Drilling and brazing a fuel tank

Steam clean, if possible. Just a little vapor can cause a lot of trouble. Old-timers would work on one if it was filled with water first. Inert gas is a good idea, but how can you tell if it's full enough? With water, there's no doubt.

Stan

You're probably safe if it's been empty for a while & the air purged out. Still the argon or CO2 wouldn't hurt :)

On steel tanks fittings tend to be soldered rather than brazed, getting thin sheet metal hot enough to braze but not to cause any number of problems you don't want is a bit of an art.

H.

Once upon a time I believe it was SOP to rinse the tank out with carbon tetrachloride prior to welding.

Most people nowadays seem to just say "don't do it".

If it were me, I think I would try drilling and cleaning by hand and soldering with one of those huge electric irons. No flames, no sparks. ____________________________________________________________________ Gardner Buchanan gbuchana(a)teksavvy(dot)com FreeBSD: Where you want to go. Today.

I have heard that the gas tank repair places fill it with water, weld it and then dump it out to dry.

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I have a 22 gallon (or so) fuel tank that originally had gasoline in it.

I want to use it for diesel.

I would like to drill it and install a through-hull fitting, which would be for the fuel return line. Ideally, I would like to braze the fitting in place also.

My question is how do I drill it and braze, so that it would not explode.

The tank has not had gasoline in it for a couple of weeks.

Today, I recently set it up with the fuel cap open, turned it over so that the fuel fill hole pionts down, and set it out so that it would becmoe quite hot under the sun.

Would it be correct to assume that after a few days I could purge it with compressed air, and then drill and braze it, without exploding?

Would purging with argon be a good idea?

i

My experience has been good with washing it out with hot soapy water, then discharging a CO2 extinguisher into the tank to displace all air and vapours.

Argon would likely work too - it is denser than air at 1.78+ g/l compared to air at something close to 1.25 g/l at atmospheric pressure

- not as heavy as CO2 at 1.96.

(a)teksavvy(dot)com

D: Where you want to go. Today.

I once worked in a gas station, across the alley from an old body man who every day would solder up old gas tanks, and radiators. My boss biggest regret was that he did not invent prohibition, himself. One night, a couple of guys spent all night getting their race car ready for the weekend. They had a case of beer with them. they realized the owner was about to arrive, so they panicked and threw the case of beer onto the roof of the shop behind us. Everything was OK. It was a HOT August day, sweltering. Al, who was about to solder up a gas tank, had been told that his heart was so weak, that he had HOURS left to live, and that was a couple years before. Al was sweltering in the back, about the solder up the gas tank, just before noon.. Ka-BOOM !!!!! Suddenly, the skylight above Al gave way, and the case of beer fell right at Al's feet. It had been up there all morning.... And let go just as Al was about to solder up the tank.... We will never know How that failed to kill him on the spot...

Nobody admitted to what they did. Everybody else was totally mystified, had no idea how a case of beer fell from the sky. Someone suggested Al might have prayed for a nice cool beer on such a hot day...

Al used a Big soldering copper on the tanks and radiators. Like an electric iron, but gas heated, and no flames or sparks near the work itself.

When I was younger, well still barely a teenager.. A welder told me to fill a gas tank to the very top, don't leave room for another drop. Wrap a wet rag around the filler to absorb / catch any fumes.. and weld away. I did that, and successfully used a big old stick welder on a thin sheet metal gas tank. He told me it was suicide to weld an empty tank, but absolutely full, no problem..

Filling an old tank with water is NO guarantee you will not have a problem - and if you do, all the water is forced out the filler at once, under high pressure. Had a friend tried welding the tank for his

53? ford that way - and he caught the tank in the chest as it emptied itself, forcefully, against the shop wall where he had it stood up. He ended up flat on his back on the driveway - quite sore. Not sure if it was just steam, or if some gasoline vapour managed to ignite - but it appeared to be significantly more powerfull than you would expect of steam, given the amount of heat involved and the short time the torch had been applied. He was just trying to solder or braze a pinholed area (rusted) on the end of the tank, which was pointed up.

You can't get the tank hot enough to solder or braze when it is TOTALLY full of water, so there had to be enough "air space" to either trap steam or gasoline vapour.

I'm betting on gasoline trapped in the rust scale at the weak spot in the tank.

I know a lot of old mechanics who would run exhaust through a tank for half an hour before attempting to solder, braze, or weld on it.,

With inert gas fill, you can weld at the BOTTOM of the tank, where you KNOW it is full of (particularly) CO2. Plug the hole as much as possible to keep all the CO2 from draining out before you finish the job.

I've repaired oil pans while still on the engine using this method - any other method is foolhardy (on oil pans)

CO2 is the cheapest purge gas. You could mostly fill the tank with water and then purge the remaining headspace with CO2 gas or get some dry ice and toss it into the tank and let most of it sublime then start heating. To remove 95% of the air you need three tank volumes of gas, assuming the exhaust line is long and skinny to keep air from back-diffusing into the tank. Without water, 22 gal is 82.5 L so 3x is 247 L. If you have a flowmeter on your MIG CO2 tank you can crank the flow up and calculate how long to wait. You will get roughly 1000-fold expansion from the dry ice so

247 L/1000= 0.25 L of dry ice. Winging the density that would be about 500 g or 1.1 lbs, so get two or three pounds and wait until 2/3 or 3/4 has sublimed then fire up the torch. Again, you want the exhaust line to be long and skinny, not just the fill neck :-).

I have a 22 gallon (or so) fuel tank that originally had gasoline in it.

I want to use it for diesel.

I would like to drill it and install a through-hull fitting, which would be for the fuel return line. Ideally, I would like to braze the fitting in place also.

My question is how do I drill it and braze, so that it would not explode.

The tank has not had gasoline in it for a couple of weeks.

Today, I recently set it up with the fuel cap open, turned it over so that the fuel fill hole pionts down, and set it out so that it would becmoe quite hot under the sun.

Would it be correct to assume that after a few days I could purge it with compressed air, and then drill and braze it, without exploding?

Would purging with argon be a good idea?

i

A long time ago, I took a course in Vacuum Tube Technology. I figured it would a last chance to learn about vacuum tubes. The course was taught by Renee Rogers who worked at Varian. And had nothing to do with ordinary vacuum tubes.

Klystrons, BWO's, TWT's, multigun CRT's, Yes. Triodes No.

But what I really learned was how Renee figured out what was causing production problems. You have a hypothesis and then you put numbers on it and see if it still could be true.

So how much gasoline vapor do you think could be in the tank. The equivalent of a drop of gasoline? Two drops of gasoline? Can you smell any gasoline fumes?

Then how much energy is in say two drops of gasoline? if it was combined with the optimum amount of air, how much energy would there be. Then if it were combined with 22 gallons of air? The flammability limits for 100 octane gasoline is 1.4 % at the lower limit and 7.6 % at the upper limit ( per Wiki ).

I have not done the math, but my guess is that you have no problem.

Dan

3X purge is not required with CO2 because CO2 is so much heavier than air. Put it in at the bottom of the tank and it will displace all air and vapour as it fills. 20% more than tank capacity is all that is really required - but I always play it safe and add a bit more part way through the job - particularly when brazing oil pans.

And a long and skinny exhaust is NOT required if the filler kneck is located at the top when filling/welding.

In order to get enough CO from the exhaust of either of my cars you'd need to run it a LONG time. Less than .03 parts per million CO on the one car, and less than .003 parts per million on the other. And CO isn't the best purge gas anyway.

Thankfully the concentration of CO2 in engine exhaust is quite high, and O2 content extremely low - so engine exhaust works reasonably well. Has the advantage of being HOT so it boils out any gasoline absorbed into rust scale etc, and trapped in pinch seams etc..

For gas tanks I generally either soldered or brazed repairs and fuel fittings

Thanks, Clare. I wanted to be sure that any error was on the side of safety, just like I would if I were the one holding the torch :-).

3X purge is not required with CO2 because CO2 is so much heavier than air. Put it in at the bottom of the tank and it will displace all air and vapour as it fills. 20% more than tank capacity is all that is really required - but I always play it safe and add a bit more part way through the job - particularly when brazing oil pans.

And a long and skinny exhaust is NOT required if the filler kneck is located at the top when filling/welding.

In fact, there are muffle-type heat-treating furnaces that use CO for fuel. It doesn't sound like something I'd fool with.

That sounds better. d8-)

My guess is you are PROBABLY right - but would I bet my life on it? Nope. There could be several times more gas than you calculated for, and when that gas evaporated out of the rust/scale holding it in the tank it could stratify, producing a pretty lethal 14:1 type mix at exactly the wrong place - producing a fairly serious whollop.

Remember, gasoline containd THREE TIMES the energy per unit of mass as compared to TNT. (or close enough for our discussion)

I sense a little bit of B/S and scare talk here.

I think that people whose tanks exploded, did nothing to purge them, had liquids in them, and got punished.

In my case, the tank is completely free of liquids (which dried out days ago) and the only thing that it has is vapors, if any.

If, say, it has an incredible high concentration of fuel vapors, then, purging the tank by something like 10x the volume of air (from a home vacuum cleaner or compressor for a few minutes), would leave, more or less, nothing as far as vapors are concerned.

The volume of the tank is less than 4 CF, and running my 15 CFM compressor for just 5 minutes, would provide about 20 times the volume of air in the tank.

i

Go ahead and blow your fool head off.

You're probably right. But, I'd use the suspenders and belt approach. No fuel plus no O2 = double safe.

A garden hose from your car exhaust to the tank only take a couple minutes.

Karl

Ignoramus24437 fired this volley in news:LdqdncFn8r5SKYbTnZ2dnUVZ snipped-for-privacy@giganews.com:

Maybe more mis-information than BS.

Gasoline tanks are repaired or modified commercially every day, with complete safety.

Empty, wash, dry, bake out, and purge with an inert substance.

If you can't smell the gasoline, there's not enough present to form an explosive mixture.

LLoyd

Actualy the common danger of oxyacetylene welding or cutting on a tank is the potential for accumulating explosive mixtures from the torch itself. People have blown them selves up cutting on tanks that never contained any flammable material.

-jim