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Metal and Metallurgy engineering FAQ

WELD CRACKS

WELD CRACKS, DEFINITIONS, CAUSES, PREVENTION & REPAIR
Posted: 11 Jul 01

ARC CRACKS

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.

Longitudinal Crack

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

Transverse Crack

Definition: A crack running into or inside a weld, transverse to the weld axis direction.

Cause: Weld metal hardness problem

Crater Crack

Definition: A crack, generally in the shape of an “X” 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

Throat Crack

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.


Toe Crack

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.


Root Crack

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

Underbead 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.

Hot Crack

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.

Cold Crack

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


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