Post-weld heat treatment (PWHT) is included in the API 510 examination syllabus, mainly in relation to vessel repairs. This makes sense as one of the roles of an API 510 inspector is to oversee repairs on behalf of the plant owner/user. Figure 11.1 shows the importance of this. Not all of the technical information relevant to PWHT is actually included in the API 510 document itself — most is contained in two well-defined (but separated) sections of ASME VIII.
This is not the end of the story. API 510 now adds (as it does with a few other topics) some requirements that can override the PWHT requirements of ASME VIII. The logic behind this is that whereas ASME VIII is a workshop-based construction code, under which PWHT can be done in a furnace under workshop conditions, API 510 deals with repairs, many of which will be carried out on site, where such closely controlled conditions are not possible. API 510 therefore provides easier alternatives that can be legitimately used during repairs. We will look at these parts of the content in turn.