The interpretation of TOFD data in the light of ASME XI and similar rules

Very few inspection codes exist which attempt to quantify the size of defects which may be tolerated when found as a result of an in-service inspection. The ASME XI rules provide a comprehensive set of criteria for the most serious, planar, defects however, and for this reason alone are likely to become increasingly used to aid the interpretation of ultrasonic data - despite the fact that, as laid down, they are aimed only at a very stringent inspection task - that of nuclear reactor pressure vessels (NRPVs). This paper considers implications of the ASME XI and other rules for the TOFD (time-of-flight) technique and defines its current limitations. Improvements in TOFD currently being researched and the use of the technique specifically for defect sizing or monitoring would give rise to more precise data than assumed in this paper