Influence of grain size and crystallographic orientation on microbially influenced corrosion of low-carbon steel in artificial seawater

Abstract

How the microstructure of steel affects a material’s response to microbially influenced corrosion (MIC) in marine applications remains largely unclear, partly because of the challenge in mapping local structure–property relationships. Focusing on sulphate-reducing bacteria, the onset and rate of MIC on low-carbon marine steel samples were analysed with a wide range of grain size and as a function of the local surface crystallography using a combination of optical and electron microscopy, mass loss measurements, and electrochemical testing. It is shown that the alloy’s resistance to MIC decreases with increasing in grain size. A significant effect of the local crystallographic orientation on the material’s dissolution rate is also recorded, which is lowest along the 〈100〉 crystallographic orientation in this steel when exposed to artificial seawater. These findings outline a clear relationship between the microstructure and the susceptibility to MIC in marine steel, which may be used to design alloys with enhanced resistance to MIC in marine applications.

Keywords

• Microbially influenced corrosion
• Sulphate reducing bacteria
• Carbon steel
• Directional reflectance microscopy
• Crystal orientation mapping
• X-ray photoelectron spectroscopy