Microbiologically influenced corrosion of AISI 202 and 316L stainless steels under manganese-oxidizing biofilms

In this work, we study the microbiologically influenced corrosion (MIC) of AISI 316L (1–2% Mn) and AISI 202 (8–12% Mn) in the presence of manganese-oxidizing biofilms. Microbiological and 16S rRNA amplicon sequencing analysis on biofilms formed on the surfaces of both the SS materials after exposure to seawater for two months showed the presence of predominant Mn-oxidizing bacteria (MnOB) groups. The Mn contents in the biofilms formed on AISI 202 and 316L were 0.577 and 0.193 ppm, respectively. Mixed biofilms of 11 pure axenic cultures of MnOB isolated and identified from both the SS biofilms were used for MIC studies on SS. Electrochemical studies showed four orders of magnitude high i corr values (1.271 × 10 –4 A.cm −2 ) and the onset of crevice corrosion potentials (502 mV) confirming the localized corrosion of AISI 202 and 316L, respectively, under MnOB biofilms. X-ray photoelectron spectroscopic (XPS) analysis on biotic surfaces showed a reduced Mn content from 10.1 to 7.9 atom.% confirming the Mn oxidation in AISI 202. This study confirms that MnOB biofilms on the SS surfaces can lead to MIC due to biogenic Mn oxidation, depletion of Fe and Mn content, and enrichment of Cr content.