NDTnet 1998 Aug, Vol.3 No.8

Abstract

Catalyst tubes in the primary reformer of an ammonia plant are vital components and a major concern is that the tube material is susceptible to creep under the prevailing service conditions, "i.e." elevated temperature and mechanical loading. Indeed, the tubes are certain to fail eventually as a result of creep. While the service life, or the time to failure, may be estimated by a number of computational models, one should not place to much reliance on the results. This is particularly because of the wide variation in material properties of the tubes. Consequently, there is a need for a non-destructive test method to establish the extent of creep damage and to estimate the remaining tube life. This would greatly faciliate the planning of maintenance and tube replacement. For this purpose an ultrasonic examination technique was developed by DSM.

Detection of creep damage is not an easy matter. The combined effects of temperature and pressure are most adverse at the center of the tube wall so it is here where the damage first starts. Subsequently, it progresses to the inside surface. Consequently, if a non-destructive test method has to reveal creep damage in time, it must be capable of detecting subsurface defects. For this purpose we opted for the ultrasonic technique. In order to cope with the coarse grain size of the austenitic cast tube material, an ultrasonic transmission technique was developed. The principle is presented in figure 1. In the paper the development and experiences of this inspection method will be discussed.

Fig.1

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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