What is the maximum allowable thickness for a single pass fillet weld?

In the context of AWS D1.1, the maximum allowable thickness for a single pass fillet weld is typically defined as 1/2 inch. This dimension is established to ensure that the weld can be properly fused and achieve adequate penetration while maintaining the integrity of the joint. Single pass welds are limited in thickness because as the thickness of the weld increases, the potential for defects such as lack of fusion, porosity, or insufficient penetration also increases.

When the thickness exceeds this limit, it often necessitates multiple passes to ensure a proper, sound weld, which can also affect the heat input and potential distortion of the materials being joined. In practical applications, adhering to this maximum thickness ensures better control over the welding process and the quality of the weld, while also simplifying inspection and meeting performance criteria specified in the code.