Welding is a common method used for joining metallic materials. Before welding can take place, welding contractors and fabricators need to develop welding procedures and qualify welders. Specific procedures must be followed to meet the requirements of recognised welding codes (e.g. ASME, AWS or CSA), in accordance with either statutory or client requirements. The basic requirements for a welding procedure are that the weld properties meet or exceed the material properties of the pieces being joined. However, a good welding procedure will also ensure simple and efficient welding and mitigate common welding problems such as distortion, hardening and weld defects. Optimisation of a welding procedure is an iterative science and normally relies on the skills and past experience of the welding engineer.