Investigating the microbial-influenced corrosion of UNS S32750 stainless-steel base alloy and weld seams by biofilm-forming marine bacterium Macrococcus equipercicus

Abstract

This study investigates the microbial-influenced corrosion of UNS S32750 super-duplex stainless-steel joints fabricated using different welding methods. Herein, the samples were introduced into a medium inoculated with Macrococcus equipercicus isolated from a marine environment. Confocal laser scanning microscopy and atomic force microscopy were used to characterise the topography and formation of pits in the corroded samples, respectively. Potentiodynamic polarisation studies were conducted on both the base alloy and weld seams exposed for 30 and 60 days in the experimental system inoculated with M. equipercicus and un-inoculated system. Results indicate that the thickness of the biofilm formed due to this bacterium increased and became heterogeneous with an increase in the exposure time, thereby resulting in micro-pits. Bacterial colonisation was observed in all the coupons after exposure to the inoculated medium. Although micro-pits were observed in all the coupons, the base metal and flux-cored arc weld seams showed highest sensitivity to bacterial attack.