Comparative investigation of localized corrosion failure in two types of gas field pipelines

• Under-deposit corrosion occurs differentially through a combination of sulfate-reducing bacteria, gas ingress, and fluid erosion. • >The scaling tendency of high-salinity produced water caused Under-deposit corrosion to occur in all pipelines. • >Gas ingress is the key factor causing variations in downhole tubing failures. • >The elbow failure differences include synergistic combination of Under-deposit corrosion and microbiologically influenced corrosion, fluid dynamic erosion. • >This material (J55) maintains sufficient mechanical strength even in areas severely corroded by environmental factors. A comparative failure analysis was performed on four pipeline samples—two from downhole tubing (DT1, DT2) and two from surface elbow pipes (EP1, EP2)—retrieved from a gas field in North China. Through integrated characterization involving macroscopic and microscopic inspection, mechanical testing, and corrosion product analysis (SEM/EDS/XRD), under-deposit corrosion (UDC) was identified as a common failure mechanism, driven by the scaling tendency of produced water. Distinct corrosion accelerators were identified between downhole and surface installations: failures in downhole tubing (DT1, DT2) were primarily accelerated by carbon dioxide and oxygen-enhanced pitting, whereas corrosion in surface elbow EP1 was mainly attributed to microbiologically influenced corrosion (MIC) caused by sulfate-reducing bacteria (SRB). For the other elbow sample (EP2), the synergistic effect of hard-particle erosion and produced-water corrosion was established as the dominant failure mechanism.