RELIABILITY ESTIMATION OF A NATURAL GAS PIPELINE WITH SURFACE CRACK

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).