Download - 98707945 Weld Technology Defects
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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)
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Electric Arc Welding
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
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Electric Arc Welding
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
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Zones in Fusion Welds
Parent Material or Base Metal
Heat Affected Zone
Fusion Zone
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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
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Manual Metal Arc (MMA)
Consumableelectrode
Fluxcoating
Core wire
Arc
Evolved gasshield
Parent metal
Slag
Weld metal
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Tungsten Inert Gas (TIG)
Non-consumabletungstenelectrode
Arc
Parent metal Weld metal
Gas shield
Filler wire
Gas nozzle
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Metal Inert Gas (MIG)
Consumableelectrode(filler wire)
Arc
Parent metal Weld metal
Gas shield
Gas nozzleReel feed
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Submerged Arc
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Submerged Arc
Consumableelectrode
Reel feed
Flux feed
Fluxretrieval
Parent metalWeld metal
Slag
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Welding Defects
Classified by Shape
Longitudinal
Transverse
Branched
Chevron
CracksClassified by PositionHAZCentreline
CraterFusion zoneParent metal
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Welding Defects
4 Crack Types
Solidification cracks
Hydrogen induced cracks Lamellar tearing
Reheat cracks
Cracks
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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
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Welding Defects
Solidification Cracking
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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