Flaw detection ability of NDT techniques on clad surfaces of reactor pressure vessels

Abstract

The flaw detection ability of non-destructive testing (NDT) methods (ultrasonic and eddy-current testing) during in-service inspections of the inner surface of PWR vessels is evaluated, especially for the area of the core weld and the coolant nozzles. A great variety of test flaws (cracks under the cladding, surface notches and underclad notches) in different clad test blocks is examined. This paper describes the results and the methods used to quantify the reliability of NDT assessments. The ultrasonic technique (70°SEL) is capable of detecting underclad flaws with through-wall dimensions from 2 mm upwards and surface flaws which reach 2 mm into the ferritic material with the same high degree of reliability. Surface flaws within the cladding, 2 mm to 3 mm deep, can be detected and interpreted clearly with a combined ultrasonic (US) and eddy-current inspection.