Cutting a Propane Tank - Best Gas Detector?

[Kid B]

I have a decommissioned 250 gallon propane tank I'm planning to cut into to make a Texas-style offset BBQ smoker. I have read lots of forums on methods to do it safely, and it seems the only 100% fool proof method is to use a gas detector/monitor. My plan is to fill the tank with soapy water several times until the gas detector reads zero. That leads to my question for those who have cut into an empty propane tank using a gas detector/monitor:

Which monitor/detector did you use? How did you do it? Since propane is heavier than air, did you need to drop the monitor into the bottom of the tank?

 

[Beelzeboss]

Cut it when it's completely full of water? I always heard that's the safest method

 

[mike93lx]

Just fill it with water... Leaves no room for gas

 

[Kid B]

Cut it when it's completely full of water? I always heard that's the safest method

That's one way, but as the tank drains out any vapors trapped in the walls could still ignite once they come into contact with air.... at least that's my understanding. I'd rather flush it completely until a monitor reads zero.

 

[58Yeoman]

I'd let someone else do it. I once had a 20 gallon tank I wanted to get rid of, so I kept rinsing it with water. When I set it out for the G-man, I could still smell propane.

 

[mike93lx]

I'd let someone else do it. I once had a 20 gallon tank I wanted to get rid of, so I kept rinsing it with water. When I set it out for the G-man, I could still smell propane.

You don't smell propane. You smell the oderant that they add. That can linger when there is no propane

 

[OccupantRJ]

I controlled and serviced a 20,000 gallon butane tank for 30 years as part of my job. The odorant used was ethyl mercaptan, 200 ml to 8,600 gallons of butane. I added the mercaptan to the butane onsite. The part that always blew my mind was that the tanker was rolling down I95 on the eastern seaboard with 8,600 gallons of unscented butane on its way to me. Can you imagine an accident where there was spillage of a highly flammable substance that had no discernible smell?
By the way, tomato juice will help knock down the smell of scented gas.

 

[LopezBart]

Dilute bleach or hydrogen peroxide will remove the mercaptan smell; they react w/ the oily stuff.

 

[TurnipTruck]

I would not trust my life to any cheap retail gas detector.
Professionally, I and many of my friends have trusted our lives to industrial multi gas detectors that were bumptested daily and calibrated monthly, and if ANYTHING was questioned or questionable, we got additional detectors.

With that said, I would have no problem with filling your tank with water full to flowing over and cut with a metal saw on a GFCI. The tank would rotate to have each cut at the very top to keep it full.

 

[jeb42]

I had a 100 gallon tank I made into a smoker. I removed all the valves and let it set outside for several months and filled it with water and let it drain. I rolled it over to a brush pile and caught it on fire. It flared out of the holes I removed valves on for awhile, but it was completely burned out when the fire was burned down. I have done that with CNG tanks also. It's what most people do in the country around my part of East Texas.

 

[Gutman]

Curiously, what's the wall thickness of a 250 gallon tank?

 

[isb cornbinder]

I'd let someone else do it. I once had a 20 gallon tank I wanted to get rid of, so I kept rinsing it with water. When I set it out for the G-man, I could still smell propane.

You cannot smell propane. That odor is added to propane to act as an alert to a leak or propane in the area it is called Ethyl Mercaptan. EM is not toxic. If propane is inhaled, it can displace oxygen in lungs. You know what happens.

 

[Kid B]

Curiously, what's the wall thickness of a 250 gallon tank?

I'd guess somewhere between 3/16" and 1/4"

 

[dcg9381]

I'm always curios about these too as there are quite a few marked with a big "X".
Do they usually fail due to internal condensation and associated rust?

Cutting one, I'd listen to the experts, but it's done here quite a bit... Just not by me!

 

[isb cornbinder]

Curiously, what's the wall thickness of a 250 gallon tank?

Probable .250"
LPG is not a high pressure. The pressure of the cylinder gas varies between 2 and 3 bars depending on the ambient temperature; however, the operating pressure of the cylinders is designed to be 17.5 bar or 255 psi.

 

[Kid B]

With that said, I would have no problem with filling your tank with water full to flowing over and cut with a metal saw on a GFCI. The tank would rotate to have each cut at the very top to keep it full.

What do you think of this idea? I fill with soapy water and run a hose connected to an argon tank under the water's surface. As the water slowly drains out, the tank fills with argon until the cuts are done. That way I don't have to worry so much about rolling the tank around as i cut.

 

[isb cornbinder]

I have a decommissioned 250 gallon propane tank I'm planning to cut into to make a Texas-style offset BBQ smoker. I have read lots of forums on methods to do it safely, and it seems the only 100% fool proof method is to use a gas detector/monitor. My plan is to fill the tank with soapy water several times until the gas detector reads zero. That leads to my question for those who have cut into an empty propane tank using a gas detector/monitor:

Which monitor/detector did you use? How did you do it? Since propane is heavier than air, did you need to drop the monitor into the bottom of the tank?

You may have the smell of mercaptan coming from the tank for years. Do you want to take the chance?
I got a free large propane tank and I used as extra storage volume for 2 decades. The air never stopped smelling like a garlic fart.

 

[Kid B]

You may have the smell of mercaptan coming from the tank for years. Do you want to take the chance?

I would think it would disappear after coating the inside with cooking oil and building a large oak fire in the firebox

 

[TurnipTruck]

I wouldn’t bother with argon, or any inert gas really. If you have enough water flow so it’s always coming out the top and you don’t mind getting wet, cut without rotating the tank.
I don’t have a good feel for how long you’ll have to air it out before welding; I’ve never done a propane tank, just old gasoline and diesel cylindrical tanks.

 

[LopezBart]

Probable .250"
LPG is not a high pressure. The pressure of the cylinder gas varies between 2 and 3 bars depending on the ambient temperature; however, the operating pressure of the cylinders is designed to be 17.5 bar or 255 psi.

No. Vapor pressure of propane is about 100 psi at 64F and 200 psi at 110F. Working pressure of hoses, etc. is normally 300 psi.

 

[LopezBart]

<glitch>

 

[larry4406]

I think Aaron Franklin fills his tanks full with water and cuts them full. Watch his videos.

One of the videos I watched showed spring back in the tank when cut, and the fabricator accounted for that when he made the doors by installing the picture framing prior.

 

[isb cornbinder]

No. Vapor pressure of propane is about 100 psi at 64F and 200 psi at 110F. Working pressure of hoses, etc. is normally 300 psi.

Really?

 

[58Yeoman]

I would not trust my life to any cheap retail gas detector.
Professionally, I and many of my friends have trusted our lives to industrial multi gas detectors that were bumptested daily and calibrated monthly, and if ANYTHING was questioned or questionable, we got additional detectors.

With that said, I would have no problem with filling your tank with water full to flowing over and cut with a metal saw on a GFCI. The tank would rotate to have each cut at the very top to keep it full.

I worked at a chemical plant for 40 years, and ANY hot work or entry required monitoring with calibrated equipment, always. There was a vertical tank outside any buildings that was going to be worked on, but the manhead bolts were rusted beyond removal. The test guy came and poked his sensor into a smaller hole at the top and declared it safe to cut with a torch. Two outside contractors proceded to cut the bolts when the gas trapped at the top of the manhead exploded (top mount manhead).

I was working in the one story lab when I heard the explosion from more than a hundred feet away. The two men died that day, very quickly.

And, I do know that there is an odor added to propane, etc., but don't most people who know that just take it for granted?

 

[Firebrick43]

Curiously, what's the wall thickness of a 250 gallon tank?

Old tanks were .250, modern ht steel that came in the 60s were a lot of time .208 but it depends on size and manufacture. It’s on the data plate

 

[LopezBart]

Really?

 

[Firebrick43]

I'm always curios about these too as there are quite a few marked with a big "X".
Do they usually fail due to internal condensation and associated rust?

Cutting one, I'd listen to the experts, but it's done here quite a bit... Just not by me!

They fail usually by external corrosion. Either setting down in the dirt, not being painted, and birds roosting under the hood and the corrosive poo not being washed off. Being around hog and dairy barn pits is also really hard on them.

Methanol is added with each load offloaded into the bullet from the transport truck. This absorbs any internal moisture.

 

[bscman]

The following is not advice! Consider it for entertainment purposes only! Propane is dangerous, as is cutting open used fuel tanks of any type. Do not attempt.
/warning over

I work for a company that has roughly 30,000 propane tanks on lease for business and residential use. These range from 120gal to 1,000gal tanks.

We rehab our own tanks, we also cut the domes off scrap tanks to repurpose for firepits. When the occasional 1,000 gets scrapped, they're cut in half lengthwise and turned into giant BBQ's for events.

All this being said, for tanks that will be rehabbed, we run them down to empty, hook them up to a special vaccuum pump (that also runs the exhaust through an orange scented chemical to reduce the mercaptan smell) for a 15min cycle. They then sit overnight and are tested again in the morning for vacuum. If it's still holding, it's straight into an industrial sandblasting cabinet. Steel shot strips 30 years of rust and paint off in a 4-1/2 minute cycle.
They get removed and primed immediately.
Tanks that don't have vacuum either have a bad valve or gauge (which gets fixed) , or they still had residual gas which vaporized and built pressure. Either way, they get put on the pump for a second round and then into the blaster if they pass the test.

Tanks that are getting cut get emptied to no pressure, all valves/gauges/vents are removed and replaced with pipe plugs (sans one).
Tank is then filled to capacity with water (and a splash of dish soap added) until 100% water filled. Tank is then fully drained, all plugs removed, and then inverted and left to sit (propane vapor sinks). After a minimum 24hrs of rest/open air vent, they're tossed on a bench and cut with a plasma torch.

We've never had an issue with this system.
When I take a tank home for myself to use, I forego the vacuum steps and the water alltogether, but I do remove all valves and let them sit for several days (usually 1week or more) inverted with all the valves and plugs removed to vent. I've never even been able to get a "pffft" of energy holding a lighter in an empty bung after this.

Propane boils at -42F
It vaporizes quickly, and doesn't seem to leave a residual in the pores of the steel.

The real key is either use water to displace where any gas can reside (the propane vapor is lighter than water and is therefore forced out the top when the tank is filled with water).
Otherwise, the goal is to open any low spots so the propane vapor (heavier than air) will vent out the bottom of the tank.

Combining both is just extra safe behavior.

For what it's worth, I'd cut open a propane tank with a torch that was never filled with water and never put under vacuum (just left venting, all valves removed) before I'd cut open a used diesel tank that was BOTH filled with water then left to vent. M And I'd surely never use an electric power tool to cut open a tank that is filled with water!

Again, this is not advice. Proceed at your own risk, and all that other safety advice!

 

[bscman]

I would think it would disappear after coating the inside with cooking oil and building a large oak fire in the firebox

In my experience cutting open and making dozens of propane tank firepits and BBQ's, the mercaptan smells burns off in the first use.
But your entire yard will smell like it for a week of your filled the tank with water and flushed some all over the lawn.

 

[chris142]

Propane boils at a very low temperature. Like way below 0F..I'm guessing that the tank if left open more than a few minutes will be empty with just odorant left .

 

[Boogerman]

bscman has been there done that; but still has disclaimer. I've not been there, never cut open a propane tank. But, do know a bit about welding gasoline/diesel tanks. Same disclaimer about not doing this at home, read for entertainment purposes only as this is an internet forum operated for your entertainment.

After draining thoroughly, they can be welded by putting a hose connected to the tailpipe of a running vehicle into them, with exhaust allowed to freely enter and exit for about 5 minutes before starting welding. Keep the vehicle running while the welding is taking place, and after until the tank cools. The inert atmosphere from the exhaust eliminates half of the fire equation (oxygen + fuel = fire) so the welding can be carried out without the tank catching fire. This presumes the fuel has been fully drained, and the hole being welded has no liquid fuel exiting it.

My dad was a plant welder, in potato processing plants. The thing they would never weld near was ammonia leaks from the coolers. Any oil of any kind in an ammonia environment can become extremely explosive. Oils were a manageable risk for welding, with inert atmosphere or protective mats, or similar measures. Cooking oils were all over the plant in addition to machinery oils, so when they had ammonia leaks, they were a real concern.

Another technique I've seen fuel tank salvage guys use to cut up tanks on removal/remediation jobs is get a calculated amount of dry ice, break it up into chunks and put in the tank with a several times the calculated amount safety factor. Control the venting out of the tank to make sure the carbon dioxide and residual gases can leak out, but air can't get back in. (clear hose from bung into water, so you can see gas venting and insure air can't go back in). Cut the tank, using duct tape if needed to reseal the cut if the operation can't be completed all at once. This was used on large tanks to reduce the size to more manageable pieces. If possible, they hauled the tanks out whole, but purged them with dry ice and sealed them before handling them or loading for transport.

 

[Youngandfree]

That's one way, but as the tank drains out any vapors trapped in the walls could still ignite once they come into contact with air.... at least that's my understanding. I'd rather flush it completely until a monitor reads zero.

If you fill it with water, it should push all the gas out of the top.

 

[Kid B]

The following is not advice! Consider it for entertainment purposes only! Propane is dangerous, as is cutting open used fuel tanks of any type. Do not attempt.
/warning over

I work for a company that has roughly 30,000 propane tanks on lease for business and residential use. These range from 120gal to 1,000gal tanks.

We rehab our own tanks, we also cut the domes off scrap tanks to repurpose for firepits. When the occasional 1,000 gets scrapped, they're cut in half lengthwise and turned into giant BBQ's for events.

All this being said, for tanks that will be rehabbed, we run them down to empty, hook them up to a special vaccuum pump (that also runs the exhaust through an orange scented chemical to reduce the mercaptan smell) for a 15min cycle. They then sit overnight and are tested again in the morning for vacuum. If it's still holding, it's straight into an industrial sandblasting cabinet. Steel shot strips 30 years of rust and paint off in a 4-1/2 minute cycle.
They get removed and primed immediately.
Tanks that don't have vacuum either have a bad valve or gauge (which gets fixed) , or they still had residual gas which vaporized and built pressure. Either way, they get put on the pump for a second round and then into the blaster if they pass the test.

Tanks that are getting cut get emptied to no pressure, all valves/gauges/vents are removed and replaced with pipe plugs (sans one).
Tank is then filled to capacity with water (and a splash of dish soap added) until 100% water filled. Tank is then fully drained, all plugs removed, and then inverted and left to sit (propane vapor sinks). After a minimum 24hrs of rest/open air vent, they're tossed on a bench and cut with a plasma torch.

We've never had an issue with this system.
When I take a tank home for myself to use, I forego the vacuum steps and the water alltogether, but I do remove all valves and let them sit for several days (usually 1week or more) inverted with all the valves and plugs removed to vent. I've never even been able to get a "pffft" of energy holding a lighter in an empty bung after this.

Propane boils at -42F
It vaporizes quickly, and doesn't seem to leave a residual in the pores of the steel.

The real key is either use water to displace where any gas can reside (the propane vapor is lighter than water and is therefore forced out the top when the tank is filled with water).
Otherwise, the goal is to open any low spots so the propane vapor (heavier than air) will vent out the bottom of the tank.

Combining both is just extra safe behavior.

For what it's worth, I'd cut open a propane tank with a torch that was never filled with water and never put under vacuum (just left venting, all valves removed) before I'd cut open a used diesel tank that was BOTH filled with water then left to vent. M And I'd surely never use an electric power tool to cut open a tank that is filled with water!

Again, this is not advice. Proceed at your own risk, and all that other safety advice!

This makes me feel more comfortable doing it myself. Unless I can find a welder in my area to do it cheaply (less than $100) I'm probably going to flip it upside down for a week and let the propane drain out. Then I'll fill with water to make the initial cuts. Once the initial cuts are made and air is flowing freely into the tank, it's safe to weld on, correct? Thanks!

 

[Lassen Forge]

The thing they would never weld near was ammonia leaks from the coolers. Any oil of any kind in an ammonia environment can become extremely explosive.

Ammonia is one of those gasses that have both a very high and low LEL/UEL (15% to 28%) so if the concentration is too high it's perfectly inert (corrosice as ****, but fairly safe) and won't burn or blow, but once in air it begins to disperse, and it will DROP into it's UEL and boom. There is a safety video taken from a fire at a refrigeration plant where 2 firefighters went in to plug a leak... rather famous in Hazmat and Firefighting circles. He is horribly scarred, his lieutenant who was with him didn't make it - their level A suits melted on them (covering both in a wonderfully impermeable molten plastic hell) when the ammonia cloud turned into a fireball... that they were in the middle of. (The other problem is it will kill off your sense of smell, so you won't notice that the ammonia percentage is going up and up and up, and then go down and down and pow....)

I don't mind a lot of hazmats even really nasty horrible "methyl-ethyl-Di-4-Sureandall" stuff (because you can suit up with air and be safe), but industrial ammonia leaks and spills makes my **** pucker because it's so effing dangerous.

 

[Metal-Marc]

I have a decommissioned 250 gallon propane tank I'm planning to cut into to make a Texas-style offset BBQ smoker.

The real question is how many full cows are you planning on smoking with that thing?

 

[58Yeoman]

The real question is how many full cows are you planning on smoking with that thing?

Best reply yet.

 

[HoosierBuddy]

The best thing I've found for mercaptan odor removal is the scented bio-spray that has mercaptan ingesting bacteria in it. The bacteria will eat about any petrochemical including mercaptan.

However, as noted above, mercaptan is highly flammable itself. It has to be, or you'd smell it coming out of your gas burners, right?

So, in minute quantities, it can be flashed off a surface with a gas torch. This might be useful after you cut the tank apart.

 

[Junker]

I have a decommissioned 250 gallon propane tank I'm planning to cut into to make a Texas-style offset BBQ smoker. I have read lots of forums on methods to do it safely, and it seems the only 100% fool proof method is to use a gas detector/monitor. My plan is to fill the tank with soapy water several times until the gas detector reads zero. That leads to my question for those who have cut into an empty propane tank using a gas detector/monitor:

Which monitor/detector did you use? How did you do it? Since propane is heavier than air, did you need to drop the monitor into the bottom of the tank?

Instead of buying a detector you'll use once why not cut it while it's full of water?

 

[Kid B]

The real question is how many full cows are you planning on smoking with that thing?

That's a great question! I plan to cook food from land, air, and sea with this thing. However, more times than not, if you you see smoke coming out of the smoke stack there will be at least 1 brisket inside.

 

[Bad Habit]