Corrosion behavior of L360 N and L415 N mild steel in a shale gas gathering environment – Laboratory and on-site studies

Abstract: Hydraulic fracturing combined with horizontal drilling has resulted in the rapid development of unconventional shale gas production during the last couple of decades. These shale gas fields have faced challenges in terms of bacterial control and pitting corrosion attacks. In the present work, laboratory and on-site corrosion tests were performed to investigate the corrosion behavior of two gathering pipelines in a shale gas field. General and pitting corrosion rates were determined via gravimetric analysis and surface profilometry, respectively. The surface morphologies of coupons and compositions of surface films were analyzed by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The results indicate an abundance of sulphate-reducing bacteria (SRB), with a concentration of over 104 cells/mL, was detected in the produced water collected from two gathering pipelines. Both laboratory and on-site corrosion tests revealed that the general corrosion rate was relatively low over a long testing period and decreased with the exposure time. A quantitative analysis of the general corrosion rate as a function of operating time for both pipelines was carried out based on the experimental and on-site corrosion tests. Pitting corrosion was a fundamental consideration and could pose a threat to the integrity of mild steel pipelines in a shale gas gathering system. Medium-to-serious pitting corrosion, with rates from 0.13 mm/y to 0.45 mm/y, was measured from 97∼653 day’s on-site samples. It is proposed that microbiologically influenced corrosion (MIC) associated with under-deposit corrosion was the predominant cause of pitting corrosion. In addition, chloride in the produced water promoted the pitting corrosion.