NDTnet 1998 Aug, Vol.3 No.8

Full-Text - Abstract

The leak detection methods used in industry and research range from the detection of a dripping valve up to a detectable gas loss of 1 cm³ over a period of 30000 years! This corresponds to a difference in leak rate of about 14 orders of magnitude. Among the known leak detection methods, the leak test with helium as the tracer gas has become the most universal method due to its high sensitivity and versatile application. State-of-the-art equipment enables the reliable detection of leaks with leak rates in the range of 10^-1 to 10^-10 mbar
l * s^-1, detection being normally performed at room temperature and a differential pressure of p = 1 bar.

In the course of developing a high-temperature solid oxide fuel cell it was necessary to examine components for leak tightness under their later operating conditions of 950 °C and only 200 mbar differential pressure.

These components included special connectors for later gas supply. The connectors consisted of two concentric metallic tubes. Due to differently selected thermal expansion coefficients, the expansion of the inner tube was greater than that of the encasing tube. This resulted in a sealing effect at high temperatures merely due to contact pressure, which had to be quantified. This was done varying both the gap width and the surface finish. Moreover, different hightemperature brazes for fluxless joining were tested for gas tightness.

For the experiments, a special vacuum-tight test vessel treatable to 950 °C was built to accommodate one test specimen at a time. The vessel was evacuated during the experiments. The test specimens were exposed to helium flowing through thin pipes leading outwards. A differential pressure of 200 mbar was adjustable by means of a special valve cycle and pre-evacuated intermediate vessels. This made it possible to determine the leak rate on red-hot components.

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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