Research On Repair Of Steel Epoxy Sleeve With X80 Pipeline With Defective Girth Welds

With the development of oil pipeline towards large diameter and high pressure,the requirements for pipes are also increasing.In order to further meet the service requirements,the X80 pipeline is constructed and put into operation in large quantities.The pipeline is the "artery" of oil and gas transportation.With the increase of service life,the accidents caused by pipeline crack type defects occur continuously.The girth weld is the weak link of the pipeline.Once the pipeline breaks from the butt girth weld,it will affect the service condition of the whole facility.At present,the domestic research method of steel epoxy sleeve repair technology is still in its infancy,so it is of great significance to combine the finite element numerical simulation and experiment.In this paper,the fracture toughness of the base metal and the girth weld of X80 pipe is studied by experiments.On the basis of the fracture toughness,the selection of the evaluation curve for the defects of the base metal and girth weld of X80 pipe is discussed.Secondly,the hydraulic blasting experiments were carried out for X80 pipeline with prefabricated girth weld defects under the condition of adding steel epoxy sleeve and not adding steel epoxy sleeve,and the pressure bearing capacity of the pipeline was analyzed.This paper also discusses the effect of the thickness change of epoxy resin layer with steel epoxy sleeve on the repair of pipeline with girth weld defect.Through the study of the influence of the thickness change of steel epoxy sleeve(resin layer)on the pipe stress,the repair scheme of epoxy sleeve is further optimized.In the research results,the stress distribution results of the pipes repaired without steel epoxy sleeve and the pipes repaired with steel epoxy sleeve are compared.The results show that after the steel epoxy sleeve repair,the peak value of the stress at the end of the defect in the pipeline is significantly reduced,and the local stress in the pipeline wall increases due to the existence of the shear force between the two,but the stress level is low and the stress is uniform.Therefore,after the steel epoxy sleeve repair,the stress concentration at the defects of the pipeline is improved,and the bearing state of the pipeline is also improved.Through the study of the influence of the thickness of the epoxy sleeve(resin layer),it is found that: with the uniform thickness of the epoxy resin layer,the internal stress of the pipe wall does not change significantly;considering the improvement of the stress at the end of the defect,it is found that the stress at the end of the defect decreases most obviously when the thickness of the epoxy resin layer is 30 mm.