NDTnet 1998 Aug, Vol.3 No.8

Full-Text - Abstract

The nondestructive in-service-inspection (ISI) of the pressure vessel of German boiling water reactors (BOOR) is done by ultrasonic testing from the outer surface and by remotely controlled visual inspection from inside. One of the goals of ISI is to verify the integrity of the 8mm-austenitc cladding. According to the German KTA-rule 3201.4, the calibration of the ultrasonic equipment is done at reference notches. In order to improve the ultrasonic-system's capability of detecting IGSCC-damage, cracks were implanted in a test assembly. The different methods of crack implantation and their advantages and drawbacks are described. The test assembly contains 6 surface breaking thermal fatigue cracks with a depth of 4 mm in different orientations to the clad strips. Additionally, a 10 mm surface breaking crack was implanted that origins from a 50 x 50 mm craze cracking area with a depth of 1-2 mm. As expected, the craze cracking reduces the corner trap effect. A reflection between clad interface and crack can be used to judge the integrity of the cladding.

Ultrasonic tests were performed with standard techniques using conventional 45° and 60° shear wave transducers. Additionally, a phased array transducer and a transducer with long focus distance were tested and evaluated. The effects of frequency and sound beam geometry were investigated. The influences of the weld direction of the cladding and the crack implantation process are discussed and compared with reference notches.
Compared to 45°-shear wave testing, other techniques do not offer significant improvements in signal amplitude nor in signal to noise ratio. The calibration with notches is suitable for crack detection also.

Figure 1: Orientation of Cracks in the Cladding

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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