If the valves are 'bolted bonnet', consider the disassembly of the valves before PWHT. If the bonnet is welded to the body of the valve, investigate if a preheat will fulfill your design requirements.
Alternatively, restrict the rate of heat input during welding by limiting the size of electrode (SMAW) and the amperage setting. Also limit the interpass temperature and weld bead width.
Regards,
Darcy Morin
Dear all,In the piping class of alloy steel, we have SW end small bore gate, globe valves. And as per the client requirements all Alloy steel piping joints shall be PWHT after welding.Now , if we performed the PWHT at site at temp. 704-760 Deg C (As per ASME B 31.3 Table 331.1.1 Requirements for heat treatments), then is there any possibility of damage to packing material which is normally graphite due to heat dissipate during PWHT.What type special consideration to be taken in this case. Members are requested to give suggustions.Thanks in advance..Regards,Vinayak
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