Study On Calculation Method Of Pipe Segment's Failure Probability In Wuhan Metering Station's Verification

Wuhan metering station,belonging to the fifth class of natural gas stations in the production scale,is one of the six major oil and gas high flow metering stations in China.In the case of a possible accident,it will have a pernicious impact on the safety of residents,economy and the society.The main work of Wuhan metering station is to measure gas,verify the instrument and check the standard,which is characteristic of frequent personnel operation,deep bite marks on the surface of the pipe segment,and large pressure change in the pipe segment.As for the conventional natural gas station field,the calculation method of failure probability does not consider above three factors.Therefore,it is of great significance to form the calculation method of the failure probability of the verification process accident of Wuhan metering station considering its features.Therefore,this paper has carried out the following aspects of research:(1)The verification process of Wuhan metering station was systemically analyzed and the characteristics and accident types of the verification process of Wuhan metering station was summarized.In the execution of verification work by staff,they need to twist the valve frequently,frequently disassemble the valve,and constantly replace the gas in the tube.These behaviors will lead to the frequent personnel operation,and deep bite marks on the surface and large pressure fluctuation of Wuhan metering station.Among them,frequent operation of staff will lead to misoperation accident.Damage accident of the pipe section could occur due to the bite marks on the surface of the pipe section and pressure fluctuation in the pipe segment.(2)Bayesian network model of personnel mistakenly operated by Wuhan Metering Station was developed,and the calculation method of failure probability of personnel misoperation accident was formed.82 kinds of personnel misoperation accidents was summarized by analyzing the working steps of the verification process of Wuhan metering station.The logical relationship between the influencing factors was specified by establishing the accident tree.The accident tree was converted into Bayesian network based on the mapping algorithm.Moreover,the failure probability of the personnel misoperation accident was calculated,with a value of 6.798 × 10-4.(3)The model of surface damage and crack propagation of pipe segment was established,and influence of bite marks on the surface of pipe segment and the pressure fluctuation in tube on the damage of pipe section was specified.The deep bite marks on the surface of the pipe segment reduced the wall of the pipe.The pressure fluctuation will lead to fatigue damage and induce the damage accident of the pipe segment.The models of non-damage pipe segment and surface damage pipe section were established respectively by using ANSYS Workbench software.And the stress and strain distribution of the pipe segment under the condition of the actual fluctuation pressure and the constant pressure of the conventional station field in Wuhan Metering station are analyzed.The results showed that the maximum equivalent stress ratio of the pipe segment was shifted from the inner wall of the pipe segment to the edge of the bite mark,and the maximum equal-force value of the non-damage and damage model decreased with the increase of the internal and external diameter ratio.The applied pressure made the pipe elastic deformation,and the maximum stress value of the pipe section was the same.(4)The calculation method of failure probability of pipe segment damage event in Wuhan metering Station was formed.Based on the influence of the bite marks and pressure fluctuation on the damage event of the pipe segment,the surface damage model and crack propagation model under the transient condition of pressure fluctuation was established,considering the size and force of the pipeline in Wuhan metering station.Based on fatigue damage accumulation theory,the number of cycles representing the life of pipeline segments were converted to failure probability,and the quantitative calculation of failure probability of pipeline segments was realized.(5)The total failure probability of the pipe segment was quantitatively calculated.Combined with the specific position of Wuhan metering station pipeline,the total failure probability of pipeline section was obtained by summing up the accident failure probability involved in pipeline section.According to the Norwegian Classification Society failure probability Classification standard,it was concluded that the failure probability grade of each section was two,and there was the possibility of failure of the section.The section with the greatest failure probability of verification process in Wuhan metering station was NG-0401-300-10A1-H,with a probability of 6.955×10-4.The order of influence degree was:personnel misoperation>surface damage and pressure fluctuation>pipe segment corrosion.