Understanding the corrosion of pipe steel due to the adhesion of sulfate reducing bacteria film combined with the deposit layer

In the production of shale gas, solid particles such as gravel and clay can adhere to the pipe wall surface and generate under-deposit corrosion (UDC). Meanwhile, the adhesion of sulfate reducing bacteria (SRB) film can further aggravate the local corrosion problem, which would easily result in the failure of pipe lines. Therefore, understanding the corrosion of the steels when SRB film and deposit layer are co-existed is of highly significance. In this work, UDC in SRB-containing shale gas flowback water was studied by means of wire beam electrode, scanning electron microscope, energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS). The results show that SRB can adhere to bare steel to form biofilm and then corrosion occurs. For deposit-covered steel, SRB cannot directly contact the metal matrix due to the barrier effect of the artificial deposit layer, therefore no SRB corrosion was observed. Bare steel and deposit-covered steel can form a galvanic couple, where the deposit-covered steel serves as the anode and the bare steel as the cathode. However, SRB could accelerate the corrosion of bare steel and enhance the cathodic reaction, thus promoting the anodic reaction under the deposit-covered steel.