We are purchasing high pressure valves and setting up test equipment to verify valve test performance based on the methods of ASME B16.34.My question is about the test fluid. The specification and similar specifications call for the tests to be done with water, which may include a corrosion inhibitor, with kerosene, or with another suitable fluid with viscosity not greater than that of water.Can anyone explain or clarify for me? Why is kerosene allowable, while its viscosity may be substantially greater than that of water, but no other fluid with viscosity greater than that of water is allowed? I have researched a little and I see some test fluids are rated for "penetration capability", which may not be well correlated with viscosity, so this may be the reason, but I am not sure.Consider that the first valve testing standards were written many years ago. Before most of use were born. The most commonly available fluid with a viscosity close to water was Kerosene. Yes it's viscosity is higher than water, but not so much to invalidate leak test results.Why Kerosene, if you use untreated water to test carbon steel valves, inevitably, some water gets trapped within crevices inside the valve and can rust and damage critical sealing surfaces or lock the valve shut. If the water is very unsanitary, you can also initiate microbiological induced corrosion (MIC). So Kerosene was used.Other petroleum products that happen to have a viscosity less than water are not safe to use for testing (e.g., gasoline). Not that Kerosene is that safe either.I haven't seen anyone use Kerosene for valve testing during the last 30 years. Nearly everyone uses air or treated water.

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