesses equal penetration can be achieved
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Time
Curr
ent
(A) Pulse
time
Cycle
time
Peak
current
Background
current
Average current
one set of variables can be used in all positions
used for bridging gaps in open root joints
require special power source
Choosing the proper electrode
Polarity Influence – cathodic cleaning effect
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Tungsten Electrodes
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Old types: (Slightly Radioactive)
• Thoriated: DC electrode -ve - steels and most metals
• 1% thoriated + tungsten for higher current values
• 2% thoriated for lower current values
• Zirconiated: AC - aluminum alloys and magnesium
New types: (Not Radioactive)
• Cerium: DC electrode -ve - steels and most metals
• Lanthanum: AC - Aluminum alloys and magnesium
TIG torch set-up
• Electrode extension
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Electrode
extension
Stickout 2-3 times
electrode
diameter
Electrode
extension
Low electron
emission
Unstable arc
Too
small
Overheating
Tungsten
inclusions
Too
large
Choosing the correct electrode
Polarity Influence – cathodic cleaning effect
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Tungsten Electrodes
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Old types: (Slightly Radioactive)
• Thoriated: DC electrode -ve - steels and most metals
• 1% thoriated + tungsten for higher current values
• 2% thoriated for lower current values
• Zirconiated: AC - aluminum alloys and magnesium
New types: (Not Radioactive)
• Cerium: DC electrode -ve - steels and most metals
• Lanthanum: AC - Aluminum alloys and magnesium
Tungsten electrode types
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Pure tungsten electrodes:
colour code - green
no alloy additions
low current carrying capacity
maintains a clean balled end
can be used for AC welding of Al and Mg alloys
poor arc initiation and arc stability with AC compared
with other electrode types
used on less critical applications
low cost
Tungsten electrode types
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Thoriated tungsten electrodes:
colour code - yellow/red/violet
20% higher current carrying capacity compared to
pure tungsten electrodes
longer life - greater resistance to contamination
thermionic - easy arc initiation, more stable arc
maintain a sharpened tip
recommended for DCEN, seldom used on AC
(difficult to maintain a balled tip)
This slightly radioactive
Tungsten electrode types
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Ceriated tungsten electrodes:
colour code - grey (orange acc. AWS A-5.12)
operate successfully with AC or DC
Ce not radioactive - replacement for thoriated types
Lanthaniated tungsten electrodes:
colour code - black/gold/blue
operating characteristics similar with ceriated
electrode
Tungsten electrode types
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Zirconiated tungsten electrodes:
colour code - brown/white
operating characteristics fall between those of pure
and thoriated electrodes
retains a balled end during welding - good for AC
welding
high resistance to contamination
preferred for radiographic quality welds
Electrode tip for DCEN
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Electrode tip prepared for low
current welding
Electrode tip prepared for high
current welding
Vertex
angle
Penetration
increase
Increase
Bead width
increase
Decrease
2-2
,5 t
imes
ele
ctr
od
e d
iam
ete
r
Electrode tip for AC
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Electrode tip groundElectrode tip ground and
then conditioned
DC -ve AC
TIG Welding Variables
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Tungsten electrodes
The electrode diameter, type and vertex angle are all critical
factors considered as essential variables. The vertex angle is
as shown
Vetex angle
Note: when welding
aluminium with AC
current, the tungsten end
is chamfered and forms a
ball end when welding
DC -ve
Note: too fine an angle will
promote melting of the
electrodes tip
AC
Choosing the proper electrode
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Unstable
arc
Tungsten
inclusions
Welding
current
Electrode tip
not properly
heated
Excessive
melting or
volatilisation
Too
low
Too
high
Factors to be considered:
Penetration
Shielding gas requirements
• Preflow and postflow
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Preflow Postflow
Shielding gas flow
Welding current
Flow rate
too low
Flow rate
too high
Special shielding methods
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Pipe root run shielding – Back Purging to prevent
excessive oxidation during welding, normally argon.
TIG torch set-upElectrode extension
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Electrode
extension
Stickout 2-3 times
electrode
diameter
Electrode
extension
Low electron
emission
Unstable arc
Too
small
Overheating
Tungsten
inclusions
Too
large
TIG Welding ConsumablesWelding consumables for TIG:
•Filler wires, Shielding gases, tungsten electrodes (non-consumable).
•Filler wires of different materials composition and variable diameters available in standard lengths, with applicable code stamped for identification
•Steel Filler wires of very high quality, with copper coating to resist corrosion.
•shielding gases mainly Argon and Helium, usually of highest purity (99.9%).
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Tungsten Inclusion
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A Tungsten Inclusion always shows up as
bright white on a radiograph
May be caused by Thermal Shock of
heating to fast and small fragments
break off and enter the weld pool, so a
“slope up” device is normally fitted to
prevent this could be caused by touch
down also.
Most TIG sets these days have slope-
up devices that brings the current to
the set level over a short period of
time so the tungsten is heated more
slowly and gently
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Most welding defects with TIG are caused by a lack of welder
skill, or incorrect setting of the equipment. i.e. current, torch
manipulation, welding speed, gas flow rate, etc.
• Tungsten inclusions (low skill or wrong vertex angle)
• Surface porosity (loss of gas shield mainly on site)
• Crater pipes (bad weld finish technique i.e. slope out)
• Oxidation of S/S weld bead, or root by poor gas cover
• Root concavity (excess purge pressure in pipe)
• Lack of penetration/fusion (widely on root runs)
TIG typical defects
Tungsten Inert Gas Welding
Advantages
• High quality
• Good control
• All positions
• Lowest H2 process
• Minimal cleaning
• Autogenous welding
(No filler material)
• Can be automated
Disadvantages
• High skill factor required
• Low deposition rate
• Small consumable range
• High protection required
• Complex equipment
• Low productivity
• High ozone levels +HF
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Welding Inspector
MIG/MAG Welding
Section 12
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Gas Metal Arc Welding
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The MIG/MAG welding process was initially developed in the
USA in the late 1940s for the welding of aluminum alloys.
The latest EN Welding Standards now refer the process by the
American term GMAW (Gas Metal Arc Welding)
• The process uses a continuously fed wire electrode
• The weld pool is protected by a separately supplied
shielding gas
• The process is classified as a semi-automatic welding
process but may be fully automated
• The wire electrode can be either bare/solid wire or flux
cored hollow wire
MIG/MAG - Principle of operation
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MIG/MAG process variables
• Welding current
• Polarity
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•Increasing welding current
•Increase in depth and width
•Increase in deposition rate
MIG/MAG process variables
• Arc voltage
• Travel speed
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•Increasing travel speed
•Reduced penetration and width, undercut
•Increasing arc voltage
•Reduced penetration, increased width
•Excessive voltage can cause porosity,
spatter and undercut
Gas Metal Arc Welding
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Types of Shielding Gas
MIG (Metal Inert Gas)
• Inert Gas is required for all non-ferrous alloys (Al, Cu, Ni)
• Most common inert gas is Argon
• Argon + Helium used to give a „hotter‟ arc - better for thicker
joints and alloys with higher thermal conductivity
MIG/MAG – shielding gases
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Type of material Shielding gas
Carbon steel
Stainless steel
Aluminium
CO2 , Ar+(5-20)%CO2
Ar+2%O2
Ar
MIG/MAG shielding gases
Argon (Ar):
higher density than air; low thermal conductivity the arc has a high energy inner cone; good wetting at the toes; low ionisation potential
Helium (He):
lower density than air; high thermal conductivity uniformly distributed arc energy; parabolic profile; high ionisation potential
Carbon Dioxide (CO2):
cheap; deep penetration profile; cannot support spray transfer; poor wetting; high spatter
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Ar Ar-He He CO2
MIG/MAG shielding gases
Gases for dip transfer:
• CO2: carbon steels only: deep penetration; fast welding speed; high spatter levels
• Ar + up to 25% CO2: carbon and low alloy steels: minimum spatter; good wetting and bead contour
• 90% He + 7.5% Ar + 2.5% CO2:stainless steels: minimises undercut; small HAZ
• Ar: Al, Mg, Cu, Ni and their alloys on thin sections
• Ar + He mixtures: Al, Mg, Cu, Ni and their alloys on thicker sections (over 3 mm)
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MIG/MAG shielding gasesGases for spray transfer
• Ar + (5-18)% CO2: carbon steels: minimum spatter; good wetting and bead contour
• Ar + 2% O2: low alloy steels: minimise undercut; provides good toughness
• Ar + 2% O2 or CO2: stainless steels: improved arc stability; provides good fusion
• Ar: Al, Mg, Cu, Ni, Ti and their alloys
• Ar + He mixtures: Al, Cu, Ni and their alloys: hotter arc than pure Ar to offset heat dissipation
• Ar + (25-30)% N2: Cu alloys: greater heat input
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Gas Metal Arc WeldingTypes of Shielding Gas
MAG (Metal Active Gas)
• Active gases used are Oxygen and Carbon Dioxide
• Argon with a small % of active gas is required for all steels (including stainless steels) to ensure a stable arc & good droplet wetting into the weld pool
• Typical active gases are
Ar + 20% CO2 for C-Mn & low alloy steels
Ar + 2% O2 for stainless steels
100% CO2 can be used for C - steels4/23/2007 294 of 691
MIG/MAG Gas Metal Arc Welding
Electrode orientation
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Penetration Deep Moderate Shallow
Excess weld metal Maximum Moderate Minimum
Undercut Severe Moderate Minimum
Electrode extension
•Increased extension
MIG / MAG - self-regulating arc
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Stable condition Sudden change in gun position
L19 mm
25 mmL‟
Arc length L = 6,4 mm
Arc voltage = 24V
Welding current = 250A
WFS = 6,4 m/min
Melt off rate = 6,4 m/min
Arc length L‟ = 12,7 mm
Arc voltage = 29V
Welding current = 220A
WFS = 6,4 m/min
Melt off rate = 5,6
m/min
Current (A)
Vo
ltag
e (
V)
MIG/MAG - self-regulating arc
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Sudden change in gun position
25 mmL‟
Arc length L‟ = 12,7 mm
Arc voltage = 29V
Welding current = 220A
WFS = 6,4 m/min
Melt off rate = 5,6 m/min
Current (A)
Vo
ltag
e (
V)
Re-established stable condition
25 mmL
Arc length L = 6,4 mm
Arc voltage = 24V
Welding current = 250A
WFS = 6,4 m/min
Melt off rate = 6,4 m/min
Terminating the arc
• Burnback time
4/23/2007 298 of 691
– delayed current cut-off to prevent wire freeze
in the weld end crater
– depends on WFS (set as short as possible!)
Contact tip
Workpiec
e
Burnback time 0.05 sec 0.10 sec 0.15 sec
14 mm
8 mm 3 mm
Current - 250A
Voltage - 27V
WFS - 7,8 m/min
Wire diam. - 1,2 mm
Shielding gas -
Ar+18%CO2
Insulatin
g slag
Crater fill
MIG/MAG - metal transfer modes
Set-up for dip transfer Set-up for spray transfer
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Electrode
extension
19-25 mm
Contact tip
recessed
(3-5 mm)
Contact tip
extension
(0-3,2 mm)
Electrode
extension
6-13 mm
MIG/MAG - metal transfer modes
Current/voltage conditions4/23/2007 301 of 691
Current
Voltage
Dip transfer
Spray
transfer
Globular
transfer
Electrode diameter = 1,2 mm
WFS = 3,2 m/min
Current = 145 A
Voltage = 18-20V
Electrode diameter = 1,2 mm
WFS = 8,3 m/min
Current = 295 A
Voltage = 28V
MIG/MAG-methods of metal transfer
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Dip transfer
Transfer occur due to short circuits
between wire and weld pool, high
level of spatter, need inductance
control to limit current raise
Can use pure CO2 or Ar- CO2
mixtures as shielding gas
Metal transfer occur when arc is
extinguished
Requires low welding current/arc
voltage, a low heat input process.
Resulting in low residual stress
and distortion
Used for thin materials and all
position welds
MIG/MAG-methods of metal transfer
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Spray transfer
Transfer occur due to pinch effect NO contact between wire and weld pool!
Requires argon-rich shielding gas
Metal transfer occur in small droplets, a large volume weld pool
Requires high welding current/arc voltage, a high heat input process. Resulting in high residual stress and distortion
Used for thick materials and flat/horizontal position welds
MIG/MAG-methods of metal transfer
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Pulsed transfer
Controlled metal transfer, one droplet per pulse,
No transfer between droplet and weld pool!
Requires special power sources
Metal transfer occur in small droplets (diameter equal
to that of electrode)
Requires moderate welding current/arc voltage, a
reduced heat input . Resulting in smaller residual
stress and distortion compared to spray transfer
Pulse frequency controls the volume of weld pool,
used for root runs and out of position welds
MIG/MAG - metal transfer modesPulsed transfer
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Controlled metal transfer. one droplet
per pulse. NO transfer during
background current!
Requires special power sources
Metal transfer occur in small droplets
(diameter equal to that of electrode)
Requires moderate welding current/arc voltage, reduced
heat input‟ smaller residual stress and distortions
compared to spray transfer
Pulse frequency controls the volume of weld pool, used
for root runs and out of position welds
MIG/MAG-methods of metal transfer
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Globular transfer
Transfer occur due to gravity or
short circuits between drops and
weld pool
Requires CO2 shielding gas
Metal transfer occur in large drops
(diameter larger than that of
electrode) hence severe spatter
Requires high welding current/arc
voltage, a high heat input process.
Resulting in high residual stress
and distortion
Non desired mode of transfer!
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O.C.V. Arc Voltage
Virtually no Change.
Voltage
Flat or Constant Voltage Characteristic Used With
MIG/MAG, ESW & SAW < 1000 amps
100 200 300
33
32
31
Large Current Change
Small Voltage
Change.
Amperage
Flat or Constant Voltage Characteristic
MIG/MAG welding gun assembly
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Contact
tip
Gas
diffuser
Handle
Gas
nozzle
Trigger WFS remote
control
potentiometer
Union nut
The Push-Pull gun
Gas Metal Arc Welding
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PROCESS CHARACTERISTICS
• Requires a constant voltage power source, gas supply, wire
feeder, welding torch/gun and „hose package‟
• Wire is fed continuously through the conduit and is burnt-off
at a rate that maintains a constant arc length/arc voltage
• Wire feed speed is directly related to burn-off rate
• Wire burn-off rate is directly related to current
• When the welder holds the welding gun the process is said
to be a semi-automatic process
• The process can be mechanised and also automated
• In Europe the process is usually called MIG or MAG
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Most welding imperfections in MIG/MAG are caused by lack of
welder skill, or incorrect settings of the equipment
•Worn contact tips will cause poor power pick up, or transfer
•Bad power connections will cause a loss of voltage in the arc
•Silica inclusions (in Fe steels) due to poor inter-run cleaning
•Lack of fusion (primarily with dip transfer)
•Porosity (from loss of gas shield on site etc)
•Solidification problems (cracking, centerline pipes, crater
pipes) especially on deep narrow welds
MIG/MAG typical defects
WELDING PROCESS
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Flux Core Arc Welding
(Not In The Training Manual)
Flux cored arc welding
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FCAW
methods
With gas
shielding -
“Outershield”
Without gas
shielding -
“Innershield”
With metal
powder -
“Metal core”
“Outershield” - principle of operation
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“Innershield” - principle of operation
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ARC CHARACTERISTICS
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Volts
Amps
OCV
Constant Voltage Characteristic
Small change in voltage =
large change in amperage
The self
adjusting arc.
Large arc gap
Small arc gap
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Insulated extension nozzle
Current carrying guild tube
Flux cored hollow wire
Flux powder
Arc shield composed of vaporized and slag forming compounds
Metal droplets covered
with thin slag coating
Molten weld pool
Solidified weld metal and slag
Flux core
Wire joint
Flux core wires
Flux Core Arc Welding (FCAW)
Flux cored arc welding
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FCAW
methods
With gas
shielding -
“Outershield”
Without gas
shielding -
“Innershield”
(114)
With metal
powder -
“Metal core”
With active
gas shielding
(136)
With inert gas
shielding (137)
FCAW - differences from MIG/MAG
• usually operates in DCEP but some “Innershield” wires operates in DCEN
• power sources need to be more powerful due to the higher currents
• doesn't work in deep transfer mode
• require knurled feed rolls
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“Innershield” wires use
a different type of
welding gun
Backhand (“drag”) technique
Advantages
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preferred method for flat or horizontal position
slower progression of the weld
deeper penetration
weld stays hot longer, easy to remove dissolved
gasses
Disadvantages
produce a higher weld profile
difficult to follow the weld joint
can lead to burn-through on thin sheet plates
Forehand (“push”) technique
Advantages
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preferred method for vertical up or overhead
position
arc is directed towards the unwelded joint , preheat
effect
easy to follow the weld joint and control the
penetration
Disadvantages
produce a low weld profile, with coarser ripples
fast weld progression, shallower depth of penetration
the amount of spatter can increase
FCAW advantages
• less sensitive to lack of fusion
• requires smaller included angle compared to MMA
• high productivity
• all positional
• smooth bead surface, less danger of undercut
• basic types produce excellent toughness properties
• good control of the weld pool in positional welding especially with rutile wires
• seamless wires have no torsional strain, twist free
• ease of varying the alloying constituents
• no need for shielding gas
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FCAW disadvantages• limited to steels and Ni-base alloys
• slag covering must be removed
• FCAW wire is more expensive on a weight basis than solid wires (exception: some high alloy steels)
• for gas shielded process, the gaseous shield may be affected by winds and drafts
• more smoke and fumes are generated compared with MIG/MAG
• in case of Innershield wires, it might be necessary to break the wire for restart (due to the high amount of insulating slag formed at the tip of the wire)
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Advantages:
1) Field or shop use
2) High productivity
3) All positional
4) Slag supports and
shapes the weld Bead
5) No need for shielding
gas
Disadvantages:
1) High skill factor
2) Slag inclusions
3) Cored wire is
Expensive
4) High level of fume
(Inner-shield)
5) Limited to steels and
nickel alloys
FCAW advantages/disadvantages
Welding Inspector
Submerged Arc Welding
Section 13
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• Submerged arc welding was developed in the Soviet Union
during the 2nd world war for the welding of thick section steel.
• The process is normally mechanized.
• The process uses amps in the range of 100 to over 2000, which
gives a very high current density in the wire producing deep
penetration and high dilution welds.
• A flux is supplied separately via a flux hopper in the form of either
fused or agglomerated.
• The arc is not visible as it is submerged beneath the flux layer
and no eye protection is required.
Submerged Arc Welding Introduction
SAW Principle of operation
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Principles of operation
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Factors that determine whether to use SAW chemical
composition and mechanical properties required for the weld
deposit
• thickness of base metal to be welded
• joint accessibility
• position in which the weld is to be made
• frequency or volume of welding to be performed
SAW methods
Semiautomatic Mechanised Automatic
Submerged Arc Welding
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- +
Power
supply
Filler wire spool
Flux hopper
Wire electrode
Flux
Slide rail
SAW process variables
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• welding current
• current type and polarity
• welding voltage
• travel speed
• electrode size
• electrode extension
• width and depth of the layer of flux
SAW process variables
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Welding current
•controls depth of penetration and the amount of
base metal melted & dilution
SAW operating variables
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Current type and polarity
•Usually DCEP, deep
penetration, better
resistance to
porosity
•DCEN increase
deposition rate but
reduce penetration
(surfacing)
•AC used to avoid
arc blow; can give
unstable arc
SAW Consumables(Covered in detail in Section 14)
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Fused fluxes advantages:
•good chemical homogeneity
•easy removal of fines without affecting flux
composition
•normally not hygroscopic & easy storage and handling
•readily recycled without significant change in particle
size or composition
Fused fluxes disadvantages:•difficult to add deoxidizers and ferro-alloys (due to
segregation or extremely high loss)
•high temperatures needed to melt ingredients limit the
range of flux compositions
SAW Consumables
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Agglomerated fluxes advantages:
• easy addition of deoxidizers and alloying elements
• usable with thicker layer of flux when welding
• colour identification
Agglomerated fluxes disadvantages:
• tendency to absorb moisture
• possible gas evolution from the molten slag leading to
porosity
• possible change in flux composition due to segregation or
removal of fine mesh particles
SAW equipment
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Power sources can be:
• transformers for AC
• transformer-rectifiers for DC
Static characteristic can be:
• Constant Voltage (flat) - most of the power sources
• Constant Current (drooping)
SAW equipment
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Constant Voltage (Flat Characteristic) power sources:
• most commonly used supplies for SAW
• can be used for both semiautomatic and automatic welding
• self-regulating arc
• simple wire feed speed control
• wire feed speed controls the current and power supply
controls the voltage
• applications for DC are limited to 1000A due to severe arc
blow (also thin wires!)
ARC CHARACTERISTICS
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Volts
Amps
OCV
Constant Voltage Characteristic
Small change in voltage =
large change in amperage
The self
adjusting arc.
Large arc gap
Small arc gap
SAW equipment
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Constant Current (Drooping Characteristic) power sources:
• Over 1000A - very fast speed required - control of burn off
rate and stick out length
• can be used for both semiautomatic and automatic welding
• not self-regulating arc
• must be used with a voltage-sensing variable wire feed
speed control
• more expensive due to more complex wire feed speed
control
• arc voltage depends upon wire feed speed whilst the power
source controls the current
• cannot be used for high-speed welding of thin steel
SAW equipment
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Welding heads can be mounted on a:
Tractor type carriage
• provides travel along straight or
gently curved joints
• can ride on tracks set up along the
joint (with grooved wheels) or on
the workpiece itself
• can use guide wheels as tracking
device
• due to their portability, are used in
field welding or where the piece
cannot be moved
Courtesy of ESAB AB
Courtesy of ESAB AB
SAW operating variables
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Welding current
•too high current: excessive excess weld metal
(waste of electrode), increase weld shrinkage and
causes greater distortions
•excessively high current: digging arc, undercut,
burn through; also a high and narrow bead &
solidification cracking
•too low current: incomplete
fusion or inadequate penetration
•excessively low current:
unstable arc
SAW operating variables
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Welding voltage•welding voltage controls arc
length
•an increased voltage can increase pick-up of alloying elements
from an alloy flux
•increase in voltage produce a
flatter and wider bead
•increase in voltage increase
flux consumption
•increase in voltage tend to
reduce porosity
•an increased voltage may
help bridging an excessive
root gap
SAW operating variables
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Welding voltage
•low voltage produce a
“stiffer” arc & improves
penetration in a deep
weld groove and resists
arc blow
•excessive low voltage
produce a high narrow
bead & difficult slag
removal
SAW operating variables
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Welding voltage
•excessively high voltage
produce a “hat-shaped” bead
& tendency to crack
•excessively high voltage
increase undercut & make slag
removal difficult in groove
welds
•excessively high voltage
produce a concave fillet weld
that is subject to cracking
SAW operating variables
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Travel speed
•increase in travel speed: decrease heat input & less
filler metal applied per unit of length, less excess
weld metal & weld bead becomes smaller
SAW operating variables
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Travel speed
•excessively high speed
lead to undercut, arc
blow and porosity
•excessively low speed
produce “hat-shaped” beads
danger of cracking
•excessively low speed produce rough beads and
lead to slag inclusions
SAW operating variables
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Electrode size
•at the same current, small electrodes have higher
current density & higher deposition rates
SAW operating variables
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Electrode extension•increased electrode extension adds resistance in the
welding circuit I increase in deposition rate, decrease in
penetration and bead width
•to keep a proper weld shape, when electrode extension is
increased, voltage must also be increased
•when burn-through is a problem (e.g. thin gauge), increase
electrode extension
•excessive electrode extension: it is more difficult to
maintain the electrode tip in the correct position
SAW operating variables
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Depth of flux
•depth of flux layer influence the appearance of weld
•usually, depth of flux is 25-30 mm
•if flux layer is to deep the arc is too confined, result is
a rough ropelike appearing weld
•if flux layer is to deep the gases cannot escape & the
surface of molten weld metal becomes irregularly
distorted
•if flux layer is too shallow, flashing and spattering will
occur, give a poor appearance and porous weld
SAW technological variables
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Travel angle effect - Butt weld on plates
Penetration Deep Moderate Shallow
Excess weld metal Maximum Moderate Minimum
Tendency to undercut Severe Moderate Minimum
SAW technological variables
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Earth position +
-
Direction of
travel
•welding towards earth produces backward arc blow
•deep penetration
•convex weld profile
SAW technological variables
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Earth position+
-
Direction of
travel
•welding away earth produces forward arc blow
•normal penetration depth
•smooth, even weld profile
Weld backing
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Backing strip
Backing weld
Copper backing
Starting/finishing the weld
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SAW variants
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Twin wire SAW welding •two electrodes are feed
into the same weld pool
•wire diameter usually 1,6 to
3,2 mm
•electrodes are connected
to a single power source & a
single arc is established
•normally operate with
DCEP
•offers increased deposition
rate by up to 80% compared
to single wire SAW
SAW variants
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Wires can be oriented
for maximum or
minimum penetration
SAW variants
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Tandem arc SAW process •usually DCEP on lead
and AC on trail to reduce
arc blow
•requires two separate
power sources
•the electrodes are active
in the same puddle BUT
there are 2 separate arcs
•increased deposition
rate by up to 100%
compared with single
wire SAW
SAW variants
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SAW tandem arc
with two wires
Courtesy of ESAB AB
SAW variants
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Single pool - highest deposition rate
Twin pool - travel speed limited by undercut;
very resistant to porosity and cracks
SAW variants
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Tandem arc SAW process - multiple wires
•only for welding thick
sections (>30 mm)
•not suitable for use in
narrow weld
preparations (root
passes)
•one 4 mm wire at 600 A,
6.8 kg/hr
•tandem two 4 mm wires
at 600 A, 13.6 kg/hrCourtesy of ESAB AB
SAW variants
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Strip cladding needs a
special welding head
SAW variants
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Narrow gap welding
•for welding thick
materials
•less filler metal required
•requires special groove
preparation and special
welding head
•requires special fluxes,
otherwise problems with
slag removal
•defect removal is very
difficult
SAW variants
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Hot wire welding
•the hot wire is connected to power source & much
more efficient than cold wire (current is used entirely
to heat the wire!)
•increase deposition rates
up to 100%
•requires additional
welding equipment,
additional control of
variables, considerable
set-up time and closer
operator attention
SAW variants
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SAW with metal powder addition
•increased deposition rates up to 70%; increased welding speed
•gives smooth fusion, improved bead appearance, reduced penetration and dilution from parent metal & higher impact strength
•metal powders can modify chemical composition of final weld deposit
•does not increase risk of cracking
•do not require additional arc energy
•metal powder can be added ahead or directly into the weld pool
SAW variants
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SAW with metal powder addition
•magnetic attachment of powder
•SAW with metal cored wires
SAW variants
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Storage tank
SAW of circular
welds
Courtesy of ESAB AB
Advantages of SAW
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• high current density, high deposition rates (up to 10 times
those for MMA), high productivity
• deep penetration allowing the use of small welding grooves
• fast travel speed, less distortion
• deslagging is easier
• uniform bead appearance with good surface finish and good
fatigue properties
• can be easily performed mechanised, giving a higher duty
cycle and low skill level required
• provide consistent quality when performed automatic or
mechanised
• Virtually assured radiographically sound welds
• arc is not visible
• little smoke/fumes are developed
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Advantages
• Low weld-metal cost
• Easily automated
• Low levels of ozone
• High productivity
• No visible arc light
• Minimum cleaning
Disadvantages
• Restricted welding
positions
• Arc blow on DC
current
• Shrinkage defects
• Difficult penetration
control
• Limited joints
Submerged Arc Welding
Welding Inspector
Welding Consumables
Section 14
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BS EN 499 MMA Covered Electrodes
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Covered Electrode
Toughness
Yield Strength N/mm2
Chemical composition
Flux Covering
Weld Metal Recovery
and Current Type
Welding Position
Hydrogen Content
E 50 3 2Ni B 7 2 H10
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Welding consumables are any products that are used up in
the production of a weld
Welding consumables may be:
• Covered electrodes, filler wires and electrode wires.
• Shielding or oxy-fuel gases.
• Separately supplied fluxes.
• Fusible inserts.
Welding consumables
Welding Consumable Standards
MMA (SMAW)
• BS EN 499: Steel electrodes
• AWS A5.1 Non-alloyed steel
electrodes
• AWS A5.4 Chromium
electrodes
• AWS A5.5 Alloyed steel
electrodes
MIG/MAG (GMAW) TIG (GTAW)
• BS 2901: Filler wires
• BS EN 440: Wire electrodes
• AWS A5.9: Filler wires
• BS EN 439: Shielding gases
SAW
• BS 4165: Wire and fluxes
• BS EN 756: Wire electrodes
• BS EN 760: Fluxes
• AWS A5.17: Wires and fluxes
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Welding Consumable Gases
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welding gases
• GMAW, FCAW, TIG, Oxy- Fuel
• Supplied in cylinders or storage tanks for large quantities
• Colour coded cylinders to minimise wrong use
• Subject to regulations concerned handling, quantities and positioning of storage areas
• Moisture content is limited to avoid cold cracking
• Dew point (the temperature at which the vapour begins to condense) must be checked
Welding Consumables
Each consumable is critical in respect to:
• Size, (diameter and length)
• Classification / Supplier
• Condition
• Treatments e.g. baking / drying
• Handling and storage is critical for consumable control
• Handling and storage of gases is critical for safety
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MMA Welding Consumables
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The three main electrode covering types used in MMA welding
• Cellulosic - deep penetration/fusion
• Rutile - general purpose
• Basic - low hydrogen
MMA Covered Electrodes
MMA Welding Consumables
Welding consumables for MMA:
• Consist of a core wire typically between 350-450mm in length and from 2.5mm - 6mm in diameter
• The wire is covered with an extruded flux coating
• The core wire is generally of a low quality rimming steel
• The weld quality is refined by the addition of alloying and refining agents in the flux coating
• The flux coating contains many elements and compounds that all have a variety of functions during welding
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MMA Welding Consumables
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Function of the Electrode Covering:
• To facilitate arc ignition and give arc stability
• To generate gas for shielding the arc & molten metal from air contamination
• To de-oxidise the weld metal and flux impurities into the slag
• To form a protective slag blanket over the solidifying and cooling weld metal
• To provide alloying elements to give the required weld metal properties
• To aid positional welding (slag design to have suitable freezing temperature to support the molten weld metal)
• To control hydrogen contents in the weld (basic type)
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1: Electrode size (diameter and length)
2: Covering condition: adherence, cracks, chips and concentricity
3: Electrode designation
EN 499-E 51 3 B
Arc ignition enhancing materials (optional!)
See BS EN ISO 544 for further information
Covered electrode inspection
MMA Welding Consumables
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Plastic foil sealed cardboard box•rutile electrodes
•general purpose basic electrodes
Tin can•cellulosic electrodes
Vacuum sealed pack
•extra low hydrogen electrodes
Courtesy of Lincoln Electric
Co
urt
es
y o
f L
inc
oln
Ele
ctr
ic
MMA Welding Consumables
Cellulosic electrodes:
• covering contains cellulose (organic material).
• produce a gas shield high in hydrogen raising the arc voltage.
• Deep penetration / fusion characteristics enables welding at high speed without risk of lack of fusion.
• generates high level of fumes and H2 cold cracking.
• Forms a thin slag layer with coarse weld profile.
• not require baking or drying (excessive heat will damage electrode covering!).
• Mainly used for stove pipe welding
• hydrogen content is 80-90 ml/100 g of weld metal.4/23/2007 397 of 691
MMA Welding Consumables
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Cellulosic Electrodes
Disadvantages:
• weld beads have high hydrogen
• risk of cracking (need to keep joint hot during welding to allow
H to escape)
• not suitable for higher strength steels - cracking risk too
high (may not be allowed for Grades stronger than X70)
• not suitable for very thick sections (may not be used on
thicknesses > ~ 35mm)
• not suitable when low temperature toughness is required
(impact toughness satisfactory down to ~ -20°C)
MMA Welding Consumables
Advantages:
• Deep penetration/fusion
• Suitable for welding in all positions
• Fast travel speeds
• Large volumes of shielding gas
• Low control
Disadvantages:
• High in hydrogen
• High crack tendency
• Rough weld appearance
• High spatter contents
• Low deposition rates
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Cellulosic Electrodes
MMA Welding Consumables
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Rutile electrodes:
• covering contains TiO2 slag former and arc stabiliser.
• easy to strike arc, less spatter, excellent for positional
welding.
• stable, easy-to-use arc can operate in both DC and AC.
• slag easy to detach, smooth profile.
• Reasonably good strength weld metal.
• Used mainly on general purpose work.
• Low pressure pipework, support brackets.
• electrodes can be dried to lower H2 content but cannot be
baked as it will destroy the coating.
• hydrogen content is 25-30 ml/100 g of weld metal.
MMA Welding Consumables
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Rutile electrodes
Disadvantages:
• they cannot be made with a low hydrogen content
• cannot be used on high strength steels or thick joints -
cracking risk too high
• they do not give good toughness at low temperatures
• these limitations mean that they are only suitable for general
engineering - low strength, thin steel
MMA Welding Consumables
Advantages:
• Easy to use
• Low cost / control
• Smooth weld profiles
• Slag easily detachable
• High deposition possible with the addition of iron powder
Disadvantages:
• High in hydrogen
• High crack tendency
• Low strength
• Low toughness values
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Rutile Electrodes
MMA Welding ConsumablesRutile Variants
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High Recovery Rutile Electrodes
Characteristics:
• coating is „bulked out‟ with iron powder
• iron powder gives the electrode „high recovery‟
• extra weld metal from the iron powder can mean that weld
deposit from a single electrode can be as high as 180% of
the core wire weight
• give good productivity
• large weld beads with smooth profile can look very similar to
SAW welds
MMA Welding Consumables
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High Recovery Rutile Electrodes
Disadvantages:
• Same as standard rutile electrodes with respect to hydrogen
control
• large weld beads produced cannot be used for all-positional
welding
• the very high recovery types usually limited to PA & PB
positions
• more moderate recovery may allow PC use
MMA Welding Consumables
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Basic covering:
• Produce convex weld profile and difficult to detach slag.
• Very suitable for for high pressure work, thick section steel and for high strength steels.
• Prior to use electrodes should be baked, typically 350°C for 2 hour plus to reduce moisture to very low levels and achieve low hydrogen potential status.
• Contain calcium fluoride and calcium carbonate compounds.
• cannot be re-baked indefinitely!
• low hydrogen potential gives weld metal very good toughness and YS.
• have the lowest level of hydrogen (less than 5 ml/100 g of weld metal).
MMA Welding Consumables
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Basic Electrodes
Disadvantages:
• Careful control of baking and/or issuing of electrodes is essential to maintain low hydrogen status and avoid risk of cracking
• Typical baking temperature 350°C for 1 to 2hours.
• Holding temperature 120 to 150°C.
• Issue in heated quivers typically 70°C.
• Welders need to take more care / require greater skill.
• Weld profile usually more convex.
• Deslagging requires more effort than for other types.
Basic Electrodes
Advantages
• High toughness values
• Low hydrogen contents
• Low crack tendency
Disadvantages
• High cost
• High control
• High welder skill required
• Convex weld profiles
• Poor stop / start properties
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MMA Welding Consumables
BS EN 499 MMA Covered Electrodes
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Covered Electrode
Toughness
Yield Strength N/mm2
Chemical composition
Flux Covering
Weld Metal Recovery
and Current Type
Welding Position
Hydrogen Content
E 50 3 2Ni B 7 2 H10
BS EN 499 MMA Covered Electrodes
Electrodes classified as follows:
• E 35 - Minimum yield strength 350 N/mm2
Tensile strength 440 - 570 N/mm2
• E 38 - Minimum yield strength 380 N/mm2
Tensile strength 470 - 600 N/mm2
• E 42 - Minimum yield strength 420 N/mm2
Tensile strength 500 - 640 N/mm2
• E 46 - Minimum yield strength 460 N/mm2
Tensile strength 530 - 680 N/mm2
• E 50 - Minimum yield strength 500 N/mm2
Tensile strength 560 - 720 N/mm2
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AWS A5.1 Alloyed Electrodes
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Covered Electrode
Tensile Strength (p.s.i)
Welding Position
Flux Covering
E 60 1 3
AWS A5.5 Alloyed Electrodes
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Covered Electrode
Tensile Strength (p.s.i)
Welding Position
Flux Covering
Moisture Control
Alloy Content
E 70 1 8 M G
MMA Welding Consumables
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TYPES OF ELECTRODES
(for C, C-Mn Steels)
BS EN 499 AWS A5.1
• Cellulosic E XX X C EXX10
EXX11
• Rutile E XX X R EXX12
EXX13
• Rutile Heavy Coated E XX X RR EXX24
• Basic E XX X B EXX15
EXX16
EXX18
Electrode efficiency
75-90% for usual electrodes
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up to 180% for iron powder electrodes
Mass of weld metal deposited
Electrode Eficiency =
Mass of core wire melted
Covered electrode treatment
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Cellulosic
electrodes
Rutile
electrodes
Use straight from the
box - No baking/drying!
If necessary, dry up to
120°C- No baking!
Vacuum
packed basic
electrodes
Use straight from the pack
within 4 hours - No
rebaking!
Covered electrode treatment
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After baking, maintain in
oven at 150°C
Basic electrodesBaking in oven 2 hours
at 350°C!
Use from quivers at
75°C
If not used within 4
hours, return to oven
and rebake!Weld
Limited number of
rebakes!
TIG Consumables
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Welding Consumables
TIG Welding ConsumablesWelding consumables for TIG:
•Filler wires, Shielding gases, tungsten electrodes (non-consumable).
•Filler wires of different materials composition and variable diameters available in standard lengths, with applicable code stamped for identification
•Steel Filler wires of very high quality, with copper coating to resist corrosion.
•shielding gases mainly Argon and Helium, usually of highest purity (99.9%).
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TIG Welding Consumables
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Welding rods:
•supplied in cardboard/plastic tubes
•must be kept clean and free from oil and dust
•might require degreasing
Courtesy of Lincoln Electric
Fusible Inserts
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Before Welding
Pre-placed filler material
After Welding
Other terms used include:
EB inserts (Electric Boat Company)
Consumable socket rings (CSR)
Fusible Inserts
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Consumable inserts:
• used for root runs on pipes
• used in conjunction with TIG welding
• available for carbon steel, Cr-Mo steel, austenitic stainless
steel, nickel and copper-nickel alloys
• different shapes to suit application
Radius
Fusible Inserts
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Application of consumable inserts
Shielding gases for TIG welding
Argon
• low cost and greater availability
• heavier than air - lower flow rates than Helium
• low thermal conductivity - wide top bead profile
• low ionisation potential - easier arc starting, better arc stability with AC, cleaning effect
• for the same arc current produce less heat than helium -reduced penetration, wider HAZ
• to obtain the same arc arc power, argon requires a higher current - increased undercut
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Shielding gases for TIG welding
Helium
• costly and lower availability than Argon
• lighter than air - requires a higher flow rate compared with argon (2-3 times)
• higher ionisation potential - poor arc stability with AC, less forgiving for manual welding
• for the same arc current produce more heat than argon -increased penetration, welding of metals with high melting point or thermal conductivity
• to obtain the same arc arc power, helium requires a lower current - no undercut
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Shielding gases for TIG welding
Hydrogen
• not an inert gas - not used as a primary shielding gas
• increase the heat input - faster travel speed and increased penetration
• better wetting action - improved bead profile
• produce a cleaner weld bead surface
• added to argon (up to 5%) - only for austenitic stainless steels and nickel alloys
• flammable and explosive
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Shielding gases for TIG welding
Nitrogen
• not an inert gas
• high availability - cheap
• added to argon (up to 5%) - only for back purge for duplex stainless, austenitic stainless steels and copper alloys
• not used for mild steels (age embritlement)
• strictly prohibited in case of Ni and Ni alloys (porosity)
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MIG / MAG Consumables(Gases Covered previously)
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Welding Consumables
MIG/MAG Welding Consumables
Welding consumables for MIG/MAG
• Spools of Continuous electrode wires and shielding gases
• variable spool size (1-15Kg) and Wire diameter (0.6-1.6mm) supplied in random or orderly layers
• Basic Selection of different materials and their alloys as electrode wires.
• Some Steel Electrode wires copper coating purpose is corrosion resistance and electrical pick-up
• Gases can be pure CO2, CO2+Argon mixes and Argon+2%O2
mixes (stainless steels).
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MIG/MAG Welding Consumables
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Welding wires:
•carbon and low alloy wires may be copper coated
• stainless steel wires are not coated
•wires must be kept clean and free from oil and dust
•flux cored wires does not require baking or drying
Courtesy of Lincoln Electric Courtesy of ESAB AB
Flux Core Wire Consumables(Not in training manual)
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Welding Consumables
Flux Core Wire Consumables
Functions of metallic sheath: Function of the filling powder:
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provide form stability to the wire
serves as current transfer during welding
stabilise the arc
add alloy elements
produce gaseous shield
produce slag
add iron powder
Types of cored wire
• not sensitive to moisture pick-up
• can be copper coated, better current transfer
• thick sheath, good form stability, 2 roll drive feeding possible
• difficult to manufacture
• good resistance to moisture pick-up
• can be copper coated
• thick sheath
• difficult to seal the sheath
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Seamless
cored wire
Butt joint
cored wire
Overlapping
cored wire
sensitive to
moisture pick-
up
cannot be
copper coated
thin sheath
easy to
manufacture
Core elements and their function
Aluminium - deoxidize & denitrify
Calcium - provide shielding & form slag
Carbon - increase hardness & strength
Manganese - deoxidize & increase strength and toughness
Molybdenum - increase hardness & strength
Nickel - improve hardness, strength, toughness & corrosion resistance
Potassium - stabilize the arc & form slag
Silicon - deoxidize & form slag
Sodium - stabilize arc & form slag
Titanium - deoxidize, denitrify & form slag4/23/2007 436 of 691
SAW Consumables
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Welding Consumables
SAW Consumables
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Welding fluxes:
• are granular mineral compounds mixed according to various
formulations
• shield the molten weld pool from the atmosphere
• clean the molten weld pool
• can modify the chemical composition of the weld metal
• prevents rapid escape of heat from welding zone
• influence the shape of the weld bead (wetting action)
• can be fused, agglomerated or mixed
• must be kept warm and dry to avoid porosity
SAW Consumables
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• Fused fluxes are normally not hygroscopic but particles can
hold surface moisture so only drying
• Agglomerated fluxes contain chemically bonded water. Similar
treatment as basic electrodes
• If flux is too fine it will pack and not feed properly. It cannot be
recycled indefinitely
Welding flux:
• might be fused or agglomerated
• supplied in bags
• must be kept warm and dry
• handling and stacking requires careCourtesy of Lincoln Electric
SAW Consumables
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Fused Flux:
Baked at high temperature, glossy, hard and black in colour,
cannot add ferro-manganese, non moisture absorbent and
tends to be of the acidic type
Fused Flux
• Flaky appearance
• Lower weld quality
• Low moisture intake
• Low dust tendency
• Good re-cycling
• Very smooth weld
profile
SAW Consumables
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TYPES OF FLUX
FUSED (ACID TYPE)
• name indicates method of manufacture
• minerals are fused (melted) and granules produced by
allowing to cool to a solid mass and then crushing or by
spraying the molten flux into water
• flux tends to be „glass-like‟ (high in Silica)
• granules are hard and may appear shiny
• granules do not absorb moisture
• granules do not tend break down into powder when being
re-circulated
• are effectively a low hydrogen flux
• welds do not tend to give good toughness at low
temperatures
SAW Consumables
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Fused fluxes advantages:
•good chemical homogeneity
•easy removal of fines without affecting flux
composition
•normally not hygroscopic easy storage and
handling
•readily recycled without significant change in
particle size or composition
Fused fluxes disadvantages:
•difficult to add deoxidizers and ferro-alloys (due to
segregation or extremely high loss)
•high temperatures needed to melt ingredients limit
the range of flux compositions
SAW Consumables
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Agglomerated Flux:
Baked at a lower temperature, dull, irregularly shaped, friable,
(easily crushed) can easily add alloying elements, moisture
absorbent and tend to be of the basic type
Agglomerated Flux
• Granulated appearance
• High weld quality
• Addition of alloys
• Lower consumption
• Easy slag removal
• Smooth weld profile
SAW Consumables
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Agglomerated fluxes advantages:
• easy addition of deoxidizers and alloying elements
• usable with thicker layer of flux when welding
• colour identification
Agglomerated fluxes disadvantages:
• tendency to absorb moisture
• possible gas evolution from the molten slag leading to
porosity
• possible change in flux composition due to segregation or
removal of fine mesh particles
SAW Consumables
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TYPES OF FLUX
AGGLOMERATED (BASIC TYPE)
• name indicates method of manufacture
• basic minerals are used in powder form and are mixed with a binder to form individual granules
• granules are soft and easily crushed to powder
• granules will absorb moisture and it is necessary to protect the flux from moisture pick-up - usually by holding in a heated silo
• granules tend to break down into powder when being re-circulated
• are a low hydrogen flux - if correctly controlled
• welds give good toughness at low temperatures
SAW Consumables
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Mixed fluxes advantages:
•several commercial fluxes may be mixed for highly
critical or proprietary welding operations
Mixed fluxes disadvantages:
•segregation of the combined fluxes during
shipment, storage and handling
•segregation occurring in the feeding and recovery
systems during welding
•inconsistency in the combined flux from mix to mix
Mixed fluxes - two or more fused or bonded fluxes are
mixed in any ratio necessary to yield the desired
results
SAW filler material
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Welding wires can be used to weld:
•carbon steels
•low alloy steels
•creep resisting steels
•stainless steels
•nickel-base alloys
•special alloys for surfacing applications
Welding wires can be:
•solid wires
•metal-cored wires
SAW filler material
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Welding wires:•carbon and low alloy wires are copper coated
•wires must be kept clean and free from oil and dust
•stainless steel wires are not coated
Courtesy of Lincoln ElectricCourtesy of Lincoln Electric
SAW filler material
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Copper coating functions:
•to assure a good electric contact between wire
and contact tip
•to assure a smooth feed of the wire through the
guide tube, feed rolls and contact tip (decrease
contact tube wear)
•to provide protection against corrosion
Welding Inspector
Non Destructive Testing
Section 15
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Non-Destructive Testing
A welding inspector should have a working knowledge of NDT methods and their applications, advantages and disadvantages.
Four basic NDT methods
• Radiographic inspection (RT)
• Ultrasonic inspection (UT)
• Magnetic particle inspection (MT)
• Dye penetrant inspection (PT)
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Non-Destructive TestingSurface Crack Detection
• Liquid Penetrant (PT or Dye-Penetrant)
• Magnetic Particle Inspection (MT or MPI)
Volumetric & Planar Inspection
• Ultrasonics (UT)
• Radiography (RT)
Each technique has advantages & disadvantages with respect
to:
• Technical Capability and Cost
Note: The choice of NDT techniques is based on consideration
of these advantages and disadvantages
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Radiographic Testing (RT)
Radiographic Testing
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The principles of radiography
• X or Gamma radiation is imposed upon a test object
• Radiation is transmitted to varying degrees
dependant upon the density of the material through
which it is travelling
• Thinner areas and materials of a less density show as
darker areas on the radiograph
• Thicker areas and materials of a greater density show
as lighter areas on a radiograph
• Applicable to metals,non-metals and composites
Radiographic Testing
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X – Rays
Electrically generated
Gamma Rays
Generated by the decay
of unstable atoms
Radiographic Testing
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Source
Radiation beam Image quality indicator
Radiographic film with latent image after exposure
Test specimen
Radiographic Testing
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Density - relates to the degree of darkness
Contrast - relates to the degree of difference
Definition - relates to the degree of sharpness
Sensitivity - relates to the overall quality of the radiograph
Densitometer
Radiographic Sensitivity
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7FE12
Step / Hole type IQI Wire type IQI
Radiographic Sensitivity
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Wire Type IQI
Step/Hole Type IQI
Radiographic Techniques
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Single Wall Single Image (SWSI)
• film inside, source outside
Single Wall Single Image (SWSI) panoramic
• film outside, source inside (internal exposure)
Double Wall Single Image (DWSI)
• film outside, source outside (external exposure)
Double Wall Double Image (DWDI)
• film outside, source outside (elliptical exposure)
Single Wall Single Image (SWSI)
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IQI‟s should be placed source side
Film
Film
Single Wall Single Image Panoramic
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• IQI‟s are placed on the film side
• Source inside film outside (single exposure)
Film
Double Wall Single Image (DWSI)
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• IQI‟s are placed on the film side
• Source outside film outside (multiple exposure)
• This technique is intended for pipe diameters
over 100mm
Film
Double Wall Single Image (DWSI)
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Radiograph
• Identification
ID MR11
• Unique identificationEN W10
• IQI placing
A B• Pitch marks indicating readable film length
Double Wall Single Image (DWSI)
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Radiograph
Double Wall Double Image (DWDI)
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Film
• IQI‟s are placed on the source or film side
• Source outside film outside (multiple exposure)
• A minimum of two exposures
• This technique is intended for pipe diameters less than 100mm
Double Wall Double Image (DWDI)
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Shot A Radiograph
• Identification
ID MR12
• Unique identification EN W10
• IQI placing
1 2• Pitch marks indicating
readable film length
4 3
Double Wall Double Image (DWDI)
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Elliptical Radiograph
1 2
4 3
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Radiography
PENETRATING POWER
Question:
What determines the penetrating power of an X-ray ?
•the kilo-voltage applied (between anode & cathode)
Question:
What determines the penetrating power of a gamma ray ?
•the type of isotope (the wavelength of the gamma rays)
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Radiography
GAMMA SOURCES
Isotope Typical Thickness Range
• Iridium 192 10 to 50 mm (mostly used)
• Cobalt 60 > 50 mm
• Ytterbium < 10 mm
• Thulium < 10 mm
• Cesium < 10 mm
Radiographic Testing
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Advantages
• Permanent record
• Little surface preparation
• Defect identification
• No material type limitation
• Not so reliant upon operator
skill
• Thin materials
Disadvantages
• Expensive consumables
• Bulky equipment
• Harmful radiation
• Defect require significant
depth in relation to the
radiation beam (not good
for planar defects)
• Slow results
• Very little indication of
depths
• Access to both sides
required
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Radiographic Testing
Comparison with Ultrasonic Examination
ADVANTAGES
good for non-planar defects
good for thin sections
gives permanent record
easier for 2nd party interpretation
can use on all material types
high productivity
direct image of imperfections
Radiographic TestingComparison with Ultrasonic Examination
DISADVANTAGES
• health & safety hazard
• not good for thick sections
• high capital and relatively high running costs
• not good for planar defects
• X-ray sets not very portable
• requires access to both sides of weld
• frequent replacement of gamma source needed (half life)
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Ultrasonic Testing (UT)
Ultrasonic Testing
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Main Features:
• Surface and sub-surface detection
• This detection method uses high frequency sound waves,
typically above 2MHz to pass through a material
• A probe is used which contains a piezo electric crystal to
transmit and receive ultrasonic pulses and display the
signals on a cathode ray tube or digital display
• The actual display relates to the time taken for the
ultrasonic pulses to travel the distance to the interface and
back
• An interface could be the back of a plate material or a defect
• For ultrasound to enter a material a couplant must be
introduced between the probe and specimen
Ultrasonic Testing
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Digital
UT Set,
Pulse echo
signals
A scan
Display
Compression probe checking the material Thickness
Ultrasonic Testing
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defect
0 10 20 30 40 50
defect
echo
Back wall
echo
CRT DisplayCompression Probe
Material Thk
initial pulse
Ultrasonic Testing
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Angle Probe
UT SetA Scan
Display
Ultrasonic Testing
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initial pulse
defect echo
defectdefect
defect
0 10 20 30 40 50
CRT Display
0 10 20 30 40 50
initial pulse
defect echo
CRT Display
½ Skip
Full Skip
Ultrasonic Testing
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Advantages
Rapid results
Both surface and
sub-surface detection
Safe
Capable of measuring the
depth of defects
May be battery powered
Portable
Disadvantages
Trained and skilled operator
required
Requires high operator skill
Good surface finish required
Defect identification
Couplant may contaminate
No permanent record
Calibration Required
Ferritic Material (Mostly)
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Ultrasonic Testing
Comparison with Radiography
ADVANTAGES
•good for planar defects
•good for thick sections
•instant results
•can use on complex joints
•can automate
•very portable
•no safety problems (‘parallel’ working is possible)
•low capital & running costs
Ultrasonic TestingComparison with Radiography
DISADVANTAGES
• no permanent record (with standard equipment)
• not suitable for very thin joints <8mm
• reliant on operator interpretation
• not good for sizing Porosity
• good/smooth surface profile needed
• not suitable for coarse grain materials (e.g., castings)
• Ferritic Materials (with standard equipment)
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Magnetic Particle testing (MT)
Magnetic Particle Testing
Main features:• Surface and slight sub-surface detection
• Relies on magnetization of component being tested
• Only Ferro-magnetic materials can be tested
• A magnetic field is introduced into a specimen being tested
• Methods of applying a magnetic field, yoke, permanent magnet, prods and flexible cables.
• Fine particles of iron powder are applied to the test area
• Any defect which interrupts the magnetic field, will create a leakage field, which attracts the particles
• Any defect will show up as either a dark indication or in the case of fluorescent particles under UV-A light a green/yellow indication
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Magnetic Particle Testing
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Electro-magnet (yoke) DC or AC
Prods DC or AC
Collection of ink
particles due to
leakage field
Magnetic Particle Testing
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A crack like
indication
Magnetic Particle Testing
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Alternatively to contrast inks, fluorescent inks may be used
for greater sensitivity. These inks require a UV-A light source
and a darkened viewing area to inspect the component
Magnetic Particle Testing
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Typical sequence of operations to inspect a weld
• Clean area to be tested
• Apply contrast paint
• Apply magnetisism to the component
• Apply ferro-magnetic ink to the component during
magnatising
• Iterpret the test area
• Post clean and de-magnatise if required
Magnetic Particle Testing
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Advantages
• Simple to use
• Inexpensive
• Rapid results
• Little surface preparation
required
• Possible to inspect through
thin coatings
Disadvantages
• Surface or slight sub-surface
detection only
• Magnetic materials only
• No indication of defects
depths
• Only suitable for linear
defects
• Detection is required in two
directions
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Magnetic Particle Testing
Comparison with Penetrant Testing
ADVANTAGES
• much quicker than PT
• instant results
• can detect near-surface imperfections (by current flow
technique)
• less surface preparation needed
DISADVANTAGES
• only suitable for ferromagnetic materials
• electrical power for most techniques
• may need to de-magnetise (machine components)
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Penetrant Testing (PT)
Penetrant TestingMain features:
• Detection of surface breaking defects only.
• This test method uses the forces of capillary action
• Applicable on any material type, as long they are non porous.
• Penetrants are available in many different types:
• Water washable contrast
• Solvent removable contrast
• Water washable fluorescent
• Solvent removable fluorescent
• Post-emulsifiable fluorescent
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Penetrant Testing
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Step 1. Pre-Cleaning
Ensure surface is very Clean normally with the use of a solvent
Penetrant Testing
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Step 2. Apply penetrant
After the application, the penetrant is normally left on the
components surface for approximately 15-20 minutes (dwell
time).
The penetrant enters any defects that may be present by
capillary action.
Penetrant Testing
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Step 3. Clean off penetrant
the penetrant is removed after sufficient penetration time (dwell
time).
Care must be taken not to wash any penetrant out off any
defects present
Penetrant Testing
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Step 3. Apply developer
After the penetrant has be cleaned sufficiently, a thin layer of
developer is applied.
The developer acts as a contrast against the penetrant and
allows for reverse capillary action to take place.
Penetrant Testing
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Step 4. Inspection / development time
Inspection should take place immediately after the developer
has been applied.
any defects present will show as a bleed out during
development time.
After full inspection has been carried out post cleaning is
generally required.
Penetrant Testing
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Colour contrast Penetrant
Fluorescent Penetrant Bleed out viewed under a UV-A light source
Bleed out viewed under white light
Penetrant Testing
Advantages
• Simple to use
• Inexpensive
• Quick results
• Can be used on any non-porous material
• Portability
• Low operator skill required
Disadvantages• Surface breaking defect only
• little indication of depths
• Penetrant may contaminate component
• Surface preparation critical
• Post cleaning required
• Potentially hazardous chemicals
• Can not test unlimited times
• Temperature dependant
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Penetrant Testing
Comparison with Magnetic Particle Inspection
ADVANTAGES
•easy to interpret results
•no power requirements
•relatively little training required
•can use on all materials
DISADVANTAGES
•good surface finish needed
•relatively slow
•chemicals - health & safety issue
Welding Inspector
Weld Repairs
Section 16
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Weld RepairsWeld repairs can be divided into 2 specific areas:
• Production repairs
• In service repairs
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Weld Repairs
A weld repair can be a relatively straight forward activity, but in many instances it is quite complex, and various engineering disciplines may need to be involved to ensure a successful outcome.
• Analysis of the defect types may be carried out by the Q/C department to discover the likely reason for their occurrence, (Material/Process or Skill related).
In general terms, a welding repair involves What!
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Weld Repairs
A weld repair may be used to improve weld profiles or extensive metal removal:
•Repairs to fabrication defects are generally easier than repairs to service failures because the repair procedure may be followed
•The main problem with repairing a weld is the maintenance of mechanical properties
•During the inspection of the removed area prior to welding the inspector must ensure that the defects have been totally removed and the original joint profile has been maintained as close as possible
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Weld RepairsIn the event of repair, it is required:
• Authorization and procedure for repair
• Removal of material and preparation for repair
• Monitoring of repair Weld
• Testing of repair - visual and NDT
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Weld RepairsThere are a number of key factors that need to be considered
before undertaking any repair:
• The most important - is it financially worthwhile?
• Can structural integrity be achieved if the item is repaired?
• Are there any alternatives to welding?
• What caused the defect and is it likely to happen again?
• How is the defect to be removed and what welding process is to be used?
• What NDE is required to ensure complete removal of the defect?
• Will the welding procedures require approval/re-approval?
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Weld Repairs• Cleaning the repair area, (removal of paint, grease, etc)
• A detailed assessment to find out the extremity of the defect. This may involve the use of a surface or sub surface NDE method.
• Once established the excavation site must be clearly identified and marked out.
• An excavation procedure may be required (method used i.e. grinding, arc-air gouging, preheat requirements etc).
• NDE should be used to locate the defect and confirm its removal.
• A welding repair procedure/method statement with the appropriate welding process, consumable, technique, controlled heat input and interpass temperatures etc will need to be approved.
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Weld Repairs• Use of approved welders.
• Dressing the weld and final visual.
• A NDT procedure/technique prepared and carried out to ensure that the defect has been successfully removed and repaired.
• Any post repair heat treatment requirements.
• Final NDT procedure/technique prepared and carried out after heat treatment requirements.
• Applying protective treatments (painting etc as required).
• (*Appropriate’ means suitable for the alloys being repaired and may not apply in specific situations)
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Weld Repairs• What will be the effect of welding distortion and residual
stress?
• Will heat treatment be required?
• What NDE is required and how can acceptability of the repair be demonstrated?
• Will approval of the repair be required – if yes, how and by whom?
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Production Weld Repairs
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Before the repair can commence, a number of elements need
to be fulfilled:
If the defect is surface breaking and has occurred at the fusion
face the problem could be cracking or lack of sidewall fusion.
If the defect is found to be cracking the cause may be
associated with the material or the welding procedure
If the defect is lack of sidewall fusion this can be apportioned
to the lack of skill of the welder.
In this particular case as the defect is open to the surface, MPI
or DYE-PEN may be used to gauge the length of the defect and
U/T inspection used to gauge the depth.
Weld RepairsThe specification or procedure will govern how the defective areas are to be removed. The method of removal may be:
•Grinding
•Chipping
•Machining
•Filing
•Oxy-Gas gouging
•Arc air gouging
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Defect Excavation
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Arc-air gouging
Arc-air gouging features
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• Operate ONLY on DCEP
• Special gouging copper
coated carbon electrode
• Can be used on carbon
and low alloy steels,
austenitic stainless steels
and non-ferrous materials
• Requires CLEAN/DRY
compressed air supply
• Provides fast rate of metal removal
• Can remove complex shape defects
• After gouging, grinding of carbured layer is mandatory
• Gouging doesn‟t require a qualified welder!
Production Weld Repairs
Production Repairs
• are usually identified during production inspection
• evaluation of the reports is usually carried out by the Welding Inspector, or NDT operator
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Production Weld Repairs
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Plan View of defect
Production Weld Repairs
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Side View of defect excavation
D
W
Side View of repair welding
In Service Weld RepairsIn service repairs
• Can be of a very complex nature, as the component is very likely to be in a different welding position and condition than it was during production
• It may also have been in contact with toxic, or combustible fluids hence a permit to work will need to be sought prior to any work being carried out
• The repair welding procedure may look very different to the original production procedure due to changes in these elements.
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In Service Weld RepairsOther factors to be taken into consideration:
Effect of heat on any surrounding areas of the componenti.e. electrical components, or materials that may becomedamaged by the repair procedure.
This may also include difficulty in carrying out any requiredpre or post welding heat treatments and a possiblerestriction of access to the area to be repaired.
For large fabrications it is likely that the repair must alsotake place on site and without a shut down of operations,which may bring other elements that need to beconsidered.
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Weld Repairs
• Is welding the best method of repair?
• Is the repair really like earlier repairs?
• What is the composition and weldability of the base metal?
• What strength is required from the repair?
• Can preheat be tolerated?
• Can softening or hardening of the HAZ be tolerated?
• Is PWHT necessary and practicable?
• Will the fatigue resistance of the repair be adequate?
• Will the repair resist its environment?
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Weld repair related problems• heat from welding may affect dimensional stability and/or
mechanical properties of repaired assembly
• due to heat from welding, YS goes down, danger of collapse
• filler materials used on dissimilar welds may lead to galvanic corrosion
• local preheat may induce residual stresses
• cost of weld metal deposited during a weld joint repair can reach up to 10 times the original weld metal cost!
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Welding Inspector
Residual Stress & Distortion
Section 17
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Residual stress
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Residual stresses are undesirable because:
they lead to distortion
they affect dimensional stability of the
welded assembly
they enhance the risk of brittle fracture
they can facilitate certain types of
corrosion
Residual Stresses
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The heating and subsequent cooling from welding produces expansion and contractions which affect the weld metal and adjacent material.
If this contraction is prevented or inhibited residual stress will develop.
The tendency to develop residual stresses increases when the heating and cooling is localised.
Residual stresses are very difficult to measure with any real accuracy.
Residual stresses are self balancing internal forces and not stresses induced whilst applying external load
Stresses are more concentrated at the surface of the component.
The removal of residual stresses is termed stress relieving.
Stresses
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Normal Stress
Stress arising from a force perpendicular to the
cross sectional area
Compression
Tension
Stresses
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Shear Stress
Stress arising from forces which are parallel to, and
lie in the plane of the cross sectional area.
Shear Stress
Stresses
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Hoop Stress
Internal stress acting on the wall a pipe or cylinder
due to internal pressure.
Hoop Stress
Residual Stresses
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Longitudinal
Along the weld – longitudinal residual stresses
Transverse
Across the weld – transverse residual stresses
Short Transverse
Through the weld – short transverse residual stresses
Residual stresses occur in welds in the following directions
Residual stress
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Heating and
cooling causes
expansion and
contraction
Residual stress
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In case of a heated
bar, the resistance
of the surrounding
material to the
expansion and
contraction leads
to formation of
residual stress
Summary
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1. Residual stresses are locked in elastic strain, which is
caused by local expansion and contraction in the weld
area.
2. Residual stresses should be removed from structures
after welding.
3. The amount of contraction is controlled by, the volume of
weld metal in the joint, the thickness, heat input, joint
design and the materials properties
4. Offsetting may be used to finalise the position of the joint.
5. If plates or pipes are prevented from moving by tacking,
clamping or jigging etc (restraint), then the amount of
residual stresses that remain will be higher.
Summary
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6. The movement caused by welding related stresses is
called distortion.
7. The directions of contractional stresses and distortion is
very complex, as is the amount and type of final distortion,
however we can say that there are three directions:
a. Longitudinal b. Transverse c. Short transverse
8. A high percentage of residual stresses can be removed by
heat treatments.
9. The peening of weld faces will only redistribute the
residual stress, and place the weld face in compression.
Types of distortion
Angular distortion
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Distortion
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Angular Distortion
Bowing Distortion Longitudinal Distortion
Transverse Distortion
Distortion
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Factors which affect distortion
• Material properties and condition
• Heat input
• The amount of restrain
• The amount of weld metal deposited
Control of distortion my be achieved in the following way:
•The used of a different joint design
•Presetting the joints to be welded – so that the metal distorts
into the required position.
•The use of a balanced welding technique
•The use of clamps, jigs and fixtures.
Distortion
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• Distortion will occur in all welded joints if the material are
free to move i.e. not restrained
• Restrained materials result in low distortion but high
residual stress
• More than one type of distortion may occur at one time
• Highly restrained joints also have a higher crack tendency
than joints of a low restraint
• The action of residual stress in welded joints is to cause
distortion
Distortion
Factors affecting distortion:
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parent material properties
amount of restrain
joint design
fit-up
welding sequence
Factors affecting distortion
Parent material properties:
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thermal expansion coefficient - the greater the value, the greater the residual stress
yield strength - the greater the value, the greater the residual stress
Young‟s modulus - the greater the value (increase in stiffness), the greater the residual stress
thermal conductivity - the higher the value, the lower the residual stress
transformation temperature - during phase transformation, expansion/contraction takes place. The lower the transformation temperature, the lower the residual stress
Factors affecting distortion
Joint design:
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weld metal volume
type of joint - butt vs. fillet, single vs. double side
Amount of restrain:thickness - as thickness increase, so do the stresses
high level of restrain lead to high stresses
preheat may increase the level of stresses (pipe
welding!)
Fit-up:misalignment may reduce stresses in some cases
root gap - increase in root gap increases shrinkage
Factors affecting distortion
Welding sequence:
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number of passes - every pass adds to the total
contraction
heat input - the higher the heat input, the greater
the shrinkage
travel speed - the faster the welding speed, the
less the stress
build-up sequence
Distortion prevention
Distortion prevention by pre-setting
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a) pre-setting of fillet joint to
prevent angular distortion
b) pre-setting of butt joint to
prevent angular distortion
c) tapered gap to prevent
closure
Distortion
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Pre-set or Offsetting:
The amount of offsetting required is generally a function of
trial and error.
Distortion prevention
Distortion prevention by pre-bending using strongbacks and wedges
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Distortion
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Clamping and jigging:
The materials to be welded are prevented from moving by the clamp or jig the main advantage of using a jig is that the elements in a fabrication can be precisely located in the position to be welded. Main disadvantage of jigging is high restraint and high levels of residual stresses.
Distortion preventionDistortion prevention by restraint techniques
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a) use of welding jigs
b) use of flexible
clamps
Distortion preventionDistortion prevention by restraint techniques
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c) use of strongbacks
with wedges
d) use of fully welded
strongbacks
Distortion prevention
Distortion prevention by design
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Consider eliminating the welding!!
a) by forming the plate
b) by use of rolled or extruded sections
Distortion prevention
Distortion prevention by design
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consider weld placement
reduce weld metal volume
and/or number of runs
Distortion prevention
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The volume of weld metal in a joint will affect the amount of local expansion and contraction, hence the more weld deposited the higher amount of distortion
Preparation angle 60o
Preparation angle 40o
Preparation angle 0o
Distortion preventionDistortion prevention by design
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use of balanced welding
Distortion prevention
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- Transverse Shrinkage
Fillet Welds 0.8mm per weld where the leg length
does not exceed 3/4 plate thickness
Butt weld 1.5 to 3mm per weld for 60° V joint,
depending on number of runs
- Longitudinal Shrinkage
Fillet Welds 0.8mm per 3m of weld
Butt Welds 3mm per 3m of weld
Allowances to cover shrinkage
Distortions prevention by design
Distortion prevention
Distortion prevention by fabrication techniques
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tack weldinga) tack weld straight through
to end of joint
b) tack weld one end, then use
back-step technique for
tacking the rest of the joint
c) tack weld the centre, then
complete the tack welding
by the back-step technique
Distortion prevention
Distortion prevention by fabrication techniques
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back to back assembly
a) assemblies tacked together
before welding
b) use of wedges for
components that distort on
separation after welding
Distortion prevention
Distortion prevention by fabrication techniques
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use of stiffeners
control welding process by:
- deposit the weld metal as quickly as possible
- use the least number of runs to fill the joint
Distortion prevention
Distortion prevention by welding procedure
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reduce the number of
runs required to make a
weld (e.g. angular
distortion as a function
of number of runs for a
10 mm leg length weld)
Distortion prevention
Distortion prevention by welding procedure
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control welding techniques by use
balanced welding about the neutral axis
control welding techniques by keeping
the time between runs to a minimum
Distortion prevention
Distortion prevention by welding procedure
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control welding techniques by
a) Back-step welding
b) Skip welding
Distortion prevention
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Back-skip welding technique
Back-step welding technique
1. 2. 3. 4. 5. 6.
1. 2. 3. 6.4. 5.
Distortion preventionDistortion - Best practice for fabrication corrective techniques
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using tack welds to set up and maintain the joint gap
identical components welded back to back so welding can be
balanced about the neutral axis
attachment of longitudinal stiffeners to prevent longitudinal
bowing in butt welds of thin plate structures
where there is choice of welding procedure, process and
technique should aim to deposit the weld metal as quickly as
possible; MIG in preference to MMA or gas welding and
mechanised rather than manual welding
in long runs, the whole weld should not be completed in one
direction; back-step or skip welding techniques should be used
Distortion corrective techniques
Distortion - mechanical corrective techniques
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Use of press to correct bowing in T butt joint
Distortion corrective techniquesDistortion - Best practice for mechanical corrective techniques
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Use packing pieces which will over correct the distortion so
that spring-back will return the component to the correct shape
Check that the component is adequately supported during
pressing to prevent buckling
Use a former (or rolling) to achieve a straight component or
produce a curvature
As unsecured packing pieces may fly out from the press, the
following safe practice must be adopted:
- bolt the packing pieces to the platen
- place a metal plate of adequate thickness to intercept the
'missile'
- clear personnel from the hazard area
Distortion corrective techniques
Distortion - thermal corrective techniques
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Localised heating to
correct distortion
Spot heating for
correcting buckling
Distortion corrective techniques
Distortion - thermal corrective techniques
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Line heating to correct angular
distortion in a fillet weld
Use of wedge shaped heating
to straighten plate
Distortion corrective techniques
Distortion - thermal corrective techniques
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Wedge shaped heating to correct distortion
a) standard rolled
steel sectionb) buckled edge of
plate
c) box fabrication
General guidelines:
•Length of wedge = two-thirds of the plate width
•Width of wedge (base) = one sixth of its length (base to apex)
Distortion corrective techniques
Distortion - thermal corrective techniques
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•use spot heating to remove buckling in thin sheet structures
•other than in spot heating of thin panels, use a wedge-shaped
heating technique
•use line heating to correct angular distortion in plate
•restrict the area of heating to avoid over-shrinking the component
•limit the temperature to 60° to 650°C (dull red heat) in steels to
prevent metallurgical damage
•in wedge heating, heat from the base to the apex of the wedge,
penetrate evenly through the plate thickness and maintain an even
temperature
Welding Inspector
Heat Treatment
Section 18
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Heat Treatment
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Why?
Improve mechanical properties
Change microstructure
Reduce residual stress level
Change chemical composition
How?
Flame oven
Electric oven/electric heating blankets
induction/HF heating elements
Where? LocalGlobal
Heat Treatments
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Many metals must be given heat treatment before and after welding.
The inspector’s function is to ensure that the treatment is given correctly in accordance with the specification or as per the details supplied.
Types of heat treatment available:
•Preheat
•Annealing
•Normalising
•Quench Hardening
•Temper
•Stress Relief
Heat TreatmentsPre-heat treatments
• are used to increase weldability, by reducing sudden reduction of temperature, and control expansion and contraction forces during welding
Post weld heat treatments
• are used to change the properties of the weld metal, controlling the formation of crystalline structures
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Post Weld -Heat Treatments
Post Hydrogen Release (according to BS EN1011-2)
Temperature: Approximately 250 C hold up to 3 hours
Cooling: Slow cool in air
Result: Relieves residual hydrogen
Procedure: Maintaining pre-heat / interpass temperature after completion of welding for 2 to 3 hours.
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Post Weld Heat Treatments
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(A) Normalised
(B) Fully Annealed
(C) Water-quenched
(D) Water-quenched & tempered
A B
C D
Post Weld Heat Treatments
The inspector, in general, should ensure that:
• Equipment is as specified
• Temperature control equipment is in good condition
• Procedures as specified, is being used e.g.
o Method of application
o Rate of heating and cooling
o Maximum temperature
o Soak time
o Temperature measurement (and calibration)
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Post Weld Heat Treatment Cycle
Time
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TemperatureSoakingTemperature
and time at the
attained temperature
Heating Soaking Cooling
heating rate Cooling rate
Variables for heat treatment process must be carefully controlled
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Post Weld Heat TreatmentRemoval of Residual Stress
Temperature (°C)
100 200 300 400 500 600 700
Yield
Strength
(N/mm2 )
100
200
300
400
500Cr-Mo steel - typical
C-Mn steel - typical
• At PWHT temp. the yield
strength of steel reduced
so that it it is not strong
enough to give restraint.
• Residual stress reduced
to very low level by
straining (typically < ~
0.5% strain)
Heat Treatment
Recommendations
• Provide adequate support (low YS at high temperature!)
• Control heating rate to avoid uneven thermal expansions
• Control soak time to equalise temperatures
• Control temperature gradients - NO direct flame impingement!
• Control furnace atmosphere to reduce scaling
• Control cooling rate to avoid brittle structure formation
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Post Weld Heat Treatment Methods
Gas furnace heat treatment
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Advantages:
Easy to set up
Good portability
repeatability and
temperature uniformity
Disadvantages:
Limited to size of parts
Post Weld Heat Treatment Methods
HF (Induction) local heat treatment
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Advantages:
High heating rates
Ability to heat a
narrow band
Disadvantages:
High equipment
cost
Large equipment,
less portable
Post Weld Heat Treatment Methods
Local heat treatment using electric heating blankets
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Advantages:
Ability to vary
heat
Ability to
continuously
maintain heat
Disadvantages:
Elements may
burn out or arcing
during heating
Welding Inspector
Cutting Processes
Section 19
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Use of gas flame
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Welding GougingBrazing
Heating Straightening
Cutting
Blasting Spraying
Regulators
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Oxygen regulator Fuel gas regulator
Regulator type
Single stage
Two stage
used when slight rise in delivery
pressure from full to empty cylinder
condition can be tolerated
used when a constant delivery
pressure from full to empty
cylinder condition is required
Flashback arrestors
Flashback - recession of the flame into or back of the mixing chamber
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Flashback
flame
quenched
at the
flashback
barrier
Flame
barrie
r
Built-
in
check
valve
Normal
flow
Reverse
flow
Flashback
Built-in
check
valve
stops
reverse
flow
SAFETY SAFETY SAFETY
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A jet of pure oxygen reacts with iron, that has been preheated to its ignition point, to produce the oxide Fe3O4 by exothermic reaction.This oxide is then blown through the material by the velocity of the oxygen stream
Different types of fuel gases may be used for the pre-heating flame in oxy fuel gas cutting: i.e. acetylene, hydrogen, propane. etc
By adding iron powder to the flame we are able to cut most metals - “Iron Powder Injection”
The high intensity of heat and rapid cooling will cause hardening in low alloy and medium/high C steels they are thus pre-heated to avoid the hardening effect
Oxyfuel gas cutting process
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Oxyfuel gas cutting equipment
The cutting torch
Neutral cutting flame
Neutral cutting flame with oxygen cutting stream
Oxyfuel gas cutting related terms
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Oxyfuel gas cutting quality
• Good cut - sharp top edge, fine and even drag lines, little oxide and a sharp bottom edge
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Cut too fast -pronounced break in the drag line, irregular cut edge
Cut too slow - top edge is melted, deep groves in the lower portion, heavy scaling, rough bottom edge
Oxyfuel gas cutting quality
• Good cut - sharp top edge, fine and even drag lines, little oxide and a sharp bottom edge
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Preheat flame too high -
top edge is melted,
irregular cut, excess of
adherent dross
Preheat flame too low -
deep groves in the lower
part of the cut face
Oxyfuel gas cutting quality
• Good cut - sharp top edge, fine and even drag lines, little oxide and a sharp bottom edge
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Irregular travel speed - uneven
space between drag lines,
irregular bottom with adherent
oxide
Nozzle is too high above the works - excessive melting of the top edge, much oxide
Mechanised oxyfuel cutting
• can use portable carriages or gantry type machines and obtain high productivity
• accurate cutting for complicate shapes
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OFW/C advantages/disadvantages
Disadvantages:
1) High skill factor
2) Wide HAZ
4) Slow process
5) Limited range of consumables
3) Safety issues
Advantages:
1) No need for power supply, portable
3) Low equipment cost
4) Can cut carbon and low alloy steels
5) Good on thin materials
2) Versatile: preheat, brazing, surfacing, repair, straightening
6) Not suitable for reactive & refractory metals
Special oxyfuel operations• Gouging
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Rivet cutting
Special oxyfuel operations
• Thin sheet cutting
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Rivet washing
Cutting Processes
Plasma arc cutting
• Uses high velocity jet of ionised gas through a constricted nozzle to remove the molten metal
• Uses a tungsten electrode and water cooled nozzle
• High quality cutting
• High intensity and UV radiation – EYES !
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Cutting ProcessesAir-arc for cutting or gouging
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Air-arc gouging features
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• Operate ONLY on DCEP
• Special gouging copper
coated carbon electrode
• Can be used on carbon
and low alloy steels,
austenitic stainless steels
and non-ferrous materials
• Requires CLEAN/DRY
compressed air supply
• Provides fast rate of metal removal
• Can remove complex shape defects
• After gouging, grinding of carbured layer is mandatory
• Gouging doesn‟t require a qualified welder!
Welding Inspector
Arc Welding Safety
Please discuss
Section 20
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Safety
• Electrical safety• Heat & Light
– Visible light– UV radiation - effects on skin
and eyes
• Fumes & Explosive Gasses• Noise levels• Fire Hazards• Scaffolding & Staging• Slips, trips and falls• Protection of others from
exposure
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Welding Inspector
Weldability Of Steels
Section 21
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Weldability of SteelsDefinition
It relates to the ability of the metal (or alloy) to be welded with mechanical soundness by most of the common welding processes, and the resulting welded joint retain the properties for which it has been designed.
is a function of many inter-related factors but these may be summarised as:
•Composition of parent material
•Joint design and size
•Process and technique
•Access
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Weldability of Steels
The weldability of steel is mainly dependant on carbon & other alloying elements content.
If a material has limited weldability, we need to take special measures to ensure the maintenance of the properties required
Poor weldability normally results in the occurrence of cracking
A steel is considered to have poor weldability when:
• an acceptable joint can only be made by using very narrow range of welding conditions
• great precautions to avoid cracking are essential (e.g., high pre-heat etc)
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The Effect of Alloying on SteelsElements may be added to steels to produce the properties required to make it useful for an application.
Most elements can have many effects on the properties of steels.
Other factors which affect material properties are:
•The temperature reached before and during welding
•Heat input
•The cooling rate after welding and or PWHT
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Steel Alloying Elements
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Iron (Fe): Main steel constituent. On its own, is relatively soft, ductile, with low
strength.
Carbon (C): Major alloying element in steels, a strengthening element with
major influence on HAZ hardness. Decreases weldability.
•typically < ~ 0.25%
Manganese (Mn): Secondary only to carbon for strength, toughness and
ductility, secondary de-oxidiser and also reacts with sulphur to form
manganese sulphide.
< ~0.8% is residual from steel de-oxidation
•up to ~1.6% (in C-Mn steels) improves strength & toughness
Silicon (Si): Residual element from steel de-oxidation.
•typically to ~0.35%
Steel Alloying Elements
Phosphorus (P): Residual element from steel-making minerals. difficult to reduce below < ~ 0.015% brittleness
Sulphur (S): Residual element from steel-making minerals
< ~ 0.015% in modern steels
< ~ 0.003% in very clean steels
Aluminium (Al): De-oxidant and grain size control
•typically ~ 0.02 to ~ 0.05%
Chromium (Cr): For creep resistance & oxidation (scaling) resistance for elevated temperature service. Widely used in stainless steels for corrosion resistance, increases hardness and strength but reduces ductility.
•typically ~ 1 to 9% in low alloy steels
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Nickel (Ni): Used in stainless steels, high resistance to corrosion from acids, increases strength and toughness
Molybdenum (Mo): Affects hardenability. Steels containing molybdenum are less susceptible to temper brittleness than other alloy steels. Increases the high temperature tensile and creep strengths of steel. typically ~ 0.5 to 1.0%
Niobium (Nb): a grain refiner, typically~ 0.05%
Vanadium (V): a grain refiner, typically ~ 0.05%
Titanium (Ti): a grain refiner, typically ~ 0.05%
Copper (Cu): present as a residual, (typically < ~ 0.30%) added to ‘weathering steels’ (~ 0.6%) to give better resistance to atmospheric corrosion
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Steel Alloying Elements
Classification of Steels
Mild steel (CE < 0.4)• Readily weldable, preheat generally not required if low hydrogen
processes or electrodes are used
• Preheat may be required when welding thick section material, high restraint and with higher levels of hydrogen being generated
C-Mn, medium carbon, low alloy steels (CE 0.4 to 0.5)
• Thin sections can be welded without preheat but thicker sections will require low preheat levels and low hydrogen processes or electrodes should be used
Higher carbon and alloyed steels (CE > 0.5)
• Preheat, low hydrogen processes or electrodes, post weld heating and slow cooling may be required
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Process Cracks
• Hydrogen Induced HAZ Cracking (C/Mn steels)
• Hydrogen Induced Weld Metal Cracking (HSLA steels).
• Solidification or Hot Cracking (All steels)
• Lamellar Tearing (All steels)
• Re-heat Cracking (All steels, very susceptible Cr/Mo/V steels)
• Inter-Crystalline Corrosion or Weld Decay (stainless steels)
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CrackingWhen considering any type of cracking mechanism, three elements must always be present:
• Stress
Residual stress is always present in a weldment, through unbalanced local expansion and contraction
• Restraint
Restraint may be a local restriction, or through plates being welded to each other
• Susceptible microstructure
The microstructure may be made susceptible to cracking by the process of welding
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Cracks
Hydrogen Induced Cold Cracking
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Hydrogen Induced Cold Cracking
May occur:
• up to 48 hrs after completion
• In weld metal, HAZ, parent metal.
• At weld toes
• Under weld beads
• At stress raisers.
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Also know as:
Cold Cracking, happens when
the welds cool down.
HAZ cracking, normally occurs
in the HAZ.
Delayed cracking, as it takes
time for the hydrogen to
migrate. 48 Hours normally but
up to 72,
Under-bead cracking, normally
happens in the HAZ under a
weld bead
Hydrogen Induced Cold Cracking
There is a risk of hydrogen cracking when all of the 4 factors occur together:
•Hydrogen More than 15ml/100g of weld metal
•Stress More than ½ the yield stress
•Temperature Below 300oC
•Hardness Greater than 400HV Vickers
•Susceptible Microstructure (Martensite)
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Hydrogen Induced Cold Cracking
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Hydrogen Induced Cold Cracking
Precautions for controlling hydrogen cracking
• Pre heat, removes moisture from the joint preparations, and slows down the cooling rate
• Ensure joint preparations are clean and free from contamination
• The use of a low hydrogen welding process and correct arc length
• Ensure all welding is carried out is carried out under controlled environmental conditions
• Ensure good fit-up as to reduced stress
• The use of a PWHT
• Avoid poor weld profiles4/23/2007 614 of 691
Hydrogen Induced Cold Cracking
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• Hydrogen is the smallest atom known
• Hydrogen enters the weld via the arc
• Source of hydrogen mainly from moisture pick-up on
the electrodes coating, welding fluxes or from the
consumable gas
H2
H2
H2
H2H2
Moisture on the electrode or grease on the wire
Water vapour in the air or in the shielding gas
Oxide or grease on the plate
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Hydrogen absorbed
in a long, or
unstable arc
Hydrogen introduced in
weld from consumable,
oils, or paint on plate
Cellulosic electrodes
produce hydrogen as a
shielding gas
Hydrogen
crack
Martensite forms from γ H2 diffuses to γ in HAZ
H2H2
Hydrogen Induced Cold Cracking
Hydrogen Induced Cold Cracking
Susceptible Microstructure:
Hard brittle structure – MARTENSITE Promoted by:
A) High Carbon Content, Carbon Equivalent (CE)
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Heat input (Kj/mm) = Amps x Volts x arc time
Run out length x 103 (1000)
CEV = %C + Mn + Cr+Mo+V + Ni+Cu
6 5 15B) high alloy content
C) fast cooling rate: Inadequate Pre-Heating
Cold Material
Thick Material
Low Heat Input.
Hydrogen Induced Cold Cracking
Typical locations for Cold Cracking
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•HSLA or Micro-Alloyed Steels are high strength steels
(800MPa/N/mm2) that derive their high strength from small
percentage alloying (over-alloyed Weld metal to match the
strength of parent metal)
•Typically the level of alloying is in the elements such as
vanadium molybdenum and titanium, nickel and chromium
Strength. are used. It would be impossible to match this micro
alloying in the electrode due to the effect of losses across an
electric arc (Ti burn in the arc)
•It is however important to match the strength of the weld to
the strength of the plate, Mn 1.6 Cr Ni Mo
HICC in HSLA steels
Hydrogen Scales
List of hydrogen scales from BS EN 1011:part 2.
Hydrogen content related to 100 grams of weld metal deposited.
• Scale A High: >15 ml
• Scale B Medium: 10 ml - 15 ml
• Scale C Low: 5 ml - 10 ml
• Scale D Very low: 3 ml - 5 ml
• Scale E Ultra-low: < 3 ml
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Potential Hydrogen Level Processes
list of welding processes in order of potential lowest hydrogen content with regards to 100g of deposited weld metal.
•TIG < 3 ml
•MIG < 5 ml
•ESW < 5 ml
•MMA (Basic Electrodes) < 5 ml
•SAW < 10ml
•FCAW < 15 ml
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Weldability
Solidification Cracking
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Solidification Cracking
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Usually Occurs in Weld Centerline
Solidification CrackingAlso referred as
Hot Cracking: Occurring at high temperatures while the weld is hot
Centerline cracking: cracks appear down the centre line of the bead.
Crater cracking: Small cracks in weld centers are solidification cracks
Crack type: Solidification cracking
Location: Weld centreline (longitudinal)
Steel types: High sulphur & phosphor concentration in steels.
Susceptible Microstructure: Columnar grains In direction of solidification
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Solidification Cracking
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Factors for solidification cracking
• Columnar grain growth with impurities in weld metal (sulphur,
phosphor and carbon)
• The amount of stress/restraint
• Joint design high depth to width ratios
Liquid iron sulphides are formed around solidifying grains.
High contractional strains are present
High dilution processes are being used.
There is a high carbon content in the weld metal
• Most commonly occurring in sub-arc welded joints
Solidification Cracking
• Sulphur in the parent material may dilute in the weld metal to form iron sulphides (low strength, low melting point compounds)
• During weld metal solidification, columnar crystals push still liquid iron sulphides in front to the last place of solidification, weld centerline.
• The bonding between the grains which are themselves under great stress and may now be very poor to maintain cohesion and a crack will result, weld centerline.
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Solidification CrackingAvoidance
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Deep, narrower weld bead
On solidification the
bonding between the grains
may now be very poor to
maintain cohesion and a
crack may result
Shallow, wider weld bead
On solidification the
bonding between the
grains may be adequate to
maintain cohesion and a
crack is unlikely to occur
HAZ HAZ
Intergranular liquid filmColumnar grains Columnar
grains
Solidification Cracking
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Precautions for controlling solidification cracking
•The first steps in eliminating this problem would be to choose a low
dilution process, and change the joint design
Grind and seal in any lamination and avoid further dilution????
Add Manganese to the electrode to form spherical Mn/S which form
between the grain and maintain grain cohesion
As carbon increases the Mn/S ratio required increases
exponentially and is a major factor. Carbon content % should be a
minimised by careful control in electrode and dilution
Limit the heat input, hence low contraction, & minimise restraint
Solidification Cracking
Precautions for controlling solidification cracking
• The use of high manganese and low carbon content fillers
• Minimise the amount of stress / restraint acting on the joint during welding
• The use of high quality parent materials, low levels of impurities (Phosphor & sulphur)
• Clean joint preparations contaminants (oil, grease, paints and any other sulphur containing product)
• Joint design selection depth to width ratios
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Solidification Cracking
Solidification cracking in Austenitic Stainless Steel
• particularly prone to solidification cracking
• large grain size gives rise to a reduction in grain boundary area with high concentration of impurities
• Austenitic structure very intolerant to contaminants (sulphur, phosphorous and other impurities).
• High coefficient of thermal expansion /Low coefficient of thermal conductivity, with high resultant residual stress
• same precautions against cracking as for plain carbon steels with extra emphasis on thorough cleaning and high dilution controls.
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Cracks
Lamellar Tearing
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Lamellar Tearing
Factors for lamellar tearing to occur
Cracks only occur in the rolled plate !
Close to or just outside the HAZ !
Cracks lay parallel to the plate surface and the fusion boundary of the weld and has a stepped aspect.
• Low quality parent materials, high levels of impurities
• Joint design, direction of stress
• The amount of stress acting across the joint during welding
• Note: very susceptible joints may form lamellar tearing under very low levels of stress
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Lamellar Tearing
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Tee fillet weld Tee butt weld
(double-bevel)
Corner butt weld
(single-bevel)
Susceptible joint types combined with susceptible rolled plate
used to make a joint.
High stresses act in the through thickness direction of the plate
(know as the short transverse direction).
T, K & Y joints normally end up with a tensile residual stress
component in the through thickness direction.
Lamellar Tearing
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Critical area
Critical
area
Critical area
Lamellar Tearing
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Modifying a corner joint to avoid lamellar tearing
Susceptible Non-Susceptible
Prior welding both plates may be grooved to avoid lamellar tearing
An open corner joint may be selected to avoid lamellar tearing
Lamellar Tearing
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Precautions for controlling lamellar tearing
• The use of high quality parent materials, low levels of
impurities
• The use of buttering runs
• A gap can be left between the horizontal and vertical
members enabling the contraction movement to take
place
• Joint design selection
• Minimise the amount of stress / restraint acting on the
joint during welding
• Hydrogen precautions
Lamellar TearingCrack type: Lamellar tearing
Location: Below weld HAZ
Steel types: High sulphur & phosphorous steels
Microstructure: Lamination & Segregation
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Occurs when:
High contractional strains are through the short
transverse direction. There is a high sulfur content in
the base metal.
There is low through thickness ductility in the base
metal.
There is high restraint on the work
Short Tensile (Through Thickness) Test
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The short tensile test or through thickness test is a
test to determine a materials susceptibility to
lamellar tearing
Friction Welded Caps
Short Tensile Specimen
Through
Thickness
Ductility
Sample of Parent Material
The results are given as a STRA value
Short Transverse Reduction in Area
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High contractional
strains
Lamellar tear
Restraint
Lamellar Tearing
Welding Inspector
Practical Visual Inspection
Section 22
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Leg Length Gauge
G.A.L.
S.T.D.
10mm
16mm
L
Throat Thickness Gauge
G.A.L.
S.T.D.
10mm
16mm
Fillet Weld Gauges
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HI-
LO
S
ing
le P
urp
os
e W
eld
ing
Ga
ug
e
1
2
3
4
5
6 Root gap
dimension
Internal
alignment
HI-LO Welding Gauge
Plate / Pipe Inspection
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Remember in the CSWIP 3.1 Welding Inspectors
examination your are required to conduct a practical
examination of a plate test weld, complete a thumb
print sketch and a final report on your findings
Time allowed 1 hour and 15 minutes
The code is provided
Plate Inspection Examination
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1) Use a pencil for the arrow lines, but make all
written comments and measurements in ink
only
3) Do not forget to compare and sentence your
report
2) Report everything that you can observe
4) Do not forget to date & sign your report
5) Make any observations, such as
recommendations for further investigation for
crack-like imperfections.
Plate Inspection Points
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After you have observed an imperfection and
determined its type, you must be able to take
measurements and complete the thumb print report
sketch
The first thumb print report sketch should be in the
form of a repair map of the weld. (i.e. All
observations are Identified Sized and Located)
The thumb print report sketch used in CSWIP exam
will look like the following example.
Plate Thumb Print Report
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After you have completed your thumb print report
sketch of your test plate the next step is to complete
your final report again the report must be completed in
ink (no pencil).
The report must be completed to your thumb print
sketch, do not leave any boxes empty, every box must
be completed or dashed out. You must also make any
comments you feel are necessary regarding any
defects observed.
The report form used in CSWIP will look like the
following example.
Plate Inspection Final Report
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Remember in the CSWIP 3.1 Welding Inspectors
examination your are required to conduct a
practical examination of a pipe test weld, complete
a thumb print sketch and a final report on your
findings
Time allowed 1 hour and 45 minutes
The code is nominated e.g API 1104
Pipe Inspection
Welding Inspector
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Application & Control of Pre heat
Section 23
Welding TemperaturesDefinitions
Preheat temperature
• is the temperature of the workpiece in the weld zone immediately before any welding operation (including tack welding!)
• normally expressed as a minimum Interpass temperature
– is the temperature in a multi-run weld and adjacent parent metal immediately prior to the application of the next run
– normally expressed as a maximum
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Minimum interpass temperature = Preheat temperature
Pre heat maintenance temperature = the minimum temperature in the
weld zone which shall be maintained if welding is interrupted and shall be
monitored during the interruption.
Pre-heat Application
Furnace - Heating entire component - best
Electrical elements -Controllable; Portable; Site use; Clean; Component cannot be moved.
Gas burners - direct flame impingement; Possible local overheating; Less controllable;Portable; Manual operation possible; Component can be moved.
Radiant gas heaters - capable of automatic control; No flame impingement; No contact with component; Portable.
Induction heating - controllable; Rapid heating (mins not hours); Large power supply; Expensive equipment
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Measuring pre heat in Welding
Parameters to be measured:
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welding current
arc voltage
travel speed
shielding gas flow rate
The purposes
of measuring
Demonstration of
conformance to
specified requirements
preheat/interpass
temperature
force/pressure
humidity
Welding
process
control
Pre-heat Application
Application Of Preheat
• Heat either side of joint
• Measure temp 2 mins after heat removal
• Always best to heat complete component rather than local if possible to avoid distortion
• Preheat always higher for fillet than butt welds due to different combined thicknesses and chill effect factors.
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Pre-Heat Application
Manual Gas Operation
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Electrical Heated Elements
Welding Temperatures
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Point of Measurement
BS EN ISO 13916
t < 50 mm
A = 4 x t but max. 50 mm
the temperature shall be
measured on the surface
of the workpiece facing the
welder
Welding Temperatures
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Point of Measurement
BS EN ISO 13916
t > 50mm
A = 75mm minimum
the temperature shall be
measured on the face
opposite to that being
heated
allow 2 min per every 25
mm of parent metal
thickness for temperature
equalisation
Combined Thickness
The Chilling Effect of the Joint
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Combined Thickness
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The Chilling Effect of the Joint
Combined Thickness
Combined chilling effect of joint type and thickness.
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The Chill Effect of the Material
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Heating Temperature Control
• TEMPILSTICKS - crayons, melt at set temps. Will not measure max temp.
• Pyrometers - contact or remote, measure actual temp.
• Thermocouples - contact or attached, very accurate, measure actual temp.
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Temperature Test Equipment
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Temperature sensitive
materials:
•crayons, paints and
pills
•cheap
•convenient, easy to
use
•doesn‟t measure the
actual temperature!
Temperature Test Equipment
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Contact thermometer
•Accurate
•Easy to use
•Gives the actual temperature
•Requires calibration
•suitable for moderate
temperatures
Temperature Test Equipment
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Thermocouple
• based on measuring the thermoelectric potential difference
between a hot junction (on weld) and a cold junction
• accurate method
• measures over a wide range of temperatures
• gives the actual temperature
• need calibration
Temperature Test Equipment
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Thermistors
• temperature-sensitive resistors
whose resistance varies inversely
with temperature
• used when high sensitivity is
required
• gives the actual temperature
• need calibration
• can be used up to 999°C
Temperature test equipment
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Devices for contactless measurement
• IR radiation and optical
pyrometer
• measure the radiant energy
emitted by the hot body
• contactless method, can be
used for remote measurements
• very complex
• for measuring high
temperatures
Welding Inspector
Calibration
Section 24
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Calibration, validation and monitoringDefinitions:
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Measurement = set of operations for determining a value of a
quantity
Repeatability = closeness between successive measuring
results of the same instrument carried out under the same
conditions
Accuracy class = class of measuring instruments that are
intended to keep the errors within specified limits
Calibration = checking the errors in a meter or measuring
device
Validation = checking the control knobs and switches provide
the same level of accuracy when returned to a pre-determined
point
Monitoring = checking the welding parameters (and other
items) are in accordance with the procedure or specification
Calibration and validation
Frequency - When it is required?
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once a year unless otherwise specified
whenever there are indications that the
instrument does not register properly
whenever the equipment has been
damaged, misused or subject to severe
stress
whenever the equipment has been rebuild
or repaired
See BS EN ISO 17662 for details!
Welding parameter calibration/validation
Which parameters need calibration/validation?
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depends on the welding process
see BS EN ISO 17662 and BS 7570 for details
How accurate?
depends on the application
welding current - ±2,5%
arc voltage - ±5%
wire feed speed - ±2,5%
gas flow rate - ±20% (±25% for backing gas flow rate)
temperature (thermocouple) - ±5%
PAMS (Portable Arc Monitor System)
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What does a PAMS measure?
Welding
current (Hall
effect
device)
Arc voltage
(connection
leads)Temperature
(thermocouple)
Wire feed
speed
(tachometer)
Gas flow
rate
(heating
element
sensor)
PAMS (Portable Arc Monitor System)
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The purposes of
a PAMS
For calibrating
and validating
the welding
equipment
For measuring
and recording
the welding
parameters
Use of PAMS
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Wire feed speed
monitoring
Incorporated pair of
rolls connected to a
tachogenerator
Use of PAMS
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Shielding gas flow
rate monitoring
Heating element
sensor
Summary• a welding power source can only be calibrated if it has
meters fitted
• the inspector should check for calibration stickers, dates etc.
• a welding power source without meters can only be validated that the control knobs provide repeatability
• the main role is to carryout “in process monitoring” to ensure that the welding requirements are met during production
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Welding Inspector
Macro/Micro Examination
Section 25
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Macro Preparation
Purpose
To examine the weld cross-section to give assurance that: -
• The weld has been made in accordance with the WPS
• The weld is free from defects
Specimen Preparation
• Full thickness slice taken from the weld (typically ~10mm thick)
• Width of slice sufficient to show all the weld and HAZ on both sides
plus some unaffected base material
• One face ground to a progressively fine finish (grit sizes 120 to ~ 400)
• Prepared face heavily etched to show all weld runs & all HAZ
• Prepared face examined at up to x10 (& usually photographed for records)
• Prepared face may also be used for a hardness survey
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Micro PreparationPurpose
To examine a particular region of the weld or HAZ in order to:-
• To examine the microstructure
• Identify the nature of a crack or other imperfection
Specimen Preparation
• A small piece is cut from the region of interest
(typically up to ~ 20mm x 20mm)
• The piece is mounted in plastic mould and the surface of interest
prepared by progressive grinding (to grit size 600 or 800)
• Surface polished on diamond impregnated cloths to a mirror finish
• Prepared face may be examined in as-polished condition & then lightly
etched
• Prepared face examined under the microscope at up to ~ x 600
Macro / Micro ExaminationObject:
• Macro / microscopic examinations are used to give a visual evaluation of a cross-section of a welded joint
• Carried out on full thickness specimens
• The width of the specimen should include HAZ, weld and parent plate
• They maybe cut from a stop/start area on a welders approval test
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Macro / Micro ExaminationWill Reveal:
• Weld soundness
• Distribution of inclusions
• Number of weld passes
• Metallurgical structure of weld, fusion zone and HAZ
• Location and depth of penetration of weld
• Fillet weld leg and throat dimensions
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• Visual examination for
defects
• Cut transverse from the
weld
• Ground & polished P400
grit paper
• Acid etch using 5-10%
nitric acid solution
• Wash and dry
• Visual evaluation under 5x
magnification
• Report on results
• Visual examination for
defects & grain structure
• Cut transverse from a
weld
• Ground & polished P1200
grit paper, 1µm paste
• Acid etch using 1-5%
nitric acid solution
• Wash and dry
• Visual evaluation under
100-1000x magnification
• Report on results
Macro Micro
Metallographic Examination
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Macro examination Micro examination