Old fuel tanks

G

ghwallice

Hero member
Location
Ipswich
I've got 2 fuel tanks that haven't had petrol in them for about 20 years. I want to check them for leaks, and if there are any holes, braze them up. (Those epoxy kits are crap)

I used to flush the fuel out of tanks and braze them when I was young, but it was always a nerve wracking process.

Can anybody tell me what liquid I can use for this? I need something with the low viscosity of petrol (water doesn't work), that is non explosive, and not oily (so it doesn't cause the bronze to not stick).

And I'm not using my beer on it!

Regards, Greg
 
wdietz186 said:
Sounds like a job for alcohol or most any quick drying solvent.
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Ah, NO...NOT alcohol. Been there, still remember the ringing in my ears from the bang....and that was after a rinse with water too. Repairing a small stainless fuel tank from a speedway car where water or petrol wouldn't show the leaks.
Better to make up the gear to lightly pressurise them and use soapy water to show the leaks.
 
There isn't anything wrong with Caswells. Worked perfectly on my original tank after the torch kept blowing bigger holes where little ones were as the metal had corroded to tissue paper thin in parts.
 
After cleaning out a tank with a flammable substance - I run a car exhaust into it - it completely deadens any explosive fumes - done this for years and I'm still here to tell the tale! - Of course you do this at your own risk. - Regards - Phil
 
Petrol vapour is very heavy. We have welded many tanks after leaving them inverted either in the hot sun or something that will warm it but without an ignition source anywhere near. You can see the vapours pouring out of the tank and can in fact smell that there are none there. Inerting as Phil says is double insurance, you could use any inert gas (e.g. MIG) for this.
 
Phil is correct and this is what I have done many times in a race paddock (sidecars usually, and nearly vibration cracked alloy slab tanks) the reason it works is that some applied hot air (or exhaust gas) will evaporate all the liquid and then heat the metal to  finish it off and lose the vapour by replacement.
At home I use a hot air paint stripper, but always try and get an air line in there and blast at 100psi for a good couple of minutes

of course you can always be patient and turn the tank so the biggest hole (the filler usually) is at the bottom, leave it outside for a fortnight and all will be gone, still do the air line bit though. This works because petrol vapour is heavier than air, so "falls" out the hole.

The next thing to do before welding is have the tank aggressively sandblasted, that DEFINATELY finds the holes, and usually leads to surprises, braze up all the holes,  then air test in a water tank preferably, suing a drain test u tube and a small rubber bulb pump, this will shows leaks even with only a few inches of air pressure, and is actually better than (say) 30psi and soapy water which can have disappointing results in finding the holes, the air "pushing" the soapy water out of the way and then escaping unnoticed

and again do all this at your own risk
E&OE
etc etc
CLEM
 
This tank hasn't had petrol in it for about 20 years, and I want to avoid using an explosive liquid for leak testing before brazing if I can. I don't want to sand blast it at the moment. I'd like to leave that until respray time.

So reading all the feedback, it's looking like Clem's suggestion of very low air pressure and a water tank is the best option at the moment.

Any other ideas?

Regards, Greg
 
CLEMTOG said:
the reason it works is that some applied hot air (or exhaust gas) will evaporate all the liquid
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That may be true, but the main reason it works is that exhaust has very little free oxygen in it (it's mostly CO2 and water vapour), so any fuel that remains in the tank is unable to ignite.
 
Dellortoman said:
That may be true, but the main reason it works is that exhaust has very little free oxygen in it (it's mostly CO2 and water vapour), so any fuel that remains in the tank is unable to ignite.
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Would you like to think about that again and then tell me which gas/chemical makes up the highest percentage of exhaust fumes?
 
first do the sandblasting and prepare to be surprised,

then dump the tank in a bigger tank of water and De-Oxc, mixed at the proper rate and leave for a week or so, this will remove any internal rust that the blaster cannot get at,

as soon as you get the tank out of the De-Oxc solution, you must rapidly dry it (use heat) and get straight to work with your testing and repairs, as the freshly de rusted tank (internally) and sand blasted (externally) will cause it to rust in as little as two hours.

CLEM

ps to Cam
what you say may well be true for I am no scientist, and from what I know of you your wisdom in that area is far greater than mine but the paint stripper gun/hairdryer works as well and that is simply warmed up fresh air.
 
Davo said:
Would you like to think about that again and then tell me which gas/chemical makes up the highest percentage of exhaust fumes?
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Yes, OK you pedantic bugger  ;) I deserved that. It's probably around 70% nitrogen which passes through the engine mostly un-changed. But I was only trying to indicate what happens to the oxygen in combustion process.
 
when welding a tank you try to get close to an inert atmosphere as possible and the exhaust gases may well do that. oxygen or breath able air is a fuel which will if mixed with LEL's / hydrocarbons will go bang (blob!).
 
 
Gravelroad said:
Come on, guys, engines are breathing air, and air contains about 78% of Nitrogen... :LOL:
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100% correct. And you, sir, win a burial at sea with the woman of your choice.  :LOL:
 
Dellortoman said:
Yes, OK you pedantic bugger  ;) I deserved that. It's probably around 70% nitrogen which passes through the engine mostly un-changed. But I was only trying to indicate what happens to the oxygen in combustion process.
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78% actually Cam, but I will let you off for that slight slip seeing as how you are much better informed than I in many other areas, especially lifting sling terminology  :LOL:. Some things really get my goat, the worst is commentators etc saying that SCUBA divers are wearing an oxygen tank.
 
When I was employed on commercial tank ships, we would inert our cargo tanks with "gas" from an Inert Gas Generator that was fueled by diesel oil.  The generator was similar to a small boiler and the flue gas was delivered to the cargo tanks after being "scrubbed" clean.

That gas was maintained at 2.5% oxygen and we kept the tanks at a positive pressure of 1.0 to 1.5 psi. 

An alarm was sounded if the oxygen content exceeded 5% (company standard) and U.S. Coast Guard required alarm at 7% oxygen IIRC.

It has been awhile, but I believe 11 - 12% oxygen is needed for combustion of gasoline.

While we never performed "hot work" on a tank (cargo, fuel oil, hydraulic) without it being certified gas free by a Marine Chemist,
there have been times when adjacent tanks had to be "inerted" before any hot work was allowed on a tank in need of repair.

BTW, a CO2 fire extinguisher may be able to provide the inert atmosphere needed.
 
Davo said:
78% actually Cam, but I will let you off for that slight slip seeing as how you are much better informed than I in many other areas, especially lifting sling terminology  :LOL:. Some things really get my goat, the worst is commentators etc saying that SCUBA divers are wearing an oxygen tank.
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Actually about 70% N2 in the exhaust Davo. But I'll let you off that little slip seeing as you're better informed than I in many other areas, especially medical stuff.  :D

Typically around 71% for a petrol engine and 67% for Diesel.

The reason it's closer to 70% (a little more or less depending on state of tune) is that it's not just air going through the engine. The addition of hydrocarbon fuel reduces the percentage of Nitrogen in the total mix. The same stuff all comes out of the exhaust, just with some of the molecules rearranged.

I agree about the "oxygen" in SCUBA tanks. It bugs me too.


PS: Years ago, I did an engineering project relating to the monitoring and reduction of emissions from a large corporate vehicle fleet. I came up with a few recommendations but I don't think the company implemented any of them. They only commissioned the study so that they'd be seen to be concerned about their carbon footprint. They didn't really give a shit. Stupid thing is that if they'd implemented a few simple measures to reduce fuel use, they would have saved a heap of money and increased profits.
 
Dellortoman said:
Yes, I agree. your figures are far more accurate as I had not taken into consideration the addition of fuel/oil.

PS: Years ago, I did an engineering project relating to the monitoring and reduction of emissions from a large corporate vehicle fleet. I came up with a few recommendations but I don't think the company implemented any of them. They only commissioned the study so that they'd be seen to be concerned about their carbon footprint. They didn't really give a shit. Stupid thing is that if they'd implemented a few simple measures to reduce fuel use, they would have saved a heap of money and increased profits.
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That was my wife's last field of employment, running a clean air program for the State Govt here in WA. As per your findings, despite the large savings in fuel very few of the large trucking companies or local councils gave it the time of day.
 
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