Welding Petrol Tank

[Russ32]

There was some discussion about welding petrol tanks last year. I think the conclusion was it is too dangerous due to explosions. However, I dont think anyone suggested the idea of filling the tank with water so that there would be no vapour left in the tank to cause an explosion. I only need to weld a new filler pipe on so the tank could hold water while kept upright. Obviously I would need to make sure the water didn't boil over. Does anyone have any views on this method. Thanks.

[steve_w]

I modified the fuel tank on my last project to fit a larger feed pipe.
Very dangerous so much caution needed but if careful possible.

I drained the fuel tank, removed it from the car then left the cap off for a week to let the vapours Dissipate. Before cutting and welding I flushed the tank through with water. Sealed the outlet and stuck the hose pipe in the intake, left water running to flush out anything remaining for an hour.
Then drained tank and got the grinder and welder out.

Did the welding at the bottom of the garden and kept a fire extinguisher close to hand though.... just in case.

[wolselliac]

Use a detergent in the water to help wash the fuel which is stuck in the seams/joints, as just water will roll-off fuel much in the same way as it does off oil.

Another is to have a 2nd gas cylinder of either Argon or Carbon Dioxide filling the empty tank, remembering to keep it constantly trickling in , this will stop the oxygen getting back in, only you will have to do this outside as the concentration of CO2 or Argon (in a confined space) will leed you to pass-out!!!!!!!!!!!!!

Or, as others have suggested fill with water but put a pipe (from the Argon or CO2) and let it bubble up (helping to displace any air left in the tank). Remember to flush out this water mixed with CO2 as it will become acidic.

Can you not Solder the pipe to the tank, does it have to be welded?

Marek

[ross@rmrrestorations]

Read something similair on another forum I frequent and it was suggested to use dry ice.
It's available cheaply from fishmongers etc. With a little water in the tank the dry ice will displace most of the oxygen apparently.

[Russ32]

Thanks for your advice. I will try flushing out with detergent and stand by with a fire extinguisher. The tank is quite old and hasn't had any fuel in for many years. I thought welding the pipe on would be stronger as it is an external tank on a Model A body with the pipe sticking up to the side of the body. I'm also better at welding (i think) after years of practice, not sure about soldering.

[stevie.t]

if you get a pipe, vacum cleaner or simalar, put one end in the tank and one on the end of your exhaust pipe run your car for about 15 miniuts and then you can weld it, would'nt hurt to fill with water for xtra safty;)

[Dano C.h.C]

another method its to do all the cleaning and all that, then fill with sand, this takes all the space up, make sure your tank is fully dry before doing so, so it cant stick to anything, (used on motorcycle tanks and no problem,) sure way of finding out if there is a vapor trail and it may sound stupid!...fill the take with which ever method you pick, then ...put a match to the breather..any vapour you will find out..and it much better than blowing you head off...!

[Russ]

empty the tank blow it out till dry, get a hose from an exhaust pipe an stick it in the tank let it run for an hour or so, its now degassed and can be welded , done this loads of times now an never had a fire, fist time i did it i lit a rag on a stick an put it in the tank expecting it to blow but not even a fart,
Russ

[Petemate]

Agree all - care to be exercised. Many years ago, we were visiting the OH's relations up in Oldham, and the tank on our Vincent Shadow combination sprung a leak on the way (much fun collecting leaking fuel during the last 40 or so miles in a can with my left hand while keeping it going with my right hand on the throttle, then stopping every few miles to tip it back into the tank - oh happy days) one of her uncles welded it up. We took the tank off, emptied it, filled it with water, turned it upside down and out came his oxy-acetylene gear. A few harmless 'plops' of flame later and we had a nice welded-up seam. Granted, a small tank like that obviously would have far less vapour hanging about, but with a large tank it needs time for the fumes to go away.

[blobby]

My brother is a MOD approved welder,some years ago he told me how best to weld a tank,trouble was he told me after i filled mine with water,emptied it,then began to weld the filler neck,the explosion was heard from my garage by my other-half indoors.The way is as Russ wrote,conect a pipe from your exhaust,into the tank,run it to nullify the fumes.