According to AWS D1.1, what must welding procedures comply with?

Welding procedures must comply with qualified welding procedures according to AWS D1.1. This requirement ensures that the welding process, materials, and conditions have been evaluated and tested to meet specified standards for structural integrity and safety. Qualified welding procedures provide a baseline of performance and reliability, establishing that the welding method is capable of producing sound welds that satisfy engineering and structural requirements.

This standardization helps to ensure that all welds are consistently performed to the same quality standards, minimizing the risk of defects and failures in welded structures. In contrast, the other options lack the rigor and accountability required in the welding process; they do not ensure compliance with established industry standards and safety practices. Therefore, relying on in-house guidelines without external standards, basic industry practices, or undocumented previously used methods would not provide the necessary assurance of quality and performance in welding.