In broad terms, the purpose of Non-destructive Testing (NDT) is to provide accurate defect information. This, in turn, allows engineers to make judgements concerning the life and/or safety of industrial plant. These judgements need to take account of the effectiveness of NDT, both in terms of flaw detection and flaw sizing. This was recognised by Sir Alan Cottrell and the Marshall Study Group, who in 1982 recommended independent validation to assess the adequacy of the inspection procedures for certain safety related components of the Sizewell "B" Pressurised Water Reactor (PWR). Independent validation of Sizewell "B" components eventually led to the establishment of a European Network for Inspection Qualification (ENIQ). In 1996 ENIQ published a European Methodology for independently qualifying that an inspection is fit for its stated purpose. The safety benefits of inspection qualification are now recognised throughout the world, both within the nuclear sector and for many other safety-critical applications. This paper reviews various approaches used to assess the reliability of an inspection, with a particular focus on flaw detection, and explains how these have arisen from different approaches to inspection qualification adopted within different jurisdictions and industry sectors. The paper outlines the strengths and weaknesses of each approach and discusses how the associated methods of analysis could be further refined and used to support inspection qualification in the future.
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