Studies on the impact of fluid flow on the microbial corrosion behavior of product oil pipelines

The effect of fluid flow on the microbial corrosion behavior of API 5L X60 pipeline steel is investigated in product oil pipelines. It is confirmed that there is a small amount of trapped water accumulated at low elevation sections along the pipelines. The trapped water and dissolved oxygen (DO) in pipelines promote the growth of both aerobic and anaerobic bacteria, causing microbiologically influenced corrosion (MIC). MIC has been detected not only in static fluid systems, but also in flow systems. In product oil pipelines, MIC is conventionally attributed to three species of bacteria namely sulfate-reducing bacteria (SRB), iron oxidizing bacteria (IOB) and total general bacteria (TGB) which were influenced by the fluid flow condition. By applying a large flow loop, we conducted the experiment that the above three species of bacteria attached to the coupons were scoured by diesel oil at three different flow velocity (1.3 m/s, 1.5 m/s and 3 m/s). The macroscopic and microcosmic analysis results indicate that after the scouring experiment all the bacterial corrosion behaviors almost remain the same as those before the experiment even at high flow velocity (3 m/s), which far exceeds the economic field flow velocity (1-2 m/s) of product oil pipelines. Consequently, once there are sessile bacteria on the inner wall of pipelines, serious corrosion will occur. Those bacteria play a key role in the corrosion of product oil pipelines.