Inspection qualification is the term currently used to describe the process of independent assessment of a specific non-destructive test to ensure that it is capable of meeting its objectives. Such activities carried out on the Sizewell B reactor inspections were referred to as validation. In the USA, the term performance demonstration is used, though this is increasingly being reserved for the part of the assessment which uses practical trials, with qualification being used, as elsewhere, when the assessment process involves assembling evidence for the efficacy of an inspection from a wider variety of sources. Most qualification activity to date has been focused on nuclear plant because of the safety implications of nuclear plant failure and also because it is here that the cost of the qualification itself is in proportion to the cost of the plant and the consequences of failure. This paper reviews worldwide practice and experience in the qualification of ultrasonic inspections of nuclear components over the past two decades. In general, qualification has been applied to in-service inspections; however, this paper includes consideration of the application of qualification to manufacturing inspections. To date, ultrasonic inspection is the inspection method to which most qualification activity has been devoted. However, the qualification principles discussed are equally applicable to the qualification of other inspection methods. This paper includes consideration of: □ Sizewell B manufacturing inspections. □ ASME XI requirements, including Appendix VIII. □ European developments, particularly the European Methodology for Qualification of Non-Destructive Testing developed by the European Network for Inspection Qualification (ENIQ). The ENIQ methodology has been adopted throughout Europe. The benefits of the ENIQ methodology are its flexibility and the requirement that qualification be developed taking into account the parameters of importance for a particular inspection. This means that it can provide confidence that an inspection can meet its objectives. The major disadvantage of the ENIQ approach is the requirement for scarce personnel skills in the physics and practice of inspection to develop and implement qualification requirements. Manufacturing inspections can have two purposes: (a) to ensure that any manufacturing defects that could threaten plant integrity are detected and correctly characterised so that they can be eliminated and do not enter service (fitness-for-purpose); (h) to detect defects of any size, including those smaller than could threaten plant integrity, taken as a measure of general manufacturing quality (acceptance standards for manufacturing). Of the two, the sizes of defects in item (a) are more easily determined in an objective way. The choice of sizes in item (b) is more subjective since they are not directly related to structural integrity issues. Design/Manufacturing codes traditionally; require any detected planar defects to be removed, independent of defect size and capability of the inspection method. This is similar to item (h) above. Such code requirements pre-date the general use of ultrasonic inspection methods in manufacturing inspections. Ultrasonic inspection during manufacture is still not an explicit general requirement in widely used Design/Manufacturing codes. Instead, typically 'volumetric' inspection will be required, with the implicit expectation that this will be based on radiography. The objectives of ultrasonic inspections, and hence the yardstick for their qualification, needs to be defined with (are. If the requirements are set too stringently, the inspection and its qualification would be over-complex. In the other direction, a lax definition of inspection requirements could lead to an inadequate inspection. Inspections should be most effective for those defects with the highest likelihood of occurrence at the sizes of concern for structural integrity. Lesser reliability is acceptable for defects with low likelihood of occurrence at sizes of concern for structural integrity, and for smaller defects. Manufacturing inspections need to detect defects and, ideally, to characterise them in terms of whether they are volumetric or planar. In practice, an important contribution to characterising a defect and determining its significance is sizing.
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Open Access
Jan 1, 2010
Hajime Ito + 4
