Question on the Applicability of NACE MR0175/ISO 15156 for 316 Stainless Steel in Sour Service Applications

Introduction

This page provides a Q&A section that addresses the use of 316 stainless steel for sour service application under the restrictions imposed by NACE MR0175/ISO 15156. The question pertains to the applicability of the standard for non-stressed vessel internals, thermowells located into sour lines or vessels, and valve internals operating above 60°C, with a particular emphasis on the use of solid 316 SS balls for ball valves.

Answer

The standard need not be applied to equipment not covered by the first sentence of Paragraph 1, as defined in NACE MR0175/ISO 15156 Part 3. Additionally, in Table 1, parts loaded in compression are considered “”permitted exclusions”” from the standard. Stress corrosion cracking (SCC) requires a tensile stress to occur, and there is no provision in the standard for a threshold tensile stress below which failure cannot occur.

Manufacturer’s and Equipment User’s Decision

The Maintenance Panel cannot analyze equipment design, and it’s the manufacturer’s and equipment user’s decision whether or not the scope or any of the exclusions listed in Table 1 apply for a specific design.

Reference

This question pertains to NACE MR0175/ISO 15156-3 Table A.2, and the reference provided is ISO 15156 Maintenance Panel Inquiry #2005-03.

Conclusion

In conclusion, the use of 316 stainless steel for sour service application under the restrictions imposed by NACE MR0175/ISO 15156 is subject to certain exclusions and the manufacturer’s and equipment user’s decision.