STRESS-CORROSION CRACKING OF MILD-STEEL IN MONOETHANOLAMINE SOLUTIONS

Potentiodynamic polarization and slow strain rate tests have been used to assess the likelihood of stress corrosion cracking in mild steels immersed in monoethanolamine (MEA) solutions containing various other substances at different potentials and temperatures. Pure MEA solutions do not promote cracking, but the saturation of such solutions with CO//2 produced intergranular cracking at potentials in the vicinity of minus 600 mV left bracket saturated calomel electrode (SCE) right bracket and transgranular cracking at lower potentials. The free corrosion potentials observed under a variety of conditions were frequently on the order of those observed to promote cracking in controlled potential tests. A sample of solution provided by the Fawley refinery did not promote stress corrosion unless it was presaturated with CO//2, its polarization characteristics in the 'as received' condition being very similar to those observed with a synthetic solution with H//2S addition. If H//2S is presented in sufficiently large concentration in relation to CO//2, it inhibits cracking by suppressing the active-passive transition that is necessary to promote stress corrosion by a dissolution-controlled mechanism.