Hafta cut and weld my gas tank.. suggestions?

Hey folks.

For several reasons, I have to cut open and weld on an MJ gas tank.

It's been empty for months and months (5-6) and been sitting outside this entire time. It doesn't have any smell of gas to it but I am still nervous.. it's a gas tank.

In order to make this as safe as possible I was thinking of the following:

1) Wash the tank as much as possible with some nice hot soapy water.
2) Rinse the tank.
3) Leave it wet and then set up a CO2 tank to a smallish hose and continually blow a stream of CO2 gas into it while I cut one end off with a sawzall. I imagine from there I can wash the inside by hand and safely be asured of welding and cutting freely.

Thoughts?

Yes.. yes.. I know.. is possibly blowing myself up really worth the risk of spending the $250 on a new tank? Well... yes. In this case, it is.

i don't know the best way to clean it, but after you clean it, I would come up with some way to safely toss a match in it. before you cut or weld on it with your body real close, you want to be SURE it's not going to blow.

fuel cell

The tank should be purged. fill it up with something non flammable and under pressure, Also seen it done using water, shove the hose in the filler neck and let it fill for a while. you want it to overfill and flush the tank of all flammable gases

try this:
go down to the welding supply/gas supply and get yourself some dry ice chunks and shove them into the tank. the more the better.
be careful with the dry ice because it can burn you.
the evaporation from the dry ice will displace fumes (again make sure you have removed all fuel and let the tank sit for a day or two (open) to let it evap.
this may be overkill but i love fire not explosions...wait yes i do love explosions...anyway...
cut the tank open according to your design. i use a zip wheel for this. (i have coppped and channeled a few gas tanks for some of the tubbed camaros out here) a sawzall might work but fit-up is critical to welding a gas tank back together.
i TIG (GTAW for all the new timers and heliarc for the ol'timers) in a kinda stitch weld manner to minimize heat input and warpage (warping?). i can't recommend MIG (GMAW...) because: 1) its just too messy. 2) to much of a chance for pinholes. 3) i don't have a MIG machine at home yet
remember lots of tacks is/are your friend(s).
after reading this i noticed that i said to fill the tank with the dry ice...i dont know for sure if its necessary to fill it before cutting into it, but thats what i do just for the extra measure of safety (probably not needed), but remember that the ice is in there cause it can be quite a mess on the garage floor if you forget its in there (DOH!)
also remember being clean is the welders best friend (contrary to popular belief?) so take your time and make sure everything is extra clean.
i hope that covers it...if not please chime in.

disclaimer: just becase i do it this way deosn't mean its the correct or best way to do it. IMHO
nim

Cut it open and then weld on it.

empty for 5-6 months????????

Once it is cut, wash it out again.

You will leave the pump out, ie have a open hole, when you are welding, right?????

Best case, have a buddy weld it for you!


hinkley

Not that this will help, but, gasoline doesn't burn. The fumes do.

Mark Hinkley said:

Best case, have a buddy weld it for you!


hinkley

Click to expand...

Not a particularly good buddy, though.
:firedevil

Actually, I would be more concerned with the weld sealing. It's not easy getting an air tight weld without using stick and I'm sure a gas tank skin would be too thin to try to stick weld it.
TIG would be the best bet but that will be a long process for a whole gas tank.

To y'all:

Thanks.

1) I like the dry ice idea.

2) Fuel cell is lame. The goal in this exercise is to expand capacity and repair some holes. .

3) I think I have a friend dumb enough for the match idea.. no.. wait.. I am that friend usually.. crap.

4) Yes, 4-5 MONTHS (as in, half a year). Hmm. come to think of it, it's been empty since April or May.

5) Yes, the pump will be out.. but it has to be CUT out.

So.. uhh.. yeah.. if I am never heard from again, you'll all know how it went!

yeah, I would worry about the seal more than the explosion....
good luck.

i just remebered something about the gas tank operations...
you can get or make some fittings to plug the filler hole (and any return line etc...). make the fittings with a "shraeder" valve so you can pressurize the tank after welding and then put a pressure guage on the valve and get some soap bubbles on the welds to see if any air is seeping out.
1) the bubbles will find the big leaks
2) the guage will show slow leaks which may take a few hours to show up.
oh yeah the fittings i use are these nifty science rubber stoppers and boat drain plugs...
i just used soap bubbles and no guages, as the guage idea comes from work where we make clystron tubes (kind of a capacitor for MRI machines?)
and yeah the dry ice idea was given to me by a friend...the co2 displaces fumes (and it looks cool bubbling out, like halloween).
of course i must again state that i am the village idiot and cannot condone cutting and welding on any vessels where the contents can combust and cause serious injury, sickness, or death.
also go to google and do a search on "gas tank fabrication" and see what comes up.
Nim
BTW TIG on a camaro tank which i would guess at about 15 gal or more...cutting tacking prep and welding usually takes me about 2 to 4 hours. testing for leaks takes a bit more time. also gas itself isnt very flammable but when mixed with oxygen it is...oxygen is a catalyst for all substances to burn...

Well.. I didn't blow up. But I also decided not to futz with this tank. It was just too holey and crappy. I am just going to go down to the sheet metal guy down the street and get some metal and fab up a nice simple box. I am not terribly concerned about leakage. I have a torch and 50lbs of lead. mmmmmm.. lead.

As for the CO2. I don't belive you would use the CO2 to displace the fumes so much, though that could work too. You would use the CO2 because it absorbs the oxygen. Which is why it works so well in fire extinguishers.