Corrosion-creep interaction of stainless alloys in acid chloride solutions

Abstract

Rupture of passive film is considered as an essential step in the stress corrosion cracking (SCC) process. At constant load, accumulation of creep strain is often associated with the strain to passive film rupture. Therefore, low-temperature creep behavior of a material is important from an SCC point of view. Constant load creep studies carried out on alloy 22 (a Ni-22Cr-13Mo-4W alloy) in acidified chloride environments at 80 °C showed a logarithmic creep behavior. The creep strain decayed logarithmically and reached values less than 4×10−9/s, which is lower than the detectable limit of laboratory scale SCC tests. 304 SS showed SCC failure in acidified chloride solutions in simulated open circuit conditions. A steady-state creep strain rate could be observed during SCC failures, of the order of 10−5 to 10−6/s. The high creep strain rate of 304 SS can be correlated to the observed higher corrosion currents, which were more than 40 times that observed in alloy 22. When the dissolution rate of alloy 22 was increased by impressing about 1 mA/cm2 anodic current, a steady-state creep strain rate of 6.5×10−8/s was observed. The results indicated that anodic dissolution increased the localized plasticity of the material, resulting in creep strain. However, alloy 22 did not show SCC.