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
- Prueter, P., 2022, “Damage Control: Stress Corrosion Cracking Detection,” Inspectioneering Journal, 28(2), pp. 45-52.
Related Topics
- Ammonia Stress Corrosion Cracking
- Carbonate Stress Corrosion Cracking
- Caustic Stress Corrosion Cracking
- Chloride Stress Corrosion Cracking
- Polythionic Acid Stress Corrosion Cracking (PASCC)
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