What essential variable change requires requalification of a WPS when welding arc spot welds?

The requirement for requalification of a Welding Procedure Specification (WPS) when there is a change in base material thickness is rooted in the significant impact that material thickness can have on the weld's mechanical properties and overall integrity.

Welding parameters and techniques often depend on the thickness of the materials being joined, as thicker materials may require different heat input, travel speed, or electrode specifications to achieve proper fusion and avoid issues like incomplete penetration or excessive heat affected zones. Alterations in base material thickness can influence the cooling rate of the weld, affecting its microstructure and mechanical properties such as strength, ductility, and toughness. Therefore, to ensure that the weld meets the required standards and specifications, a requalification of the WPS is necessary whenever there is a change in base material thickness.

In contrast, while changes such as the type of electrode, the design of the weld joint, or the welding position also influence the welding process, they don't inherently compromise the fundamental structural integrity in the same way that varying thickness does. Each of these factors may warrant evaluation or adjustment of specific procedures, but a change in base material thickness is particularly critical, necessitating a requalification to ensure the weld will perform as expected under service conditions.