Dip tubes in storage tanks

[Bill the Dog]

I've got 2 separate 1000 gallon steel tanks that I want to use as storage. Each tank was previously used as farm fuel tanks and they came much less expensively than any propane tanks I cold find. To connect these up to my EKO 80 using NoFossil's diagrams, I'm going to want to have a couple of dip tubes going through the 2" threaded openings on the tops of the tanks. Where can I find the hardware to make these fittings/dip tubes?
Any and all help is appreciated.

Bill the Dog

 

[stee6043]

You're going non-pressurized, correct?

You can get fittings at most hardware stores. I bought most of my less common items from (broken link removed).

 

[Bill the Dog]

No, this will be a pressurized system.

Bill the Dog

 

[maple1]

DO NOT DO THAT.

 

[goosegunner]

Bill pm me your phone number I live near Baraboo and might be able to steer you towards some lp tanks cheap.

gg

 

[Bill the Dog]

DO NOT DO THAT.

Maple1, why? What's wrong with using steel tanks for storage?

Bill the Dog

 

[goosegunner]

Not rated for pressure are they?

Or are you going to have the open system?

gg

 

[maple1]

Maple1, why? What's wrong with using steel tanks for storage?

Bill the Dog

Steel fuel storage tanks are a BIG no no - or else they would see widespread use.

If you try to use them in an open (unpressurized) system, they will rust.

If you try to use them in a closed (pressurized) system, they will rupture.

 

[stee6043]

Maple1, why? What's wrong with using steel tanks for storage?

Bill the Dog

If these tanks are not rated for pressure (fuel tanks typically are't) it can be very dangerous to pressurize them. It may seem like a "steel tank is a steel tank" but many folks will assure you that a pressure vessel is very, very different than a liquid storage tank.

I'd take the above poster up on his offer and let him help you find LP tanks...

 

[2.beans]

You could use them unpressurized with properly treated water.

 

[EffectaBoilerUser (USA)]

You definitely do not want to use a normal fuel storage tank as a pressurized water storage tank. If you look closely at all pressure vessels you will see that the ends of these vessels are always a dome shape. This is done so that the welds that attached these ends to the shell are always in pure tension. A weld is very strong in tension but not as strong when it is subjected to side loading as is the case with most fuel storage tanks. Not having seen the tanks your talking about I would guess that the ends are welded at right angles to the shell and thus as the tank is pressurized the ends will move/bulge and put the welds in other than tension loading scenarios. I did a calculation today for a person who was looking to use a 4' diameter fuel tank also. When doing the math on a 4' diameter tank at 20 psi the force pushing on the ends of the tanks was 36,000 lbs. When taken to 30 psi the force increased to 54,000 lbs.

You can certainly use fuel tanks for open systems (but for many reasons I would not recommend open systems) but make sure you maintain the water quality as open systems tend to rust out quite quickly if not maintained.

 

[stee6043]

You definitely do not want to use a normal fuel storage tank as a pressurized water storage tank. If you look closely at all pressure vessels you will see that the ends of these vessels are always a dome shape. This is done so that the welds that attached these ends to the shell are always in pure tension. A weld is very strong in tension but not as strong when it is subjected to side loading as is the case with most fuel storage tanks. Not having seen the tanks your talking about I would guess that the ends are welded at right angles to the shell and thus as the tank is pressurized the ends will move/bulge and put the welds in other than tension loading scenarios. I did a calculation today for a person who was looking to use a 4' diameter fuel tank also. When doing the math on a 4' diameter tank at 20 psi the force pushing on the ends of the tanks was 36,000 lbs. When taken to 30 psi the force increased to 54,000 lbs.

You can certainly use fuel tanks for open systems (but for many reasons I would not recommend open systems) but make sure you maintain the water quality as open systems tend to rust out quite quickly if not maintained.

I thought you were a mechanical engineer? An ASME certified pressure vessel welder would laugh at you if you told him a pressure vessel had domed ends because of the characteristics of "his weld" under tension. Your comments on the fuel tank seemed pretty okay but I think you're way off with your assessment of why spherical or torispherical shapes are used on pressure vessels.

 

[EffectaBoilerUser (USA)]

Thanks for bringing that up. Yes, there is another reason (the more important one) that hemispherical ends are used on tanks. These ends being domed are much stronger than a flat end of the same material type/thickness. Thus, a flat end on a tank would need to be much thicker material if it were to be used in a pressure vessel application. A normal flat ended tank (a fuel tank, etc.) will bulge/oilcan when subjected to pressures. If the pressure gets too great the tank will blow apart! That is why you don not see pressure vessels using flat end caps. The other problem that flat end caps welded to a cylinder present is the complicated stresses/stress concentrations that occur at the fillet welds.

When using a double butt weld (as is most commonly found on pressure vessels) the stress concentrations and complicated stresses go away.

I hope this helps to clarify the reason why a vessel that is not designed for pressure should never be used as a pressure vessel.