NDTnet 1998 Aug, Vol.3 No.8

Abstract

Advanced quality management today provides for the application of methods to implement a quality strategy designed for the integrity of products. Keeping a product under observation during its useful life and in particular recording and assessing parameters of safety significance is therefore indispensable. The knowledge gained from fracture mechanics studies cannot be put to use in evaluating an object without precise methods of locating as well as identifying the size and shapes of flaws. An actual situation was given by several cracks in various pump shafts and globe valve journals in pumped storage powerstations, detected during quality inspections.

Such cracks are known to shorten the calculated service life of these components considerably. Until recently, it has been common practice to give dismounted shafts merely surface crack tests, in particular magnetic particle tests. When doing so, two problems have to be coped with: the shafts have to be dismounted and the areas of the shrunk-on rotors are not accessible for testing. A system of diagnosis is therefore needed to allow statements to be made on the integrity of the outer surface of the shafts without having to dismount them and to remove the shrunk-on rotors. To subject the shafts to an in-service quality inspection, only the central borehole has to be made accessible to insert a manipulator with ultrasonic sensors. Such sensors follow a square wave pattern on a circular path and can be moved on by a defined stoke length. A computer system controls the movements of the motor and at the same time records the test data, Fig.1. Difficulties arose, however, when measurements on globe valve journals detected crack depths of more than 15 mm and crack orientations deviated distinctly from the perpendicular orientation in the component. So the SAFT technique was tested for its applicability never been used before evaluating such deep cracks. The area measured here could be correlated directly with the cracks since the globe valve journal was dismounted some time after the measurement had been taken and was scrapped. The flaw-affected area was broken open so to make the entire fracture areas accessible. The comparison with the results obtained from SAFT showed an excellent agreement of the entire run of the crack.

Fig. Schematic draw of the test scenery

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:

Publication Contact:
7th ECNDT, Park Alle 345, DK-2605 Broendby, Denmark, Fax: +45 46 26 70 11, Email: 101373.3414@compuserve.com