2026 年 112 巻 3 号 p. 149-160
Microbiologically influenced corrosion (MIC) is increasingly recognized as a key factor affecting the reliability of welded stainless steel structures. Recent studies highlight early-stage MIC under service-like conditions, emphasizing electrochemical–microbial interactions.
Laboratory tests using natural freshwater from industrial facilities have revealed corrosion risks in sensitized austenitic stainless steels such as SUS304. In these materials, the open circuit potential (OCP) often shows time-dependent ennoblement that begins earlier and reaches higher values than in non-sensitized base metal. This behavior is linked to microstructural degradation, notably chromium depletion at grain boundaries, and may contribute to the higher MIC susceptibility of sensitized regions.
Long-term exposure studies across stainless steel grades demonstrate that corrosion morphology—ranging from general to localized or negligible—varies with chromium content and correlates with distinct microbial communities. These findings suggest that microbial populations adaptively localize in response to electrochemical heterogeneity, promoting corrosion initiation and progression.
To probe this effect, weld-like model systems simulating the interface structure between sensitized and non-sensitized stainless steel regions were tested in a three-electrode setup under controlled micro-scale potential gradients. Electrochemical measurements combined with microbial community profiling indicated functional differentiation between anodic and cathodic areas, with certain taxa preferentially colonizing cathodic sites, suggesting the functional localization of microbial activity driven by electrochemical heterogeneity.
Overall, these studies highlight the complex interactions among microstructure, electrochemistry, and microbial distribution in MIC initiation. Such integrated insights provide a basis for improved diagnosis and mitigation strategies of MIC in welded stainless steel structures under realistic environmental conditions.
