[77cruiser]

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I put this tank in the bed of my truck, not realizing it was too tall to keep the toneau cover on.
So I want to cut it down about 3 inches.

[Warrenh]

Has there ever been fuel in it?

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[MinnesotaDave]

If you're experienced with aluminum fab and welding, and experienced with proper tank evacuation safety (if it had gas in it) it's not too bad of a job.

If either of those are a "no" then it will likely be difficult and/or dangerous.

Can you buy a shorter tank and sell this one?

[ex framie]

So the measure twice weld once part of the build went a bit wrong eh.
If you have had fuel in it as the guys have said, build a new one or do your homework on what proceedures are required to prevent an earth shattering kaboom.
Dont just suck it and see, I have shared a hospital room with a young bloke who was told to cut the top off a drum. He lost an eye, smashed jaw, broken arm, but he was lucky enough to live.
Yep its that serious.
Cheers

[77cruiser]

It had diesel in it.

[Lightning]

It had diesel in it.

Anything that burns, from nitromethane to motor oil to asphalt, can go KBOOM when you cut or weld on a tank that held it.

More than "a few" people have been blown into bloody pieces doing this. Be careful out there!

[John Chamorro]

It had diesel in it.

I have had very good luck with Tide and warm water pressure washing to clean diesel tanks for welding. Also to be safe , after cleaning make your cuts with a sawzall/skill saw. That eliminates any hot spark from a plasma. Be smart and think smart and you will be fine.

[tweake]

the other simple thing is to take the bungs and cap off.
even if it the fuel ignites, if its got a way to get out it won't build up pressure. no pressure means the burn won't increase in speed and its burn speed that makes it "explosive".

[Oompa]

Easiest way is toset the tank up so it's very stable and fill it with water to just below your cut line. Cut it with a sawzall or something that doesn't make sparks. Remember that water and electricity don't play well together. Once you have cut the top or bottom off either salvage the top or bottom or make a new top or bottom and weld it on with the water once again just below your joint. Leave the cap off the top if welding on a new top or the drain bung off if it's a bottom. It's the vapour that explodes so by minimizing the possible air gap you minimize the chance of an explosion. You can also flood the remaining air space with Argon to be extra sure just leave it running a little while before you start and whilst you are welding.

[Graveyard]

Welding fuel tanks is what I do, I’ve welded close to 1000 and thats not an exaggeration. That being said everything I do is gasoline so I have no experince with diesel. Being that the tank is aluminum you’re at an advantage like others have stated you can clean it out with water and soap without the risk of rusting the inside. I always make sure and get all the fuel out and let it air out. I know diesel doesn’t evaporate like gas so the water and soap would be my personal angle on this project. Also leaving the cap off while cutting is always best when working on fuel tanks. I would recommend cutting it with band saw if it’s at all possible. It will create way less heat. Once it’s cut clean it again and let it air out more before you reeled the pieces back together. Good luck and don’t cut corners. Be careful.

[Graveyard]

Easiest way is toset the tank up so it's very stable and fill it with water to just below your cut line. Cut it with a sawzall or something that doesn't make sparks. Remember that water and electricity don't play well together. Once you have cut the top or bottom off either salvage the top or bottom or make a new top or bottom and weld it on with the water once again just below your joint. Leave the cap off the top if welding on a new top or the drain bung off if it's a bottom. It's the vapour that explodes so by minimizing the possible air gap you minimize the chance of an explosion. You can also flood the remaining air space with Argon to be extra sure just leave it running a little while before you start and whilst you are welding.

I do not recommend leaving the water inside while cutting. But I do agree with leaving the cap off during cutting and purging during welding.

[77cruiser]

Thanks for all the tips so far, haven't started on it yet.

[Maniak]

I have done these before also and agree with the others about filling with water to just below the cut/weld line, and purging the rest with argon or Co2 and venting. Biggest Thing, approach this with caution, especially if you have never done this before, if you even think it will explode it probably will, maybe have someone that does this on a regular basis do it for you, safest way.
On a side note, I have never been a big fan of mounting tabs on aluminum tanks, to prone to cracking even in a truck bed, I would suggest over the tank straps, just my opinion.

[77cruiser]

Tank is apart & cut to size. Since I'm not an expert alum. welder, would it be better to use a a strip 1" to 1 1/2" wide & do lap welds instead of a butt weld? Might be less prone to cracking too?
As far as the tabs for mounting, I don't have them bolted tight, but have a spring on the bolt to allow a bit of movement.

[ThaiGuy]

Personally, I am more of a hobby welder, but not bad quality...However, I have been in oil & gas refining most of my life. Your problem is not so big. If the diesel is gone..no liquid? Your concern is not flashing. Diesel in America can be full of goofiness, flash being 125F. to around 200F, but so what? If nothing is left, nothing to flash.

Like any aluminum welding, you MUST have clean metal with proper purging. I have welded some outside joints with no inside purge and done OK...If you have doubts, purge the inside too! Combustion cannot happen. Again, your metal needs to be clean, so your puddle is too.

If really worried, let it sit in the sun for a while...open of course. Open with a low point and a high point. (Heat rises) Natural vaporization happens. The porous aluminum will gas off quite easily. Wipe all surfaces with acetone or isopropyl alcohol.

[77cruiser]

No BOOM, didn't come out too bad for first time welding aluminum. Made some straps for it, instead of the tabs being bolted to the box.

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[MarkL]

Looks really nice, you must have done a good job cutting it to get a nice tight joint. When you first posted I looked up Frostbite Falls, I thought you were being a wise guy. I never knew it was a real place but was one of my favorite imaginary places as a kid.

[77cruiser]

Maybe just a little bit of a wise guy, Frostbite Falls home of Rocky & Bullwinkle AKA International Falls,MN.

[MinnesotaDave]

Maybe just a little bit of a wise guy, Frostbite Falls home of Rocky & Bullwinkle AKA International Falls,MN.

Everyone knows Bemidji is the Cold Capital and I-Falls is just a close second

Tank looks great

[77cruiser]

Maybe just a little bit of a wise guy, Frostbite Falls home of Rocky & Bullwinkle AKA International Falls,MN.

Everyone knows Bemidji is the Cold Capital and I-Falls is just a close second

Tank looks great

I don't care you can have the cold capital.

Thanks

[Maniak]

No BOOM, didn't come out too bad for first time welding aluminum. Made some straps for it, instead of the tabs being bolted to the box.

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Nice Job, especially for your first aluminum, I do like the straps!