Analysis of Localized Corrosion Morphology and Microbial Distribution in Duplex Stainless Steel Tubes of Seawater Heat Exchanger

Corrosion was observed in a seawater heat exchanger equipped with duplex stainless steel aSUS329J4L tubes. An investigation into the corrosion morphology and operating conditions indicated that the damage was attributable to hot-spot corrosion. The analysis revealed inappropriate flow rate management and insufficient chlorination. Given the concern of microbiologically influenced corrosion associated with insufficient chlorination, the microbial community structure was analyzed. To our knowledge, no previous studies have reported on detail microbial analysis in hot-spot corrosion environments. Although the direct impact of microorganisms on hot spot corrosion remains unclear, their distribution within the heat exchanger tubes was elucidated. Detailed analysis of the damaged areas showed that corrosion frequently occurred at the boundary between the high- and low-temperature regions along the tube length. This suggests the formation of a corrosion cell between these regions. Based on these findings, a mechanism for the onset of hot spot corrosion is proposed.