B31.3 Piping Post Weld Heat Treatment
B31.3 Piping Post Weld Heat Treatment
(OP)
I have a few pipe spools that will be designed for H2S / sour gas service. The spools are basic schedule 80 (0.337" wall) API 5L X42 pipe material.
The wall thicknesses are under the required ASME B31.3 thicknesses (19 mm) requiring stress relieving, but the spools will need to be NACE MR0175 compliant. We will be using normalized flanges (SA105N) and fittings. My questions are:
1.) Will post weld heat treatment be required for the welds?
2.) Will API 5L X42 piping material need to be stress relieved? SA234 WPB fittings?
3.) What part of NACE MR0175 would deal with post weld heat treatment requirements for this type of spool?
I do not know the H2S partial pressure at this time, but we can assume it will be over the required NACE limits for normalization of materials.
Thank you in advance for your help!
The wall thicknesses are under the required ASME B31.3 thicknesses (19 mm) requiring stress relieving, but the spools will need to be NACE MR0175 compliant. We will be using normalized flanges (SA105N) and fittings. My questions are:
1.) Will post weld heat treatment be required for the welds?
2.) Will API 5L X42 piping material need to be stress relieved? SA234 WPB fittings?
3.) What part of NACE MR0175 would deal with post weld heat treatment requirements for this type of spool?
I do not know the H2S partial pressure at this time, but we can assume it will be over the required NACE limits for normalization of materials.
Thank you in advance for your help!





RE: B31.3 Piping Post Weld Heat Treatment
NACE MR0175 doesn't mandate PWHT, except for fibre elongation, much like Sec. VIII Div. 1. It does require hardness testing of completed welds, or during procedure qualification. (250HV Max.) You also need to make sure materials purchased comply with MR0175.
That being said, I have still had customers would wanted PWHT, even though it isn't mandatory.
RE: B31.3 Piping Post Weld Heat Treatment
Many years ago, a major natural gas company used the logic that X42 could be used in sour service without the need for chemistry controls (since in earlier times the CE was low enough) or PWHT but found out after the fact that the material nearly met X60 and the hardness in the HAZ could not meet NACE requirements without PWHT. The penchant for steel makers to make steels meeting multiple grades (cost savings) is not always beneficial to the end user.
RE: B31.3 Piping Post Weld Heat Treatment
There are no such "limits."
The pertinent text of ISO 15156-2 for stress relief is in A.2.1.4
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.