Some stainless steel trays were found corroded in an amine unit during a turnaround in one of the
plants. Corrosion products and corrosion features were characterized on three tray samples through
various techniques: XRD, SEM/EDX, TGA-FTIR, ICP-MS, head-space GS-MS. Only part of the steel
trays was visually corroded, with black, grey, or rusty brown colored corrosion products. The
uncorroded steel surface no longer showed original shiny grey surface, rather a slightly greenish
discoloration.
Evidence of intergranular corrosion, however, was found in the visually un-corroded and discolored
steel surface, which was mainly covered by FeCO3. The corrosion products on the visually corroded
surface were identified as mainly FeCO3 and FeS; in addition, some organics and foreign elements
were also discovered in the corrosion products.
Based on the fact part of the steel trays was corroded and the splashed S-rich deposits were still
present on the visually uncorroded surface without being washed away, it was reasonably stated that
these amine trays of concern were not always or completely wetted by the amine solution during
process condition. Condensation or deposits, therefore, could adhere to the surface, resulting in the
formation of intergranular corrosion across the steel surface. Splashing, caused by foaming and freefall
impact from the amine solution, wetted some of intergranularly corroded surface with S-containing
solution with/without small particulates. The steel at these areas started to crack. The attacked grainboundaries
opened up, resulting in the disintegration of the grains. Circular pits were subsequently
formed. With the expansion and coalescence of the pits, large amounts of materials were wasted,
leading to severe corrosion of the amine trays.
Key Words: amine, corrosion, intergranular corrosion, pits, contaminants, S-containing compounds