his was the subject of a recent discussion here and I can make the following comments, which are my personal views – others may add or disagree:
1. In our case PWHT on carbon steel is generally service related e.g. Carbon steel pipe work in Amine and Caustic service.
2. The code says that NDT should be performed after welding and as heat treatment is a part of the welding technology, it should be performed after heat treatment.
3. Many sites will want to perform NDT before heat treatment as this saves the time and money of having to repair welds and again perform heat treatment on the repair. As the owner we are willing for the contractor to do the NDT before heat treatment, but at his own cost.
4. The NDT carried out before heat treatment should be the same as the NDT carried out after heat treatment. Generally the NDT before heat treatment has been radiography, but as the owner we have substituted this for UT after heat treatment. The theory being, that the only repairable defects likely after heat treatment (if this has not been performed correctly) is cracking and the preferred method for crack detection in this instance would be UT.