Microbiologically influenced corrosion of 316L stainless steel in the presence of Chlorella vulgaris

Chlorella vulgaris is a commonly found alga in the marine environment and has been widely associated with steel corrosion and biofouling. In this study, the corrosion of 316L stainless steel (SS) in the presence of C. vulgaris was monitored using electrochemical measurements like open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves. Surface and corrosion product analysis was conducted using scanning electron microscopy (SEM), energy dispersive spectrum (EDS) and X-ray photoelectron spectroscopy (XPS). SEM images showed the tendency of C. vulgaris cells to cluster together by their exuded extracellular polymeric substances (EPS) and easily adhere to the SS surface, subsequently causing microbiologically influenced corrosion (MIC). The pitting corrosion was observed in the presence of C. vulgaris cells with pit depth of 20 μm formed on the SS surface after 21 days of incubation, indicating that C. vulgaris accelerated the localized corrosion of 316L SS. XPS and EDS analysis indicated that there were more organic C, O and P in the biofilm in the presence of C. vulgaris, suggesting the better growth of C. vulgaris on the 316L SS surface. In the daytime, C. vulgaris was more active and corrosive as it could produce oxygen through photosynthesis, resulting in increase of the dissolved oxygen (DO) concentration in the bulk solution and biofilm. These results indicated that the change of DO was closely related to the corrosion process.