Study On Strength Design Coefficient Of Natural Gas Pipeline Grade Ⅰ Based On Reliability

At present, the design factor of domestic natural gas pipeline in location Class1is still adopting0.72, but this design factor of gas pipeline has larger construction investment and lower transport efficiency. In recent years, domestic natural gas pipeline’s steel metallurgy, manufacture, construction technology and other aspects have the rapid development, and the gas pipeline safety management level has improved significantly. That laid a good foundation and conditions for improving our pipeline design factor of the location Class1. Therefore, combined with the domestic actual situation, in order to saving pipeline’s construction in-vestment and improving the efficiency of pipeline to research the design factor which based on the theory of reliability, that has a certain guiding significance.Through researching the domestic and foreign literature and engineering practice, this paper sums up the design factor for influence of gas pipeline’s accident rate of the North America area; combines engineering projects to analyse the anti-crack toughness’requirement which based on improving design factor of gas pipeline,and adopted pipeline failure calcula-tion model and pipeline consequences estimates model to respectively calculated the individ-ual risk level which around the gas pipeline of design factor is0.72and0.8; according to the probabilistic method and the principle of reliability,established reliability mathematical mod-el which based on stress-strength of design factor’s0.8, and adopted C#to work out the cor-responding calculation procedure, and combined with the natural gas pipeline’s engineering projects to verify the feasibility of improve design factor of nature gas. Come to the following conclusion:(1)According to the statistics data of the failure gas pipeline of America, the pipeline failure rate is2.5×10-4/(km-a) when the design factor≤0.72, and the pipeline failure rate is3.1×10-4/(km·a) when the design factor>0.72, that the natural gas pipeline’s accident rate increases0.6×10-4/(km-a), but still in the acceptable range. when the design factor increases from0.72to0.8of the natural gas pipeline in location Class1(X80steel, delivery pressure12MPa), crack arrest impact energy has a significant increase,that increased from215J to263J.(2)Adopt probabilistic statistical method and reliability principle, through variable sub-stitution make the nonstandard reliability calculation model transform to standard normal dis-tribution function, that changed the calculate target from pipeline reliability to pipeline relia-bility coefficient Z and determine the reliability criterion is Z≥3.2when the design factor is0.8.(3)Based on the data of the gas pipeline’s engineering projects, studied the influence law and sensitivity analysis which caused by the related parameters of Z. The results show that improve the design factor is reasonable and feasible,because under certain condition when the design factor is0.8in location Class1that Z≥3.2. The sensitivity of the related parameters’ deviation factor of Z from high to low:minimum yield strength, pipe wall thickness, operat- ing pressure, pipe diameter.(4) Put forward the potential impact radius of High Consequence Areas to be418m, spe-cific value of the yield strength and tensile strength recomended for0.95; recommends static hydraulic test pressure for1.25MAOP, and100%SMYS of X80which the design factor’s0.8that under certain condition; recommends the interval evaluation of hydrostatic pressure testing, internal inspection and direct assessment to modify for4,8,12and16years; adjust-ing the crossing angles between gas pipeline and faults, increasing the ductility of natural gas pipelines, reducing interaction between the pipe and the soil to control excessive deformation of the pipe.