Simultaneous handling of variability and uncertainty in probabilistic and possibilistic failure analysis of corroded pipes

Abstract

Corrosion in the pipes, transporting oil and gas, significantly increases the likelihood of pipe failure due to rupture or leakage under internal pressure. Hence, calculation of the strength of corroded pipes is an important parameter in the development of the maintenance strategy of the pipes. One of the commonly used models for calculating the strength of corroded pipes is the ASME B31G. For calculation this model uses the data about (a) the diameter of the pipe; (b) the wall thickness; (c) the length of corrosion pits; and (d) the depth of corrosion pits. Unfortunately the inspection data of these parameters always contains imperfections of various kinds. This paper presents two different approaches for simultaneously handling the variability and uncertainty in the inspection data for calculating the likelihood of failure of corroded pipes. The first approach is the probabilistic approach based on the concept of two-dimensional Monte Carlo simulation. The second approach is the possibilistic approach. In the possibilistic approach the variability and uncertainty membership functions are combined to obtain the possibility distribution function of a variable. These resultant membership functions are used to calculate the possibility and necessity measures of failure. The possibility and necessity measures are, respectively, more and less conservative than the probability of failure.