Development of Accelerated Evaluation Method for Microbially Influenced Corrosion Resistance of Stainless Steels

Abstract

The accelerated evaluation method for microbially influenced corrosion (MIC) resistance of stainless steels was investigated on the basis of the mechanism for MIC. Corrosion potential of stainless steels was determined in natural seawater and in synthetic seawater containing glucose oxidase (GOD) to simulate the bacterial metabolism because the corrosion potential of stainless steels in natural seawater becomes noble by hydrogen peroxide as an intermediate of the metabolism. The corrosion potential ennoblement was reproduced completely in synthetic seawater by adding GOD. This method can be applied to evaluate MIC resistance of stainless steels. The most appropriate test condition was examined to simulate natural seawater environments, and it was determined as 1mg/l of GOD and 10g/l of glucose in synthetic seawater below 50°C. In this condition, results of crevice corrosion tests for one week showed a good correlation with results of the immersed tests in natural seawater for six months. The test method can be also applied to fresh water environments containing low concentration chloride ions. It revealed that SUS 304 stainless steel has a susceptibility to MIC even in fresh water containing 5mgCl^-/l at room temperature. This result corresponds with corrosion damages experienced in pipings and structures of stainless steels. These results suggest that this newly developed test method can be applied to evaluate the MIC resistance of stainless steels.