Research On Residual Strength Evaluation Of X80 Steel Pipeline With Internal Corrosion Defects

As the fifth largest transportation method in the world today,pipeline transportation plays a very important role in the transportation of oil and natural gas due to its economical and efficient characteristics.With the increasing demand for energy in my country,the requirements for high-strength and large-diameter transmission pipelines are getting higher and higher.X80 steel pipelines are widely used in pipeline construction in my country due to their high strength and high elasticity and plasticity.Corrosion is the main cause of pipeline accidents,and inner wall corrosion is a common form of pipeline corrosion.The environment where the pipeline is located is complex.An accurate evaluation of the residual strength of the pipeline with inner wall corrosion under multiple loads can effectively guide the repair and replacement of the pipeline..In this paper,focusing on the analysis and evaluation of residual strength of X80 steel pipelines with internal corrosion defects,the corrosion defects are characterized regularly,and the finite element analysis method is used to analyze the stress of X80 steel pipelines with internal corrosion defects.The load mainly considers the internal pressure of the pipeline,soil stress and The axial stress of the pipeline is studied,the interaction law between corrosion defects is studied,and the residual strength evaluation model,method and program of X80 steel pipeline with internal corrosion defects are constructed.1.In view of the diversification of defect forms of corrosion-containing pipelines,the local corrosion profile is simplified to uniform wall thickness corrosion,and the types of corrosion defects are divided into single corrosion defects,double corrosion defects and complex corrosion defects,and the three defect forms are ruled characterization.2.The finite element model of X80 steel pipeline under complex internal corrosion defects is established,and the pipeline length,mesh size and boundary conditions are set reasonably.The pipeline length is set to 2 times the outer diameter,the inner wall of the pipeline is applied with internal pressure load,and the outer wall is applied Soil load,axial load is applied at one end,and the correctness of the finite element model is verified based on the previous blasting experimental data.3.The stress analysis of the X80 steel pipeline with internal corrosion defects was carried out,the influence of the internal pressure of the pipeline,the soil stress and the axial stress of the pipeline on the pipeline stress distribution was comprehensively analyzed,and the influence of the soil stress of the buried pipeline on the pipeline stress was studied.The soil stress at the top of the outgoing pipe and the bottom of the pipe is the largest,and the stress on both sides is smaller;for a single corrosion defect,the increase of the defect depth and defect length will reduce the stress level in the uncorroded area,making the pipe show local failure.There is an interaction between the double corrosion defects.When the axial spacing is small,there will also be high stress concentration in the axial spacing area of the double corrosion defects.When the pipeline fails with overlapping corrosion defects,the high stress concentration mainly occurs at the bottom of the inner defect and the axial region of the outer defect.4.The research on the interaction law of corrosion defects in X80 steel pipelines was carried out.For a single corrosion defect,the depth of the defect is the main factor affecting the residual strength of the pipeline.The diameter of the defect only affects the residual strength of the pipeline when the defect depth is deep.The effect of strength is also affected by defect depth,and to a lesser extent by defect width.For symmetrical double corrosion defects,the increase of defect diameter,defect length and defect depth will enhance the interaction between double corrosion defects and increase the limit interaction distance of double corrosion defects.Decreasing the volume parameter of one of the defects weakens the double-corrosion interaction strength and reduces the limit interaction distance.For circular overlapping corrosion defects,the depth of the inner and outer defects is the main factor affecting the interaction strength and the residual strength of the pipeline,and the diameter of the inner and outer defects has less influence.For rectangular overlapping corrosion defects,the depth of internal and external defects and the length of internal and external defects are the main reasons,and the width of internal and external defects has little effect.5.Based on the finite element calculation results of the stress of pipelines with internal corrosion defects,an empirical model for calculating the residual strength of X80 steel pipelines with single corrosion defects,axial double corrosion defects and complex corrosion defects is obtained,and its accuracy is verified by comparing with the experimental data of pipeline blasting.The residual strength evaluation method program of X80 steel pipeline with internal corrosion defects is constructed,and the residual strength of X80 steel pipeline under different corrosion defects is obtained,and its reliability and applicability are verified by examples.