Mechanical property degradation of X80 pipeline steel due to microbiologically influenced corrosion caused by Desulfovibrio vulgaris.

Abstract

Apart from pinhole leaks, MIC (microbiologically influenced corrosion) can also cause catastrophic failures such as pipe ruptures and support beam collapses due to mechanical property degradation or stress corrosion cracking. In this work, X80 pipeline steel dogbone coupons and square coupons were immersed in 150ml broths containing Desulfovibrio vulgaris, a common corrosive sulfate reducing bacterium (SRB), for up to 14days. The headspace volumes in the anaerobic bottles were increased from 150ml to 200ml and 300ml to increase MIC severity. After 14days of SRB incubation in ATCC 1249 culture medium with X80 coupons at 37°C, the sessile cell counts were 6.5 × 107 cells cm-2 for 150ml, 2.3 × 108 cells cm-2 for 200ml and 1.4 × 109 cells cm-2 for 300ml headspace volumes, respectively owing to reduced H2S cytotoxicity in the broth with a larger headspace because it allowed more biogenic H2S to escape from the broth. Weight losses were 1.7mg cm-2, 1.9mg cm-2 and 2.3mg cm-2 for 150ml, 200ml and 300ml headspace volumes, respectively. The corresponding pit depths were 2.6μm, 4.2μm and 6.2μm for 150ml, 200ml and 300ml headspace volumes, respectively. Electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR) and potentiodynamic polarization results corroborated the increasing weight loss and pitting data trends as a result of increased headspace. Tensile testing of dogbone coupons after the 14-day SRB immersion test indicated that more severe MIC pitting led to a higher ultimate strain loss by up to 23% (300ml headspace) compared to the abiotic control, while the ultimate strength losses for all headspace volumes were quite small (3% and lower).