Pressure testing

Discussion in 'Projects & Proposals' started by Andrew Cooper, Feb 28, 2020.

  1. Andrew Cooper
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    Andrew Cooper New Member

    Hi all.this is my first post ,ive no idea if im in the right forum but ive seen someone talking about pressure testing a tank at 3 psi. Could anyone tell me where i can go to do a pressurd testing course for bunded fuel tanks to 2 psi please in the uk ive looked all over but ive had no luck.

    Kind Regards

    A.Cooper
     
  2. bajansailor
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    bajansailor Marine Surveyor

    Welcome to the Forum Andrew.
    I don't think that you necessarily have to do a course in pressure testing unless you are looking to get a qualification to allow you to become a qualified (?) pressure tester / inspector?
    If you want to test your own tank, would it be feasible to simply fill the tank with water?
    If this is possible, then a pressure head of 2 psi would correspond to a head of 55 inches of water - you could achieve this by using a 6' / 2 m. long vertical hose attached to a filling spigot on the top of the tank, and then filling the hose with water.
    Convert psi to water column [inch] - Conversion of Measurement Units https://www.convertunits.com/from/psi/to/water+column+[inch]

    However it is probably a lot more complicated for bunded tanks, as they have inner and outer skins.
    Bunded Fuel Tanks Guide [Fuel Storage Tanks] // Octane https://www.octane.uk.com/bunded-fuel-tanks-guide/
    If there is a leak (visible by the water level in the hose dropping), then I presume it would be much more difficult to find in a bunded tank, unless it is possible to remove the inner tank from the outer (?).
    In which case it would be easier to remove the tank first to test it?
    However I can see that this would be a bit impractical for an underground diesel tank......
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    Hi Andrew,

    In addition to the excellent advice from bajansailor above, i would add that a min 2psi + 1 psi for every 2 feet of head - is an old measure we use. If welded, the min is 5 psi.
    And, since it is a fuel tank, pressure test for 12 hours.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    This can't be right, surely ? A slender hose attached to a large tank will only increase the pressure in the tank, by the minimal amount of weight of water in the hose.
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    Then you clearly have no idea about hydrostatics and hydraulics.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    You are wrong.
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    Your statement above clearly suggests otherwise.
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    So, you are saying that if I have a one metre square tank full of water, and I attach a vertical hose one meter long to the top of it, filled with water, that has a cross section of one square centimetre, I can double the pressure at the bottom of the tank ? I would say the pressure at the bottom of the tank has increased by 1 ten thousandth. What would be the point of doing that ?
     
  9. DCockey
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    DCockey Senior Member

    Hydrostatic pressure is completely independent of the volume of fluid. Hydrostatic pressure depends only on the density and difference in height.
     
  10. Ad Hoc
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    Ad Hoc Naval Architect

    Could not have put it any better myself.

    As noted, some clearly do not understand hydrostatics and hydraulics.
     
  11. DCockey
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    DCockey Senior Member

    Yes, the pressure would be doubled if the fluid is static, ie not moving.

    Look at an introductory text on fluid mechanics.
     
  12. Ad Hoc
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    Ad Hoc Naval Architect

    For those that do not understand the basics of hydrostatics:...

    Lets say a diver is swimming about underwater, dives down to say 18m of water depth. Pretty far. What pressure is on the diver?

    So, lets assume a cross sectional area (CSA) A, extending from the diver to the surface, the depth being, h.

    Thus, vertically, you have the forces being exerted on the base of that column of of water (the A) and the weight of the water of that column of water.

    Pressure x area of base = density of water x the column of water
    Density call w, as I can't do Rho
    P.A = w. Ah

    The A cancels out leaving
    P = w.h.

    Just to be clear:-

    QED

    Ergo, you do not understand hydrostatics at all...

    OOppss... forget the diver!!

    So the pressure on the diver is simply P=w.h, or P = w.g.h = 1025 x 9.81 x 18 = 180,994.5 N/m^2. And with 1 Bar = 10^5 N/m^2, the pressure is 1.8 Bar.

    Thus the h, is the important bit, it is the HEAD, the hydrostatic, or the hydraulic head.
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    This is ridiculous, I could double the pressure in a million gallon tank, with a thimble full of water, by that reckoning. All that would be needed, is to elevate the vertical height of the thin tube. What a saboteur's delight that would be.
     
  14. DCockey
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    DCockey Senior Member

    Mr Efficiency, what are you basing your claim on - intuition?
     

  15. Ike
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    Ike Senior Member

    All this talk about pressure heads aside, you can pressure test a tank with a bicycle pump, some duct tape and a simple gauge. I don't know about bunded tanks, but on recreational boats with gasoline tanks, the tanks and fuel system are required to be tested. The regulation requiring a static pressure test specifies no more than 3 psi. On a small tank it can be done by sealing any vents and pick up tubes. At the low pressures used, this can be done with duct tape. Insert the hose from the pump and the gauge into the fill pipe and seal it with duct tape. Pump the pressure up to 2 psi or so, and let stand for 15 minutes. If it decreases it's leaking somewhere. Use a soapy solution to find the leak. You can get test solution any place that sells propane tanks. You don't want kitchen or cleaning soap because they contain ammonia. If the leak is in the tape put some more on to seal it up. If it still decreases, test gaskets, and in metal tanks seams, looking for bubbles. It is a very simple test. On tanks the size of bunded tanks I can't imagine the procedure would be much different, just maybe more sophisticated equipment such as an electric air pump. Back when I was working in a ship yard they used to pressure test huge tanks (some 100's of thousand of gallons) with not much more than an air pump and a fitting that screwed into the sounding tubes that connected to the pump.
     
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