The reliability estimation of API 5L X65 natural gas pipeline with a semi-elliptical crack along a pipeline surface is performed by utilizing the probabilistic methods, such as the First Order Reliability Method (FORM) and the Second Order Reliability Method (SORM). The probabilistic method accounts for the uncertainties in the load and the resistance parameters on the Limit State Function (LSF). The LSF is formulated with the help of fracture control concept including the Stress Intensity Factor (SIF) for a natural gas pipeline with cracks or crack like defects. The hoop stress due to the internal pressure is considered to be a major load. The effects of probabilistic distribution characteristics of random variables, on the failure probability are systematically investigated. The probabilistic distribution characteristics of random variables include the normal, the log-normal and the Weibull distributions. The results obtained by using the FORM and the SORM are compared with those determined by the Monte Carlo Simulation (MCS).
In this paper, the reliability estimation of Polyvinyl chloride (PVC) pipelines is performed by utilizing the probabilistic method, which accounts for the uncertainties in the load and resistance parameters in the limit state function (LSF). The LSF is formulated with the help of fracture control concept including the stress intensity factor (SIF) for the pipeline having crack or crack like defects. The common cracks found at pipeline can be assumed as semi-elliptical shape and the main load is hoop stress due to the internal pressure. The FORM (first order reliability method) and the SORM (second order reliability method) are carried out to estimate the failure probability of pipeline utilizing the SIF for semi-elliptical crack. The reliability is assessed using this failure probability. It is found that the failure probability increases with the operating pressure, and the decrease of the pipeline wall thickness, and the increase of the crack depth, the crack length, the outside diameter of pipeline. The failure probability increases when the initial crack approaches to a semi-circle shape of crack and the failure probability steeply increases at the ratios of larger than 0.5 of a/t and larger than 30 of D/t. Moreover, it is recognized that the effects of the fracture toughness and the pipe wall thickness on the failure probability are the significant one.
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