Selection of an optimal, non-destructive inspection technique for welded components

Khalifa, Mohamed (2009) Selection of an optimal, non-destructive inspection technique for welded components. Masters thesis, Memorial University of Newfoundland.

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Abstract

The objective of this work is to select an optimum Non-Destructive Inspection (NDI) technique and its associated inspection interval for welded components subjected to cyclic loading. -- The objective function (total cost) is formulated as a function of the decision variables (controllable) and condition of the inspected asset (uncontrollable). Total cost consists of inspections cost and repairs cost over the lifetime and risk of failure as a result of the failure to detect a growing crack before it reaches 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 the NDI techniques. These are the Probability of Detection function (POD) and the Probability of False Calls, (PFC). Condition of the inspected asset is represented by the probability of the presence of a crack in the inspected asset at inspection time and the expected time to failure. The objective function is minimized for different NDI techniques subject to a safety constraint: that the probability of failure as a result of failure to detect a growing crack before it reaches the critical size does not exceed a predefined limit. The minimum values of the objective functions for all candidate NDI techniques are compared to determine the optimal NDI technique and its associated inspection interval.

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