A component leak test apparatus investigates the performance of fittings at low temperature and/or high pressure. Its performance was quantified by measuring the ability to hold cold pressurized gaseous helium (He) with a He mass spectrometer. The apparatus was developed to certify small fittings for use with He at high pressure and cryogenic temperatures (< -238 °F) using current torque values.
The system uses a lab-sized cryorefrigerator to chill small fittings down to cryogenic temperatures inside a custom-built vacuum chamber. The fitting is pressurized with He at the desired test pressure. A lab-sized He mass spectrometer connected to the vacuum chamber measures any He seepage from the fitting. The fitting’s outside temperature and He pressure are continuously recorded during the process.
Typically, leakage measurement is done using bubble count with water at room temperature or pressure decay. This new system, however, offers a higher level of accuracy. All the tools and instrumentation are commercially available and have a low operation cost.
The system is composed of a cryogenic refrigeration system, an analysis chamber (a vacuum vessel comprised of two major components: the chamber and the lid), high-pressure helium piping, a test article, and testing equipment (the mass spectrometer). The chamber was fabricated by welding a 30” section of stainless steel pipe and a 20”-diameter, 0.25”-thick stainless steel plate. The chamber is equipped with three ports, and three lift lugs are welded on the end plate to lift the chamber off its lid.
The lid is a modified 20” ISO blank flange. A center hole was machined to accept the cryorefrigerator cold head. Two ISO100 rings are welded on 5” extensions. Stainless steel tubes measuring 0.25 × 0.035” that deliver high pressure He to the test article are welded thru the ISO100 blank flange. With this setup, only two He leak paths — on either side of a KC fitting union — are subjected to the vacuum drawn on the analysis chamber.
During testing, the analysis chamber was evacuated using an Adixen ASM Graph D+ He mass spectrometer. The first ten minutes of pump-down were augmented by a standalone vacuum pump. Once the test fitting had reached the desired pressure and temperature, the analysis chamber vacuum level and the He leakage was recorded on the mass spectrometer. This equipment can detect He leaks from 10-11 mbar.L.s-1 to 3.10-4 mbar.L.s-1.
This innovation has a high potential for commercial application. Valve, fitting, and other component manufacturers could use this apparatus to certify their components for use at high pressures and cryogenic temperatures.