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Fitting Leak Test Report: Ground-Based Cryogenic Leak Test of Fittings for Cryogenic Fluid ManagementEXECUTIVE SUMMARY
Mechanically connected joints used in cryogenic fluid lines as part of space flight elements need to survive launch vibrations and remain leak-free to minimize the loss of on-board commodity and hazardous gas accumulation. In 2020, a cryogenic test apparatus was developed which can evaluate the leak performance of pressurized threaded fluid fittings. The fittings were mounted in the TVAC and cooled to cryogenic test temperature and pressurized with helium while the leak rate was measured using a calibrated GHe leak detector. The test articles for the initial proof of concept testing were ¼ and 1 inch Swagelok VCR fittings with three different types of seal rings copper, nickel, and Ni. Each fitting configuration (size/seal material) was subjected to two consecutive cryogenic thermal cycles, followed by exposure to a launch vibration profile at ambient temperature, after which two additional TVAC cycle tests were performed.

The testing reported here is a continuation of the 2020 tests with a statistically significant large number of samples and test runs. Three Swagelok VCR fitting sizes were tested ¼, ½ and 1 inch, and five (5) samples of each fitting size, each sample was tested with SST and Ni seal rings (Total of 30 unique test articles). Each test article was subjected to four (4) thermal cycles. Half of these cycles were performed before vibration testing and half were performed after vibration testing. The vibration testing was performed to evaluate the ability of the fittings to survive launch-type vibration profiles and remain leak-free. Leak checking of each fitting was completed at temperatures between 20K – 30K. The test procedure in Section 8.0 was designed to facilitate a qualification test program by allowing a higher test throughput rate coupled with repeatable test profiles.

Results were very positive and show that out of the 30 samples they all passed with leak rates a factor of 2-3 lower than the established 10-6sccs GHe leak threshold. The result showed the Ni seals had lower leak rate, but the SST was more rugged. There were two deviations where damage to the Ni seal ring during assembly resulted in a leaky fitting, this is discussed in Section 10.7 Test Deviations. These fittings show great promise for space flight use and further testing is recommended to fully qualify the fittings per the ASTM F1387-19 and/or other relevant NASA specifications.

The test equipment hardware and software capability developed for this testing is generic and not restricted to VCR fittings. It can be employed to evaluate/qualify the leak performance of other types of fittings and a wide range of other cryogenic fluid components such as valves, gages, connectors, etc.
Document ID
20230004260
Acquisition Source
Kennedy Space Center
Document Type
White Paper
Authors
Gabor Tamasy
(Kennedy Space Center Merritt Island, Florida, United States)
Andrew Kelly
(Kennedy Space Center Merritt Island, Florida, United States)
Jaime A Toro Medina
(Kennedy Space Center Merritt Island, Florida, United States)
Philip D Stroda
(Kennedy Space Center Merritt Island, Florida, United States)
Adam Swanger
(Kennedy Space Center Merritt Island, Florida, United States)
Rudy Werlink
(Kennedy Space Center Merritt Island, Florida, United States)
Tommy Thompson
(Marshall Space Flight Center Redstone Arsenal, Alabama, United States)
Clark Herrington
(Consolidated Program Support Services (CPSS PP&C))
Mike Guthrie
(LASSO)
Felipe Loo
(Engineering Research and Consulting LLC)
Barry Meneghelli
(Amentum)
Donald Payne
(Engineering Research and Consulting LLC)
Will Reaves
(Science Systems & Applications, Inc. Hampton, VA, USA)
Mark Velasco
(Engineering Research and Consulting LLC)
Date Acquired
March 31, 2023
Publication Date
February 28, 2023
Subject Category
Fluid Mechanics and Thermodynamics
Funding Number(s)
PROJECT: 954879.04.03.76.18
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
Cryogenic
FITTING LEAK TEST REPORT GROUND-BASED CRYOGENIC LEAK TEST OF FITTINGS FOR CRYOGENIC FLUID MANAGEMENT
Fitting
leak
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