Reliability based optimal inspection and maintenance for pipeline under corrosion

Nondestructive inspection tools used for pipeline inspection are uncertain in detecting corrosion pits and in sizing detected defects. Probability-based optimal inspection schedule analysis must taken these uncertainties into account. In this paper, the probability of time to failure is formulated as integral equations with domain of integration expressed as unions and intersections of domains of failure, defect detection, defect nondetection and maintenance criterion. The rate of defect detection as a function of defect size and the maintenance criterion are used as filters to eliminate the defects that are not fit for service in an expected remaining service life after inspection. Simulation procedure is given to estimate the probability distribution of time to failure by using the integral equations. To facilitate the probabilistic analysis, a standard uniformly distributed variate is introduce and used in defining the domain of detected defect and the domain of nondetected defect. The advantages of using the proposed simulation procedure are discussed. Optimal inspection schedules are selected based on the minimum value of the maximum probability of time to failure before inspections and before the time at the end of service life. Effect of inspection quality and maintenance criterion on probability of time to failure and on selecting optimal inspection schedule is presented through an illustrative application study.