NACE MR0175 and the requirements for HSC, GHSC and SSC

Galvanic Corrosion NACE: Understanding HSC and GHSC

The inquiry concerns HSC, which describes hydrogen embrittlement in metals that are not sensitive to SSC but can be embrittled when galvanically coupled with another metal that is actively corroding. The term “”galvanically induced HSC”” is used to describe the mechanism for this cracking. However, in NACE MR0175-1 clause 3.23, SSC is a form of hydrogen stress cracking (HSC). This creates confusion as the two paragraphs seem contradictory.

Two Types of HSC: GHSC and SSC

The sender proposes that HSC has two types: 1) “”galvanically induced HSC”” (GHSC), which is cracking in metals that are not sensitive to SSC but can be embrittled by hydrogen when galvanically coupled, and 2) “”Sulfide induced HSC”” (SSC), which involves embrittlement of the metal by atomic hydrogen that results from acid corrosion on the metal surface, and which is promoted by the presence of sulfides.

It is important to note that there is some confusion in the definitions related to HSC. The ballot process will be initiated to clarify the definitions. This inquiry pertains to NACE MR0175/ISO 15156-1 3.1.3, and the ISO 15156 Maintenance Panel Inquiry reference is #2016.

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