Welding Propane Tanks [Be Carefull!!]

My experance with welding these tanks [I,m still alive] I have welded all my life but I should have checked into this I guess. I got an old propane tank,was around 85 to 100 Gal. short fat one, I took gauge and top valve out looked inside was empty, still smelled bad. I let it air out for 2 weeks, heck I thought all was well? I was getting ready to weld on some other thibgs and was grinding about 20 feet from tank when some sparks went into tank,and WOW I had on ear gards for noise on and cant here good anyways but even with that on I heard this, a 2 foot blue flame shot out top of tank for about 10 seconds I ran across yard and stood there shaking, I could not believe what just happen and how lucky I was it did not blow up. I dont understand how this hapened when I had it air out so long and looked inside seen nothing??
Anyways, all you who are about to weld on these be carefull

that's why they should be filled with water to remove the propane before welding. The water is heavier than the propane and will force any propane out the top.

Holy Crap.... Glad you made it alive....

I was advise to let the tank air out with the opening toward the bottown at first (propane heavier than air, Propane must have been trap in our case)
Then do the same as mention fill with water with the opening on Top.
Tilt the tank so the area to be welded on is full of water, Buy some bigger fitting than needed & weld it to tank... but cut out the hole with a holesaw after the fitting is finish welding.
Play it safe & do more research....

Hope this help someone stay alive,

Thanks for sharing your experience

I dont think you can weld it full of water. You will get a cold weld. Not much penatration. Someone can correct me if I'm mistaken.

If you have an opening of any decent size the tank will not blow up, it might scare the hell out of you though. I wouldn't try to weld it full of water because of probable poor weld penetration. Hook up some sort of blower with a good static pressure & move the fumes out of the tank when welding it. Maybe you can partly fill it with water ? Randy

I routinely test large tanks with an O2/LEL meter (lower explosive limit) before entry and any work such as welding on. It makes me nervous hearing about what backyard mechanics have to do in order to get the the job done. Any tank should be cleaned enough so it can not generate any vapors while any hot work is being done. Filling with water will force out any explosive vapors but you can't weld against something filled with water as the weld cools too quickly and can crack. A partially filled tank would seem to minimize the amount of potential vapors. I like to see any holes cut first as a cold cut, i.e, hole saw and then welded. Any heat on a on a tank can cause a big surprise. Thoroughly purge the tank with a blower/air compressor line for a good long time and keep it going while welding. Without a LEL meter you can never know for sure what is safe but with good preparation you can minimize the risk. Letting a tank sit with no forced ventilation, not cleaning it, and "just looking inside" is asking for trouble as ozzie88 found out.

the low down on welding tanks water should be used any time it can be.... it should be 5 to 7 inches from the weld no more no less
beware if you use a fan or compress air you may wash the gas /argon away if you are mig welding leaving pin hole welds and will leak for sure
i have welded dozens of tanks over the years ...oil...diesel ...propane..hydraulic and gas .....yes gas...and am some how still here
that's my two cents Brent

if you can stand outside [not crawl in] Just remove one leg of the fire triangle. in most cases an inert gas [CO2 is easy] can be added to the tank while welding.

Thanks Brent for the added info on the water level, I've did notice that the mig was leaving pin holes, Stick was the way to go.

Ventilate the tank with forced compressed air and the fill it with argon has been what I typically do. Propane is heavier is than Argon, thus the compressed air flushing first.

Purging and inerting will work but the one problem is that without actually measuring for explosive vapors and/or O2 content is that you just never really know what your up against. I have welded on an enclosed space with fuel inside but it was flooded with CO2 and constantly monitored for vapors. Even partially filling with water would be no guarantee in my line of work. Anyone attempting this kind of work should be extremely cautious.

Its not that difficult for these tanks. I've done my own. Washed them out and all that. Just flash them off first. What i mean by that is fire yes fire. Wash them out thoroughly first then flash them with torch. Sounds scary. Well it is for your first time but if theres anything left it will just burn off. Not explode. Cannot explode with hole in it. Just burn off vapors thats it. And yes i've done it. Still here.

Good to hear your not hurt Ozz. Thanks for sharing. We all have to keep in mind just how fragile life is. I have had a few close calls myself over the years. Makes you really think. Stay safe! Have a good heating season. It is coming quick.

I am not an expert.

I let my tank vent for a month (the positive side of procrastination). I put a ball valve on the bottom hole. I filled mine clear to the top and used a hole saw to cut the 2 5/6" holes need for 2" pipe to just barely slide through. I drained it all and refilled it to overflowing. I let out about 6". My brother (outstanding welder) struck an arc at one of the holes. Not so much as a hint of a flame. Slid the pies to the level I wanted and stick welded. It would seem that the system works well (burning for one month). I put my supply to boiler about 4" from bottom, my return from boiler about 2" from top, my hot to house directly at the top and my return from house about 16" from bottom.

Bill

I think the idea with using water is to fill the tank completely with water, then dump/purge the water out. This way you know the water will have displaced all the propane. If you are concerned that the atmosphere the replaces the water may be explosive - push the water out with CO2. I do this all the time with beer kegs although not for welding reasons. Fill keg with water, push water with CO2, when no more water comes out the vessel is known to be full of CO2 as well as being under positive pressure so once opened CO2 will shoot out instead of sucking air (containing O2) in.

We should all be aware that supposedly the pores of the steel can still hold propane after they have been rinsed several times or so I've been told. I couldn't find any local welding shops that would touch my already rinsed tanks. Now that they have sat vented for another year, I think I may fill them with water and cut some holes with a holes saw (2 5/16 to slip a 2" pipe into). I always thought the fittings needed to be cut thru the very ends of the bells of the tank, but now I'm wondering if the holes could all be made on the top side of the tank (normal horizontal position) then welded is place after draining 6" or so of water. Granted the water wouldn't enter or exit at the very top or very bottom but I don't think that would matter all that much. A benefit of this also would be less mixing since the water would enter from the side rather than the top. One would still need a way to bleed the air out of the top of the bell (when mounted vertical as a storage tank) but I believe the thickness of the bell is enough that a 1/4 or 3/8" hole could be drilled and tapped without the need to weld a fitting. Anyone have any thoughts on this? If this is not viable I may have to see if an actual tank place would weld mine but since the tanks are scrap I'm betting they won't touch them for that reason.

Petroleum products, sure, but significant volumes of propane gas escaping from pores in steel?

Even so, propane is heavy and venting for a year doesn't necessarily mean all the propane is gone. It's just a matter of flowing air though the tank in a way that guarantees any combustibles are diluted to non-explosive levels, no water filling required if properly vented with sustained flows of fresh air that will displace any remaining propane.

[I assume you're talking about vertical tanks.] You can weld half-couplings to the ends of the bells and cut the holes afterwards with a good hole saw. I plumbed the completed manifolds to the couplings and tacked the couplings in place and then got the manifolds out to the way before the final welds, which I suspect saved some grief fitting the manifolds to the tanks after they were in place. I used diffusers to cut down on jetting from vertical ports, but I think it was a waste of time. The flow rates are pretty low, and even if there's a layer of mixed water who cares.

However although I built the shed to fit the tanks, space above an below the tanks was crowded enough without the plumbing. If I had to do it over again I'd figure out some way to come in from the side. Some guys have been using short angled risers and dip tube to reach the top and bottom of the tanks from the side.

The closer to the ends the better, but no sense chasing the last five gallons if it makes things easier to let it go.

Tank should be plenty thick enough for 1/8" pipe, just make sure you have the right size drill bit and then tap carefully. A little Permatex and you're good to go.

Had everything cleaned up and tacked in place and called a few places that wouldn't do the final welding. But this one guy that ran a bona fide boiler repair business told me to run shopvac air in the top, with exhaust from a diptube into the bottom of the tanks for a few hours before I brought them over and he went ahead and welded the couplings with the tanks on the trailer while I waited. Two passes of 6011.

Yeah, 1/8" would be plenty and I've got index set of bits, so I would just need a tap. The short angled riser is a good idea, but like we said not sure if the last 5 gallons matters that much. If I can find someone to come out like you did, maybe with the proper LEL/O2 tester that would be way to go. If not, think I will get a buddy that can weld bring his welder and just drain water 6" below the hole. We could even jack one end of the tank up 6" to keep the air pocket small when we weld on that end. I think that would be about as safe as you can get. Did you just use black iron couplers cut in half? I would like to find some big truck rims to weld to the bottom for stands too.

Sounds good. If you're using short couplings then like I said you can hole-saw the holes afterwards, so you're not doing any sparking inside the tank to begin with. Plus it makes it easy to pressure test the welds with 100 psig or more of air since you don't have to fill the tank, just the coupling.

You can get what's called a half-coupling, or you can save a little and cut a regular coupling in half. For couplings need forged steel, not cast iron, you can look them up online from Grainger, McMaster-Carr, or some such if not available locally. Some guys have used half-nipples with success.

You mention side-arm DHW in your sig. Now would be the time to switch to a tankless coil in the top of one of the storage tanks if you storage will be anywhere close to where DHW is needed. Just need to add tankless coil port to the tank when you're doing the other welding.

Are there coils you can put in the tank that are made of materials other than copper?

I have slightly aggressive DHW.

gg

I'm considering TIG welding a bung into my aluminum 30 Lb propane tank for insertion of a liquid level gage. My thoughts are: (1) any tank that has ever had any petroleum in it will have an oily residue on it's surface that can be vaporized when heated and form an explosive mixture with oxygen, (2) the larger the internal volume and the smaller the holes leading to the atmosphere, the more potential exists for stronger explosion. I am thinking that if I remove the valve/s and flush the inside 3 or 4 rinses of gasoline, then dry the inside by flushing with CO2 or argon gas until dry, most of the oil surface residue will be removed. To weld, fill the tank with Argon, cut hole using hole saw, Vee the sides of the hole, and TIG weld using 4043 filler rod while feeding argon into the inside of the tank. Also possibly fill the tank to about 3/4 full with water. Please critique.

Can you plug everything, fill with oxygen-free gas, weld on a fixture, and drill the hole afterwards?

I believe the steel "holds" a bit of propane.

A few weeks ago I was torch cutting a trailer house frame for the I beams. They had propane heat and a bunch of black pipe to feed everything. It was all open to air and had been for 5-6 months. I just torch cut the pipes into pieces I could load into the truck. Couple sections turned into mini "rockets" doing the "whomp.... whoooooooshhhhhhhhh" for a min or two!

I had the same thing happen about a month ago when welding an exhaust on my diesel Jetta. I guess there was enough soot/fumes on the inside of the pipe that I had sort of a chimney fire going. I grabbed it and put it outside, had flames shooting out of the ends a good foot or so, again had that rocket noise. It burned for a few mins and got hot enough that it turned the pipe a dull red!

Last year I had to weld some fittings on a 275gal diesel tank, I just ended up filling it with water/degreaser/dish soap and draining it out a few times (mainly to clean all the crap out of it) and then went I cut and welded on it I had it filled as much as I could again with water. I wasn't exactly excited about it, knew two guys doing similar and the tank exploded. One of them died and the other lost his hearing, part of his face and an arm. It blew away the whole corner of the garage and part of the roof too!

Anyhow, it welded up just fine and no KABOOM!

Always fill the tank with water and rinse it out good. Then, AS you weld on it have an inert gas like Nitrogen or CO2 flowing into the tank.

Propane/LP/Butane vapors or heavier than air so if you simply take the valve off the top of the tank the vapor will remain in the tank for a very long time. Years.
Inverting the tank so the opening is on the bottom helps a little but only if you have a second opening for air to get in. LP tanks have to be purged no mater how long they have been "vented".

Someone was watching out for you..........

My horizontal tanks had openings in top & bottom when I got them. They had been open for quite a while before I brought them home. Once I got them laying in my yard, I rigged (duct taped) up a big funnel and shop vac hose into the top hole with the funnel pointing into the prevailing winds. Left like that for a couple weeks, had to move the funnel when the wind changed. There was a bit of a stink in the yard when that was going on. Before I did that though, just for kicks, I put some flame into the bottom holes with the help of a long stick. I was kind of disappointed with the lack of reaction - nothing. My welder also wasn't too worried about them. He just welded. I also pressure washed before he got them though.