Pressure testing integral fiberglass diesel tanks

I agree that the formula for air pressure and water pressure are different.

I also agree that testing procedure pressure is different.

In air pressure testing, pressure is constant on all sides, in water pressure testing, pressure is greatest at the bottom and diminishes towards the top.

But 1 psi will always be 1 psi as it is a unit of measure.

 

Geeze pete, a man of eloquence
welcome,
switch to metal mate)

 

It's hard to imagine one of them not expanding and doming.

The USCG allows the tank to deform , just not leak.

All plastic fuel tanks will expand a few percent on first fuel fill.

Most boat mfg will fill them , THEN foam the tank in place , after it has expanded.

FF

 

Yes, when using water you have the applied pressure plus any head of water. In fact this applies in an air test as well, but the weight of air is so small that the difference is negligible, You might notice it in a very tall building. Remember that atmosperic pressure is caused by the head of air in the atmosphere. Thats how the old altimeters used to work, probably the new ones as well.

I'm not sure that you fully picked up my point about the difference between test mediums. It was in the 2nd and 3rd paragraphs of post# 20.

To simplify the conundrum, I would say that for strength testing they are equal, but not for safety or for leak-detecting. Water is safer and air will find smaller leaks.

 

Sam Sam, I will not abide by the attitude this guy carried, nor yours. The fact that he can turn it on and off at a whim doesn't matter - I say "get some meds". I don't believe I agreed with him, I just really don't care to have someone asking for help being arrogant and demanding rather than grateful. As to you...

 

I agree,
Dry tank with a water manometer is the only way I have ever seen double bottom steel tanks tested in commercial vessels.
With temp monitored to ensure the rise and fall is correct and the surveyor looking on over a couple of days

 

yes it is a great pity that people post , on what they actually have no first hand exprience of and thereby confuse the issue
Still all ok, 100 to one we agree on the way to tank test

 

Amen Whoosh... makes the forum a whole lot less useful and extraordinarily less friendly.

BTW, I did make a manometer and the tank tested out fine at 3 psi. A bit creaky on the way to 3 psi (83" wc) the first time, but cycled up and down a few times just fine after that. And as for the other speculation... my very fine swiss-made lab calibration dial pressure gauge, which reads to the 1/100th of a PSI and 2psi per rotation, agreed precisely with the manometer. Also, when pressurizing a large tank (this one is 95 gal) using a bicycle pump would be a crazy amount of pumping. A compressor at 40psi output works great and you can sneak up a fractional inch of wc at a time even with this input pressure. I used a tire chuck on the hose and a schrader valve on the test jig. Worked great.

 

You should tweak yout mathematical skills! 5:3 or 6:3 is not 100:1. There was no agreement, just different opinions and experience.

 

I don't want to be a pest, but that is the worth type of tank positioning system.
It is find on cheap production boat. I mean cheap by the way they are built, not the showroom price nor the brand.
It is dangerous (if leaking happens is in the foam) and when you want to remouve the tank, good luck.
A tank as to be remouvable at any time, without spending time nor destroying half of the boat.
As for air testing, well I am not around so I don't care what other do, or insist doing.
Daniel

 

Here is what Gerr has to say about tank testing...

http://books.google.com/books?id=euQZ16elT5kC&pg=PA83&lpg=PA83&dq=dave+gerr's+tank+pressure+test&source=bl&ots=dmXAIJzmKp&sig=J_ZXwHrU_56AhjVY5PZUg38b4xc&hl=en&ei=sjscTJiJF8iKnQeuy-3qDQ&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBIQ6AEwAA#v=onepage&q&f=false

 

Very interesting thread. Let me clarify a few things about the USCG regs for pressure testing tanks. It was my job in the USCG Office of Boating Safety to interpret and explain the regulations to boat builders and the public, and I was a member of the ABYC Fuel and ventilation Committee.

First Sec. 183.542 Fuel systems: says
(a) Each fuel system in a boat must have been tested by the boat manufacturer and not leak when subjected to the greater of the following pressures:

(1) Three pounds per square inch; or

(2) One and one-half times the pressure created in the lowest part of the fuel system when it is filled to the level of overflow with fuel.

(b) The test pressure shall be obtained with air or inert gas.

and

Sec. 183.580 Static pressure test for fuel tanks. A fuel tank is tested by performing the following procedures in the following order:

(a) Fill the tank with air or inert gas to the pressure marked on the tank label under Sec. 183.514(b)(5). Which Says (5) The pressure the tank is designed to withstand without leaking.

(b) Examine each tank fitting and seam for leaks using a leak detection method other than the pressure drop method

The reason we (and ABYC by the way) picked 3 psi as max is because the maximum pressure head on a recreational boat is most likely not going to exceed 10 feet. (yes there are exceptions but those are mostly very large yachts that are built to ABS, LLoyds, MCA or other standards)

As for the air and inert gas, these regulations (if you read the applicability section at the very beginning of 33 CFR 183) apply specifically to manufacturers. This assumes the tank is new and has never had fuel in it. In fact the tanks are usually tested at the tank manufacturers factory and tested at 3 psi because the tank manufacturer usually does not know where the tank is going. However the tank can be tested at a lower psi if it will see a lower pressure head, and you know what the pressure head is. But the minimum is 1/4 psi.

Thes rules apply to tanks of all sorts of materials. Plastic tanks usually expand like a ballon at 3 psi. I have also seen fiberglass tanks tested using 3 psi at Hatteras Yachts without any problems. These were integral diesel tanks.

It is very common to test tanks on recreational vessels with air. Of course one must be very careful doing this if the tank contains gasoline. The tank should emptied and purged.

For passenger carrying vessels exceeding 6 passengers (commercial) the rules are different and contained in subchapter T of 46 CFR, not 33 CFR.

On large vessels he water method is more common but I have seen tanks on ships pressure tested using air, but they were not gasoline or other volatile fuels. They were usually oil of one grade or another from bunker C to diesel.