LP Tank Converstion

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.
Status
Not open for further replies.

bryankloos

Member
Oct 31, 2013
132
Weston, CT
Hey Guys,

Are there any good links to building storage from discarded LP tanks.
What types of modifications are needed?
What welding skills are necessary?

I'm interested in learning about the process.

Thanks,

Bryan
 
Might not have to do anything to them - depends what they have for existing tappings, and if that will meet your needs. There's some pics in my install thread. If you do want to add tappings, get it done by a pro welder - my advice from my experience.
 
Not to hijack, but is it possible to just drill and tap threads into the side of a tank, as opposed to welding?
If you're careful it can be done with 1/8" pipe, it helps if you don't tap quite all the way through. Wall thickness is only about 0.250" to 0.300", so larger pipe would pretty much out of the question even if you could make a hole the right size, and even if you could find an affordable tap.
 
Last edited:
  • Like
Reactions: Coal Reaper
i wouldnt trust just threaded fittings, tapped into the tank. with the tank on a trailer, holes bored into tank, surface prepped and taken to a welding shop the expense would be pretty minimal, imo. that thick of stee is hell on a hole saw, not to mention in order to tap you need pretty tight tolerance on your initial hole.
 
Also, from experience - don't make more holes than the tank already has unless you really need to.

Some like to have lots of holes for drains & fills on each end, lots of temp & aquastat wells, supplies & returns on each end, etc. etc.. My tanks have only one supply fitting on top, and one return fitting on bottom. They're on opposite ends, but if you have existing holes on the same ends you might be able to make those work with a diptube or the such to get the water going the way you want. I also have a small fitting for bottom drain on one end, another for top fill/vent on the other. But you might be able to do those with T's off the supply/return fitting. And temp guages & aquastats can be strapped on or mounted on the surfaces of pipes & the tank itself.
 
I understand the need for decent welds, as the device is under pressure... That said, I assume with 12psi in the hydronic system and more for thermal expansion these tanks wouldn't see much more than 30-35psi??? With a decent tig weld I would think any fitting would be good to go. Then again with 500 gallons of hot water inside maybe the pro weld would be worth the peace of mind.
 
They shouldn't see any more than what your boiler would see - which is governed by its relief valve. Mine is around 22psi.

A pro did mine, and even then he had to come to my house to fix up a couple of leaks that showed when I pressure tested them when I got them back home. That was due mainly to the supply place I got my fittings at having cast fittings in the same bins with non-cast ones, and the leaks were at welds that looked great - certainly a ton better than I could do. I think if I had done the welding myself, I would have had a LOT more leaks show up & to deal with. And not as much peace of mind.
 
google thread-o-lets
 
IMHO- welding storage tanks should be done by a qualified welder for P.O.M. prepping tank and tacking fittings in place saves much time for the welder. to weld a few fittings does not take too much time.

not that one could not learn to weld, I just think practicing is best on other projects like exhaust, furniture, body panels and smokers.

Having watched many a certified welder grind and fix welds that did not pass inspection for structural components grumbling all the way. not too many will like to repair others work with out grinding off and starting over.
 
Our tanks are set vertically to save floor space and better stratification in our boiler barn. I was going to use Thread-o-lets, in fact bought them. But decided that since I was going to spray 4" of foam on everything I didn't want any threaded joints under the foam. So bought (I think) 12" long 1 1/2" nipples cut them in half and welded the ~6" one end threaded nipple to the tank in 5 locations (one in the middle to help even the temp between the two tanks). This gave me ~2" of male threads outside the surface of the 4" thick foam. My welder is VERY good and the joints were Mig'd, not Tig'd. I bought a set of 1 1/2" caps for all the nipples for leak/pressure tests. We leak checked with I think ~50 psi and soapy water and found quite a few small leaks which he patched/repaired. Even very good welders may get leaks in their welds and it's a must to check before foaming. My vent on the very top is an 1/8" NPT directly into the dome material. We welded the very bottom nipple as close to the bottom as possible so my bottom manifold will have a drain except as part of the bottom manifold. No tapped holes on the very bottom just the welded long nipple which will be the return to boiler manifold on our two vertical storage tanks.

I did the weld length calcs for myself and another guy here asking about safe weld lengths for legs (and got criticized as "showing off"). I used four 3"x3"x 1/4" angles vertically welded to the tank as legs and provided ~3" between the dome and floor. Rarely can we give bad free advice here that could get someone killed but in the case of supporting +5000 lbs of storage tank and water the welds on the legs are actually the most important. A leak won't kill you, but a failed leg weld could on vertical tanks. Search for welds or legs to find that old thread or PM me and I can provide the length of weld with a big safety factor if you go vertical since I welded the legs to the barrel side of the tank, not the dome.

Buy one set of caps and leak test each tank before they leave the weld shop and especially before foaming. Best wishes.
 
It's not so much having a lot of ports, but large diameter ports in the correct locations. I'd use at least 1-1/2 maybe 2", to allow for passive circulation. A port at the very top and bottom allows for an air vent and a fast drain, use 3/4" for those. Two ports for boiler input, maybe two at the other end for loads, gives you a buffer and hydro separator and air and dirt separation.

I think this conceptual drawing, from Siggy has some ideal hydraulics. VS pump provides return temperature protection, and properly piped I think it would thermosiphon for power outage, overheat protection.

The pumps present much less pressure drop compared to a 3 way thermostatic valve and should allow passive circulation for no power conditions. There are a ton of inexpensive pump choices and virtually all can be speed controlled with PWM or a simple inexpensive "wave chopper" control, some pumps have the functions built in or a solar controller is a good option.
 

Attachments

  • Screen shot 2014-01-30 at 9.44.25 AM.png
    Screen shot 2014-01-30 at 9.44.25 AM.png
    9.6 KB · Views: 153
With a decent tig weld I would think any fitting would be good to go.

would tig do the job. usually done via stick with a root pass and cover pass using differant rod.
 
I would highly recommend welding all taps, plus adding lift hooks,plates, etc.
I would goto boiler buddy site or any buffer tank site and copy exactly what they have. Even if you do all the prep and work less welding and hire that part, you will end up with a job well done. Goto the welding forums and look up guys in your area with ASME qualifications. You might be surprised at what you find. I have an ASME pressure vessel friend now because of exactly this, 2 miles away with shop. It started with fuel cells, suspension parts, etc. but although I have a tig and mig welder, I am not setup for Ti or purge welding, and my aluminum isn't good enough for structure and pressure all the time.

I bet it would cost less than $200 to weld up 4- 2" taps , drain/dirt flush cock and 3-4 temp wells. I did an old used superstore 40 gallon into a buffer tank for $80. Did 4 inch and a half sch80 threaded stubs. The large taps or ports help maintain strat, too small and even a 007 will stir up the strat layers. 1" inch is too small if strat is very important. Think Bernoulli
 
Status
Not open for further replies.