What is the minimum nominal thickness of backing required when using ER70S-X filler metal?

The AWS D1.1 Structural Welding Code outlines various specifications and requirements for welding practices, including the use of backing bars. When using ER70S-X filler metal, the minimum nominal thickness for backing is specified in the code to ensure adequate support and heat distribution during the welding process, which helps in achieving a sound weld.

For welding with ER70S-X, the minimum backing thickness should be 1/4". This is significant because a thinner backing might not provide sufficient support for the weld joint, which could result in defects such as poor penetration or incomplete fusion. The chosen thickness helps maintain the necessary heat to achieve proper melting of the filler metal and parent material, facilitating a well-formed weld. Additionally, ensuring that the backing is of adequate thickness contributes to the overall integrity and strength of the welded structure.

Other thicknesses, such as 1/8", 1/2", or 3/8", exceed or do not meet this minimum requirement, making them inappropriate for use with ER70S-X filler metal under the conditions specified in the AWS D1.1 code.