Air Testing of Roof
Air Testing of Roof
(OP)
Air Testing of roof is required as per the following clause in API 650:
F.4.4 When the entire tank is completed, it shall be filled with water to the top angle or the design liquid level, and the design internal air pressure shall be applied to the enclosed space above the water level and held for 15 minutes. The air pressure shall then be reduced to one-half the design pressure, and all welded joints above the liquid level shall be checked for leaks by means of a soap film, linseed oil, or another suitable material. Tank vents shall be tested during or after this test.
I have tanks with design pressure about 1.5 kPa(g). The contractor wants wants to fill the tank upto the apex of the cone roof and use a stand pipe and fill it to exert the required pressure.
API does not say that Air Test or a hydrotest may be used.
Can somebody advise me if hydrotest can be used to substitute Air Test?
F.4.4 When the entire tank is completed, it shall be filled with water to the top angle or the design liquid level, and the design internal air pressure shall be applied to the enclosed space above the water level and held for 15 minutes. The air pressure shall then be reduced to one-half the design pressure, and all welded joints above the liquid level shall be checked for leaks by means of a soap film, linseed oil, or another suitable material. Tank vents shall be tested during or after this test.
I have tanks with design pressure about 1.5 kPa(g). The contractor wants wants to fill the tank upto the apex of the cone roof and use a stand pipe and fill it to exert the required pressure.
API does not say that Air Test or a hydrotest may be used.
Can somebody advise me if hydrotest can be used to substitute Air Test?





RE: Air Testing of Roof
I believe API-650 allows this type of test, provided the tank is designed for it.
RE: Air Testing of Roof
If you can touch all the seams to feel for 'weeps & seeps', I would call it slightly more rigorous, but if you just stand and look at it from a distance, that would not be as revealing a test as soap-bubble.
Also, keep in mind that a standpipe 2-ft taller than the roof peak is what is used to 'pop' back up a sucked-in roof on a 650 tank. 24" W.G. is 14 ounces/inch^2 is 0.866 psi. Make sure that your roof will not fail at this pressure. 650 is for Atmospheric storage tanks.
RE: Air Testing of Roof
The air testing of the roof clause is in Annex F, which is for tanks designed with small internal pressures up to 2.5 psig. Your concern still holds, though as any tank other than one that is very small is not economical to construct with that high a design pressure.
RE: Air Testing of Roof
I am sorry, I should have converted 1.45 kPa to water column. Well, the stand-pipe would be about 150 mm tall. My feeling is that testing with water may not be able to reveal the leak for a gas-tight roof. But, in the past I have heard from some fabricators they replaced Air Test with Water-fill test. I am not convinced.
RE: Air Testing of Roof
RE: Air Testing of Roof
So far as detecting leaks with gas vs liquid, keep in mind that the shell itself is tested with liquid, never with gas, and roof seams would generally be considered less critical than shell seams.
RE: Air Testing of Roof
Thank you for your advice.
I agree with you. The tank in my case is to be blanketed using fuel gas. Therefore, we must make sure there is no leakage whatsoever.
Ashok