Impact of gravity on biofilm growth and corrosion of X65 pipeline steel by a sulfate reducing bacterium.

Desulfovibrio ferrophilus (IS5) corrosion of X65 carbon steel was impacted by gravity. Six o'clock position (6P) had the highest sessile count due to gravity assisting planktonic cell settling in early biofilm formation, leading to most severe static corrosion followed by 9P and 12P. The 7-d weight loss at 6P was 49.6 ± 4.4 mg/cm2 (3.3 mm/a in uniform corrosion rate) followed by 9P with 35.7 ± 2.6 mg/cm2 (2.4 mm/a) and 12P with 20.5 ± 5.5 mg/cm2 (1.4 mm/a). The trend was supported by electrochemical measurements. The weight loss differences reduced considerably when there was agitation, supporting the gravity hypothesis. • Early SRB biofilm growth is impacted by gravity, favoring 6 o'clock position (6P). • The biofilm sessile cell count sequence is 6P > 9P (side way) >12P (face down). • Weight loss and pit depth sequences after 7-day SRB incubation are 6P > 9P > 12P. • 6P has a uniform corrosion rate of 3.3 mm/a vs. 1.4 mm/a for 12P for 7-d incubation. • Agitation lowered weight loss differences, supporting gravity impact hypothesis. [ABSTRACT FROM AUTHOR]