Effects of d-Phenylalanine as a biocide enhancer of THPS against the microbiologically influenced corrosion of C1018 carbon steel

Microbiologically influenced corrosion (MIC) is caused by biofilms such as those of sulfate reducing bacteria (SRB). To mitigate MIC, biocide treatment is often needed. Tetrakis (hydroxymethyl) phosphonium sulfate (THPS) is an environmentally friendly biocide that is often used in the oil and gas industry. However, its prolonged use leads to biocide resistance, leading to dosage escalation. A biocide enhancer can be used to slow down the trend. In recent years, d-amino acids have been investigated as an enhancer for THPS and other biocides. Published works used anaerobic vials and flow devices, which could not reveal the real-time changes of the biocide treatment on corrosion. In this work, it was proven that the biocide enhancement effects of d-Phenylalanine (d-Phe) on THPS against the Desulfovibrio vulgaris biofilm on C1018 carbon steels could be assessed in real time using linear polarization resistance and electrochemical impedance spectroscopy to collaborate sessile cell count, weight loss and pitting depth data. The results showed that 500 ppm (w/w) d-Phe effectively enhanced 80 ppm THPS against MIC by the D. vulgaris (a corrosive SRB) biofilm. The sessile cell count and pit depth were all reduced with the enhancement of d-Phe.