Study On Theory And Method Of Improving Design Coefficient Of Gas Transmission Pipeline

With the development of national economy and energy strategic reserves,the demand for natural gas is increasing.In the process of natural gas transportation,how to reduce the cost of gas pipeline and improve the pressure bearing capacity of gas pipeline is one of the most important research topics in oil and gas storage and transportation.One of the most effective way is to improve the design coefficient of the pipeline.The parameters of gas pipeline,such as pipe wall thickness,pipe diameter,pipe pressure has some uncertainty.The traditional deterministic analysis will have certain limitations,so this paper uses the design method based on reliability,choose to use the Monte-Carlo method to calculate the reliability of pipeline.The reliability of pipeline is calculated by probability,so a decision criterion is needed to determine the safety performance of pipeline.In view of our country is still in the research stage,summed up the international commonly used oil and gas pipeline target reliability evaluation criteria,finally choose the API579 criteria.The failure model of residual strength of oil and gas pipeline at home and abroad is introduced.The conclusions are as follows: NG-18 is suitable for the evaluation of low strength steel pipeline;ASME B31 G is suitable for evaluating low strength steel pipeline and medium strength steel pipeline;RP-F101 and PCORRC are suitable for evaluating high grade pipeline.It is recommended to use the finite element method to evaluate the residual strength of the pipeline with super steel grade.In this paper,the PCORRC criterion is chosen as the failure model of pipeline reliability calculation for X70 pipeline and X80 pipeline.The limit state equation of the complete pipeline and the pipeline with defects is established.The results show that the internal pressure has the greatest influence on the reliability of the whole pipeline,the depth of defects and the internal pressure of pipeline have the greatest influence on the reliability of pipeline with defects.The remaining life of X70 pipeline and X80 pipeline is calculated,and it is feasible to improve the design factor of gas pipeline in the first class.The way to increase the design factor to a higher level is to reduce the fluctuation of the pipe pressure,to adopt a higher grade pipeline and to reduce the corrosion rate of the pipeline through the integrity management.