The effect of defect size and soil aggressivity on corrosion of underground oil & gas pipelines

Abstract

Nowadays, the oil & gas industry has limited number of non-destructive corrosion techniques for assessment of life-time of existing infrastructures, especially on low and medium pressure pipelines exposed to aggressive soil environment where defect in isolation and presence of water formed ideal conditions for corrosion attack. Efficient non-destructive corrosion monitoring can be achieved using mobile potentiostat through the selection of appropriate monitoring techniques and special kind of sensor. OCP potential is monitored for 10 minutes and actual corrosion rate of pipeline with corrosion products in soil mixture was determined using Stern polarization technique in non-invasive arrangement. Using global database with range of minimum and maximum corrosion rate limits obtained from terrain measurements we can determine active or passive role of corrosion products and assess risk joint with aggressiveness of soil in location of interest. Finally, values were divided between high active, medium active and passive corrosion. Output is alarm, which can help in decision if reconstruction of underground pipelines where isolation failed in time is sufficient or not. When done properly, corrosion monitoring using non-invasive “in-situ” technique can serve as an early warning system before the onset of corrosion related failures.