Cause Analysis on Corrosion Zone on Inner Wall of Oil-carrying Spiral Welded Pipelines in An Oilfield

Although the water content of the liquid medium in oil pipeline of a certain oilfield is relatively low (<1%), it was found during internal inspection that there are locally distributed corrosion zones on the inner wall of the spiral welded pipe. Therefore, physical and chemical performance testing, scanning electron microscopy and energy spectrum analysis were carried out for the pipe and corrosion products to clarify the causes of corrosion bands, and residual strength evaluation and anti-corrosion strategy formulation were carried out for this pipeline. The results show that the content of C and Mn elements of the pipe base material and the tensile strength does not meet the standard requirements. The main cause of corrosion is corrosion under scale. At the same time, due to the presence of trace amounts of water in the conveying medium and the presence of S and Cl - ions in the water, corrosion is further promoted. This pipeline can operate safely in the event of corrosion on the inner wall, but timely monitoring of the corrosivity of the medium transported within the pipeline should be carried out, and measures such as regular cleaning or adding corrosion inhibitors should be taken to preventor reduce the tendency of corrosion on the inner wall of the spiral welded pipe.