98707945 weld technology defects

7/29/2019 98707945 Weld Technology Defects

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NDT 2/20 Revision 1 Sep 2004 World Centre for Materials Joining Technology

Weld

Technology and Defects


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Welding Terminology

Butt Joints

Single Sided Butt

Double Sided Butt

Square EdgedClosed Open

Vee Bevel

Vee Bevel


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Welding Terminology

Fillet Joints

Lap

Corner

Tee


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Welds

An ideal weld must give a strong bondbetween materials with the interfacesdisappearing

To achieve this

Smooth,flat or matching surfaces

Surfaces shall be free from contaminants

Metals shall be free from impurities

Metals shall have identical crystalline structures


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Welding

A union between pieces of metal at facesrendered plastic or liquid by heat,pressure orboth.BS 499

UltrasonicsElectron beam

FrictionElectric resistanceElectric arc

Possible energy sources


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Electric Arc Welding

Power

supply

Work piece

Electrode

Clamp(Earth)


7/40NDT 2/20 Revision 1 Sep 2004 World Centre for Materials Joining Technology


Electric discharge produced between cathodeand anode by a potential difference (40 to 60volts)

Discharge ionises air and produces -veelectrons and +ve ions

Electrons impact upon anode, ions uponcathode

Impact of particles converts kinetic energy toheat (7000o C) and light

Amperage controls number of ions andelectrons, Voltage controls their velocity




Arc Welding Processes Manual metal arc

Tungsten Inert Gas

Metal Inert Gas

Submerged Arc

Differences between them:

Methods of shielding the arc Consumable or Non-consumable electrode Degree of automation



Zones in Fusion Welds

Parent Material or Base Metal

Heat Affected Zone

Fusion Zone



Manual Metal Arc Welding

Shielding provided bydecomposition of fluxcovering

Electrode consumable

Manual process

Welder controls

Arc length

Angle of electrode Speed of travel

Amperage settings



Manual Metal Arc (MMA)

Consumableelectrode

Fluxcoating

Core wire

Arc

Evolved gasshield

Parent metal

Slag

Weld metal



Tungsten Inert Gas (TIG)

Non-consumabletungstenelectrode

Arc

Parent metal Weld metal

Gas shield

Filler wire

Gas nozzle



Metal Inert Gas (MIG)

Consumableelectrode(filler wire)

Arc

Parent metal Weld metal

Gas shield

Gas nozzleReel feed



Submerged Arc



Submerged Arc

Consumableelectrode

Reel feed

Flux feed

Fluxretrieval

Parent metalWeld metal

Slag



Welding Defects

Classified by Shape

Longitudinal

Transverse

Branched

Chevron

CracksClassified by PositionHAZCentreline

CraterFusion zoneParent metal



Welding Defects

4 Crack Types

Solidification cracks

Hydrogen induced cracks Lamellar tearing

Reheat cracks

Cracks



Welding Defects

Solidification

Occurs during weld solidification process

Steels with high sulphur content (low ductility atelevated temperature)

Requires high tensile stress

Occur longitudinally down centre of weld

e.g. Crater cracking

Cracks



Welding Defects

Solidification Cracking



Welding Defects

Hydrogen Induced

Requires susceptible grain structure, stress andhydrogen

Hydrogen enters via welding arc

Hydrogen source - atmosphere or contamination ofpreparation or electrode

Moisture diffuses out into parent metal on cooling

Most likely in HAZ

Cracks


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Welding Defects

Hydrogen Cracking


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Welding Defects

Lamellar Tearing

Step like appearance

Occurs in parent material or HAZ

Only in rolled direction of the parent material Associated with restrained joints subjected to

through thickness stresses on corners, tees andfillets

Requires high sulphur or non-metallic inclusions

Cracks


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Welding Defects

Lamellar Tearing

Restraint

High

contractionalstress

Lamellar tear


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Welding Defects

Re-Heat Cracking

Occurs mainly in HAZ of low alloy steels duringpost weld heat treatment or service at elevated

temperatures Occurs in areas of high stress and existing defects

Prevented by toe grinding, elimination of poorprofile material selection and controlled post weld

heat treatment

Cracks


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Welding Defects

Incomplete root penetration

Causes

Too large or small a root gap

Arc too long

Wrong polarity

Electrode too large for jointpreparation

Incorrect electrode angle

Too fast a speed of travel forcurrent


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Welding Defects

Causes

Too small a root gap

Arc too long

Wrong polarity

Electrode too large forjoint preparation

Incorrect electrode angle

Too fast a speed of travel

for current

Incomplete root Fusion


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Welding Defects

Root concavity

Causes Root gap too large Insufficient arc energy Excessive back purge TIG


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Welding Defects

Excess Root Penetration

Causes Excessive amperage during welding of root Excessive root gap (poor fit up) Excessive root grinding

Improper welding technique


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Welding Defects

Root undercut

Causes Root gap too large Excessive arc energy Small or no root face


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Welding Defects

Cap Undercut

Causes Excessive welding current Welding speed too high

Incorrect electrode angle Excessive weave Electrode too large


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Welding Defects

Lack of fusion

Causes Contaminated weld preparation

Amperage too low Amperage too high (welder increases speed of

travel)


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Welding Defects

Incompletely Filled Groove& Lack of Side wall Fusion

Causes

Insufficient weld metal deposited

Improper welding technique


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Welding Defects

Inter run Incompletely Filled Groove

Causes

Insufficient weld metal deposited Improper welding technique


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Welding Defects

Gas pores / Porosity

Causes Excessive moisture in flux or preparation Contaminated preparation

Low welding current Arc length too long Damaged electrode flux Removal of gas shield


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Welding Defects

Inclusions - Slag

Causes Insufficient cleaning between passes

Contaminated weld preparation Welding over irregular profile Incorrect welding speed Arc length too long


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Welding Defects

Inclusions - Tungsten

Causes Contamination of weld Caused by tungsten touching

weld metal or parent metal during welding using the

TIG welding process


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Welding Defects

Burn Through

Causes Excessive amperage during welding of root Excessive root grinding Improper welding technique


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Welding Defects

Spatter

Causes Excessive arc energy

Excessive arc length Damp electrodes Arc blow


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Welding Defects

Arc StrikesCauses

Electrode straying onto

parent metal

Electrode holder withpoor insulation

Poor contact of earthclamp


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Welding Defects

Mechanical Damage

Chisel MarksChisel MarksChisel Marks Pitting Corrosion Grinding Marks

98707945 weld technology defects

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