Study On Quantitative Failure Probability Calculation Method For Crack Defects Of Long-distance Natural Gas Pipeline

With the vigorous development of natural gas and oil pipelines in China,pipeline safety has become the most important part of the pipeline sector.At the same time,crack defects will inevitably occur in the production,transportation,installation and service of oil and gas pipelines.The existence of cracks is likely to lead to leakage of pipelines,which will also cause combustion and explosion of natural gas pipelines,and pose a great threat to the public's personal safety and safety.Therefore,the safety evaluation of long-distance natural gas pipelines with crack defects is of great significance to ensure the safe operation of pipelines.In this paper,the internal and external detection methods of pipelines are summarized and analyzed,and the advantages and disadvantages of various detection methods are compared.A case study of three-axis magnetic flux leakage internal detection of target pipelines is carried out,and the formation mechanism of crack defects and the mechanical analysis method of defects are given.On this basis,combining the theory of fracture mechanics and Monte Carlo stochastic simulation,the qualitative risk assessment and quantitative failure probability calculation of the target pipeline crack defects are carried out.In this paper,three evaluation methods of crack defects in ‘Guide to methods for assessing the acceptability of flaws in metallic structures'(BS7910)are compared and analyzed,and five crack defects are qualitatively evaluated by 2A deterministic evaluation method.Grade 2A deterministic evaluation is greatly influenced by sub-item safety factor,and the opposite evaluation results are often obtained.At the same time,because there are some measurement errors in the evaluation parameters(fracture toughness,specified minimum yield strength,defect depth,defect length),the three-axis high-definition magnetic flux leakage internal detection can not achieve absolute accurate detection due to its own reasons,and the measurement results are within a certain range.The quantitative evaluation method of crack defect based on Monte Carlo random simulation is proposed.The failure probability of target defect can be obtained by generating random numbers which obey the corresponding distribution and pass the test.According to the evaluation results,sensitivity analysis and index weight analysis of the evaluation parameters are carried out.It is concludedthat the sensitivity of four indexes affecting the failure probability of crack defects is from high to low: defect depth,fracture toughness,specified minimum yield strength and defect length.The index weights are 0.8348,0.1321,0.0247 and 0.0084,respectively.