Overview of Amine Stress Corrosion Cracking (SCC)

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 hydrogen sulfide (H₂S) and carbonate cracking, as amines, carbonates and wet sulfides often exist together in amine treating systems. Amine cracking typically occurs on the surface and the cracks are usually radially projected from set-on nozzles. Because of this, most properly applied methods of surface nondestructive examination (NDE) will find the cracks.

Postweld heat treatment (PWHT) is an effective means of mitigating amine cracking, so this affliction is most commonly associated with equipment handling lean amine solutions that has not been stress relieved or may have been inadequately stress-relieved. That would include contactors, absorbers, strippers, regenerators and accumulators as well as any equipment that is subject to inadvertent amine carry over or steam cleaning in preparation for maintenance. Though cracking is most often associated with non-stress relieved weldments (especially the Heat Affected Zone), it can also affect non-stress relieved base metals that have been cold worked and not been subject to PWHT. Examples include bent pipe/tube, knuckle region of formed heads, and formed plate.

Amine cracking is more prevalent in MEA and DEA systems, but can also occur in MDEA, DIPA, and ADIP systems. Critical causal factors include stress level, temperature, and amine concentration. Though cracking has been reported under some circumstances at ambient temperatures, it is more prevalent with increasing temperatures, depending upon solution concentration. 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. Since cracks are normally surface breaking, most properly applied methods of surface NDE will find the cracks, though liquid penetrant testing (PT) may miss tight-fine amine cracks.

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