NDTnet 1998 Aug, Vol.3 No.8

Abstract

The method of laser ultrasonics is well established in many laboratory applications. However, in spite of large efforts such as demonstrations of different applications, until now the industrial use of laser ultrasonics is limited to a few applications in aeronautics (1). In steel industry there is a demand to measure the wall thickness of seamless, rolled tubes during the production. Fast information about this parameter is important in order to control the manufacturing process. In addition the accurate specification of the wall thickness is requested by the customers. The best method to measure wall thickness on the hot tubes is ultrasonics, but due to the difficult coupling conditions only laser ultrasonics seems applicable. From literature at least two attempts to tackle this problem are known but to our knowledge there is worldwide no tube manufacturer applying laser ultrasonics in order to measure wall thickness.

There are several reasons why the method of laser ultrasonics is not yet widely established in industry. In former trials large and cumbersome so called time-of-flight interferometers have been used as ultrasonic detectors (2). This approach was given up because of the huge handling problems. Later a specially build Nd:YAG long pulse laser was used in combination with a confocal Fabry-Perot-interferometer (3), but also this solution was never established in industrial praxis. This paper presents an in-plant trial in order to measure the wall thickness on hot tubes during the production. Only commercially available lasers have been used. As interferometer the confocal Fabry-Perot-interferometer from Ultra Optec Inc., Quebec, Canada, has been used. The paper describes the optical set-up and presents some results. During two days the system was working well. After two days of operation the system was dissembled and checked. All the optical components have been found in good state.

In the paper the problems encountered with the operation of a laser ultrasonic system in industrial environment are discussed and costs are estimated. For the system described the costs of the optical probe comprising both lasers, the interferometer and the optical components are estimated with about 80,000. The running costs for the two lasers are estimated with 10,000 $ per year assuming 10 Hz repetition frequency. It is assumed that these costs will fall down considerably in the next future.

1.C.J. Fiedler, T. Ducharme, J. Kwan, Rev. of Progr. in QNDE, Vol 16, Plenum Press, NewYork, 1996, 515-522
2.R. Keck, B. Krüger, G. Coen und W. Hasing, Stahl u. Eisen 107, 1057 (198 7)
3. J.-P. Monchalin, Rev. of Progr. in QNDE, Vol 12, Plenum Press, New York, 1993, 495-506

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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