Research On The Resistance Of Oil And Gas Pipeline Girth Weld To External Load

The pipeline is a bridge for oil and gas transportation to all parts of the country and even all countries in the world.Stable oil and gas energy transmission is inseparable from stable pipelines.However,buried pipelines will be subjected to loads from all sides during service.The pipeline with defects in the girth weld is the first to be damaged.At present,the research on the ability of the girth weld with defects to resist external loads is imminent.In order to study the anti-external load capacity of pipeline girth welds,this paper first analyzes the performance of a typical X80 pipeline girth weld,and shows the performance of common pipeline girth welds.Then,the external load resistance of the girth weld of an X70 pipeline is predicted.The full-scale physical test results show that the prediction results are acceptable.Finally,the prediction method is used to predict the external load resistance of the girth welds of the West Second Line and China-Myanmar Line pipelines,which provides a reference for the design of long-distance pipelines and the external load control of in-service pipelines.The performance analysis of the girth weld of an X80 pipeline includes the measurement of the outer diameter,wall thickness,weld reinforcement,misalignment,width and grinding depth of the pipeline,as well as the non-destructive testing,chemical element analysis,tensile test,impact test,hardness test,metallographic analysis and fracture analysis of the girth weld.A series of tests show the X80 pipeline is welded with unequal wall thickness,and there are grooves left by grinding on the girth weld.There may be unpolished original defects in the grooves,resulting in large stress concentration.Under the action of welding residual stress,internal pressure and loads,the possible original defect or groove tip expands from the root welding position to the outer surface,and finally forms the whole crack defect.According to SY / T 6477-2017 ’ Evaluation method for residual strength of defective oil and gas pipelines ’,the external load resistance of a X70 pipeline with defective girth weld was predicted.The result shows that the crack-type defective girth weld can operate normally under 10 MPa internal pressure,and the maximum bending load of the defective girth weld is predicted to be 880 kN.The full-scale physical test result shows that the circumferential weld with defect can serve normally under 10 MPa operating internal pressure,and the maximum bending load is 1371 kN.Finally,by analyzing the reasons for the difference between the test result and the predicted result,it is shown that the predicted result is acceptable.The prediction result of the external load resistance of the girth weld of the West Second Pipeline shows that when the crack length and depth are 100 mm and 5 mm respectively,the girth weld of the pipeline can serve normally under 10 MPa internal pressure,and the maximum external axial load resistance is 165 MPa.The prediction result of the external load resistance of the girth weld of the China-Myanmar pipeline shows that when the crack length and depth are 80 mm and 5mm respectively,the girth weld of the pipeline can serve normally under 10 MPa internal pressure,and the maximum external axial load is 255 MPa.