What is crater cracking and how can it be prevented?

• A. Cracking at the end of a weld bead due to thermal contraction; prevented by proper stop/start technique, filling the crater, back stepping, and controlling cooling.
• B. Cracking in the middle of the bead due to moisture.
• C. Cracking caused by rust.
• D. Cracking due to misaligned joint.

Answer: (A)

Crater cracking happens when the end of a weld bead experiences solidification shrinkage and the resulting tensile stresses as it cools. If the crater isn’t addressed—by leaving an open, unfilled end or by too rapid cooling—the last deposited metal can crack as it contracts and the stresses aren’t relieved.

Prevention focuses on how the weld is finished. A proper stop/start technique prevents leaving a crater at the end of the bead. Filling the crater ensures the end of the bead is part of the same solidified mass rather than a vulnerable termination that concentrates stress. Back stepping helps manage heat input and cooling by depositing short, controlled passes that reduce steep temperature gradients. Controlling cooling—via appropriate heat input, possible preheating, and slower cooling when needed—minimizes residual tensile stresses in the weld area and its heat-affected zone.

Other options describe issues unrelated to crater cracking, such as cracking from moisture, rust, or joint misalignment, which are not about the end-of-bead solidification stresses.