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.
Is this definition incomplete? You can help by contributing to it.
|
November/December 2003 Inspectioneering Journal
By John Reynolds at Intertek
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 always), while SOHIC is a type of cracking that can easily lead to failure and needs to be mitigated. HIC is a form of tiny blistering damage that is mostly parallel to the surface and to the direction of hoop stress, hence is usually not damaging until it is extensive and affects material properties or gives rise to step-wise cracking that propagates into a weld or begins to go step-wise through the wall. |
|
May/June 1995 Inspectioneering Journal
By Dr. Russell D. Kane at CLI International Inc., and Dr. Michael S. Cayard at Flint Hills Resources
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 (SSC). Documented cases of leaks and failures of pressure containing equipment have been attributed to these forms of corrosive damage. |
