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Amine Stress Corrosion Cracking

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Amine Stress Corrosion Cracking, often referred to as alkaline SCC or simply amine cracking, is a form of stress corrosion cracking (SCC) caused by the combined effects of an aqueous alkanolamine solution (typically used to absorb H2S and/or CO2 from gaseous or liquid hydrocarbon process streams) and the presence of either applied or residual tensile stress. Amine cracking is typically branched and intergranular in nature with the potential for being oxide-filled. Critical causal factors of amine cracking include stress level, temperature, and amine concentration. Although cracking has been reported under some circumstances at ambient temperatures, susceptibility for amine cracking is higher the greater the process temperature, depending upon solution concentration.

Areas Susceptible to Amine SCC

Amine cracking usually occurs near welds in carbon and low-alloy steels, especially in equipment that was not subject to stress relief. It can also appear in highly cold-worked components (with residual stresses being the primary crack driving force). While cracking can occur in the weld deposit or heat affected zone (HAZ), it most often manifests adjacent to weld HAZs in the base metal, where tensile weld residual stresses are regularly most severe.

Amine cracking is most commonly associated with equipment handling lean amine solutions that has not been stress relieved or may have been inadequately stress-relieved. This includes contactors, absorbers, strippers, regenerators, heat exchangers, filters and piping, as well as any equipment that is subject to inadvertent amine carry over or steam cleaning in preparation for maintenance. In general, amine cracking is more prevalent in monoethanolamine (MEA) and diethanolamine (DEA) services, although it can also occur in other amine services such as methyldiethanolamine (MDEA) and diisopropanolamine (DIPA). In rich amine service environments, the formation of iron sulfide scale usually impedes amine SCC, and damage in these cases is more often due to wet-H2S damage mechanisms such as sulfide stress cracking (SSC). 

Amine SCC Prevention/Mitigation

Post weld heat treatment (PWHT) can be an effective means of mitigating amine cracking. API RP 945 (R2008), Avoiding Environmental Cracking in Amine Units, 3rd Edition, provides guidance on PWHT of equipment to avoid amine cracking. One should also note that austenitic stainless steels and alloy 400 are resistant to amine cracking.

Amine SCC Inspection

Because amine cracking typically occurs on the surface, most properly applied methods of surface nondestructive examination (NDE) will identify the cracks. 

References

  1. Prueter, P., 2022, “Damage Control: Stress Corrosion Cracking Detection,” Inspectioneering Journal, 28(2), pp. 45-52.

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Articles about Amine Stress Corrosion Cracking
July/August 2022 Inspectioneering Journal

This final installment of a 3-part series on SCC mitigation will provide practical, actionable steps to improve long-term equipment reliability through design, fabrication/welding, heat treatment, maintenance/repair, and process operating practices.

May/June 2022 Inspectioneering Journal

Part 2 of the three-part series on stress corrosion cracking (SCC) that examines common engineering and FFS methods that can be leveraged to understand and evaluate the propensity for an existing form of SCC to lead to loss of containment.

March/April 2022 Inspectioneering Journal

This article provides an overview of some of the more common forms of stress corrosion cracking (SCC) with a focus on effective inspection methods for detecting these forms of cracking.

January/February 2005 Inspectioneering Journal

Amine cracking is a form of stress corrosion cracking, which is related to alkaline and carbonate stress corrosion cracking. Amine cracking is often intertwined with wet H2S and carbonate cracking, as amines, carbonates and wet sulfides often exist...

Authors: John Reynolds
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