Safety Study Of Pipes Containing Depressions

As the main means of transportation of oil and natural gas,pipeline plays an important role in the industrial system,and how to maintain a high level of pipeline integrity and reliability of the oil and gas industry is essential.Mechanical damage is one of the important reasons for the failure of the pipeline,and the dent is the most typical type,which can cause stress and strain concentration,which can cause serious threat to the safe operation of the pipeline.Therefore,it is very necessary to carry on the reasonable safety evaluation to the dent of pipeline,and according to the evaluation results to take appropriate measures to deal with.This paper studies the following for the safety of the dented pipeline:First of all,this paper summarizes the evaluation methods of dented pipeline.Based on the PDAM depth criterion and Minimum Elongation Limit Criterion,the strain analysis is carried out on the spherical dent of pipeline.Therefore,the damage degree of the pipeline under different parameters was studied by using the ductile fracture failure model and the depth criterion was verified.At the same time,the critical failure strain of different pipe under internal pressure spherical dent,according to the critical failure strain selected safety factor to determine appropriate allowable strain,strain through evaluation method identified the need to repair or replace pipe engineering.Secondly,on the basis of the research of the spherical dent of pipeline,the critical indentation depth using API 579 standards as the research object.In this paper,the safety analysis of the pipeline is carried out analyzes and the critical depth of the API 579 criterion is used as the research object.The variation of strain and strain distribution under different parameters are analyzed and the minimum elongation limit criterion is used to evaluate it.In order to further explore the accuracy of the critical depth,study on the damage degree of ductile fracture with different parameters on kinked dent of pipeline failure model,according to the criterion of whether the ductile failure damage reaches the threshold to detennine whether the occurrence of fracture.Then analyze the critical failure strain of different dented pipe under internal pressure,according to the strain evaluation process,the paper analyzes the safety of the kinked dent and gives the suggestions.Finally,according to the ASME B31.4 standard,this paper makes a preliminary study on the safety of the defective pipeline under the combined action of internal corrosion and dent.Through the plastic failure criterion on different parameters of corrosion defect pipeline can withstand the critical depth under pressure head pressure,safety operation of pipelines with corrosion defects.In order to further verify whether the critical depth is accurate after removing the indenter,the damage degree of the pipeline with internal corrosion is analyzed based on the depth criterion and the ductile failure model.The results show that the critical depth can't be used as the critical depth of the pipeline,but under certain conditions,it is safe to use internal corrosion defects pipeline based on ASME B31.8 depth criterion.In order to explore the more accurate safety depth of dent,the ASME B31.8 strain evaluation method is used to analyze the safety depth of the pipeline with internal corrosion defects.The results show that the proposed method is more accurate than the depth of safety dent based on depth criterion.More importantly,this paper puts forward two kinds of evaluation methods for the safety evaluation process of the pipeline,which will provide reference for the project evaluation.