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Stress-Oriented Hydrogen Induced Cracking (SOHIC)

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Stress-Oriented Hydrogen Induced Cracking (SOHIC) is a common, insidious form of wet H2S cracking. SOHIC is a type of cracking that can easily lead to failure and needs to be mitigated. It is made up of a series of HIC (hydrogen induced cracking) cracks that are stacked perpendicularly in the direction of through wall cracks and driven by high residual or applied stresses. It's fairly well known that above 50 ppm of H2S content, below 180F temperature in aqueous sour waters, that our pressure equipment is susceptible to wet H2S cracking. It's also fairly well known that cyanides in overhead systems of cat crackers and cokers can significantly increase susceptibility.

All susceptible systems should be inspected and maintained according to the latest edition of NACE RP0296. Equipment that is susceptible to SOHIC needs to be post weld heat treated (PWHT) or alloyed up. HIC resistant steels and polymeric coatings have been successfully applied, as well as stainless steel clad materials in more aggressive environments.

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Articles about Stress-Oriented Hydrogen Induced Cracking (SOHIC)
November/December 2003 Inspectioneering Journal

There are a variety of forms of wet H2S cracking. In this short article I will focus on two of the most common forms: hydrogen induced cracking and stress-oriented hydrogen induced cracking (HIC/ SOHIC). HIC is often fairly innocuous (but not...

Authors: John Reynolds
May/June 1995 Inspectioneering Journal

Exposure of carbon steel equipment to wet H2S service environments can lead to various forms of attack, e.g. hydrogen blistering and hydrogen induced cracking (HIC), stress oriented hydrogen induced cracking (SOHIC) and sulfide stress cracking...

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