PWHT NACE: Dealing with Minimum Post-weld Heat Treatment Temperature for Carbon and Low Alloy Steels

Question 1: What Is the Minimum PWHT Temperature Requirement for Carbon and Low Alloy Steels as per NACE MR0175?

ANSI/NACE MR0175/ISO 15156-2 in Clause A.2.1.4 specifies that the minimum PWHT temperature requirement is specific to low alloy steels and is 1150°F. Carbon steels, on the other hand, do not have a minimum temperature requirement for PWHT.

Question 2: Is PWHT Necessary for Weldments that Do Not Comply with the Hardness Requirements Standard as per NACE MR0175?

Clause A.2.1.4 of NACE MR0175/MR 15156-2(2015) states that weldments not complying with the hardness requirements standard shall undergo PWHT. An MP inquiry related to the revised Section A.2.1.4 of NACE MR0175/MR 15156-2(2015) sought clarification regarding the applicability of minimum PWHT temperature at 1150°F to carbon-manganese steel and low alloy steel, and whether there is a specified PWHT temperature requirement for carbon-manganese steel. The response specifies that the 1150°F requirement is specific to low alloy steels only. As-welded carbon steels, carbon-manganese steels, and low-alloy steels complying with the hardness requirements of Table A.1 do not require PWHT. There are no defined minimum temperature requirements for PWHT for carbon and carbon-manganese steels. The product resulting from PWHT must comply with the other requirements defined by NACE MR0175/ISO15156-2 Clause A.2.1.4.