What is the minimum backing thickness for process classification E71T-5?

For process classification E71T-5, the minimum backing thickness is specified in the AWS D1.1 Structural Welding Code – Steel to ensure adequate support during the welding process. This thickness is crucial because it provides enough material to absorb the heat generated during welding, preventing burn-through and ensuring a proper weld bead formation. A backing of 3/8" is determined to be the minimum necessary to achieve these purposes effectively.

In this case, other thicknesses listed would not meet the code requirements for this particular process. For instance, a 1/4" backing may not provide sufficient thermal stability, potentially leading to incomplete fusion or weak weld joints. Similarly, while thicker options like 1/2" and 3/16" could offer more support, the requirement specifically calls for a minimum thickness of 3/8", making it the only correct answer. Understanding these specifications helps in maintaining structural integrity and ensuring quality welds in fabricated metal work.