The ASME B31.3 code underwent significant updates from 2012 to the 2022 edition regarding
preheating and PWHT.
1. 2012 edition mandated preheating to 10 deg. C before welding while the 2022 edition emphasizes
more stringent requirements based on material and thickness, chemical composition, and service
conditions allowing for tailored preheat strategies depending on specific welding scenarios in
preventing weld hydrogen induced cracking. a minimum of 120 to 150 deg. C is typically required
for high strength steels, depending upon thickness.
2. In the 2012 version, PWHT a]was required for certain materials based on thickness. The 2022
edition introduces more flexibility, permitting exemptions under specific conditions, provided
that adequate preheat is applied and service experience supports such decisions. The PWHT is
mandatory particularly for CS and Low Alloy Steels along with defined procedures for conducting
PWHT, such as temperature control during heating and cooling phases. These changes aim to enhance
safety and reliability in process piping systems.
C Sridhar
--------------------------------------------------------------------------------------------------------------------------------