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how can we convert the allowable leakage rates of API 598?

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etrobal

Mechanical
May 27, 2008
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gentlemen:

we ordered two units, 30-inch motorized gate valves for our system. the valves were leak tested in the country of origin without the motor coupled, and it passed the leak tests in accordance with the requirements of the API 598.

when these valves were delivered and prior to motor coupling, our maintenance department conducted an air leak test. there were bubbles which we were not able to quantify.

table 5 of API 598 where the maximum allowable leakage rates for closure tests on an all metal-seated valves except check, column on gas test, is 120 bubble per minute.

can we measure the air flow and translate this into bubbles per minute? if this can be translated, i need to go back on how to measure the air flow. any ideas, please?

this correlation will help us decide if we will return the valves to the supplier or accept these if the computed bubbles will pass the maximum allowable required by API 598.

thank you again indeed.
 
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I don't understand your problem with the test. It asks to pressurize the valve to 100 psi and hold it under water for the prescribed time. You should easily see if you are getting 120 bubbles/min. Basically, if you are getting more than 2 per second, it fails, otherwise it passes. Test over.
 
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