NACE MR0175, UNS S31600, S30940 and types 3a and 3b, what is the difference?
Understanding Materials Type 3a and 3b in ASME B31.3 and NACE MR0175
If you’re working with a pipe skid system that requires compliance with ASME B31.3 and NACE MR0175, you may have come across an inquiry related to the use of materials. Specifically, the inquiry refers to Table A.8 and materials type 3a and 3b, and seeks clarification on the maximum temperature rating for UNS S30940, which is the equivalent UNS number for ASTM A312 Gr TP 316.
What Are Materials Type 3a and 3b?
Materials type 3a and 3b are defined at the bottom of Table A.8 based on the alloy’s chemical composition. The temperatures listed in the table represent the maximum values known to be acceptable for the given H₂S partial pressure, pH, and chlorides limits.
What About UNS S30940?
The alloys UNS S31600 and S30940 fall under Table A.2 and Clause A.2 as austenitic stainless steels. However, the Maintenance Panel does not provide advice on specific applications.
Clarification on NACE MR0175’s Environmental Limits for CRAs
It’s worth noting that this question pertains to NACE MR0175/ISO 15156-3 A.3.2, Table A.8, and the reference cited is ISO 15156 Maintenance Panel Inquiry #2010-12. An offer to provide clarification on NACE MR0175’s environmental limits for CRAs is also made.
By understanding these materials and their limits, you can ensure that your pipe skid system meets the necessary compliance requirements.