Metal Bellows Valve Reliability Testing

Abstract

Swagelok B ® series metal bellows-sealed valves were tested for their cycle performance longevity to evaluate their use in tritium service. The valves selected differed in the size of their pneumatic actuator and the stem tip material. Valves tested had one of three actuator sizes (1C, 3C, or 5C) and one of two stem tip materials: a cobalt-based metal, Stellite™, and a polyimide material, Vespel ® . An automated valve manifold was constructed, allowing for the simultaneous cycling of a total of 10 valves. Automation controls allowed for user inputs, controlling the number of valve cycles per test and the number of tests per experiment. Valves installed on the valve testing manifold to be cycled following a valve frequency test plan. After a defined number cycles, the valves would undergo leak testing using an inline leak detector. The inline helium leak detector provided qualitative detection of any failing or failed valves. If a valve had failed, a leak rate greater than at 1.0 x 10 -7 std cc He/sec, the valve would be removed from the manifold and quantitative leak rate measurements made. After specific cycling milestones were reached, quantitative valve leak rate measurements were performed to assess the adequacy of the qualitative measurement method. Valve evaluation began with initial leak tests: valve inlet/outlet seat rates and total body leak rate. The as received 1C valves, with PTFE stem tips, passed initial leak tests; however, stem tips replacements with either metal or polyimide stem tips essentially created valves which failed subsequent leak tests and were not subject to valve cycling. The 3C actuated valves had been cycled 150,000 times, resulting in 60% of the Stellite™ and Vespel ® tipped valves still passing the leak rate criteria. Failure analysis on the other 40% has yet to be conducted. Eight of the 5C valves had reached 150,000 cycles with 80% of the valves passing the leak rate criteria: two Vespel ® tipped 5C valves failed leak rate testing after 120,000 cycles.