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Welder Red Seal · Question

After completing a critical root pass on a carbon steel pipe, a welder notices a distinct, fine linear crack appearing directly in the centre of the weld bead while it is still cooling. What type of discontinuity is this, and what is its most common cause?

A fine linear crack occurring in the weld bead during cooling is characteristic of hot cracking. Hot cracking is often caused by factors like high sulfur conten

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Question: After completing a critical root pass on a carbon steel pipe, a welder notices a distinct, fine linear crack appearing directly in the centre of the weld bead while it is still cooling. What type of discontinuity is this, and what is its most common cause?

Answer options:

  • Porosity; entrapped gases
  • Slag inclusion; improper cleaning ✅ Hot cracking; high sulfur content or excessive restraint
  • Cold cracking; hydrogen embrittlement

Correct answer: Hot cracking; high sulfur content or excessive restraint

Explanation: A fine linear crack occurring in the weld bead during cooling is characteristic of hot cracking. Hot cracking is often caused by factors like high sulfur content in the base or filler metal, or excessive restraint on the joint during solidification, leading to tensile stresses. Cold cracking occurs after cooling to near ambient temperatures and is often linked to hydrogen.

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