We have SS321 tubes for one of the furnaces. After welding of the SS321 tubes, what is the recommended PWHT cycle? I understand that to avoid Knife line attack in SS 321 and so to dissolve Chromium carbide and precipitate Titanium carbide, PWHT is done within 850 DegC to 1250 DegC. Some procedures recommend for 2 heat treatment cycles (1050 DegC 1 hr soaking with water quenching and then 900 DegC 4 hrs soaking with water quenching) whereas some procedures ask to do one heat treatment (1050 Degc 1 hr soaking with water quenching). I also saw a procedure asking for 900 DegC with slow cooling (air cooling) and not fast cooling (water quenching). So, I request you to provide clarity in number of heat treatment cycles, soaking temperature, soaking time and quenching medium (air/water) and its metallurgical consequences ?