Reliability Analysis Of X80 Corrosion Pipeline Based On Fracture Limit State

Corrosion inevitably occurs in the process of pipeline operation. The existence of corrosion defects will reduce the pressure of the pipeline, and affect the safe operation of the pipeline. With the construction and operation of the second west to east pipeline project, X80 pipeline steel has been more widely used. It has a very important engineering significance to analyze the failure pressure and reliability of X80 corrosion pipeline.In this paper, the following studies are carried out:(1) The application conditions of ASME B31G, Modified B31G, RSTRENG, DNV-RP-F101, PCORRC, API 579 and finite element method are analyzed to determine the failure pressure prediction method for X80 pipeline with corrosion defect.(2) Nonlinear finite element analysis models of X80 pipelines with typical cylindrical surface groove corrosion defects are established. The failure pressure from nonlinear finite element analysis are compared with the burst test data. It turns out that the maximum relative deviation is 3.13%, which verifies the reliability of the finite element models and the accuracy of finite element analysis method.(3) Fifty-four failure pressure values of X80 pipelines with different sizes of corrosion defect are obtained by numerical simulation of nonlinear finite element. The influences of the depth, the axial length, the circumferential length of corrosion defects to failure pressure are also analyzed. Based on the definition of short-corrosion and long-corrosion defects from the Modified B31G specification, the failure pressure prediction formula which based on nonlinear finite element method and is applicable to X80 corroded pipelines are established.(4) The limit state function of X80 corrosion pipelines in the rupture limit state is established on the basis of the failure pressure prediction formulas. The reliability calculation model is established based on the Monte Carlo Method after making a comparison for the applicability of the FOSM, JC Method and the Monte Carlo Method. A failure probability calculation program for corroded pipelines is written by using the GUI function of MATLAB.(5) In view of a certain X80 pipe section, the probability distribution function of each random variable is determined reasonably after making statistics and analyses in the collected data such as pipeline inner inspection data, steel pipe inspection data, etc.The failure probability are obtained with the help of the failure probability calculation software. Parameter sensitivity analysis for diameter, wall thickness, depth of corrosion, axial length of corrosion defects, internal pressure, pipe tensile strength, corrosion rate are carried out to make out that the key parameters which impact the failure of pipelines are the wall thickness, the internal pressure, corrosion depth and radial corrosion rate.The reliability calculation method based on the X80 corrosion pipeline in the rupture limit state can be used for the quantitative risk assessment and integrity management of high strength steel pipe to improve the safety of the oil and gas pipelines in operation.