NDTnet 1998 Aug, Vol.3 No.8

Abstract

In Austria, as well as all over Europe, the repetition tests of steam drums in the paper mills are required for security reasons within fixed time intervals. In the today's industry the pressure and the rotation speed of the paper production machines will be increased for a higher output, which means, that all safety aspects from the design and the material will be exploited totally, which resulted in big accidents in the early nineties. On the other hand cast iron is also not a smooth and comfortable material.

Because also the size and the wall thickness of these cylinders are exploited till to the boarder, it's impossible to perform repetition inspection by hydrotests, because the drums loose their roundness and balances. From the global commercial pressure it's now unacceptable for the paper industry to perform replacement tests (e.g. UT,MT and ET), which elongate the shut down significantly.

The only one possibility is to perform a pneumatic test of the drums, because this doesn't superimpose the stress by the weight of the water, and monitor this pressure test with Acoustic Emission (AE). The application of AE as a pre-warning system against a catastrophic failure during a gas pressure test, for such brittle material, like cast iron, is only permissible, due to the rapid development in the computer technology with its direct influence in the manufacturing of new ,state-of-the-art" AE equipment. But also under these circumstances we have to take care, that pressure slope is constant and smooth with pressure holds.

The cylindrical part of the drums will be checked with a planar location set, subsistent from 5 up to 12 sensors, according the size, and the bottoms will be tested with I specific sensor, but due to the complicated geometrical shape without location. Beside its ,pre-warning" ability the AE will be used also as a NDT method for the vessels. According the detected defects (corrosion, cracks and production defects within the bottoms) we could demonstrate, that AE is a more powerful testing method for these specific cylinders, than all others.Since 1994 this kind of testing is applicated by the TOV Austria regularly and it has inspected 334 pressure equipments successfully and during these a lot of defects, which also result in the replacement of the steam drums, were detected.

The biggest advantage of the testing method is, that the drums can remain during the pneumatic loading in the machine, and we can test 2 or 3 drums at the same time. Therefore we are able to test a sufficient big number of drums during a short shut down period and can increase the availability of the plant. Because these problems don't only exist in Austria it's important, that the complete European industry get the chance of the application of this new method, for their improvement of their competition on the global market.

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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