In case of PWHT is required (due to code requirement or process requirement), welding procedure and selection of consumable will become more specific. Schaeffler diagram normally be used to predict phases of the welded metal and its effect to PWHT.
Crack due to embrittlement always the main...
With the same process condition, that section will experience lower temperature due to metal will conduct energy (heat) faster than surrounding. Through thickness heat gradient will result thicker section will experience lower temperature at the inner surface.
As for offshore pipeline, closer...
