Stress-Oriented Hydrogen Induced Cracking (SOHIC) is a common, insidious form of wet H2S cracking made up of a series of hydrogen induced cracking (HIC) cracks that are stacked perpendicularly in the direction of through-wall cracks and driven by high residual or applied stresses. Because this damage can easily lead to mechanical integrity failures, facility owners should take measures to prevent or mitigate SOHIC when possible.
Areas Susceptible to SOHIC
Pressure equipment operating in environments with above 50 ppm of H2S content, at or below 180ºF temperature in aqueous sour water is more susceptible to wet H2S cracking, incuding SOHIC. Cyanides in overhead systems of cat crackers and cokers can also significantly increase susceptibility.
SOHIC Prevention/Mitigation
All systems susceptible to SOHIC should be inspected and maintained according to the latest edition of NACE RP0296. Susceptible quipment should also be post weld heat treated (PWHT) or alloyed up when possible. HIC resistant steels and polymeric coatings have been successfully applied to reduce the risk of SOHIC, as well as stainless steel clad materials in more aggressive environments.
References
- Prueter, P., 2021, “Damage Control: Wet H2S Damage Detection,” Inspectioneering Journal, 27(5), pp. 45-52.
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