NDT - VALUE FOR MONEY

Plant operators must make appropriate decisions on the level and frequency of inspection required and balance this against economic and safety benefits. With increasing developments in NDT, operators need to make value judgments on where to apply this new technology and where existing methods may be adequate. This paper will concentrate on the increasing emphasis being placed on value and cost of inspection in industry and how these factors will probably dominate in the future. It will be shown that both the value and the cost of any NDT procedure depends on an overall performance figure that has four main factors: sensitivity, speed, coverage and reliability. The relative importance of these factors will be discussed. In the authors opinion, the NDT R&D community has spent a large effort on sensitivity over the last twenty years and the balance of effort will shift in future years to the practical problems of speed, coverage and reliability. If these values can be quantified, then it is possible to make value judgments on the benefit of different levels of NDT. Examples of inspections will be given, from both manufacturing and plant maintenance. These are intended to illustrate how improving the value-to-cost ratio of an inspection procedure depends on all the factors of NDT reliability. In addition, account must be taken of other factors such as defect population and fracture probability which are outside the usual scope of NDT. Recent developments within the National NDT Centre of PC-based models and databases to help quantify inspection reliability in terms of POD, false-calls and ROC are presented, together with recent information on human reliability. Currently, these models cover various ultrasonic methods and radiography. Examples of the use of such models in optimising inspection and inspection planning are described. The future health of the NDT profession depends on a better understanding of the reliability factors as well as awareness of the ''Non-NDT'' factors which affect the effective value and cost of any inspection.