04 Basic Joints and Welds

5/26/2018 04 Basic Joints and Welds

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PowerPoint to accompany

WeldingPrinciples and Practices4th edition

Edward R. Bohnart

2012 The McGraw-Hill Companies, Inc. All rights reserved.

Chapter 4

Basic Joints

and Welds


2/111 2012 The McGraw-Hill Companies, Inc. All rights reserved.

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Objectives

1. Describe five basic joints and the welds appliedto each.

2. Measure fillet and groove weld sizes.

3. Determine position of welding for groove andfillet welds on plate and pipe.

4. List factors that will affect strength of a weldedjoint.

5. Describe difference between a welddiscontinuity and a weld defect.

6. Describe visual inspection and its limitationsand advantages.



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Five Types of Joints

Butt joint

Corner joint

Edge joint Lap joint

T-joint

In Chapter 28, the most

common joints will be

described in terms of their

use, advantages anddisadvantages, joint

preparation, and economy.



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Four Weld Types

Bead (surface) weld

Fillet weld

Groove weld Plug or Slot weld

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Bead Welds

Also called surface welds

Single-pass deposits of weld metal

Used to build up pad of metal and to

replace metal on worn surfaces

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Fillet Welds

Consist of one or more beads deposited inright angle formed by two plates

Take right triangular cross section due to

location placed in weld joint

Used for lap joints, T-joints,

and open corner joints

Weld symbol takes sameright triangle shape as weld

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Fillet Weld

Important aspectis its profile

American Welding Society, Welding Inspection Technology, 4th ed., p. 4-24, Fig. 4.22, 2000.




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Groove Welds

Consist of one or more beads deposited ingroove

Used for butt joints

Unprepared with square

edges

Prepared with bevel or J-groove

If both members prepared same, take shape ofV or U and named V-groove or U-groove butt joint

Weld applicable on both plate and pipe




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Groove Welds

American Welding Society




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Plug Welds

Similar to slot welds

Used for filling slotted or circular

holes in lap joints

Fillet weld may be made

around faying surface of joint

if hole large

May or may not completely fill joint Hole or slot may be open at one end

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Examples

American Welding Society, Welding Inspection Technology, 4th ed.,

pp. 4-20 and 4-21, Figs. 4.16d and 4.17a,b, 2000.





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Weld Size and Strength

Design engineer determines load-carrying

capacity of welded joint

Specified on drawing

Use welding symbols

Symbols covered in Chapter 30



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Groove Welds

Measured and sized by depth ofpenetration/fusion into joint

Size does not include reinforcement on face

or root of weld Generally referred to as partial joint

penetration (PJP) welds or complete joint

penetration (CJP) No size reference, then considered to be CJP

PJP weld designated on welding symbol




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14

CJP V-groove Butt Joint

Note that the reinforcement on the face

and/or root does not count as part of weld size.

Complete

joint

penetration

groove welds

used wherethe maximum

load-carrying

capacity is

requiredfor the joint.

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ractices,4e

15

Groove Weld Fusion Terms

The weld interface is the line between the weld and the HAZ.







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16

Seal Welds

Continuous welds running entire length ofriveted joints seal

Usually single-pass welds deposited along

root of joint Not expected to carry

heavy load

Intended primarily

to provide leak tightness





17




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17

Groove Weld





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19R i f t f G


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19Reinforcement for GrooveWelds

Excessive reinforcement

above allowable limit

waste of time and weldmaterial and also

decreases working

strength of joint because

of concentration ofstresses at toe of the

weld.



20


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Groove Weld

Metal deposited beyond groove face wasteof time and filler metal

Adds to overall heat input

Increases resultant residual stressesAdds cost to joint

Decreases strength

CJP welds designed to possess maximumphysical characteristics of base metal Minimum size called for on welding symbol

must be made to fit intended purpose

21Partial Joint Penetration


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21Partial Joint PenetrationV-groove Weld Butt Joint

It would only be considered incomplete joint penetration

if CJP groove was called for.

American Welding Society,

Welding Inspection Technology,

4th ed., p. 4-25, Fig. 4.24, 2000.




22


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Fillet Welds

Most common weld used in industry

As strong or stronger than base metal if weld

correct size and proper welding techniques used

Contour is shape of face of weld Flat

Convex

Concave




23


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Convex Fillet Weld

American Welding Society, Welding Inspection Technology,

4th ed., p. 4-26, Fig. 4.27, 2000.




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Excessive Convexity

Should be avoided

Increases cost

Wastes filler metal

Concentrates more stresses at toes of

weld

Based on width of weld face

Only slight amount of convexity if specified to

be convex

25Maximum Convexity


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25Maximum ConvexityAllowable on Fillet Welds

Table 4-1 from Text

Width of weld face of total maximum

joint or weld bead (in) convexity(in)less than or equal to 5/16 1/16

greater than 5/16 1/8

greater than or equal to 1 3/16

26


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Concave Fillet Weld

American Welding Society, Welding Inspection Technology,

4th ed., p. 4-26, Fig. 4.27, 2000.




27


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Concave Fillet Weld

Size and leg two different dimensions Leg is dimension from weld toe to start of

joint root

Size is measured as largest right triangleinscribed within weld profile

Special fillet weld gauge used to measure

Stress concentrations improved over other

types Better endurance limit under fatigue loading

28


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28

Ideal Fillet Weld Shape


29


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29

Type of Fillet Profile to Use

All three types widely used

Design engineer specifies on the weld

symbol

Determined by: Position of welding

Process

Type of consumables (gas, electrode) Type of joint

Job requirements

30Measuring Fillet Welds by


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30Measuring Fillet Welds byThroat Size (Three Methods)

1. Theoretical throat Extends from point where the two base metal

members join to the face of the largest right

triangle that can be inscribed in the weld Convexity on convex fillet weld and concavity

on concave fillet weld need not beconsidered

Penetration not figured into this throat size



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2. Effective throat Measured from depth of joint root penetration

No credit given for convexity

On convex and concave fillet welds,measured to face of largest right triangle that

can be drawn in weld

Measuring Fillet Welds byThroat Size (Three Methods)



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32Measuring Fillet Welds byThroat Size (Three Methods)

3. Actual throat Same as effective throat on concave fillet

weld

Can be used to indicate size and strength

33


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Correct Weld




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Over Welded




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Under Welded

Remember: A weld or weld joint is nostronger than its weakest point.




36Joining Metals of Different


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Joining Metals of DifferentThicknesses

Rule: Size of the

fillet weld legshould equal

the thickness of

metal beingwelded.




37Equal Leg 1/2 inch Fillet


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Equal Leg 1/2 inch FilletWeld

Wasted weld metal, time,

and extra heat input.

Weakest point will be at

the toes of weld on the1/4 inch plate.

C

opyrightTheMcGraw-HillCom



38Equal Leg 1/4 inch Fillet


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Less time, less weld metal,less heat input = better weld

Just as strong as two

prior examples

Equal Leg 1/4 inch FilletWeld

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Weld Length

Fillet and groove welds usually made alongfull length of joint Sometimes full strength can be achieved by

welding a portion of joint

Effective length of fillet weld measured asoverall length of full-size fillet weld

Start and stop of weld must be allowed for

Not square, so allowance made when measuring

Space between welds determined by center-to-center distance of weld which is calledpi tch

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Weld Area and Stress

Easily calculated Important to determine how much stress

joint can take

area = weld lengthweld size

Safety margins are built in to ensure

the weld is able to withstand the load.

stress load

weld area

41


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Continuous Welds

Extend across entire length of joint fromone end to the other

For structures to develop maximum

strength andtightness, needto weld all seamscompletely

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Intermittent Welds

Series of short welds spaced at intervals

Cannot be used where maximum strength

required or work must be watertight or

airtight Cost reduced

Frequency, length, and size depend upon

thickness of plates, type of joint, method ofwelding, and job service requirements

Usually employed in lap and T-joints

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Intermittent Weld

WeldSpace

Weld

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Tack Welds

Short welds spaced at intervals to join partsto whole in process of assembly beforewelding

Must be strong

Hold part in position

Able to resist stress when expansion andcontraction occur during welding

Number and size of tack welds depend uponthickness of plate, length of seam, andamount of cold working to be done

45


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Tack Welds

Use more heat for tack welding than formajor welding

Must have good fusion and good root

penetration Flat and smooth


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S


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Stringer Bead

Weld made by moving weld pool alongintended path in straight line

Fast cooling rates because of faster travel

speed Can impact grain structure and affect distortion

level


p. 4-27, Fig. 4.32, 2000.

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47

W B d


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Weave Bead

Weld made by moving weld pool alongintended path but with side-to-side

oscillation

Generally done to increase weld size Codes will limit width

Reduced travel speed increases heat input

and slows cooling rate Impact grain structure and affect distortion

level

48

W B d


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Weave Bead

Controlling maximum weave width will helpeliminate slag inclusions and incompletefusion type discontinuities


p. 4-27, Fig. 4.32, 2000.


49

W ld P iti


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Weld Positions

Four basic positions: Flat

Horizontal

Vertical Overhead

Designated with number system to aid in

oral or written communication

50

Fl t P iti (N b 1)


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Flat Position (Number 1)

Position used to weld from upper side ofjoint

Weld axis approximately horizontal

Weld face lies in approximately horizontal plane

Bead Weld

Flat Plate

Groove Weld

Butt Joint Corner Joint

Fillet Weld

Tee Joint Lap Joint


51

H i t l P iti (N b 2)


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Horizontal Position (Number 2)

Weld on upper side of horizontal surfaceagainst vertical surface

Weld axis at point of welding: horizontal

Weld face: vertical plane

Bead Weld

Flat Plate

Groove Weld


Fillet Weld

Tee Joint Lap Joint


52

V ti l P iti (N b 3)


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Vertical Position (Number 3)

Weld axis at point of welding vertical Weld face lies in approximately vertical plane

Travel up, torch pointed up, at angle ahead ofweld

Travel down, torch pointed up, at angle to weldpool

Bead Weld

Flat Plate

Groove Weld


Fillet Weld

Tee Joint Lap Joint


53

O h d P iti (N b 4)


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Overhead Position (Number 4)

Welding performed from underside of joint Reverse of flat position

Bead Weld

Flat PlateGroove Weld


Fillet Weld

Tee Joint Lap Joint


54Example Welds and Welding


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Example Welds and WeldingPositions



55Plate Weld Designations


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Plate Weld DesignationsGroove Welds

1G - Flat position

3GVertical position

2G - Horizontal position

4G - Overhead position


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56Pipe Weld Designations


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Pipe Weld DesignationsGroove Welds

1GFlat position Pipe axis horizontal and pipe rotated

2GHorizontal Pipe axis vertical

5GMultiple-position Overhead, vertical, and flat

Pipe axis horizontal and pipe not rotated

1GFlat position Pipe axis horizontal and pipe rotated


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57Plate Position Designations


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Plate Position DesignationsFillet Welds

1FFlat position

4FOverhead position

2FHorizontal position

3FVertical Position

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58Pipe Position Designations


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1FFlat position Pipe axis 45 from horizontal

2FHorizontal Pipe axis vertical

4FOverhead Pipe axis vertical

5FMultiple positions Pipe axis horizontal, pipe fixed


Pipe Position DesignationsFillet Welds

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59Pipe Position Designations


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6FMultiple position Pipe 45 from horizontal

Pipe not rotated


Pipe Position DesignationsFillet Welds

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60Production Welding Positions


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gDiagram for GrooveWelds in Plate

Horizontal reference plane

always taken to lie below

weld under consideration.


61Production Welding Position


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gDiagram for FilletWelds in Plate

Horizontal reference plane

always taken to lie below

weld under consideration.


Angle of rotation of theweld face is determined by

a line perpendicular to

weld face at its center

which passes through

the weld axis.


62Production Welding Position


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gDiagram for GrooveWelds in Pipe

Positions for circumferential

groove welds indicated by

shaded areas for pipe

with axis varying fromhorizontal (0) to

vertical (90).


63

Strength of Welds


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Strength of Welds

Welded joints as strong (or stronger) thanbase metal being welded

Good welding design specifies welds that

require minimum amount of weld metal Weld metal costs more than base metal and

labor costs for application

64Factors Determining Strength


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g gof Welded Joint

Strength of weld metal Type of joint preparation

Type of weld

Location of joint in relation to parts joined Load conditions to which weld subjected

Welding process and procedure

Heat treatment Skill of welder

65Common Weld and


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Weld-Related Discontinuities

Weld discontinuityany interruption innormal flow of structure of weldment

Interruption can be found in physical,mechanical, or metallurgical characteristics

Discontinuity becomes a defect when itexceeds the acceptance criteria

All metals and welds have discontinuities

Metals crystalline structures, interruptions ateach grain boundaries reflects interruption ofnormal flow of material

66Location of Welds in


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Relation to Parts Joined

Has effect on strength of welded joint

Transverse welds stronger

than welds parallel to

lines of stress.


67

Stress Reduction


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Stress Reduction

Resistance to turning effect of one memberat joint best obtained by welds that are well

separatedExample of proper placement

of welds to resist turning effectof one member of the joint.

Single weld at A not as

effective as welds atboth A and B.


68

Stress Concentration


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Stress Concentration

A lap weld havingpoor distribution of

stress throughthe weld.

Excessive convexity

A lap weld having amore even distribution

of stress.

A lap weld in whichthere is a uniformtransfer of stressthrough the weld.

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69Minimizing Stress


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gConcentration

Stress greater at ends of weld than inmiddle for many load conditions

Advisable to box the bead around joint Far greater resistance to tearing action on weld

Length of boxing should be minimum of twice sizeof weld specified

Example of weld boxing around

the corners to obtain resistanceto tearing action on welds when

subjected to eccentric loads.


70

Fillet Weld Profiles


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Fillet Weld Profiles

Desirable

Desirable

Acceptable

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71Fillet Weld with Insufficient


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Throat

Reduction of effective throat materiallyreduces size of weld

Concentrates stress at center

Weaken weld and invitejoint failure

Defect caused by

too fast travel andexcessive welding current

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72Fillet Weld with ExcessiveC it


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Convexity

May contain great deal of porosity Due to slag and gas entrapment

Poor fusion at root of weld and poor fusion

of weld metal to plate surfaces Stress concentrates attoe of weld

Usually caused by lowwelding current and slowrate of travel

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73Fillet Weld with Incomplete


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pFusion

At problem area A,there is incomplete

fusion in the fillet

welds.At problem area B,

the weld has bridged

the joint root and isan incomplete

fusion. American Welding Society

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74Fillet Weld with ExcessU d t


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Undercut

Decreases thickness of plate at that pointleads to plate weakness

Invites joint failure Designed load of joint based on original plate

thickness Failure increased when under-cutting occurs at toe of weld High stress concentration point

Defect caused by improper arcmanipulation, fast travel, andexcessive welding current


75

Fillet Weld with Overlap


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Fillet Weld with Overlap

Sign of poor fusion (poor bond) betweenweld metal and base metal

Load applied to welded joint, weld will peelfrom surface (weld failure)

Failure certain whenoverlap located at toeof weld

Caused by low weldingcurrent, fast travel, orimproper electrode manipulation


76Fillet Weld with InsufficientL


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Leg

Reduction in leg length is reduction in sizeof fillet weld

Results in weld that does not possessphysical properties needed for safeoperation

Usually caused by improperelectrode angle and faulty

electrode manipulation May be accompanied by

too fast travelCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

77Fillet Weld with PoorP t ti d F i


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Penetration and Fusion

Defect usually found at root of weld andplate surfaces

Stress concentrated at toe of weld

Poor penetration and fusion caused by: Welding with current too low

Improper speed of travel

Improper electrode manipulation

Deposited weld metal may become porousdue to slag and gas entrapment

78Fillet Weld with Various OtherDi ti iti


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Discontinuities

Uniformly

scattered

and piping

porosity

Cluster porosity

Aligned

porosity

Slag

inclusionIncomplete

fusion

Undercut

Overlap


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Delamination Lamination

Seam and lapLongitudinal crack


DiscontinuitiesCo





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Transverse crack

Toe crack

Underbead and

heat-affected zone cracks

Root crack

Crater crackThroatcrack


DiscontinuitiesCo



81

Porosity


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Porosity

Cavity-type discontinuities (pores) formedby gas entrapment during solidification

Discontinuities are spherical and may beelongated

Usually caused by contamination of fillermetal or base metal or impropergas shielding

Not considered assevere concern ascracks or incomplete fusion

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82Acceptable Porosity LimitsGuideline (structural steel)


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Guideline (structural steel)

Sum of diameters

Type of weld of individual Length

and location Diameter porosity pores of weld

Groove-transverse No visible piping N/A N/Ato tensile loading porosity allowed

Groove-fillet > 1/32 3/8 3/8 1

Groove-fillet 3/8 3/4 12

Fillet-CJP groove 3/32 single pore 4piping porosity

Table 4-2 from Text *Note: inch measurements


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84Groove Weld with InsufficientSize (Underfill)


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Size (Underfill)

Decrease in size, reduces size of butt weld Thickness of weld less than thickness of

plate Weld will not be as strong as plate

Failure under maximum load certain Caused by combination of high welding

current and too fast travel


85Groove Weld with ExcessiveConvexity


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Convexity

Less strong than weld with insufficient size Concentration of stress in weld

Caused by travel that is too slow or low

welding current Possibility of porosity and slag inclusion in

weld

Poor appearance


86

Groove Weld with Undercut


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Groove Weld with Undercut

Results in reduction of actual plate thickness Reduction in plate surface, and

concentration of stress at toe due to sharpcorner may cause failure of welded joint

Discontinuity to be avoided Does not need to be repaired unless

exceeds acceptance criteria

Caused by high weldingcurrent, too fast travel,or improper electrodemanipulation

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88Groove Weld With OtherDiscontinuities


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Discontinuities

Slag inclusions, betweenpasses at A, and atundercut at B

Incomplete fusion andincomplete penetration

in a groove weld

Incomplete fusion from

oxide or dross of centerof joint, especially inaluminum


89Groove Weld with VariousOther Discontinuities


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Single-bevel

groove weld in a butt joint

Uniformly

scattered

and pipingporosity

Cluster porosityAligned

porosity

Slag inclusion

Incomplete fusion

Incompletejoint

penetration


Other DiscontinuitiesCopyrightTheMcGraw-HillCompa

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actices,4e

Single-bevelgroove weld in a butt joint

Undercut

Underfill

Overlap

Lamination

Delamination

Seam and lap

American Welding SocietyCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Other Discontinuities



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Other Discontinuities

Single-bevel groove

weld in a butt joint

Longitudinal crack

Transverse crack

Crater crackThroat crack

Root crack

Underbead and heat-affected

zone (HAZ) cracks

American Welding SocietyCopyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

92Other DiscontinuitiesCracks


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Cracks

Fracture-type discontinuity with sharp tipand length greater than its width or

opening

Not allowedconsidered defects and mustbe repaired

Considered stress riser because of sharp

tip Propagate rapidly across joint or weldment

93

Cracks


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C ac s

Hot cracks Hot cracks caused by insufficient ductility athigh temperatures

Move between grains in weld metal or at weld

interface Cold cracks Occur once weld metal has solidified

Weld metal, heat-affected zone, or base metal

affected Occur because of improper welding procedure

or techniques or welding service condition

94

Example of a Crack


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p

Note the crack in the crater area of the weld. Crater was notproperly filled to full cross section of weld. Small crack formed

in crater due to shrinkage forces, and crack propagated out of

crater all the way around the joint.American Welding Society, Welding Inspection Technology, 4th ed., p 9-6, Fig. 9.7, 2000.

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95

Hydrogen Cracking


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y g g

Delayed cracking Brought about by one of the following:

Presence of hydrogen

Hard grain structuresAmount of restraint in the joint

Low temperature operation of weldment

Only hard grain structures sensitive to thistype of cracking

96

Hydrogen Cracking


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y g g

Hydrogen in form of moisture comes frommany sources

Coating on SMAW electrode

Flux in core of FCAW electrode Oxides on metal

Lubricants

Contamination on plate or filler metal Moisture in air


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98

Hydrogen Cracking


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actices,4e

y g g

Good practice to use proper weldingprocedures to control cooling rate

Use of preheat and interpass temperatureand postweld heat treatment may berequired

Usually found in heat-affected zone (HAZ) Cracks may not open to surface so called

underbead cracks Difficult to locate Final inspection delayed to allow crack to come to

surface

99

Incomplete Fusion


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actices,4e

p

Weld discontinuity that occurs when weldmetal is in contact with other weld metal,

joint groove, or rootface, but does not fuse

with itExamples of incomplete fusion at various locations

Co




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102

Incomplete Joint Penetration


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ractices,4e

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Undesirable because:At root of joint, may be subject to tension orbending forces, weld size not large enoughand failure occurs

Shrinkage forces of weld cooling may lead tocracks May propagate from root out into base metal or out

through subsequent weld passes

Penetration is measured by how far weld

penetrates into joint (not the base metal) Line indicating depth of effective throat also

indication of amount of root penetration


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105

Underfill


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WELDING:P

rinciplesandP

ractices,4e

Exists when weld face or root surfaceextends below surface of material beingwelded

Results from poor welder observation and

technique Some usually allowable depending upon

code

Usually provide better fatigue properties

than overwelding


106Discontinuities, Defects, andVisual Inspection


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WELDING:P

rinciplesandP

ractices,4e

Visual Inspection

Avoid all defectslittle tolerance permittedin critical or code work

Criticality of discontinuity one way of

assessing importance of classifying it asdefect

Actual repair of discontinuity may create more

problems

Engineer take all issues into consideration

when determining if meets acceptance criteria


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111

Visual Inspection


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LDING:P

rinciplesandP

ractices,4e

Effective tool in controlling overall weldquality

VI limited to visible surface of weld

External surfaces of weldments see higheststresses in service

Cost-effective inspection method

Sees defects as they occur

VI and Handheld Scanner allows discovery

and repair of defects as they occur!

Documents

04 Basic Joints and Welds