Qualification of NDT Sizing Ability. Lessons Learned
E. Österberg, L. Skånberg, Swedish Nuclear Power Inspectorate, Sweden
ABSTRACT
According to the Swedish regulation of NDT inspections in the nuclear power plants, all NDT of the components in control groups A and B must be performed with the NDT systems which have been qualified to reliably detect and characterise and also correctly size degradations. The Swedish NDT Qualification Centre (SQC) was set up and approved for operation by SKI in 1997 when SQC has established a quality system including qualification methodologies and instructions. SKI has, in its approval, emphasised the need for SQC to continuously evaluate and reconsider the effectiveness and appropriateness of applied qualification methodologies. A half decade after the operational approval of SQC, a great number of qualifications have been carried out and the practical experiences in the field of NDT qualification have been obtained. There is no doubt about a fact that the implementation of the qualification requirements has increased reliability and effectiveness of the NDT inspections in the field. However, the future development of the qualification methodologies is needed. This paper emphasises on qualification of NDT sizing ability. It has become a common practice to describe the NDT sizing ability in terms of the defect dimensions to be sized and sizing accuracy to be achieved. Qualification of sizing ability is based on the practical assessments using non-blind artificial defects with known dimensions. However, the practical trials are expensive and not always give good statistic; the uncertainty about artificial flaw dimensions can exceed the required sizing accuracy; it is unclear how the sizing accuracy is correlated to measurement uncertainty and essential variables. Another problem to qualify the NDT sizing ability is the interaction between the sizing ability and the ability to correctly characterise degradations as embedded or surface breaking. The representativeness of the artificial flaws in qualification test blocks is another problem that must be considered.
Publication Source: 3nd International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurized Components, November 14-16, 2001, Seville Spain. Publisher: Tecnatom s.a. - [Homepage]
