Tank mounting crack

Ta.

needing said:

Hi comnoz.
Your assumptions are correct but your qualification of "Water with a little air trapped above it..." is disaster due to gravity and lack of risk assessment.

A tank filled with water and any conceivable air pocket not directly beneath the weld site is safer than a tank full of petrol. Welding with the water filled tank in a container of water further mitigatesthe consequences of possible explosion.

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Without an air pocket under the weld site, welding is not possible. Or maybe I should say welding with any chance of penetration is not possible if there is water in contact with the backside of the metal being welded. Water in the tank does not mitigate the chances of explosion. It just means the tank is likely to be sealed, which will make combustion very hazardous.

I would not suggest welding a tank full of gasoline either -not due to explosion risk but a fire would be a big risk.

Just to clarify, water is used on large tanks to reduce the volume so that the remaining smaller volume can be purged with inert gas.

Motorcycle tanks are small enough to purge easily with argon,CO2 or helium.

It's easy to purge with CO2, After washing the tank with soap and water, use dry ice and let it fume for a while in the tank with an opening at the top. The CO2 will fill the tank from the bottom and all the oxygen will rise to the top and be expelled through the opening. The it is safe to weld. Do not seal the tank when welding.

A sealed tank full of water with a small pocket of air to enable welding is not safe. The small pocket of air may contain fuel in a combustible mixture. It does not take much of an explosion in a closed container to rupture the tank rather violently. Jim

Ta.

needing said:

Hi Jim. I take the expert advice as you seem to some-one with actual experience in these matters. but but but
1. It seems at least Baz and I have successfully welded waterfilled tanks and lived to tell the tale. Did it, it worked.



2. Penetration on tank skin of says 1.2 / 1.5 mm never seemed to be an issue to me.

3. The fire cracker in the safe will not work if the firework is on the floor of the safe - only if it is in the dry airspace at the top. Did your teacher actually explode a safe of just describe it to you in conceptual form?



4. Further off topic, how does 'underwater' welding occur as water must form an effective heat sink in, around and over the metal being welded?



These are rhetorical - no need to answer, food for thought if you like.

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1.Wouldn't say it won't work, probably even most of the time. The rest of the time is the problem.

3. We watched a movie of a demonstration. It was a wax coated small firecracker pushed into a fitting in the top of a large water filled fire extinguisher bottle. There was a cap with a hole just large enough for the fuse. It split the whole side out of the bottle. He equated that to blowing a safe with a firecracker. Supposedly it can be done.

The control bottle that had no water in it just made a tiny pop with a little smoke that came out of the fuse hole. There was plenty of room for the gasses to expand.

4. I don't know anything about that. Jim

I once mig welded a new bottom skin onto my army trucks 27 gallon!!!! (english imperial not smaller US) petrol tank. It was a flat plate about 2 feet wide an 4 feet long an took hours to seem weld all the way round.
I first removed the tank from truck then removed all senders pumps (internal) and piping and left the tank outside to vent for 2 weeks!! by then no smell of petrol was left in tank so not danger of explosion.
So my advice to anybody trying to repair their feul tank at home is don't be in a rush an the longer the tank vents the safer it will be to work on.

The discussion here has been very helpful
Seems under the right (or wrong conditions) things can go pear shaped
Safety is the best option so while my tank has now vented for nearly 2 weeks the tank will be washed and soaked thoroughly for 4 hours in hot soapy water, drained and then purged with Argon as its welded. The petrol smell is faint but it is still there
The lowdown on pressure testing was an unexpected bonus as I could have literally overblown that task, blissfully unaware such a low pressure is needed to test for leaks at no more than 3-4 PSI
Thanks far all that, I will post some pictures as the respray project progresses which will be a first for me
The worst that can happen is sending it to the paint shop if things don't go as hoped

Jed

needing,

You know I thought he liked me until he gave me a 1954 Ferguson tractor that I flipped trying to pull stumps. Bounced me right off the seat then torqued itself over backwards.
Pete

I'm a little late to the party here, but I've watched Concours fix a Triumph tank for me using the drygas wash method and I watched another friend braze a split seam in a Triumph tank (never a Norton tank :shock: :lol: ) by water rinsing and then filling it with exhaust gas from another bike before putting the torch to it. Both times I tried to put something solid between me and the work cause it made me pretty nervous. They claim that if you're quick enough you can plunge a lit cigarette into a can of gasoline without it exploding because it's the fumes that are explosive and not the liquid. I'm not that quick so I guess I'll just take their word on it.

Always be alert to fuel ignition sources but I grantee you Can Not Light gasoline w/o a electric spark, open flame or red hot embers even with white cloud of boiled-steamed gasoling poured on glowing embers trying to get it to flame up while blowing on embers to send bright sparks off so I often as can toss a lig cig in puddle of gasoline to worry others. The heat of metal glowing red can ignite fuels of all sorts of course. I like the torch type crack repairs by braze or silver solder better than electric methods and if fails just redo again by torch but very unlikely as torch methods don't leave sheet metal as brittle to crack again and the fill material is more flexible than the sheet or hardened electric stick or wire filler. Muggy Weld has neat rods for various metals that usually don't need but propane torch.

Many ways not to blow up so real issue is getting the crack area cleaned so metal will bond and found phos acid and other pickle agents work a treat where grinder can reach and no need to wash off as similar ingredients as fluxes.

Deets55 said:

needing,

You know I thought he liked me until he gave me a 1954 Ferguson tractor that I flipped trying to pull stumps. Bounced me right off the seat then torqued itself over backwards.
Pete

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One nearly flipped on my wife doing the same thing but she jumped on the clutch just in time and wondered why the exhaust pipe hit her in the head
Not funny at the time (or I could not let her think so) but hilarious now!

Ta.

Cycles and tractors can all reare up on ya and too often even if de-clutching in time tractor may then roll/slide backwards jackknifing the impliment being towed to pinch-split metal and driver to death.

Don't forget uncovered PTO shafts and in my case direct drive from rear differential to PTO. Without an overrun "clutch" spinning brush hog will push tractor forward until blades stop rotating.
Sorry off topic................

I grew up on old tractors so know the bushhog flywheel back powering over runs in panics and not having long hair, necklaces or loose clothes around spining shafts with UV joint snagers. One of Peel machinists finishing up something leaned over lathe to reach something and raw end of shaft twisted his shirt up and almost him with it. He retired soon after with mild side effects but his body parts still intact. Wearing metal working around electrics is also taboo to me now. Short hair was required when I worked at Fla. State Mental Hosp and women not allowed out in common area w/o trimmed men back up. Funnest tractor to start was tricycle JD with hand spun flywheel ya tried to close compression release after first big POP and smoke ring out the stack. A thick layering of Casswell's Novalac sealer definitely reenforces against flex and banging fatigue.