MIC Impact on Mechanical Property Degradation of X80 Pipeline Steel by A Sulfate Reducing Bacterium

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Product Number: 51321-16274-SG

Author: Zhong Li/Jike Yang/Sith Kumseranee/Suchada Punpruk/Magdy E. Mohamed/Mazen A. Saleh/Tingyue Gu

Publication Date: 2021

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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 stresscorrosion 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 w ere 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, 2.3×108cells/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).