All of the weld processes described in Chapter 7 are capable of producing high quality welds. As further described in that chapter, some processes are limited either by the process itself, or for practical reasons, to the production of certain types of welds. Regardless of the weld process or type, numerous variables affect weld quality. Examples of these are the process itself, base metal and filler metal, groove design, filler metal diameter, weld preheat, electrical characteristics, and post weld heat treatment (PWHT). The ASME BPVC and other codes for pressure vessels and components have long recognized the need to control these variables in order to ensure the quality of welds. this chapter describes how this is accomplished.