Using sodium thiosulphate for carbon steel corrosion protection against monoethanolamine and methyldiethanolamine

Corrosion resistance against amine solvent monoethanolamine (MEA) and mixtures of MEA with methyl-diethanolamine (MDEA) was studied. Stainless steel (SS316L) was tested as a baseline to compare with carbon steel (C1018) alone and with the inhibitor sodium thiosulphate (STS). Immersion testing used mass change, Fe ion concentration in solution (ICP-OES), surface imaging (SEM), and analytical techniques (EDX, XRD) to assess the corrosion. Generally, the use of STS improved C1018 resilience relative to C1018 alone, though SS316L was superior to both. Multiple inhibition mechanisms were observed, and are a function of temperature and solution composition. Whilst the surface adsorption mechanism was demonstrated in some cases, reactions between solution reactants and STS resulted in different outcomes.