Welding on a used fuel tank

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So what is the cleaning process so you don't blow yourself up if you are welding on a tank that has contained fuel?  I'm looking to cut the bottom off of one tank and modify it to fit another tank so that the new tank can mount to the old frame (motorcyle tanks, btw).  Both tanks have been used, so obviously i dont want to blow myself up.  I've been trying to read lots of articles on this.  So far what seems to be generally accepted as safest is take the tanks to a shop and have them boiled in a caustic solution so that all traces of fuel are removed.  I guess i just am wondering what others have done.  I mean, is there any way to do this at home, rather than having to take it somewhere - or does everyone just take it somewhere else?  I read a few articles on people doing this with different degreasers and solutions, but i don't know what to use.  Any advice from personal experience will be helpful.PS.  I was thinking of mig or oxy/acetalene.  I haven't cut the tanks up yet, so don't know how thick the material is and wouldn't want to blow through it with mig if its really thin.Also, since the tank is on a bike with gravity fed carbs (no fuel pump, no excess pressure), what pressure should i check for leaks at? I was thinking i would just fill the tank up with some soapy water, cap off all the openings except one and hook an air hose up to that but i dont know what pressure to check for.Thanks!
Reply:http://www.weldingweb.com/vbb/showthread...ding+gas+tanksTry reading this. I guess having them boiled out would work but I'd have it checked with a combustionable gas detector before welding it.Edited to add: 1-3 psi is enough to leak check any fuel tanks. They aren't make to take much pressure. A small tank might stand more pressure but there's no reason to go higher. Any more pressure than that on a larger gas tank and you'll be wearing it.Last edited by tresi; 04-08-2007 at 12:27 PM.
Reply:Originally Posted by cbrf23So what is the cleaning process so you don't blow yourself up if you are welding on a tank that has contained fuel?  I'm looking to cut the bottom off of one tank and modify it to fit another tank so that the new tank can mount to the old frame (motorcyle tanks, btw).  Both tanks have been used, so obviously i dont want to blow myself up.  I've been trying to read lots of articles on this.  So far what seems to be generally accepted as safest is take the tanks to a shop and have them boiled in a caustic solution so that all traces of fuel are removed.  I guess i just am wondering what others have done.  I mean, is there any way to do this at home, rather than having to take it somewhere - or does everyone just take it somewhere else?  I read a few articles on people doing this with different degreasers and solutions, but i don't know what to use.  Any advice from personal experience will be helpful.PS.  I was thinking of mig or oxy/acetalene.  I haven't cut the tanks up yet, so don't know how thick the material is and wouldn't want to blow through it with mig if its really thin.Also, since the tank is on a bike with gravity fed carbs (no fuel pump, no excess pressure), what pressure should i check for leaks at? I was thinking i would just fill the tank up with some soapy water, cap off all the openings except one and hook an air hose up to that but i dont know what pressure to check for.Thanks!
Reply:cool.  thanks guys!  I read that article that was linked to as well.  I was planning on taking the tanks to a radiator shop (one like 5 mninutes from my house) so i think i'll do that.Thanks again guys!I'll probably end up oxy/ac'ing it cause i'm more comfortable with it than mig.  I like mig for big things where quick beads and whatnot are great.  But i like the control i have over every little thing when i torch weld.  I really need to learn tig....stupid advanced welding class at my school has not been offered or has been cancelled due to too little people registering the last 3 semesters i've signed up for it. Oh yeah i forgot to add that the tanks cost me 40 and 200 respectively for used ones and are about 4-600 a piece new, just in case anyone was going to tell me to not do it and just buy a new tank.  Its a sportbike not a chopper, so pretty hard to make the curves i want.Last edited by cbrf23; 04-08-2007 at 01:55 PM.
Reply:Be safe and do the right thing..We wanna see pics.. And if you do the wrong thing..Then no pics.. ...zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:this thread might help to http://www.weldingweb.com/vbb/showthread.php?t=6081ChuckASME Pressure Vessel welder
Reply:He washed it out with soap and water and put his car exhaust pipe into it for about 15 minutes to dry it out. Yep, I've known a few oldtimers that used the car exhaust method. I purposely chose not to bring that up because it won't work very well with computer controlled vehicles. Even on older cars it backfire on you depending on the fuel air mixture.
Reply:Sweet, thanks for all the help guys!  I'll defintately post up some pics if it ever gets done...i'm waiting for the 954 tank to get here so that i can measure up and see if what i want to do will even work.  Oh, btw, i'm planning on fitting the bottom of an f2 tank to the top half of a 954 tank.  That way the tank will mount correctly and fit over the airbox (biggest issue) and the fuel tap and hoses will all line up.  Hopefully it will all workout!
Reply:Originally Posted by tresiHe washed it out with soap and water and put his car exhaust pipe into it for about 15 minutes to dry it out. Yep, I've known a few oldtimers that used the car exhaust method. I purposely chose not to bring that up because it won't work very well with computer controlled vehicles. Even on older cars it backfire on you depending on the fuel air mixture.
Reply:I purge the tank with nitrogen or CO2 and maintain a blanket purge on it while welding
Reply:When I built & restored Harleys in the late 70's, we used to wash out the tank, blow it out with compressed air the best you can, dry it in the sun for a day or two and then purge it with car exhaust until warm-just before the repair.  Standing away from the cap & petcock, carefully wave a flame across to see if it flashes.  If not, proceed with brazing a crack, hole or mounting bracket.  It won't blow up if it has somewhere to go.  If it does flash, it clears the volatiles and your done.  Never had one flash though with this method.To clean rust out, use a piece of chain and fill it part way with some water with a cleaning solution.  Cap it up and shake it around for a while.  It'll knock off any loose scale, dirt or other stuff from laying around.  Of course, it will never be like new, but we never had any issues with a dirty fuel tank.Hobart 140 Handler w/ gasHyperTherm Powermax 380 Plasmaoxy/acetylene
Reply:I had to repair the gas tank on my SA-200.  What a joy, the bottom of the tank was pitted and rusted all the way through.  I thought about it for a while, and decided it's full of water already so there shouldn't be a problem cutting the bottom off and cleaning out the inside, so that's what I did (with a cut off saw).  I looked around to find a suitable replacement piece for the bottom of the tank and it ended up being a piece of the door of a 68 Cutlass, it had a nice curve to it similar to the fuel tank in question.  After it was all clean and pretty in side I welded the bottom on with my 3200HD, flux core, (a man's got to use what he has available some times),  added a fitting for the sediment bowl, rigged me up a 20oz Mountain Dew bottle duck taped it to the filler neck with a air nozzle attached, pressurized the tank and squirted soap and water on it, had 6 or 7 spots I had to re weld, did that, checked it again, put it on filled it up with gas and I am using it today.  No problems.  When you're poor you do things like this.  I have more time in the gas tank of my SA-200 than I did the entire project of it's restoration.  But it was worth every minute.Last edited by rodinator1234; 04-10-2007 at 02:35 PM.
Reply:Originally Posted by rodinator1234I had to repair the gas tank on my SA-200.  What a joy, the bottom of the tank was pitted and rusted all the way through.  I thought about it for a while, and decided it's full of water already so there shouldn't be a problem cutting the bottom off and cleaning out the inside, so that's what I did (with a cut off saw).  I looked around to find a suitable replacement piece for the bottom of the tank and it ended up being a piece of the door of a 68 Cutlass, it had a nice curve to it similar to the fuel tank in question.  After it was all clean and pretty in side I welded the bottom on with my 3200HD, flux core, (a man's got to use what he has available some times),  added a fitting for the sediment bowl, rigged me up a 20oz Mountain Dew bottle duck taped it to the filler neck with a air nozzle attached, pressurized the tank and squirted soap and water on it, had 6 or 7 spots I had to re weld, did that, checked it again, put it on filled it up with gas and I am using it today.  No problems.  When you're poor you do things like this.  I have more time in the gas tank of my SA-200 than I did the entire project of it's restoration.  But it was worth every minute.
Reply:Came across a procedure the other day for this (CSX railroad safe practices book, a couple pages before instructions for office workers not to stand on rolling chairs. Remember that, very important  )Summary:Clean with detergent and watersteam cleanfill with waterKEEP VENTED (so steam formed can escape and if anything goes pop in a trapped air space,  the pressure is released)weldFirst written procedure Iv'e seen for this. I am told NJ Transit, Amtrak, etc all have similar or the same in their books.
Reply:I worked for a guy that does fuel tanks frequently. Does nothing fancy, but has been welding them for years without blowing up. He washes them twice with a product called "sudsy ammonia" and if didn't see it I wouldn't believe it. I hid everytime he did one... nothing ever happened... not even a little "fooooof". Tried it myself and it works fine after years of being afraid of these things.Be careful out there!
Reply:I have welded a few in my day, did all the usual to clean and dry them, but before I welded them I still put them under my welding bench and stayed on top of the bench and ran a flame into the filler just to be sure there were no fumes. figured as long as I had an inch of steel between me and the tank I should be safe - well,  fairly safe.Dan.Repair Specialties LLC