Numerical Analysis Of Safety Assessment Of Gas Polyethylene Pipes With Defects

As the gas production and the speed of consumption grow,the scale of urban gas pipeline develops rapidly.At the end of "the twelfth five-year",the total length of town gas pipeline had been over 600,000 kilometers,along with the increasing gas pipe length of upstream and the rising gas demand of downstream,and the city gas industry scale will continue to expand.Gas pipeline accident will cause populated urban population casual-ties and property losses and huge damage,so it has a potential threat.Whether it’s domes-tic or imported PE pipe,there are different degrees of defects inevitably.Moreover be-cause of the influence of various factors,such as the load,medium and pressure,new defects may be initiated during the process of use.But from the point of engineering application,the research of safety assessment of the mechanical properties of gas PE pipe containing defects is very few both at home and abroad.This paper is funded by a scientific research project "the town gas polyethylene pipe-line risk assessment method system research"(project number:210310159)in General Administration of Quality Supervision,Inspection and Quarantine of the PRC.The sim-ulation numerical analysis and the safety assessment were carried out on the object of the gas PE pipe containing two kinds of defects(local thinned and pits).The main research contents and conclusions are as follows:(1)According to the characteristics of gas PE pipe,the tensile test with different strain rates was done.Then the Suleiman hyperbolic model was chosen,and the PE pipe material constitutive model was fitted based on the experimental data.(2)According to the literature analysis,the common defects of gas PE pipe are vol-ume defects,namely local thinning defects and pit defects.And the type of defects is represented by the dimensionless quantities such as relative depth and slope and the length of defect types.The strength analysis model of PE pipe containing defects was established based on finite element analysis software ABAQUS under internal pressure and bending load respectively.It showed that the depth of the defects has the most effect in the strength of the PE pipe under the constant load.In addition to the relative slope of pit defect and limit load present positive correlation,the defect types are negatively related with the limit load.(3)According to the principle of tie up,the strength analysis model of PE pipe con-taining defects is set up under the effect of tie up.The influence of the strength of PE pipe was studied with the tie up parameters and other factors(such as PE pipe defect type).It is concluded that:the displacement of the PE pipe occurred at the top center of symmetry under the tie up loading.With the increase of the tie up load,the maximum Mises stress appears in the defect,and the influence of stress in defect depth is the largest.To simplify the traffic load as the pulse load,analysis,the influence of the defect depth of pipe and load.Through simulation calculation,Under the action of traffic load in a short time,defect relative depth are positively correlated with the fill section rate.(4)According to the results of the numerical simulation and the national standard "in the safety assessment of pressure vessels containing defects"(GB/T19624-2004),the safety curve of the gas PE pipe under the internal pressure and bending moment function at the same time is drawn.Finally the safety assessment method of the pressure PE pipe containing defects is proposed.Results of this study can be used to guide safety assessment and the life prediction of gas PE pipes.