Helium leak testing for design verification and product acceptance

There are various leak test methods used to verify the integrity of seals for underwater hardware; these methods have a wide range of sensitivity and cost. Helium leak testing with the use of a high vacuum mass spectrometer leak detector provides the greatest sensitivity; however, in more complex sealing systems, the utility of the results is entirely dependent upon the test configuration and method. In the case of polymeric or epoxy based seals, diffusion mechanisms must be understood and quantified in order to develop appropriate upper and lower control limits. High reliability systems with redundant sealing mechanisms add additional challenges to developing test methods and control limits. High pressure gas testing and low pressure permeation testing are two approaches that can be used to effectively characterize and validate product. This paper addresses these two methods and describes a study in developing test parameters and acceptance criteria. Included are results from testing for low pressure and high pressure permeation and steady state Helium leak rates for redundant sealing paths; the use of these test methods for product validation is also discussed.