We recently conducted a high pressure impulse cycle (50 to 4500 to 50 psig) test on a manifold assembly with boss fittings on it. The port is per AS5202-12 with MS21902J12 fitting and boss O-ring (NAS1612-12) installed in it. After about 9000 cycles at 140F, the O-ring extruded and broke down resulting in leakage through the port. The other ports in the manifolds were checked and even though we did not have leakage through the other ports, we did find O-ring nibbling and O-ring particles in the port implying the O-ring could have failed after a few more cycles. We inspected the port dimensions and the port was iaw AS5202 spec, including all tolerances and roughness. We are in process of inspecting Fitting. We already check the compatibility of the O-ring with respect to Skydrol and found to be good at 140F. What could be the cause for this failure? The unit has to go through 200,000 cycles of impulse pressure cycles with 150,000 cycles at 140F, 20,000 cycles at 212F, 20,000 cycles at 14F and 10,000 cycles at 248F.
Any kind of help, advice is highly appreciated.
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