Underground tank calibration

What is PMS. Is it completely buried, or is there some means of accessability

We used to close off all connections to the tank and then hook an air compressor to it through a tree containing a pressure gauge and valving to lock off the input line. Pump to requisite pressure, close the input connection, and noting the exact pressure reading, go home. Next day read pressure and you will find if your tank has integrity.

j.

Refer to the original design drawings and calculations before carrying out any testing, so as to discover what the tank is capable of withstanding at design stage. It would be best to use an incompressible fluid like water instead of compressed air to carry out any test, for safety reasons; after all, if the tank were to fail under pressure during the test it would be inadvisable for the roof to be heading for low-earth-orbit.

"5psig is dangerous if it is propelling a manhole cover towards you."

These days, above gound liquid storage tanks have a pressure rating of, for example, "full +5m H₂O".

Hi all,

As previously posted, you have to check the tank design pressure and the code or rules according it was manufactured. Then yo have to take into account the local laws for periodic pressure tests if any. I don't know the Nigerian case but in my country there is a "Rule on pressure vessels" that has to be complied with.

Note I've supposed it's a periodic test, because if it were the initial pressure test, it should have been made in the factory before burial.

Once you've determined the maximum test pressure according to above mentioned, you can make two different test: Pressure test (resistance test) whose intent is to determine the ability of tank to withstand pressure loads. The other is a leak test, intended just to see the integrity of pressure boundary.

You can perform both in a separate way or even at the same time if, for example, you arrange a pump, a pressure indicator, a flowmeter and a pressure controller. If you apply the test pressure and during holding time the flowmeter sees no flow, then you've made both tests satisfactorily. If during holding time there is some leak (not too great, of course), the pressure controller keeps the pressure constant and flowmeter gives you the leak rate.

Of course, as already said, it's better to use a liquid than a gas as test medium, but take into account the compatibility of fluid with the intended service (I don't know the meaning of PMS) but if, for example the "P" stands for "Petrol" and it's a periodic test, water could contaminate the tank and a buried tank isn't easy to clean.

Best regards

Hi Friday

I thought PMS was a hormonal condition. What is it?

I would feel OK about using dry compressed air or dry bottled nitrogen with a low pressure regulator to raise the pressure in the tank approximately 5 psig, sterilized if that PMS is temperamental stuff. Then block the flow in and record the decay rate. The rest is a mater of mathematical skull drudgery. If I do it for you that will cost extra.

As an alternative you could cap the tank at sea level with one atmosphere, 14.7 psia, inside and haul it to a decent mountain top. At 15,000 feet, if you get there before the internal pressure bleeds down as in sealed tight, you will have 6.4 PSIG in the tank. When you get it back down it will return to 0 psig or 14.7 psia. If you take the plug out on top of the mountain and then re-plug on the mountain no leaks occurred until well after you get back down home the tank will have a vacuum of -6.4 psi.

If you pressure test and see the ground swelling it is time to quit filling. Tom

You can Calibrate underwater tank or even water boring or water well. Try this sensor.

http://www.sensotec.com/pdf_catalog06/LLV.pdf

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