Download - Welding Techniques & Welding Defects
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Am e r i c a n We l d i n g S o c i e t y
Module 3 -
Module 3
Metal Joining
and
Cutting Processes
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Welding Process Knowledge -A Benefit to Inspectors
Helps spot problems
Leads to better inspection
Gains respect of welders Gains cooperation
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Common Features of Welding
Processes Source of energy
Source of shielding
Filler metal (optional)
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Shielded MetalArc Welding
(SMAW)
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SMAW
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E X X X XSMAW Electrode Identification SystemElectrode
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E X X X XSMAW Electrode Identification SystemStrength
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E X X X XSMAW Electrode Identification System
Position
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Position Description
1 - used in all positions
2 - used in flat or horizontal fillets only
3 - not used at present time 4 - used for downhill progression
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E X X X XSMAW Electrode Identification System
Coating/Operating Characteristics
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Module 3 - 1
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Low alloy steel electrodes
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Low Hydrogen Electrodes
Types end in a 5, 6, or 8
Purchase in sealed, metal containers
Store after opening in heated, vented oven Limit atmospheric exposure
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Stainless Steel Electrodes
E308, E308L - Weld 304 and 304L
E316, E316L - Weld 316 and 316L
E309 - Weld Stainless to Carbon Steel
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SMAW Equipment
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SMAW Limitations
Relatively slow
Slag removal
Electrode storage considerations Arc blow- solutions noted in text
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GTAW Nomenclature
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Gas Tungsten ArcWelding
Equipment
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AWS Tungsten ElectrodeClassifications
Class Alloy Color
EWP Pure tungsten Green
EWCe-2 1.8-2.2% ceria Orange
EWLa-1 1% lanthanum oxide BlackEWTh-1 0.8%-1.2% thoria Yellow
EWTh-2 1.7-2.2% thoria Red
EWZr 0.15-0.40% zirconia Brown
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GTAW application
AL welding
- EWP ( Green)
- AC ( Cleaning action )
Ferrous metals welding
- EWTh-2 ( Red )
- DCEN
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GTAW Shielding gases
Argon ( 7-16 L / min )- High density
- weld all metals except reactive andrefractory
Helium ( 14 24 L / min )- Light gas ( suitable for overhead )
- Good penetration
Argon + helium or Argon + hydrogen15 % H2 increase welding speed by 50 %
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GTAW Advantages
Good for thin materials ( .005 inch ) High quality welds
Good appearance
High quality for weld root by using current remote contro
No arc striking with high frequency start current No slag
No spatter
Autogeneous & heterogeneous
Mechanization potential
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GTAW Limitations
Relatively slow
Low tolerance for contamination
Shielding gas expensive
Purging gas expensive
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Causes of Tungsten Inclusions
Contact between:
Tungsten and base metal
Tungsten and filler metal
Excess current
Excess tungsten extension
Improper tungsten tip grinding
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SubmergedArc Welding
(SAW)
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SAWEquipment
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SAW
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Defect
A flaw or flaws that by nature oraccumulated effect render a part or productunable to meet minimum applicable
acceptance standards or specifications. Theterm designates rejectability.
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Discontinuity
An interruption of the typical structure of amaterial, such as a lack of homogeneity inits mechanical, metallurgical, or physical
characteristics. A discontinuity is notnecessarily a defect.
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Weld Joint Discontinuities
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Module 3 30Weld Joint Discontinuities Misalignment (hi-lo)
Undercut
Underfill
Concavity or Convexity
Excessive reinforcement
Improper reinforcement
Overlap
Burn-through
Incomplete or Insufficient
Penetration
Incomplete Fusion
Surface irregularity
Overlap
Arc Strikes
Porosity
UniformlyScattered
Cluster Linear Piping
Cracks Longitudinal Transverse Crater Throat Toe Root Underbead and
Heat-affected zone Hot Cold or delayed
Inclusions
Slag
WagontracksTungsten
Spatter
Arc Craters
Heat-affected zone
microstructure alteration Base Plate laminations
Size or dimensions
Base Metal Discontinuities
Lamellar tearing
Laminations andDelaminations
Laps and Seams
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Module 3 3
Cracks
Longitudinal
Transverse
Crater
Throat
Toe
Root
Underbead and Heat-affected zone
Hot Cold or delayed
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Am e r i c a n We l d i n g S o c i e t y
Definition: A crack running in the direction of the weld axis. Ma
found in the weld or base metal.
Cause: Preheat or fast cooling problem. Also caused by shrinkag
stresses in high constraint areas.
Prevention: Weld toward areas of less constraint. Also preheat to
even out the cooling rates.
Repair: Remove and reweld
Longitudinal Crack
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Definition: A crack, generally in the shape of an X which is fo
in a crater. Crater cracks are hot cracks.
Cause: The center of the weld pool becomes solid before the out
of the weld pool, pulling the center apart during cooling
Prevention: Use crater fill, fill the crater at weld termination and
preheat to even out the cooling of the puddle
Repair:
Crater Crack
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Am e r i c a n We l d i n g S o c i e t y
Definition: A crack in the base metal beginning at the toe of the
weld
Cause: Transverse shrinkage stresses. Indicates a HAZ brittlenes
problem.
Prevention: Increase preheat if possible, or use a more ductile fil
material.
Repair:
Toe Crack
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Am e r i c a n We l d i n g S o c i e t y
Definition: A crack in the weld at the weld root.
Cause: Transverse shrinkage stresses. Same as a throat crack.
Prevention: Same as a throat crack
Repair:
Root Crack
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Am e r i c a n We l d i n g S o c i e t y
Definition: A crack in the unmelted parent metal of the HAZ.
Cause: Hydrogen embrittlement
Prevention: Use Lo/Hi electrodes and/or preheat
Repair: (only found using NDT). Remove and reweld.
Underbead Crack
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Am e r i c a n We l d i n g S o c i e t y
Definition: A crack in the weld that occurs during solidification.
Cause: Micro stresses from weld metal shrinkage pulling apart w
metal as it cools from liquid to solid temp.
Prevention: Preheat or use a low tensile filler material.
Repair: Remove and reweld, correct problem first, preheat may benecessary, increase weld size.
Hot Crack
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Am e r i c a n We l d i n g S o c i e t y
Definition: A crack that occurs after the metal has completely
solidified
Cause: Shrinkage, Highly restrained welds, Discontinuities
Prevention: Preheat, weld toward areas of less constraint, use a
more ductile weld metal
Repair: Remove and reweld, correct problem first, preheat may bnecessary.
Cold Crack
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Am e r i c a n We l d i n g S o c i e t y
Repairs to Cracks
Determine the cause
Correct the problem
Take precautions to prevent reoccurrence
Generally required to repair using a smallerelectrode
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Am e r i c a n We l d i n g S o c i e t y
Porosity
Single Pore
Uniformly Scattered
Cluster
Linear
Piping
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Am e r i c a n We l d i n g S o c i e t y
Definition: Slag entrapped within the weld
Cause: Low amperage, improper technique, Trying to weld in an
area that is too tight. Slow travel in Vertical Down Prevention: Increase amperage or preheat, grind out tight areas to
gain access to bottom of joint.
Repair: Remove by grinding. Reweld.
Slag Inclusion
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Am e r i c a n We l d i n g S o c i e t y
Definition: A tungsten particle embedded in a weld. (Typically
GTAW only)
Cause: Tungsten electrode too small, amperage too high, AC
balance on +, Upslope too high, electrode tip not snipped, electroddipped into the weld pool or touched with the fill rod, electrode
split.
Prevention: Eliminate the cause
Repair: Grind out and reweld
Tungsten Inclusion
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Incomplete or Insufficient
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Am e r i c a n We l d i n g S o c i e t y
Incomplete or InsufficientPenetration
Definition: When the weld metal does not extend to the required
depth into the joint root
Cause: Low amperage, low preheat, tight root opening, fast travel
speed, short arc length. Prevention: Correct the contributing factor(s).
Repair: Back gouge and back weld or remove and reweld.
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Am e r i c a n We l d i n g S o c i e t y
Incomplete Fusion
Definition: Where weld metal does not form a cohesive bond with
the base metal.
Cause: Low amperage, steep electrode angles, fast travel speed,
short arc gap, lack of preheat, electrode too small, unclean basemetal, arc off seam.
Prevention: Eliminate the potential causes.
Repair: remove and reweld, being careful to completely remove th
defective area. This is sometimes extremely difficult to find.
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U d
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Am e r i c a n We l d i n g S o c i e t y
Undercut Definition: A groove cut at the toe
of the weld and left unfilled.
Cause: High amperage, electrode angle,
long arc length, rust Prevention: Set machine on scrap metal. Clean metal before
welding.
Repair: Weld with smaller electrode, sometimes must be low
hydrogen with preheat. Sometimes must gouge first.
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Am e r i c a n We l d i n g S o c i e t y
Insufficient Fill
Definition: The weld surface is below the adjacent surfacof the base metal
Cause: Improper welding techniques
Prevention: Apply proper welding techniques for the weld type an
position. Use stripper beads before the cover pass.
Repair: Simply weld to fill. May require preparation by grinding.
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Am e r i c a n We l d i n g S o c i e t y
Reinforcement
Excessive
Insufficient
Improper contour
Face Reinforcement
Root Reinforcement
The amount of a groove weld which extends beyond the surface of the
plate
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Am e r i c a n We l d i n g S o c i e t y
Excessive Reinforcement Definition: Specifically defined by the standard. Typically,
Reinforcement should be flush to 1/16(pipe) or flush to 1/8 (platestructural shapes).
Cause: Travel speed too slow, amperage too low
Prevention: Set amperage and travel speed on scrap plate.
Repair: Remove excessive reinforcement and feather the weld toe
to a smooth transition to the base plate.
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Am e r i c a n We l d i n g S o c i e t y
Definition: When the weld exhibits less than a 1350 transition ang
at the weld toe.
Cause: Poor welding technique
Prevention: Use proper techniques. A weave or whip motion can
often eliminate the problem.
Repair: The weld face must be feathered into the base plate.
1350
Improper Weld Contour
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B h h
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Am e r i c a n We l d i n g S o c i e t y
Burn-through (non-standard)
Definition: When an undesirable open hole has been completely
melted through the base metal. The hole may or may not be left
open.
Cause: Excessive heat input.
Prevention: Reduce heat input by increasing travel speed, use of a
heat sink, or by reducing welding parameters.
Repair: Will be defined by standards. Filling may suffice.
Otherwise, removal and rewelding may be required. Some standamay require special filler metal and/or PWHT.
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A S ik
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Am e r i c a n We l d i n g S o c i e t y
Arc Strike
Definition: A localized coalescence outside the weld zone.
Cause: Carelessness
Prevention: In difficult areas, adjacent areas can be protected usinfire blankets.
Repair: Where applicable, arc strikes must be sanded smooth and
tested for cracks. If found, they must be remove and repaired usin
a qualified repair procedure and inspected as any other weld.
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S tt
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Am e r i c a n We l d i n g S o c i e t y
Spatter
Definition: Small particles of weld metal expelled from the weld
operation which adhere to the base metal surface.
Cause: Long arc length, severe electrode angles, high amperages
Prevention: Correct the cause. Base metal can be protected with
coverings or hi-temp paints.
Repair: Remove by grinding or sanding. Sometimes must be test
as if it were a weld.
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L i ti
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Am e r i c a n We l d i n g S o c i e t y
Laminations
Base Metal Discontinuity
May require repair prior to welding
Formed during the milling process