Analysis of contributing factors to internal corrosion of refined oil pipelines and corresponding prevention and control measures

Internal corrosion is a common issue affecting refined oil pipelines, posing significant risks to the safe transportation and quality of refined oils, and potentially leading to economic losses and safety hazards. To address this problem, the contributing factors to internal corrosion in refined oil pipelines were investigated using multiple methods, including macroscopic measurements and analysis, physical and chemical performance experiments, and pigging product analysis. Based on the results of these analyses, corresponding prevention and control measures were proposed. The study results are summarized as follows: 1) Corrosion traces are distributed axially, covering a width of approximately 80 mm and located at the six o'clock position along the pipe. All wall thickness measurements are below the nominal wall thickness of 6.400 mm, and exacerbated corrosion was observed at localized positions. 2) The elongation after fracture in the sample affected by corrosion is reduced compared to that in the normal pipe sample, with the tensile bearing capacity dropping by 4.97%. 3) The internal corrosion of the refined oil pipeline originated from the construction period and developed gradually over time. Particularly, oxygen-consuming corrosion occurred at the bottom of the pipeline during construction, resulting from liquid loading due to insufficient pigging after pressure testing. 4) Chloride ions reduce the pH value of the solution, leading to the formation of corrosion pits in the pipe. 5) Impurities such as silt, scale, and rust in the refined oil pipeline roughen the bottom of the pipeline, thereby increasing the capacity to trap free water in the oils. This accumulation of water intensifies electrochemical corrosion on the inner wall of the pipeline. Corresponding prevention and control measures are proposed as follows: 1) The internal corrosion rate of pipelines can be reduced during operation by increasing the frequency of pigging, injecting corrosion inhibitors, and optimizing oil properties. 2) Corrosion is controlled for new pipelines by selecting corrosion-resistant materials, applying additional inner coatings, and ensuring the removal of residual water from pressure testing before commissioning.