What is the purpose of backfilling the crater at the end of a weld?

• A. To prevent crater cracking by smoothing out the end of the weld.
• B. To reduce filler metal usage.
• C. To cool the weld rapidly.
• D. To vent gases.

Answer: (A)

When a weld ends, the last bit of molten metal can shrink and contract as it solidifies, creating a small indentation or crater at the end. That crater can become a stress concentration that starts a crack as the metal cools and is loaded in service. Backfilling the crater—adding a finishing pass or extra metal to smooth and fill that end—helps create a gradual, continuous transition and distributes the heat more evenly. This removes the sharp termination and reduces the likelihood of a crack forming from the crater, improving the overall integrity of the weld. It’s not primarily about using less filler, speeding cooling, or venting gases; it’s about preventing a weak, prone-to-crack end by finishing the weld smoothly.