ABSTRACT
Postweld heat treatment (PWHT) of the vessel is decided based on the material of construction, fabrication methods, thickness of shell sections, etc., as contained in clause UW 40 (see Chapter 21, Section 17). Usually, vessels of 1½ in. (38 mm) and over in thickness have to undergo PWHT. Those in the range of 1¼ to 1½ in. (32 to 38 mm) need not go for PWHT, provided preheat at a minimum temperature of200°F (93.3°C) is given during welding. Further, vessels that are subjected to low temperatures shall also undergo PWHT irrespective of thickness. As this is a design criterion, it is not elaborated here. However, as this requirement is indicated in the drawings, we try to carry out the PWHT according to the provisions of the code.
