A tank's a tank, right?

Well, some tanks have higher burst pressures than others.

Take a look at this interesting video...


Tank burst test




Watching the video, you'll see the man filling the tank with water before beginning the hydrostatic burst demonstration. The reason for the water is that there is a very small amount of stored energy in the tank since water is essentially incompressible, vs pumping the whole tank full of air -a LOT MORE stored energy to release.



When a propane tank is filled with liquid fuel, and there is little air, vapor or other gases inside, there isn't much 'energy' being stored if for some reason pressure builds up inside -just a little.

A fire is the only thing I can think of that would cause the pressure inside to build up, significantly. The vapor pressure of gasoline would tend to increase with increasing heat.

This is hard to communicate...


Anyhow, without looking at the vapor pressure for gasoline charts to find out what temp would be required to reach the bursting pressure of the tank, in the video, abt 1500 psi, ---it seems in a fire, gasoline vapor might reach that pressure and the resulting KABOOM would be rather -dramatic.

Fuel stored in MFC's or NATO cans, have an inherent pressure release mechanism, the caps can fail and blow off or the plastic can melt, allowing the fuel to burn but without the KABOOM if the fuel reaches a high temp.

The fuel will mostly burn, not unlike being poured out on the ground and lit.

However, super heated fuel when released from the burst tank, will vaporize and release a lot of energy -just the same as super heated steam released from a ruptured pressure vessel -you prolly don't want to be around it.



Now combine the kinetic energy released from the fuel in a propane tank [I think that's the right term] with the fact that the fuel is flammable ---and you have the makings for something FAR MORE dramatic -----than a ruptured steam vessel with the same kinetic potential energy.



A fuel-air bang. If you know whatcha I'm talking abt...

Most of the fuel will instantly vaporize with great mechanical energy, and mix with the atmosphere...

From reading the posts of folks, I'm not sure the significance of needing a pressure release valve calibrated to the vapor pressure of gasoline -slightly higher than a very hot day, is being always considered.


So, it seems if you are going to store gas in a propane tank, or any other tank with significant burst pressure [hot water heater tank, etc] more consideration needs to be given than just pouring the fuel in and screwing the valve back on. Thereby making something that I don't want to type out.

Maybe redundant relief valves...

A serviceable pressure relief valve seems to be an essential requirement.

For very obvious reasons and extreme potential for liability. Of ALL kinds....


How can an acceptable relief valve be made or where can they be purchased?

Another thing...

One gallon of liquid propane when turned to vapor, expands to IIRC, almost 300 gallons of vapor.

One reason super heated steam is so dangerous. One CF expands to almost 2000 cu ft.


[Fixed it]

In previous posts about propane tanks holding gasoline there have been mentions of using stuff other than stock valve.



I believe someone used a plastic screw in plug of some sort and had a pressure relief valve, perhaps the type used on a water heater but I forget what they had.



Someone else had a setup where they used a propane tank to provide propane as the pressure to propane tank filled with gasoline and the propane would push gasoline out another line so that you did not have to siphon fuel.



I do not know what others are doing but I do recall mentions of the above because it made me think of something other than just using the stock valve.



I halfway want to look in my empty old rust 100 lb tanks and see how bad the inside looks.  After thinking about what it would cost to clean em up and retest them I figure new tanks don't really cost that much if I catch them on sale, co-op sells them and a first fill for a discount from what a friend says.



So that means I have some old tanks around.



At worst they would make some cool windchimes.

Prolly me mentioning the thinned out plastic plug.

I mention it every time...

I've also posted about mod'ing a hot water tank relief valve w/ a Viton gasket and other solutions as well.


Your old tanks may look rusty on the outside but probably are OK on the inside. Not much moisture and O2 to rust the insides.

Even if they were a bit rusty, a little rust never hurt nobuddy...

How are you going to pull the valve?

You know, I think it would be handy to cut out the 3/4 inch or whatever valve port threads and braze in a 2 inch bung to make filling and emptying easier.

You can mount a fluid/fuel pump in a 2 inch opening.

I think the key term here is "BLEVE". Fuel stored in such a way that it can vaporize under pressure is bad, m'kay?

I see no more danger in storing gas in propane tanks than propane.

Actually, the BTU capacity of gas is ~ half as again as much propane.

If the safety pressure relief valve designed for propane, is activated by gasoline vapor...

Will it have the ability to withstand the different forces and temps, if in fact they actually are, different.

Here's another video of a propane tank, presumably filled w/ propane with a fire lit under it for demonstration purposes.

There is a blue area with 'bubbles; photo shopped on the tank, illustrating the mechanism of what we're talking about.

You can see the vapor being released in bursts, and the vapor pressure activating the valve due to the fire is probably in the several hundred psi range.

Note that when the safety valve opens, there is a TREMENDOUS cooling effect due to the expanding propane. That's what causes the cycle to repeat a couple times until the metal gets hot enough to fail ----below the calibration of the safety valve, then in the video, all hell breaks loose when the tank ruptures.

At about 1:30 Look at the shock wave... And the resulting fuel-air splocion




We'd need to look up the vapor pressure of gasoline to try to see what would happen if gasoline were substituted for propane.


My guess- since the vapor pressure at STP of gasoline is way lower than propane, the temperature that a tank filled with gasoline would have to reach before the safety valve activated, would be considerably higher.


The question is, would the safety valve operate more effectively w/ gasoline than with propane...

And would the higher temps reached by the tank cause it to rupture before the safety valve vented.


Video of propane tank failing...

What Seek2 mentions happening is at 1:30 in the video...  

I think it would singe the eyebrows any chickens nearby.  



Youtube video of Tank




This is why I have always advocated here putting an adequate pressure relief valve on  'stronger' higher burst pressure tanks, that fuel might be stored in.

Thanks for the clarification Seek2...


The principles involved are similar to water heated in a pressure cooker.


Of course, for the Preppers who think water can be siphoned UPHILL...

Well, this is all prolly lost on them.  

Uphill.... ? Hydraulic Ram...

Hydraulic rams don't work on siphon principles...  


They're more of an Inertia thing.

Fuel can be dangerous in plastic cans or metal, I store mine in a dump 150' from the house.
propane tanks full of any fuel are likely to explode in a fire, plastic cans will just make it burn sooner and faster.

Don't store fuel in your home.

It takes quite a lot if heat and pressure to make a large propane tank explode. I have lit burners and fires under them (1000 gallon tanks) 100 of times and have never had a problem. I have had them to well over 100psi and they did just fine and didn't pop the safety valves.

I would think that if you were worried about it you could install a vent like on a normal gas tank, install a lower pressure pop off valve, or store diesel.

what could possibly go wrong?

If the valve is replaced back onto the tank would the LP relief valve not be sufficient?


FWIW, DOT LPG bottles should vent around 375 PSI
I can't find a vapor pressure chart for gasoline or LPG that go that high but I can "guess" where the curve would end up based on the direction it's headed, and I would guess that 375 would roughly correspond to 150 deg. F for LP, 190 deg F for Ethanol, and gasoline is a tough one to figure out due to the numerous components that make up gasoline, but it's not much further behind if you average the vapor pressure of the main components...

I honestly think you're make a big a-do about nothing. A BLEVE can certainly happen with anything. I don't think gasoline is really much more dangerous than LP in an LP tank...

I have come across you talking about thinning the plastic someplace else today, the one I am talking about was a plastic cap and I think the guy threaded in a pressure relief valve to the plastic cap.



2 of the ones I have will accept the protective cover cap.  One is goofy and the valve is done in such a manner that you can not put on a protective cap if you wished to do so.



Mostly I need to pull em out of the weeds and clean em up and I want to see when the dates on them were good and just clean em up and perhaps repurpose them to hold fuel.



I figure the whole valve setup should screw out of the tank, if the threads are common I might just go with the plastic plug because I don't really know if I need the whole big ting on it right now, and the one won't let me put the protective cap on it anyway.



Just me being me, I kind of like the protective caps.

If you are filling the tank with gasoline in this case???

Who knows?

I can't find the vapor pressure of gasoline at let's say 800 degrees F to even make a guess.

It'd be like rebuilding the wing on an aircraft with different material and flying it.

You just became a Test Pilot!  


I think the safest thing to do would be to replace the Propane relief valve with a modestly high capacity overpressure valve of, say 20 or 30 psi.

That would retain any vapors resulting from extreme environmental conditions...

It would also vent vapors before any significant BELEVE conditions built up and prevent a detonation.


A white plastic PCV pipe plug will prolly fit a standard propane tank with NPT pipe threads, IIRC they are 3/4"

Thin the material on the plug so it doesn't take but a small amount of over pressure to rupture it.

It might be the answer...


As far as building fires under 1000 gallon propane tanks, I don't have any issues with folks doing it, if they aren't doing it too close to me...

I like them too to keep dirt and stuff out...

I'm going to make a fire under a donut and see what happens...  

Or doing so could result in a BLEVE much sooner (even if the bleve is "smaller" I still don't want to be around.

Keep in mind, that in accordance with the demonstration posted above, a BLEVE doesn't occur purely because of the boiling fuel, it's because the fuel-stock boils away and there is no longer liquid present on the other side of the tank wall to keep the tank cooled. The tank metal heats up, gets weak, and ruptures. Lower relief pressure means your fuel boils away much faster yielding weaker tanks much sooner. The "critical point" is when the tank material is weaker than the pressure in the tank.

The curve at which steel weakens related to temperature is fairly steep, it doesn't take much temperature change between the critical point at 375 psi and 30 psi...

Again we don't know.

Size the relief valve according to good engineering practices.

Well, the valves on the 100 pound bottles are 3/4" NPT.

One key point about pressure vessels is to store them full.  That way, when exposed to fire, they will overpressureize and eventually activate the engineered pressure release device.

However, storing vessels well below they intended level, can result in pressure increase without activating the release mechanism.  And the vessel would eventually fail from physical damage.The expansion ration depends on the material.  Water expands 1,700 times at atmospheric pressure.  But it takes 970 BTU's per pound of water for the conversion.

For propane, it's 1:270.  MSDS sheet for propane

If I was going to store a fuel for use, I'd opt for propane over everything else.

BTW, I'm a career firefighter with 25 years of experience.

whats pressure for propane is pressure for gas, I don't  see any problem.

?

Problem with what??

And Why?

Along a similar line of thought:

A typical propane tank valve uses seals made of some sort of rubber.

Does this particular rubber tolerate long-term exposure to gasoline without breaking down?

I have some propane tanks that have been storing gasoline over a year as of now. When I get time, I will inspect the valve and look for signs of problems.

 

You loose me here. How can a pressure vessel WITH engineered pressure relief valve for the container have the CONTAINER fail w/o the relief blowing? Pressure is pressure whether the tank is 95% full or 5% full. Once a certain PSI is reached, the relief blows.

 

I was confused too but I decided not to bump the thread up just to call him out. The only thing I can figure is that he was referencing in a fire situation, which is mostly true. If your vessel isn't full then there is no direct liquid contact with the inner wall of the tank to provide cooling to the steel. Therefore it's possible that the steel heats up enough above the fluid level to a point that the strength of the steel is reduced so much that the steel itself now becomes the "relief valve" or "weakest link" and you get a kaboom before the actual relief activates.

Who stores gasoline in a propane tank?

I'm looking for a large one right now to store Diesel in, the propane distributors have tanks that can not be re-qualified, or perhaps they were used for Butane and they only sell Propane.

They can be re-purposed for storing liquid fuels, i.e. Gas, Diesel.

Rancher

Many people... old LP tanks that may no longer be acceptable for storing LP are readily available at relatively low cost, yet they offer the advantage of being a pressurized fuel vessel so you don't lose the more volatile fractions of gasoline to evaporation.... it's becoming "more common" of preppers to do long-term fuel storage in this manner if it suits them.

For me, I don't have a use/need for storing fuel like that, but for others, if it suits them then I don't really care.

Have a fire related incident using propane tanks as gasoline or diesel storage tanks and see how many state and federal alphabet agencies pounce on you.

Still don't see it. If the tank gets that hot, the gasses inside should have well reachedppressure relief levels.

 

You keep saying that...

But how do you know???

Gasoline has entirely different properties than propane.

Tell me what the vapor pressure of gasoline is at, let's say, 600 degrees F.

1 gallon of water turns into 1700 gallons of steam....

Not necessarily. I'm not trying to insult your intelligence here but do you at least understand the principle of vapor pressure of liquids? If not, I can explain that and it may help connect the dots.

An example of a very extreme case of what I'm trying to say would be: I have an oxy-acetylene torch. Oxy-acetylene can reach something like 5,000 degrees (well above the melting point of steel). I can fill a 20 quart stock pot 100% full of water, hold the torch against the side of the pot and nothing will happen to the pot because the water (liquid) against the inside of the "tank" or pot keeps the metal below melting point. But let the water level get below the point I'm holding my torch and there is no longer liquid to cool the metal and the torch melts/blow/cuts a hole through. The water, in this case, protects the metal from over-heating the same way propane or gasoline inside of a propane tank will protect the tank from overheating. Will the contents boil away? Yes, as the tank contents heat up, and the vent relieves pressure, they will boil away but it will at least buy you time... But if at any point the metal is heated up to the point that it becomes weaker than the 375 psi that the relief valve is holding, the tank will rupture, instantly vaporizing the high-pressure liquid fuel inside and causing an explosion/fireball.

Just for the record, those aren't propane tanks on that truck/highway in Russia. If I remember correctly they were Acetylene.

Other than that, given that I work for a propane company, I can't contribute here other than to say you should follow the manufacturer's instructions and all legal requirements when dealing with hazardous materials and their containers, valves, regulators and other fittings or equipment.

Tell me, where are you going to be when the gasoline reaches 600 degrees F?

I will already be French fries.

Rancher

If you are storing fuel in significant quantities, you'd be wise to mitigate the risk in some manner. I get the concept of a flamable pressure vessel being a hazard, but this is not an issue if you've moved your tanks to a proper distance.

If you're that worried, insulate it it some manner: sandbags stacked 360, dirt, etc. Score the tank? Keep it in a metal shed, grounded.

I've seen a aux diesel tank go up on a mil 60k generator setup, the aluminum tank held together and a chunk above the fuel level finally gave out and popped free...about a 6" round section. There was no explosion. Gasoline is another story.

Sadly, you have missed the entire point of the original post...  

Ok....

-this is dangerous and may explode in some exponential manner
-use a pressure relief, but i may not help if temps get too high too fast

So, are you advising never to do this or offering advice to mitigate the risks?
A 55 gallon drum is safer?

Edit: we have service stations w above ground tanks and tractor trailers driving on the roads

I had never really thought about using this tank, rather a beer keg.

I'm with JKM -> please tell us what the point of thread is.............

Because I'm really missing what is so earth shattering about a pressure vessel being used for a purpose other than it's intended purpose could be dangerous.

I thought I made my points very clear when read -with good reading comprehension applied.

Apparently not.  

Please pick ONE issue for me to respond to. To start with.

You pretty much have gotten it JKM.  


I'm NOT advising NOT to do it.  

I'm suggesting to use COMMON SENSE and good engineering practices when storing gasoline in a high pressure capable vessel.

For reasons I have enumerated.



A 55 drum -metal- in my mind is safer, for most folks, for a couple reasons... [What do you think they are?]


I have no issue with storing gasoline in large propane tanks ----if set up using good engineering practice and COMMON SENSE.

[However, this is my opinion as an internet NOBODY so take it for what it's worth  


I'm offering SUGGESTIONS to MITIGATE the risk, as you so well put it.

Not intended as definitive ADVICE.  

I may have overlooked some critical issues...

and, YMMV  




ETA- I like the way you put it JKM...  

"and may explode in some exponential manner"

That's putting it mildly...  

It's amazing how little Reading Comp is applied to the original post and a few sequential ones, in this thread...  

My bed is over a 35 gal gasoline tank, and my feet right now are over a 7 gal propane tank....

#RVERSLIVESMATTER  

OMG, you are truly going to scare the Sheeple!



RV's are the bomb!  

I think the burst pressure of a 55 gallon drum is significantly lower than that of an LP tank...

Is there a specific thread on converting propane tanks? I am shopping for a couple of 500s now.