Tuesday, March 24, 2009
Amine Stress Corrosion Cracking (Amine SCC) - Basic
General:
It is a specific form of stress corrosion cracking on carbon steels under combined action of stress (residual or applied) and corrosion in lean aqueous amine. Amine (e.g. MDE, MEA, DEA, DIPA) is a catalyst solution used to absorb CO2 and H2S from natural gas. In LNG/Gas plant, it generally occurs at Acid Gas Removal unit on weld joint which is not stress relieved.
Apprearance:
1. Crack in the HAZ, typically parallel to the weld.
2. Crack in the weld, transverse or longitudinal with the weld.
Picture: Example of Amine SCC that occurs on weld due to exposure of Amine to non-stress relieved joint.
Main factors affecting susceptibility:
1. Tensile stress – residual stress from welding
2. Amine concentration – more susceptible in lean amine
3. Temperature – higher temperature more susceptible
Preventions / Mitigations:
1. PWHT all carbon steel welds in piping and equipment that carry amine solution during construction or repair.
2. Material upgrade – e.g. stainless steel clad, alloy 400
Other related corrosion mechanism: Amine Corrosion
General:
It is a specific form of stress corrosion cracking on carbon steels under combined action of stress (residual or applied) and corrosion in lean aqueous amine. Amine (e.g. MDE, MEA, DEA, DIPA) is a catalyst solution used to absorb CO2 and H2S from natural gas. In LNG/Gas plant, it generally occurs at Acid Gas Removal unit on weld joint which is not stress relieved.
Apprearance:
1. Crack in the HAZ, typically parallel to the weld.
2. Crack in the weld, transverse or longitudinal with the weld.
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| From Corrosion for Dummies |
Picture: Example of Amine SCC that occurs on weld due to exposure of Amine to non-stress relieved joint.
Main factors affecting susceptibility:
1. Tensile stress – residual stress from welding
2. Amine concentration – more susceptible in lean amine
3. Temperature – higher temperature more susceptible
Preventions / Mitigations:
1. PWHT all carbon steel welds in piping and equipment that carry amine solution during construction or repair.
2. Material upgrade – e.g. stainless steel clad, alloy 400
Other related corrosion mechanism: Amine Corrosion
Labels: Amine SCC
¶ 9:54 PM
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Another approach to prevention is using UIT (www.appliedultrasonics.com) to treat welds and other areas that are susceptible to SCC. This process provides stress relief, compressive stress and grain structure refinement. It's a lot easier to apply than PWHT, and we've seen much better results.
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# posted by 
: 10:41 PM
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