Inspection and maintenance planning of pipeline under external corrosion considering generation of new defects

Safe operation of aging pipeline systems under external corrosion can be achieved through inspection and maintenance programs. Tools used for the pipeline inspection are uncertain in detecting a corrosion defect and in sizing a detected defect. The process of generation of new corrosion pits is an uncertain process. These uncertainties must be taken into account in the reliability analysis and in the pipeline inspection and maintenance planning. In this paper the effect of corrosion defect size on the remaining pipeline strength is modeled by a Markov process. Analytical solution of the probability transition matrix is obtained by solving the Kolmogorov forward differential equation. The matrix of probability transition function, the probability of defect detection and the probability distribution of sizing a detected defect is incorporated in estimating the probability of failure. The generation of new corrosion defects is modeled by a Poisson process. The optimal inspection and maintenance schedules are selected based on the reliability constraint. The sensitivity of optimal inspection schedule to the quality of inspection tools and to maintenance criteria is illustrated through examples.