99 Diseases of Pressure Equipment: Amine Cracking

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 together in amine treating systems. Post-weld 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 HAZ), it can also affect non-stress relieved base metals that have been cold worked and not PWHT’d, e.g. bent pipe/tube, knuckle region of formed heads, and formed plate.

An interesting feature of amine cracking, as is often the case with stress corrosion cracking, is that cracks are usually radially projected from set-on nozzles, while they follow the HAZ of set-through nozzles, as well as circ and long seams. 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, and 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(3) provides guidance on PWHT of equipment to avoid amine cracking. 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 PT may miss tight-fine amine cracks.

Do you have non-PWHT'd equipment in your amine systems that might be susceptible to amine cracking, especially from steam out or inadvertent carry over of amines?