Optimal selection of non-destructive inspection technique for welded components

The objective of this paper is to select the optimum non-destructive inspection (NDI) technique and its associated in-service inspection interval for welded components subjected to cyclic loading fatigue. The objective function (total cost) is formulated as a function of the decision variables (controllable) and the condition of the inspected asset (uncontrollable). Total cost consists of inspection cost and repair cost over the lifetime of the asset in addition to the cost of unexpected failure as a result of failure to detect a growing crack before reaching a critical size. The decision variables are the reliability of the NDI technique and the inspection interval. Two main parameters are used to quantify the reliability of NDI techniques. These are the Probability of Detection function (POD) and the Probability of False Calls (PFC). The condition of the inspected asset is represented by the probability of existence of a crack in the asset at the inspection time and the expected critical time to failure. The objective function is minimised for different NDI techniques subject to a safety constraint that the probability of failure does not exceed a predefined level. The NDI with the lowest objective function level is chosen as the preferred solution.