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Metal and Metallurgy engineering FAQ
WELD CRACKS, DEFINITIONS, CAUSES, PREVENTION & REPAIR
Posted: 11 Jul 01
Definition: A depression left at the termination of the weld where the weld pool is left unfilled.
Cause: Improper weld termination techniques
Repair: If no cracks exist, simply fill in the crater. Generally welding from beyond the crater back into the crater.
Definition: A crack running in the direction of the weld axis. May be found in the weld or base metal.
Cause: Preheat or fast cooling problem. Also caused by shrinkage stresses in high constraint areas.
Prevention: Weld toward areas of less constraint. Also preheat to even out the cooling rates.
Repair: Remove and reweld
Definition: A crack running into or inside a weld, transverse to the weld axis direction.
Cause: Weld metal hardness problem
Definition: A crack, generally in the shape of an ôXö which is found in a crater. Crater cracks are hot cracks.
Cause: The center of the weld pool becomes solid before the outside of the weld pool, pulling the center apart during cooling
Prevention: Use crater fill, fill the crater at weld termination and/or preheat to even out the cooling of the puddle
Definition: A longitudinal crack located in the weld throat area.
Cause: Transverse Stresses, probably from shrinkage. Indicates inadequate filler metal selection or welding procedure. May be due to crater crack propagation.
Prevention: Correct initial cause. Increasing preheat may prevent it. be sure not to leave a crater. Use a more ductile filler material.
Repair: Remove and reweld using appropriate procedure. Be sure to correct initial problem first.
Definition: A crack in the base metal beginning at the toe of the weld
Cause: Transverse shrinkage stresses. Indicates a HAZ brittleness problem.
Prevention: Increase preheat if possible, or use a more ductile filler material.
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
Definition: A crack in the unmelted parent metal of the HAZ.
Cause: Hydrogen embrittlement
Prevention: Use LOW HYDROGEN electrodes and/or preheat
Repair: (only found using NDT). Remove and reweld.
Definition: A crack in the weld that occurs during solidification.
Cause: Micro stresses from weld metal shrinkage pulling apart weld 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 be necessary, increase weld size.
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 be necessary.
Repairs to Cracks
Determine the cause
Correct the problem
Take precautions to prevent reoccurrence
Generally required to repair using a smaller electrode
Here is a link to a powerpoint presenation. http://pntbeldyk.wirefire.com
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