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Copyright 2005, TWI Ltd World Centre for Materials Joining Technology 1
EXAMINATION
Examination in 5 (or 8) Parts(Each part has a 70% pass mark)
1. Technical Paper (1h 15min) 6 Questions given (4 answers required) Question #1 must be answered Answer 3 other questions from the remaining 5 questions
2. Interpretation of Welding Symbols (1h) Engineering drawing has welding symbols for 12 joints Interpret the symbols & comment on any errors or inconsistencies
3. Fracture Face Examination (1h) Examine fracture faces of 2 specimens & interpret modes of failure
4. NDT Reports (1h) Scrutinise 3 NDT Reports & list all errors and all omissions
5. Oral (~ 10 to 15 min) 1 Question: - subject will be related to supervision of welding
inspectors or to safety matters
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EXAMINATION
Examination in 5 (or 8) Parts(Each part has a 70% pass mark)
If a candidate for the Senior Welding Inspector Examination does nothold a recognised qualification in Radiographic Interpretation(a CSWIP or PCN Certificate) he is required to sit 3 additionalexamination parts, namely: -
6. Radiographic Interpretation (1h 30min) 6 dense metal welds - steel
7. Multi-Choice Radiographic Theory Paper (30min) 30 questions
8. Radiographic Density & Sensitivity (1h) Densitometer calibration using a Density Strip Sensitivity calculations for 5 welds
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THE SENIOR WELDING INSPECTOR
A Senior Welding Inspector may be Senior through beingput in charge of a team of Welding Inspectors.
In this role he may have a predominantly managerial rolethat requires organising and supervising their work and so
may have title of Team Leader or Supervisor.
In other circumstances he may have a more technicallydemanding role that requires detailed knowledge ofparticular activities.
The CSWIP Senior Welding Inspector Course is intended tocover aspects of both these roles.
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THE SENIOR WELDING INSPECTOR
TYPICAL REQUIREMENTS - TECHNICAL KNOWLEDGE
Welding Technology
(Welding Inspector . plus)
NDT Techniques
( ability to carry out / interpret)
Codes/Application Standards
(ability to interpret)
Planning Systems
(ability to understand and also supply inspectionscheduling to project schedule)
Quality Assurance
(ability to plan & carry out some auditing)
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THE SENIOR WELDING INSPECTOR
LEADERSHIP / SUPERVISION
A Supervisor is a person who has been given authority andresponsibility for: -
planning the work of others
controlling this work
A Supervisor is a man in the middle between operators andmanagement and subject to pressures from both directions
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THE SENIOR WELDING INSPECTOR
LEADERSHIP
Is leadership an ability that a person is born with orcan it be acquired !!!!!! ?????
Personality is very influential - hence leadershipsometimes considered to be in the genes and a personreferred to as a born leader
Ability to be a good leader can be improved byexperience & from knowledge of managementtechniques through training
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THE SENIOR WELDING INSPECTOR
TYPICAL REQUIREMENTS - LEADERSHIP SKILLS / ABILITY
Complex mixture of skills & attitudes - such as
being prepared to accept responsibility
willing to direct the work of others willing, and able, to delegate tasks to others
having a commitment to ones staff
able to solve / overcome problems (from greater & wider experience)
able to do all (or most of) the work done by ones staff
able to communicate - downwards & upwards within the Company
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THE SENIOR WELDING INSPECTOR
What Makes a Good Leader / Supervisor ?
Qualities that are associated with a Good Supervisor are: -
has good technical skill & knowledge and good at solving problems
has ability to quickly determine priorities
is intelligent and confident shows good judgement
has enthusiasm for work and is usually cheerful & optimistic
sets a good example at work - high standards - leads by example
has no favourites and able to apply discipline fairly
is approachable - good listener - and prepared to consult staff
informs staff of important decisions affecting them and backs his team
is able to identify needs of team and obtain equipment and training
good at planning and delegation
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PRODUCTION PLANNING
PRESSURE VESSEL FABRICATION
T 1 T 2 T 3 H 1 H 2 N1
N2
N3
W 1 W 2
S1 S2
T = TierH = Head
N = Nozzle
W = Wrapper plate
S = Saddle
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PRODUCTION PLANNING
PRESSURE VESSEL: Typical Production Sequence
1. Prepare drawings & material list
2. Order materials - plate
3. - fittings
4. - heads
5. - weldingconsumables
6. Mark out, cut & roll shell plates7. Weld longitudinal seams
8. Fit & weld - T 3 to H 2
9. - T 2 to (T 3 H 2 )
10. - N 1 + H 1
11. Fit & weld - N 1 + H 1
12. Mark out, cut & roll wrapper plates
13. Weld W 1 & W 2 to shell plates
14. Fit & weld nozzles N 2 & N 3
15. Cut, assemble & weld saddles S 1 & S 2
16. Fit & weld S 1 & S 2 to W 1 & W 2
17. Carry out all final inspection
18. Pressure test
19. Blast & paint
20. Deliver
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A Preliminary Welding Procedure Specification (pWPS) is written for each test weld required
Welder makes a test weld in accordance with the pWPS Welding Inspector records all welding details used for making the test weld (as -run details) (EN standard states that an Independent Examiner or Examining Body or a Third PartyInspector may be required to monitor the qualification process)
Welding Procedure Qualification Record (WPQR) prepared giving range of qualificationallowed by the Welding Standard (EN or ASME IX) WPQR package submitted to Independent Examiner for endorsement (& usually to Client)
Test weld subjected to destructive testing according to specified methods Application Standard or Client may require additional tests such as impact tests, hardnesstests (for some materials - corrosion tests)
Finished test weld is subjected to NDT by the specified methods(EN Standard requires visual, MT or PT & RT or UT)
Welding Procedure Qualification
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Destructive Testing
pipe diameters> 323.9mm
1 2 3 4 5
678
1211
10 9
SPECIMEN TYPE POSITIONS
macro + hardness 1, 9, 11transverse tensile 2, 8, 10, 12Charpy weld metal 3, 5, 6Charpy fusion line 4, 7
WELD PROCEDURE QUALIFICATION TESTING (example)
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Destructive Testing
QUANTITATIVE TESTS & QUALITATIVE TESTS
QUANTITATIVE TESTS
for measuring a quantity ( quantity = a mechanical property )
typical mechanical tests - tensile test
- hardness test- Charpy V-notch test (& CTOD)
QUALITATIVE TESTS
for assessing joint quality (quality = good fusion & free from defects)
typical qualitative tests - bend tests- macro examination(micro examination for some metals)
- fillet fracture & nick-break tests
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Destructive Testing
Tensile Testing - Transverse Tensile Test
gaugelength
weld
TEST OBJECTIVETo measure the Tensile Strength of the welded joint
RESULTSSatisfactory if Tensile Strength greater than min. specified for base metal
(Some standards accept 95% of base material Tensile Strength)
Position of failure not usually in weld metal but in base material or HAZ
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Destructive Testing
Tensile Testing: All-Weld Tensile Test
TEST OBJECTIVETo measure Yield Strength & Tensile Strength of weld metal(% Elongation also measured & usually also % Reduction of Area)
RESULTSSatisfactory if all values are not less than minimum specified for basemetal (or required by desig) at ambient or at elevated temperature
from WPQ test piece electrode classification test piece
gauge length: all weld metal
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Destructive Testing
MECHANICAL TESTING: Charpy V-notch Test Positions
weld metal (surface)
weld metal (root)
fusion line + 2mmfusion linefusion line + 5mm
For each notch position 3 specimens are tested . May need to take testpieces from weld metal, fusion line, fusion line + 2, fusion line + 5 from bothweld faces and from root - total of 36 tests
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Destructive Testing
MECHANICAL TESTING: Charpy V-notch Impact Testing
TEST OBJECTIVE
To measure the impacttoughness of eachregion of the weld joint(weld metal, HAZ &
base metal) at aspecified temperaturethat is related to theservice conditions
RESULTS
Satisfactory if allvalues are not less theminimum specified bythe ApplicationStandard
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Welding Technology
HAZ toughness transitiontemp. has shifted to ahigher temperature
(caused by high heat inputwelding)
HAZ TOUGHNESS
unweldedfine grained
steel
no significantchange in HAZ
toughness ifmoderate heatinput used
Toughness Charpy
V-notch energy
(Joules)
Impact Test Temperature design temperature
good toughnessin steel atdesign temp.
low toughnessin HAZ atdesign temp.
degraded HAZ
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Welding Technology
THE HEAT AFFECTED ZONE (HAZ)
unaffected basematerial
tempered zone
grain growth zone
recrystallised zonepartially transformed zone
MaximumTemperature solid-liquid transition zonesolid
weldmetal
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Destructive Testing
MECHANICAL TESTING: Hardness Testing
HARDNESS TEST METHODS
Vickers example 248 HV10Rockwell example Rc 22Brinell example 220 BHN-W (not usually used on macro sections)
TEST OBJECTIVE To measure the max. hardness in the weld joint(always in HAZ for steels)
RESULTS Satisfactory if no values are above the max.specified by the Application Standard
usually the hardest region
HAZ
fusion line(fusion
boundary)HAZ
~1.5 to 3mm
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Welding Technology
HAZ Hardness of Carbon-Manganese Steels
intermediate heat-input willgive satisfactory hardness
Rate of Cooling of HAZ
HAZHardness
high heat-input
welding tends togive a softer HAZ
low heat-inputwelding tendsto give a highHAZ hardness
fast slow
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Welding Technology
HAZ Hardness of Low-Alloy Steels
(such as the higher Cr-Mo grades)
Time to Cool
HAZHardness
low heat-input welding
fast cooling slow cooling
high heat-input welding
HAZ hardness always high (> ~ 400 HV)
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Destructive Testing QUALITATIVE TESTS: Bend Tests
full thickness of joint in tension = side bend
for joint thicknesses> ~ 12mm
face in tension = face bend root in tension = root bend
for joint thicknesses< ~ 12mm
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Destructive Testing
Tests are used instead of radiography or ultrasonic examination to show
that satisfactory fusion has been achieve
that the weld is has no defects
QUALITATIVE TESTS: Fillet Fracture & Nick Break Tests
force
fracture from root
machined slotmachined slot
FILLET FRACTURE NICK-BREAK
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PWHT
Steels are given a PWHT to reduce residual stresses caused by
welding [and also to temper (soften) the hardest regions of the HAZ] The main benefit of reducing residual stresses is to improveresistance to brittle fracture - explained as follows: -
Residual stresses can be higher than the max. allowed design stressand are powerful driving forces for propagating flaws (usually cracks)
In the as-welded condition, the steel joint has a lower tolerance toflaws that may become initiation points for brittle cracks
A crack that could cause brittle fracture is called a critical crack
The size of a critical crack depends on the material toughness and
total stress that the crack experiences in the joint (design + residual) An as-welded joint may only be able to tolerate a small critical crack- possibly so small that it could be missed by RT or UT
When residual stresses are removed, a critical crack should be so bigthat it could not be missed during NDT and so would be repaired
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PWHT
Removal of Residual Stress
Temperature (C)
100 200 300 400 500 600 700
YieldStrength(N/mm 2 )
100
200
300
400
500 Cr-Mo steel - typical
C-Mn steel - typical
At PWHT temp. the yieldstrength of steel reduced sothat it it is not strong
enough to give restraint. Residual stress reduced tovery low level by straining(typically < ~ 0.5% strain)
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PWHT
The toughness of the HAZ may be improved - particularly for the morehardenable low alloy steels & improves brittle fracture resistance
Removal of residual stress will give steels resistance to stresscorrosion cracking in certain media - for example in sour oil/gas, inammonia or in contact with nitrates and chlorides
It enables a welded component to be machined to accurate tolerancesthat may otherwise be impossible due constant re -balancing of tensileand residual stresses when metal is removed during machining. Thismay be referred to as a stabilising* PWHT
(* not to be confused with stabilised when referring to stabilising stainlesssteels by alloying additions of Nb or Ti)
Other Benefits of PWHT
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PWHT
PWHT Procedures - Basic Requirements
A PWHT should specify the following: -
The max. heating rate
usually from 300 or 400C depending on Code or item to ensure temp.gradients are not excessive (up to ~ 200C/h max. may be allowed)
large temp. gradients cause high stresses which may give cracking ordistortion
The soak temperature
depends on steel type and usually specified by Code (~550 to ~750 C )
The soak time
to ensure full thickness, and whole item, is at soak temp.
Codes typically require 1h per 25mm of max. joint thickness
The max. cooling rate
usually to 400 or 300C - same reasons as for heating rate control
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PWHT
PWHT Procedures -Additional Considerations
Before a PWHT commences it is necessary to: -
Decide the number of thermocouple attachments and their positions
so that the temperature of the whole component is monitored
If the item needs to be given any additional support
to avoid distortion due to self-weight because it is relatively weak atthe soak temp.
For Localised PWHT
Need to also specify: -
The width of the heated band to ensure that residual stresses at a distance from the weld are removed
The width of the temp. decay bands beyond the heated zone
to ensure high stresses are not produced by large temperature gradients
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Post Weld Heat Treatment
Localised PWHT
PWHT procedures also need to also specify: - The width of the heated band
to ensure that residual stresses at a distance from the weld are removed
should be specified by Code
The width of the temp. decay bands beyond the heated zone to ensure high stresses are not produced by large temperature gradients
should be specified by Code - usually same width as heated band
The position of the thermocouples to monitor the width of heatedbands and the temp. gradient in the decay bands
pipeline weld
heated bandtemp.decay
temp.decay
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Cracking in Weld Joints
RE-HEAT CRACKING
Cracking that occurs when weld joints in certain steels when they arebeing heated to their PWHT temperature or are put into elevated temp.service without PWHT
( this gives this type of cracking the name re - heat )
Susceptible PWHT temp.range ~ 500 to ~ 650C or service 350 - 550 C
Cracking occurs in the HAZ - usually in the zone that has the largestgrain size (the grain growth zone nearest to the fusion line)
grain growth zone
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Cracking Mechanisms
RE-HEAT CRACKING
Re-heat cracking occurs because: -
some strengthening of the steel occurs during heating to the PWHTtemp. (or if in as-welded condition while in service at an elevated temp.)
strengthening occurs by carbide formation
- steels with Vanadium, Chromium and Molybdenum are mostsusceptible because these elements are strong carbide formers
the carbides & nitrides strengthen the grains so that relief of residualstresses takes place by all the strain concentrating at the weaker grainboundaries
if the steel contains certain levels of impurities (such as Tin, Arsenic& Phosphorus) they concentrate at the grain boundaries and reducetheir rupture strength
the presence of large grains in the HAZ means that the impurities aremore concentrated and such regions become the most sensitive tocracking
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Cracking Mechanisms
AVOIDING RE-HEAT CRACKING
The risk of re-heat cracking can be minimised by: -
using steel that has very low impurity levels
various formulas have been developed to relate sensitivity to crackingto levels of impurities
for particularly sensitive steels (usually those with higher Vanadium)ensure that: -
weld bead positions and heat input are controlled to give a finegrained HAZ (temper-beading)
avoid stress concentrations - poor fit-up and sharp weld toes
heat through the sensitive temperature range quickly during PWHT
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Quenched & Tempered Steels
Q & T STEELS
Steels that are strengthened by rapid cooling from an elevatedtemperature (quenching)
Quenching temperature depends on steel composition but typically~900C
Steels are very strong in the quenched condition but ductility and
toughness usually too low for any application Tempering reduces the as- quenched strength and gives usable ductility
and toughness
Tempering temperatures typically ~550 to 760C
Strengthening by quenching is achieved by certain alloying additions thatallow the stronger phases (martensite & bainite) to form (rather than theferrite)
The % of the alloying elements that allow strengthening must be highenough to allow the stronger phases to form through the full thickness
For some steels, the alloying levels need to be higher in thick sections toensure through - hardening
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Quenched & Tempered Steels
Typical Mechanical PropertiesSTEEL TYPE C Si Mn Cr Mo Ni Nb V Yield / 0.2%PS
(N/mm 2)Tensile Strength
(N/mm 2)Elongation(% on 50m
water quenched & tempered at 595 to 480C(100mm round section)
AISI 4130UNS G41300W. Nr. 1.7218ASTM A 505, 646
-0.04
0.400.60
0.81.1 - - - 540 to 655 703 to 800 20 to 25
water quenched & tempered at 595 to 480C(100mm round section)
AISI 8630UNS G86300W. Nr. 1.6545ASTM A 322, 331, 505
0.280.33
0.150.30
0.700.90
0.400.60
0.150.25
0.400.70 - -
495 to 595 660 to 780 21 to 26
oil quenched & tempered at 650 to 540C(100mm round section)
AISI 4140UNS G41400W. Nr. 1.7225ASTM A 322, 331, 505, 519, 646
0.701.00
0.801.10
0.150.25 - - - 580 to 685 772 to 883 19 to 23
oil quenched & tempered at 650 to 540C(100mm round section)
AISI 4340UNS G43400W. Nr. 1.6565ASTM A 332, 505, 519, 547, 646
0.380.43
0.150.30
0.600.80
0.700.90
0.200.30
1.652.00 - - 786 to 1000 924 to 1138 16 to 20
EXAMPLES of Q & T STEELS
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Quenched & Tempered Steels
EXAMPLES of Q & T STEELS
Mechanical PropertiesSTEEL TYPE C Si Mn Cr Mo Ni Nb V N
OtherYield / 0.2%PS
(N/mm 2)Tensile Strength
(N/mm 2)Elongation(% on 50mm)
A 335-P91X10CrMoVNb9-1(steel number 1.4903)
0.080.12
-0.50
0.300.60
8.009.50
0.851.05
-0.40
0.060.10
0.180.25
0.0300.070
Al-
0.040= 415 585 = 22
12CrMoV11-1
(steel number 1.4922)
0.170.23 0.40
0.301.0
10.012.5
0.801.20
0.300.80
- 0.200.35
- - = 500 700 -850 = 16
A 335-P9110.100.13
0.100.30
0.300.60
8.509.50
0.901.10
0.200.40
0.060.10
0.150.25
0.0500.080
W0.901.10 = 440 = 620 = 22
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Quenched & Tempered Steels
EXAMPLES of Q & T STEELS
Typical Chemical Composition Typical Mechanical Properties (t=25mm)STEEL TYPE
C Si Mn Cr Mo Ni Nb V Ti Al OtherYield/0.2%PS
(N/mm 2)Tensile Strength
(N/mm 2)Elongation(% on 50mm)
WELDOX 700 -0.20
-0.60
-1.60
-0.70
-0.70
-2.0
-0.04
-0.09
-0.04
-0.015
N (min) 0.0015B (max) 0.005 = 700 780 - 930 = 18
WELDOX 900 -0.20
-0.50
-1.60
-0.70
-0.70
-2.0
-0.04
-0.06
-0.04
-0.018
N (min) 0.0015B (max) 0.005 = 900 940 - 1110 = 16
WELDOX 960 -0.20
-0.50
-1.60
-0.70
-0.70
-2.0
-0.04
-0.06
-0.04
-0.018
N (min) 0.0015B (max) 0.005 = 960 980 -1150 = 16
WELDOX 1100 -0.21
-0.50
-1.40
-0.80
-0.70
-3.0
-0.04
-0.08
-0.02
-0.020
N (min) 0.0015B (max) 0.005 = 1100 1250 - 1550 = 12
WELDOX is a registered Trade Name of SSAB Oxelosund
Chemical compositions and tensile properties of some HSLA steels used for structural applications
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Quenched & Tempered Steels
Welding of Q & T Steels
Alloying additions used to achieve strengthening also will givehardening of the HAZ
Higher HAZ hardness give higher risk of cracking and the needto always use low Hydrogen welding processes and also theneed to use pre-heat for most grades
Higher HAZ hardness usually mean that many of these steelsrequire PWHT to improve resistance to brittle fracture
Careful control of heat input - not too high - may be needed forsome steel types to avoid softening of the HAZ and loss ofstrength
For the highest strength grades there may be difficulty inachieving matching strength weld metal that has goodtoughness and ductility
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Pre-Heat & Interpass Temperature
Pre-Heat Temperature
Applied to reduce risk of cracking - helps to allow H to escape fromthe weld joint and can reduce hardness of HAZ for some steels
Pre-heat temperature should be checked on both sides of the jointat a distance of at least 75mm from joint edge
Pre-heat should be checked on the other side from the pre-heatedside - if access allows
If hand held gas pre-heating is used, temp. should be checked ashort time after the heating torch has been removed
Interpass Temperature
This is the temp. at the position that the welder will re-startwelding in a muti-run weld
Temperature should be measured on the steel as close as practicalto the re-start position (it can be taken on the weldat that point)
Recommended