Apart from pinhole leaks, MIC (microbiologically influenced corrosion) can also cause catastrophic failures such as pipe rupture and support beam collapse due to mechanical strength degradation or stress corrosion cracking. In this work, X80 pipeline steel dogbone coupons and square coupon were immersed in 150 mL Desulfovibrio vulgaris (a sulfate reducing bacterium or SRB) broths for up to 14 days. The headspace volumes in the anaerobic bottles were varied from 150 mL to 300 mL to increase MIC severity. After 14 days of incubation at 37oC, the sessile cell counts were 6.5×107 cells/cm2 for 150 mL, 2.3×108 cells/cm2 for 200 mL and 1.4×109 cells/cm2 for 300 mL headspace volumes, respectively owing to reduced H2S toxicity in the broth with a larger headspace. Weight losses were 1.7 mg/cm2, 1.9 mg/cm2 and 2.3 mg/cm2 for 150 mL, 200 mL 300 mL headspace volumes, respectively. The corresponding pit depths were 2.6 μm, 4.2 μm and 6.2 μm for 150 mL, 200 mL and 300 mL headspace volumes, respectively. Electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR) and potentiodynamic polarization results corroborated the increasing weight loss and pitting data trends. Tensile testing after the 14-day immersion indicated that more severe MIC pitting led to a higher ultimate strain loss by up to 22%, while the ultimate strength losses for all headspace volumes were quite small (5% and below).
MIC has become a major concern in marine, oil and gas, and water utilities industries, etc. MIC accounts for 20% of all of corrosion losses.1 Walsh estimated that MIC leads to substantial financial losses of approximately $30-50 billion per year in the US.2 In addition to pinhole leaks, MIC can cause mechanical property degradation, leading to metal fracturing/rupturing and cracking that reduce equipment service lifespan.3 Most MIC studies so far focused on pitting corrosion. There is a lack of studies on the impacts of MIC on mechanical property degradation. In practical applications, disastrous consequences such as pipeline rupture and support beam collapse can be caused by mechanical property degradation due to MIC.
