propane tank freezing

Been working in the fire a lot more than usual and my tank keeps freezing up. It the 20 lbs. tank in the truck. I was trying to practice my hot fitting this morning and only got two shoes done before it froze up. Any ideas?

What was the temperature and what was the liquid level in your bottle? What pressure do you run at? Do you shut the forge off if not useing it.

I carry a pair of 30#s on a manifold so I can have them both open on cold days. The additional tank volume helps a lot, but moving to Florida is even better!

I have a 40lb and a 30lb in my rig and only use them individually. Never had them freeze up, even in our lovely Michigan winters, BTW it froze and snowed last night here; my blood is not thick enough yet but in a couple of months today's temp will be a freakin' heatwave.

It has been freezing up at any tank level. I have been running 15 psi. The temp has been 45-70 deg. Fahrenheit.

Almost no tank should freeze at those temps if you're getting a good commercial blend (90% propane). If your getting some special farm blend for crop drying or some such with a bunch of butane, there could be problems. i.e. National outfits like Amerigas give good blends (required by law). Some farm supply may not. A two burner forge should use about two pounds per hour -8 to 10 hours of burn on a tank. Sound about right?

Looking at liquid temps (not air temp). Pure propane will deliver 15 psi or more down to about minus ten, pure butane only down to about plus 70. Thats why lighters are butane, not propane. No high pressures and if they quit due to 50 or so degrees, you can warm them in your hand. I have done some hot shoeing at minus 10 (only once) and by shutting the forge off whenever I could, I got along.

At those temps, I wouldn't get more than a foot or two away from the forge, let alone turn it off.
It rarely gets cold enough for me to have trouble, but a few times when it starts running slow, I put a steel plate I have on the truck in the forge. When it gets to a few hundred degrees, I lean it against the tank, problem solved. This method my not be found in a propane instruction and safety manual, however.

By freezing do you mean forming ice on the outside of a full tank? When it freezes what is the pressure reading on the regulator with the forge turned off? I'm thinking Jack might be on to something with the butane blend ratio being too high.

Yes, I mean ice forming on the outside of the tank but it was doing it when the tank was full and has continued every time I've used it. The tank is almost empty now. I had it filled last at a local propane company.

Butane has a higher density than propane. I have heard, but cannot confirm, that sometimes when the products are blended that the butane can settle to the bottom of the storage tank, then if you fill other tanks from the liquid side of that reservoir without stirring the contents you can wind up getting almost pure butane. I'm not asserting this as fact, just some information I picked up from ABANA forums years ago. It sure sounds like that is a likely cause of the problem you are describing, but then maybe it is gremlins leftover from Halloween. Ya never know for sure with supernatural phenomenon.

Yeah seems like I have been waging my own private war against gremlins from a tender young age. The tank is almost empty now so maybe if I have it filled at a different place the problem will solve itself.

OK, this is a good data point. Your tanks are still giving you pressure at temps lower than 32 degrees. First let's define freezing. To me that says that the temp of the liquid has dropped so low at to prevent you getting the pressure that you need. For propane meeting interstate (federal) standards , this is a temp around zero or below. Condensation on the tank will occur if the liquid temp drops below the dew point. Frost forms if the temp is both below freezing and below the dew point. This is normal in high humidity areas like draftshoer's. Hard to prevent and has nothing to do with forge operation. It's a bit of a PITA if it then melts off and gets into parts of the rig where it rusts tools and/or causes other damage. A plastic dish washing tub to set the tank in can solves that problem. OK, why does the liquid cool. Let's consider water - it's a liquid between 32 degrees and 212 degrees. It can still be a liquid above 212 if it is pressurized (a pressure cooker or even your car radiator). If you relieve that pressure, it will boil for a few minutes, then quit as it cools. Propane is the same except it boils at minus 44 degrees F under atmospheric pressure. If you'll excuse me (I'm not a great typist) I'll just post someting I wrote on another forum and go from there,

To reply to the statements about insulation, propane can supply about 20 psi of delivery pressure at zero degrees F (liquid temperature, not air temp) and probably 12 psi or so at minus 10*F. In other words unless the ambient temp around the tank is below zero, it would be counterproductive to insulate.

The complication is that almost 185 BTUs is required to vaporize a pound a propane. This either comes from outside the tank and is conducted through the walls or it comes from cooling the liquid. 0.6 BTUs will change the temperature of one pound of liquid 1 degree F. This means the energy required to vaporize one pound would cool a pound of liquid by about 300 degrees (185/0.6). If you are running at a level of about 2 pounds/hr (a 20 pound bottle lasting 10 hours),you must supply 185 times 2 = 370 btu/hour to vaporize the liquid. Assuming there is 10 pounds of liquid in the tank and all of the heat came from the liquid, the liquid temp would drop by 62 degrees (370/.6/10). That's OK if the liquid temp was 60 or 70 when you started and you only wanted to run an hour. It's not OK if the liquid was at something like 20 degrees when you started. It's also not OK if there's only 2 or 3 pounds of liquid.

In a practical case, then the heat of vaporization comes from both sources, but if the air temps are low and a limited amount of propane starts out already chilled, there won't be much heat conducted through the walls and the propane temp will drop quickly into an unuseable range. Water, a heat lamp, hairdryer, etc can help, but a larger tank kept relatively full is probably the best answer. As a farrier, I do travel with 20 pound tanks and on cold days my forge welds often get brazed instead of welded.


Now lets consider a day when the temp is 50*, the dewpoint is 30* and the bottle is half full (10 pounds). As an estimate, heat. can flow in at 10 BTU/hr/degree F and you are using 2 pounds of propane per hour. The energy draw on the tank to get that two pounds is 2x185 = 370 BTU /hour. With no heat transfer into the bottle the propane will cool at a rate of 370BTU/ 10 pounds * /0.6 Btu/degree or about 60 degrees/hr. It will reach the 30 degree dew/frost point in 20 minutes ((50-30) degrees/60 degrees per hour), and frost will begin to form. That frost doesn't effect the forge operation. You can drop the liquid temp on down to zero for a 50 degree temp differential across the tank walls. Now 50 x 10 = 500 BTU per hour is transferred across the walls of the tank, more than enough (370) to hold the liquid temp at zero degrees and maintain pressure. Actually the liquid temp should stabilize around 10 degrees.
If frost is the problem, It's hard to do anything about it. If pressure is the problem, there's a propane composition problem.

Will you need to readjust your regulator as the propane (bottle) drops from 50 degrees, 80 psi, to 10 degrees (30 psi)? Probably.

Tom, I question the Butane settling out, but as a tank is used, the propane vaporizes first and the liquid left behind gets richer in butane. If the supplier's tanks are low when you fill your bottles, you will get a higher butane mix. On my house propane tank, if I let it get below 10% I can have trouble at temps around zero when propane should be good to minus 40.

Jack you said that frost doesn't affect the forge operation but when I first start my forge there is no problem. When I get frost on the bottle my forge starts cooling down. It gets to the point that my metal will only get cherry red. When this happens I can shake the bottle and I can instantly hear the forge "pick up" and burn hotter. That only last a few seconds then it slows down again.

Then I suspect you have a fuel composition problem. A high butane content and low pressure. I'll get pics of how to measure bottle pressure.

A second possibility is a connector problem. I have half dozen 20 pound bottles, BBQ, forge, weed burner, camper, etc.. One of those does not work well with the newer hand type bottle connector. Guess I could exchange it, but my camper is the only place it gives trouble so I marked it and don't use it there.

So if you and I put money in a joint account, as you take your money out of the account I get richer?

As long as I only take the small change until I have half the money pieces. I may be dumber than a rock, but I'm still smarter than propane or is it the butane that stays cooped up that's dumb. Danged if I know. 'Course the propane is headed from the tank to the fire, guess the butane is better off.