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Physical Sizing of Discontinuities in Helium Leak Tests: An Approach to Compare Leakage Rates and Leak Diameters

In engineering industries that manufacture critical pressure vessels or heat exchangers, helium leak testing (LT) is practiced as in-process and final testing for certifying reliability. The reliable location of discontinuities and measurement of leakage rate are derivatives of this. Normally, in all three types of tests, the leakage rate, which is the quantity of fluid leakage per unit time flowing through a leak at a given temperature because of a pressure difference across a leak, is measured. In most nondestructive testing (NDT) techniques, physical discontinuity sizing is performed. The capability of various techniques is expressed in terms of the minimum detectable discontinuity size in the respective techniques, and this is synonymous with sensitivity. Though there are technical references about equations to convert leakage rates into leak sizes, the practice of expressing leakage rates in terms of equivalent leak sizes is not generally prevalent in industrial tests. Therefore, to also practice this concept of physical leak sizing in helium tests, an attempt is made with industrial and basic principles to convert leakage rates into leak sizes using mathematical theory of gas flow through leaks.

References
  • ANSI, ANSI N14.5-1997, Radioactive Materials – Leakage Tests on Packages for Shipment, American National Standards Institute, Washington, D.C., 1997.
  • ASNT, Nondestructive Testing Handbook, third edition: Vol. 1: Leak Testing, American Society for Nondestructive Testing, Columbus, Ohio, 2004.

  • ISO, ISO 12807:1996 (E), Safe Transport of Radioactive Materials – Leakage Testing on Packages, International Organization for Standardization, Geneva, Switzerland, 1996. 

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