Monel metal gasoline tanks 145 gallon from 1970 did they have the USCG static pressure test ?

Discussion in 'Boat Design' started by sdowney717, Jun 14, 2017.

  1. sdowney717
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    sdowney717 Senior Member

    Tanks are not leaking are in good condition.
    Tanks are made by Seafarer.
    I would like to know if in 1970, the USCG required the same 3 PSI pressure test as today.
    So then theoretically the 3 psi pressure test, these 1970 tanks would have been required to pass?
    I am desiring to switch fuel fills to the newer partially sealed fuel cap design which is normally not vented unless pressure exceeds 1 or 1.5 psi inside of the tank. I would not want to pressurize a tank which was not required to be in compliance of the minimum 3 psi just for safety reasons. Tank has welded in baffles maybe every 15 inches.


    http://www.uscgboating.org/assets/1/AssetManager/ABYC.1002.01.pdf
    From the fuel systems PDF page 107
    The tank should be empty for this test. Testing pressure can be supplied by pressurized air or compressed inert gas. The tank's rated testing pressure is marked on the tank, but in no case will it be below 3psig. During the test, the sides, top and bottom of the tank should be accessible. All openings except the one used to admit the pressure should be sealed.
     
  2. Ike
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    Ike Senior Member

    simple answer; no. However it was the industry standard at the time. The Coast Guard simply adopted it.
     
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  3. SamSam
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    SamSam Senior Member

    Is 3 psi of pressure a dangerous amount for a tank? It doesn't seem to be very much and I imagine it's mainly a test for leaks. I wonder how much pressure is exerted on a tank when half full and slamming around in waves...?
     
  4. Ike
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    Ike Senior Member

    actually the standard says not to exceed 3 psi. However 3 psi is not excessive. I have seen plastic tanks tested at that and they do get rather bloated, but metal tanks aren't affected much. It is primarily a leak test for gaskets and fittings. As far as slamming goes, tanks are also required to meet pressure impulse tests and slosh tests, especially tanks mounted forward of amidships.
     
  5. Barry
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    Barry Senior Member

    I would not exceed 4psi to test a tank. Assume your 145 gallon tank has a top with a dimension of say 60 by 30 inches. If pressurized to 4 psi, the walls attached to the top sheet must resist a total load of 30 x 60 x 4 = 7,200 pounds or 3.6 tons

    Bending stresses are introduced and as the thickness of the plate is minimal , say 14 guage at .0747 inches, the bending stresses will build quickly.

    Additionally, there will be vertical shear stresses due to the pressure and tensile stresses coming from the side plates trying to pull this plate in both horizontal directions.

    I was unable to find a calculator for a rectangular tank that you could impact data to find out the actual calculated stress as square pressure tanks are rarely built for modern day applications.

    (in fact pressure vessels, certainly high pressure vessels are round or cylindrical with domed ends to reduce bending stresses)

    Certainly properly installed and welded baffles will assist tremendously in reducing these loads, but my word of caution is not to exceed 4psi if the tank has a top anywhere as large as the measurements that I have given.
     
  6. SamSam
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    SamSam Senior Member

    Then is this a serious typo in an official document? (from the op) "The tank's rated testing pressure is marked on the tank, but in no case will it be below 3psig."
    Or am I somehow reading this wrong? It seems to say you can't test with less than 3psi, but doesn't say anything about how much is too much pressure, which would seem to be not very much, considering your calculations. Maybe not a typo, but it seems sort of lacking in safety advice.
     
  7. SamSam
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    SamSam Senior Member

    Reading up a little, the stored energy of pneumatic pressure and liquid pressure are two different animals, like the Jekyll and Hide of tanks.
    As for the op, if the tank can be expected to encounter 1.5 psi, testing to double that would seem like the minimum safety 'over rating'.
    Especially considering it's 47 years old.
     
  8. Barry
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    Barry Senior Member

    The reason that I responded to this thread is that it is important to realize that you could not put say 15 pounds of pressure into the tank. It could literally blow up, crack seams, break a baffle weld.
    If you take a thin strip of 14 guage about a foot long and 1 inch in width, grab both ends, put the middle over the edge of a table you can permanently bend the strip. You have effectively with very little FORCE, created stresses in the steel
    above 36,000 pounds per square inch, approx. yield strength mild steel. This is due the shape and that yield stress occurs first at the outer surface. Most people do not realize the magnitude of the bending stresses that can be created with small forces.

    So I took the opportunity to suggest to follow the "not less than 3 psig" but not get over exuberant and think that you can pump in much more than the 3psig threshold.

    Back in the 70's and 80's, our company was building auxiliary steel fuel tanks for pick up trucks as well as slip tanks so contractors could carry anywhere between 50 to 150 gallons of fuel and pump it into equipment.
    We set our water immersion test basin at 5 psi. Our larger slip tanks were in fact 60 inches long, and 30 inches wide. Occasionally, even with this low test pressure, (and it seemed to occur on tanks built on a Monday morning after a liquid weekend) we would have the odd baffle weld failure. (Three baffles, so the outside baffles could only be welded from one side due to accessibility)

    If I were testing the monel tank, I would test to 4psi. If the OP cannot immerse the tank for testing, then there are products on the market, similar to dish soap, to spray over the welds. While you can seal all of the openings, hook up a static pressure gauge to see if the pressure drops over time, a small leak on the gauge or hook up could tell you that you have a tank leak but it might not be the tank. Snoop is a good test liquid

    There is also a product that you can spray on welds, and I do not recall the name that you spray on the welds and it is like a thin, 1/32 inch rubber coating. It dried quickly but remained pliable. After 15 minutes, you pressurized the tank and left it. If the leak was very slow, the air would exist the pinhole and lift the rubber off the weld. So spray it, pressure up, come back in say half an hour and look for some lifted rubber.
     
  9. TANSL
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    TANSL Senior Member

    Sealing test : I have seen use of soapy water.
     
  10. sdowney717
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    sdowney717 Senior Member

    Thanks for all the responses.
    I installed the new Perko vented fuel fill with the normally VOPR sealed cap. Cap is designed to open at 1 psi. I actually adjusted it to open at 0.85 psi
    With empty tank, I added 25 gallons of gas at noon.
    I hooked up a pressure gauge 1 -10 psi and all day the pressure sayed at zero.

    I installed an ICV inlet check valve in the fill
    I will use an Attwood fuel demand valve, cool device that wont let fuel out from the fuel line unless a suction from a pump pulls open the valve. Good for pressurized tanks.
    And I have the vented fill that directs vented tank air back to the fuel fill.
    And I have a VOPR style pressure-vent cap.
     
  11. sdowney717
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    sdowney717 Senior Member

    There are 2 allowable ways toady in a modern fuel system, either use a charcoal cannister, or use a slightly pressurized tank, tank not to exceed 1psi.
    Personally, I think the slightly pressurized tank is the best one. I think it also helps preserve this awful E10 gas since there is less time the fuel is exposed to air, as the cap is normally sealed shut like your car.
    And I have read some complaints about charcoal cannister systems being awful slow to fill you tank as all the vented air from a tank has to run through it.



    The two valves, FLVV and grade, aid a user in not overfilling the tank, that is all.
    I always use a stick in my tank to measure the level.

    The Perko inline ICV actually fits in the fill hose, and I tested it. It easily opens with 1/4 cup of water.

    I poured in 25 gallons using a monster sized funnel into the tank, 5 gallon cans at a time and the ICV and vented Perko fill handled it perfectly, no burping, it all went smoothly and quickly into the tank
     
  12. sdowney717
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    sdowney717 Senior Member

    Adding, the tank is about 8 foot long, 18" height by 18"width.
    The corners are rounded large radius. All seams are welded electrically.

    There are baffles every 15" or so on.
    The fill pipe is bronze and 1.5" NPT fits into the tank top.
    The vent is 1/2 threaded fitting
    The output pickup tube 1" NPT theaded.
     

  13. sdowney717
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    sdowney717 Senior Member

    Interesting news. I installed everything yesterday by noon.
    Put in 25 gallons.
    Put a 0-10 psi gauge on the tank.
    So had a full day-night-day cycle.
    I went out at 7pm tonight.
    Looked at the gauge, reads 0 psi.
    Then loosened cap and got a very light hiss as vapors exited the tank.
    It seems to feel like it would have been 0.25 psi in my gut guestimation.
    It gassed out for about 2.5 seconds with very low pressure sound. There is a lot of air in the tank with only 25 gallons in there.

    So my gauge can not read that low pressure. that gauge works fine, I know cause I used it to set the Carter fuel pump pressure regulator and it easily read 1 psi to 3 psi. I could watch the pump come on and see the gauge start reading.

    Low today was about 72, high was 82.

    Sunday and Monday will be better test, low 74 high 91 predicted.
     
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