Research On Pitting Characteristics And Corrosion Depth Prediction Of Buried Oil And Gas Pipelines

Oil and gas industry plays an important role in the development of national economy,and its pipelines are mainly laid in three ways: buried type,overhead type and submarine type.Buried oil and gas pipeline is the most common form of raw material transportation.Due to the complex soil environment,it is easy to form all kinds of corrosion on the outer wall of oil and gas pipeline.Pitting of pipe wall is characterized by strong concealability and great destructiveness.It is difficult to detect pitting process of pipe wall,analyze influencing factors of pitting process and judge pitting pit depth by experimental method.Therefore,it is of great significance to analyze pitting characteristics of buried pipelines and predict pitting pit depth.Based on the theory of metal pitting corrosion,this paper analyzes the pitting characteristics of buried oil and gas pipe wall,and predicts the corrosion depth by establishing a prediction model.The main research work is as follows:Firstly,the mechanism and influencing factors of pitting corrosion in buried oil and gas pipelines were analyzed.In this paper,the chemical corrosion module in COMSOL Multiphysics simulation software was selected to analyze the pitting characteristics of pipe walls,and the simulation model of pitting corrosion on pipe walls was established.In order to better simulate the whole process of pitting on pipe wall,this paper adopts the cubic current distribution and deformation geometry physical field to realize the realization,so as to fully consider the influence factors of ion transport,diffusion and concentration change in the corrosion electrolyte domain.At the same time,the irregular deformation of pitting pits is analyzed,and the simulation results of single physical field on metal pitting are compared with those of relevant literatures.The results show that the simulation results in this paper have the same trend as that of single physical simulation analysis and can better explain the influencing factors of pitting process.Secondly,in order to analyze the influence of pitting pit morphology on the pitting characteristics of pipe wall,the main pitting pits are semicircular and rectangular.The influence of different pit radius and depth on pitting corrosion expansion,edge local current and edge corrosion rate was compared and analyzed.The results show that the pitting pit depth value is more likely to lead to the formation of autocatalytic reaction conditions for pitting the pipe wall,so it will promote pitting pit to the inner corrosion of the pipe wall,resulting in local corrosion defects of the pipe wall and a potential safety hazard.Finally,the simulation analysis shows that pit depth is the key factor to determine the reliability and service life of oil and gas pipelines.Therefore,in order to accurately grasp the depth of the pit,timely maintenance and replacement of the pipeline can reduce the frequency of accidents.The least square method was used to optimize the background value and initial value assignment of the traditional GM(1,1)prediction model.The results showed that the average relative error of the improved GM(1,1)prediction model was 0.0346,the variance ratio was 0.127,the correlation degree was0.8672,and the prediction accuracy level was 1,so the prediction effect was better.