FAQ's

Inconel X750 (UNS N07750),can it be used for sour service?

 

Inconel X750 (UNS N07750) is a precipitation hardened nickel based alloy that is listed in NACE MR0175 / ISO 151656 part 3tables A.35 and A.36 as a valid material for non-pressure containing components and springs.
This material was previously listed in NACE MR0175-2002 as an approved Nickel-Chromium alloy. It is still listed in NACE MR0103 as an approved precipitation-hardenable Nickel alloy.

a) Is the correct interpretation that this material is prohibited from use as a pressure boundary component for any NACE MR0175 application under any conditions?

b) If yes, can you provide any explanation for why it was removed? Was there testing or a ballot submittal to justify its exclusion?

Question 1: Is the correct interpretation that this material is prohibited from use as a pressure boundary component for any NACE MR0175 application under any conditions?

Answer: Yes, that is the correct interpretation.

Question 2: If yes, can you provide any explanation for why it was removed? Was there testing or a ballot submittal to justify its exclusion?

Answer: The alloy was removed in the NACE MR0175 2003 rewrite and this was carried over in NACE MR0175/ISO 15156 in 2003. We cannot provide a definitive answer as to why it was removed but we know that the alloy is susceptible to hydrogen embrittlement and there have been some failures with the alloy. Please review the subject in “H2S Corrosion in Oil & Gas Production: A Compilation of Classic Papers, NACE, 1981” and NACE Corrosion 2003 conference paper 03133.

Reference: Maintenance Panel Inquiry #2015-15 and in reference to NACE MR0175 part 3 A.9

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