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In NACE MR0175 Table A.22, are martensitic stainless steels “limitless”? Do they need qualifying?

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Question:

In NACE MR0175/ISO 15156 -3, Table A.22 lists the “Environmental and materials limits for martensitic stainless steels used as compressor components.” The maximum partial pressure requirement for H2S directs you to see Remarks, and the Remarks state “Any combination of temperature, partial pressure of H2S, chloride concentration and in situ pH occurring in production environments are acceptable.” Does this remark indicate that conformance to the NACE MR0175/ISO 15156 is required for any amount of H2S? I am looking for clarification as to what “acceptable conditions” is referring to. As a centrifugal compressor manufacturer, we often build compressors for process gases which are a hydrocarbon mix containing a few parts per million or trace amounts of H2S.

Answer

Conformance to the Standard is required for any trace amount of H2S. In the case of Table A.22 the listed martensitic stainless steels can be used in any production environment provided they are in conformance with the metallurgical requirements indicated in the lower part of the Table. Note that item c) in Table A.22 requires a resistance in the anticipated service environment of at least 95% of the actual yield strength of the impeller material using Annex B for laboratory testing. Qualification requirements to ISO 15156 are listed in §8 of NACE MR0175/ISO 15156-1.

This question is in relation to NACE MR0175/ISO 15156-3 A.6.2, Table 22

Reference: ISO 15156 Maintenance Panel Inquiry #2010-06

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