Amine Stress Corrosion Cracking

Amine stress corrosion cracking (also known as amine cracking or amine SCC) is a specific form of alkaline stress corrosion cracking that can occur in carbon steel or low-alloy ferritic steels exposed to aqueous solutions containing alkanolamines.

Parameters Affecting IOW – Step 2

See Step 2.

See below the relevant parameters affecting amine SCC severity and, also, an indication of those that should be included in the IOW.

Amine SCC Parameters affecting severity & IOW:

StF – Step 7

See Step 7.

Susceptibility to amine cracking depends on the amine solution characteristics (type of amine, amine concentration, type and level of impurities, and temperature) and the level of tensile stress (residual and applied) present.

Not Susceptible:

• Not exposed to lean Amine; or
• Stress Relief Heat Treated, and appropriate guidelines are followed.

Low Susceptibility:

• Stress Relief Heat Treated, but appropriate guidelines are not followed.

Else:

If not Stress Relief Heat Treated, then further consider the below-mentioned parameters (as well as the Parameters table above in Step 2) to determine the Susceptibility:

Type of Amine: The likelihood is very dependent on the amine type. Cracking is most prevalent in MEA systems, with the likelihood decreasing according to MEA -> DIPA -> DEA -> MDEA -> DGA -> Sulfinol.

Amine Concentration: Increasing the concentration of the amine reduces the likelihood of amine cracking. Amine cracking typically occurs in lean amine solutions, which are alkaline and contain relatively low levels of acid gases along with other impurities.

Impurities: The presence of CO₂ or other corrosive impurities in the lean amine solution is considered essential for cracking to occur.

Temperature: Cracking is most pronounced at the highest temperatures in amine treating units, e.g., 115°C (240°F) and above. Amine cracking has however been reported at ambient temperatures in many MEA systems, and in low concentration (15-20%) DIPA systems. Note: The metal temperature is most important, not the normal process temperature. Heat-traced /steamed-out Equipment may experience higher metal temperatures (even if operating at low temperatures) and will therefore have a higher likelihood of cracking.

Stress Relieve Heat Treated: Amine cracking is controlled primarily by application of a stress-relieving heat treatment to reduce tensile stresses. If appropriate stress relieve guidelines are followed, the likelihood of cracking will be low (e.g., API RP 945 specifies for what type of amine and at which temp should post-weld heat treatment (PWHT) be applied). Note: It is however common practice to still stress relieve steel Equipment and piping that are normally operating below the guideline temperatures if they are heat-traced /steamed-out.

Guidelines: If the appropriate guidelines (e.g., NACE and API RP 945) are followed, the likelihood of cracking will be low.

Confidence – Step 10

See Step 10.

Follow the guidance below to determine answers for an amine SCC Confidence Assessment.

Amine SCC Confidence Assessment Guidance:

Required Inspection Effectiveness – Step 11 & Step 12

See Step 11 and Step 12.

Use the Required Inspection Effectiveness, determined in Step 11, to determine the Inspection technique and coverage. See below examples of highly and usually effective inspections.

Amine SCC examples of highly and usually effective inspections: