long welds on sheet aluminum

[dvice]

I cant seem to find a fuel tank for my boat (other than new at $400+) in the width I need. But I have one that is about 3/4" too wide. I plan to cut it length wise along one side and weld a new piece of sheet aluminum to it resulting in a narrower tank.

so I have experience warping sheet aluminum...because once I got the hang of it, I got greedy. I know the tank doesn't need to be aesthetically pretty, but if I can learn how to weld better I am all for it. I have a Miller 250 MIG machine, a 30a spool gun, .030" dia 4043 wire. and 100% argon.

the aluminum is about .090" thick I am guessing.

should I stich weld and let air cool or stitch weld and flip , or stitch weld and cool with a wet rag ( the surrounding areas...not the exact weld).

I need to make the weld air tight!

this is what I am going to do...so with what is on hand and what equipment I have, what is the best course of action...or suggested course of action

thanks

BOB

[Rhinox]

long welds on sheet aluminum

pulse + back step

[Portable Welder]

Rhinox, The back step is what we do on stainless, I doubt pulse is available the spool gun and .090 is to thin in my opinion.

This is hands down a tig job in my opinion, especially since we are talking a fuel tank in a boat.

[dvice]

I did say I have a Miller 252 MIG machine..

I could TIG it at work....but that's a lot of welding time...

is it that hard to pick up a stitch weld later on??...I guess I could just cut up something and try...I figured id ask here for suggestions with the equipment at hand.

the material MIGHT be as thick as .125... I haven't cut it yet...

bob

[dave powelson]

seal tight AL welds

I did say I have a Miller 252 MIG machine..

I could TIG it at work....but that's a lot of welding time...

is it that hard to pick up a stitch weld later on??...I guess I could just cut up something and try...I figured id ask here for suggestions with the equipment at hand.

the material MIGHT be as thick as .125... I haven't cut it yet...

bob

Getting seal tight welds with MIG is tough, unless you're a real crackerjack with a MIG. Every start and stop can be a potential leak, which means grinding into those, then running into them; or hot overlay on a series of small tacks.
Plan on having some or many of those leakers, washed over with TIG.

A good fitting, lapped or otherwise joint to help limit distortion, with TIG lay rod goes pretty **** quick.

??and you're using 4043 on 5000 series AL….becuz??

[dvice]

thanks, I did weld together an Offshore bracket for another boat when I bought this mig machine..it was all .125 sheet...it seemed to weld nice, and when I got into trouble I just over welded. but that bracket had a framework underneath , and I haven't actually put it in water. I was thinking this gas tank and HAS to be 100% leak proof.

I actually had some 5000 series wire , but previously I was patching some .060" aluminum pieces on the boat and I was afraid the 5000 series would need more heat to melt, and I was worried about blow throughs , and even with the 4340, I got some blow throughs...

my GUESS was that the stronger aluminum wire would be more problematic with thin material...my thought process is being developed by a limited experience welder!!!!!!! so if my settings are off or my speed, ect, the stiff wire is poking holes in my puddles....yeah, I know learn how to do it right, and that wont happen....its a long learning curve... and I was looking to just make it as smooth as POSSIBLE .

the guy as the welding supply shop suggested 4340...anyway...

dvice

[WillieB]

Getting seal tight welds with MIG is tough, unless you're a real crackerjack with a MIG. Every start and stop can be a potential leak, which means grinding into those, then running into them; or hot overlay on a series of small tacks.
Plan on having some or many of those leakers, washed over with TIG.

A good fitting, lapped or otherwise joint to help limit distortion, with TIG lay rod goes pretty **** quick.

??and you're using 4043 on 5000 series AL….becuz??

There are people qualified to build a gas tank with a spool gun. I am not! TIG is a better bet. I'd feel confident doing it with TIG, and 5356 filler.

[JSFAB]

Also realize the US Coast Guard has very specific rules and regulations involving fuel tanks on boats, and they do have jurisdiction, even if you are in inland waters. It might be worth checking out their website.

[ja baudin]

Also realize the US Coast Guard has very specific rules and regulations involving fuel tanks on boats, and they do have jurisdiction, even if you are in inland waters. It might be worth checking out their website.

Tank can not be gravity feed, must have a pick up on top of tank. This will prevent tank emptying if fuel line is cut.





Tig it, good luck



ja

[dvice]

Also realize the US Coast Guard has very specific rules and regulations involving fuel tanks on boats, and they do have jurisdiction, even if you are in inland waters. It might be worth checking out their website.

after reading through several pages, I am convinced those rules apply to boat manufacturers....not boat owners doing their own repairs...

but Ill just test it to 3psi anyway.... it already has all the other required fittings...


dvice

[ja baudin]

after reading through several pages, I am convinced those rules apply to boat manufacturers....not boat owners doing their own repairs...

but Ill just test it to 3psi anyway.... it already has all the other required fittings...


dvice

#1 If your working on a boat that already has a coast guard placard, yes you can get away with making your own repairs and even fabricate new equipment..In the event of an accident, you will be held responsible not the boat manufacturer.

#2 If you are working on or building a "home made boat", to acquire insurance coverage the vessel will have to be inspected by the coast guard. Otherwise again you are held responsible/liable.


Just some info, not preaching.

[Tryagn5]

I cant seem to find a fuel tank for my boat (other than new at $400+) in the width I need. But I have one that is about 3/4" too wide. I plan to cut it length wise along one side and weld a new piece of sheet aluminum to it resulting in a narrower tank.

so I have experience warping sheet aluminum...because once I got the hang of it, I got greedy. I know the tank doesn't need to be aesthetically pretty, but if I can learn how to weld better I am all for it. I have a Miller 250 MIG machine, a 30a spool gun, .030" dia 4043 wire. and 100% argon.

the aluminum is about .090" thick I am guessing.

should I stich weld and let air cool or stitch weld and flip , or stitch weld and cool with a wet rag ( the surrounding areas...not the exact weld).

I need to make the weld air tight!

this is what I am going to do...so with what is on hand and what equipment I have, what is the best course of action...or suggested course of action

thanks

BOB

First if this tank has had fuel in it, stop gasoline tanks are a bomb if they have been filled. There are very few ways to clean them to avoid this. If it is a new tank your going to need to backer bar the seam, basically use a 3/8 aluminum key stock behind the weld to keep the weld from falling out, if you lose the puddle once your done, also start in the center of the tank and work towards the corners. I have welded thin pontoons with a 30a and trailblazer, it is not easy. Fyi it would be bettar to overlap the piece vs a corner seam. If you can overlap it by an inch and then cut it back you will have bettar luck.
Kevin

[dave powelson]

A man's gotta do--what a man's gotta do!

after reading through several pages, I am convinced those rules apply to boat manufacturers....not boat owners doing their own repairs...

but Ill just test it to 3psi anyway.... it already has all the other required fittings...

dvice

You began this thread with the caveat:

" this is what I am going to do...so with what is on hand and what equipment I have"

…..so considering the above, just go for it.
Experience is a dear teacher, it gives the test-first and the lesson-after.

Thin wall rectangular tanks are pressure tested in a cradle to prevent rupturing--but I'll bet u know that.
Any residual fuel vapor in a tank being pressure tested, can ignite/explode spontaneously--but I'll bet u know that.
Cutting open a tank with residual fuel is dicey--unless cleaning and inert gas purging with 02 and LEL monitoring is done, with purge plan and calc's-but I'll bet u know that.
Ditto for welding on such tank as other's have said-but I'll bet u know that.
Lapped seams--who cares? ---but I'll bet u know that.
Seal tight welding?
Controlling AL sheet distortion?

For whatever it's worth, yours truly has designed, fabbed, tested, repaired tanks to DOT, CARB, Coast Guard, Corps of Engineers and FAA standards. Over 1500 used tank repairs.

[H80N]

It takes a remarkably small quantity of flammable substance by WEIGHT mixed with air to create an explosive atmosphere of great destructive force..

http://www.engineeringtoolbox.com/explosive-concentration-limits-d_423.html

a vessel that the weldor might consider to be clean... may very well contain a deadly explosive mixture... just waiting for a spark...

[ja baudin]

I cant seem to find a fuel tank for my boat (other than new at $400+) in the width I need. But I have one that is about 3/4" too wide. I plan to cut it length wise along one side and weld a new piece of sheet aluminum to it resulting in a narrower tank.

so I have experience warping sheet aluminum...because once I got the hang of it, I got greedy. I know the tank doesn't need to be aesthetically pretty, but if I can learn how to weld better I am all for it. I have a Miller 250 MIG machine, a 30a spool gun, .030" dia 4043 wire. and 100% argon.

the aluminum is about .090" thick I am guessing.

should I stich weld and let air cool or stitch weld and flip , or stitch weld and cool with a wet rag ( the surrounding areas...not the exact weld).

I need to make the weld air tight!

this is what I am going to do...so with what is on hand and what equipment I have, what is the best course of action...or suggested course of action

thanks

BOB

Just spend the 400+ dollars and buy a quality professional tank. Gain experience by welding scrap, not a bomb.

look up on you tube people who cut or weld on 55 gallon drums which previously had flammable materials in them. Youll change your mind.

http://youtu.be/9DP5l9yYt-g

http://youtu.be/pwqXrXp-q4U