NDTsi 2001 Session: Structural Integrity and NDE I-II
Ultrasonic Detection and Sizing of Complex Defects and Implications for Structural Assessment Procedures
A. Wooldridge, V. Baborovsky, E. McDonald, B. Banahan, BNFL Magnox, UK
ABSTRACT
Defects, which occur in plant, are often not the simple, idealised shapes, which lend themselves to straightforward ultrasonic sizing and subsequent structural assessment. This is particularly true of defects arising during manufacture rather than those, which occur in service. When applied to defects of complex shape, and particularly to multiple defects, ultrasonic detection and sizing procedures need to be pragmatic yet conservative. For critical applications, especially those involving inspection qualification, this may introduce significant conservatism. Before deciding on the appropriate defect sizes for structural assessment, further conservatisms are built in when standard characterisation rules are applied to allow for possible interaction effects amongst adjacent defects. This paper will give examples of such effects and demonstrate the magnitude of the inherent safety factors, which may result with certain kinds of complex defect. If repeat inspections are required to assess potential growth of defects in service, particular care is required to ensure adequate sensitivity and repeatability whilst minimising the risk of false alarms. Using specific examples from in-service inspection of Magnox pressure circuit components, this paper will illustrate some of the difficulties of assessing repeat inspections and make proposals for assessing the ultrasonic data so that an optimum balance is struck between detecting real changes and avoiding false alarms.
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]
