MIG Welding Aluminum Fuel Tank ?

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I've got a friend that has boat that he uses to fish offshore & he needs a new fuel tank as the original is beyond hope. The original was made from 10 ga. but I have no idea what series aluminum. The dimensions are 82" L x 21" W x 7" D & I plan on having a local sheet metal place cut the parts for me using 3/16" plate. The bottom & sides can all be one piece since the sheet metal folks can brake it. Then all I have to do is put the end plates & top on it, plus a few fittings. Being right on the Texas gulf coast, the sheet metal guys have made plenty of marine fuel tanks & they told me that 5000 series alum is best for a salt water environment but that it has to be annealed before it can be bent on a brake. I think we can get away with 4000 series & maybe some type of coating as well as some anode devices after its done.       My main concern is that I don't have a TIG welder. I've only got a Miller 211 MIG welder with a spool gun which works pretty good except for those damn cold starts that are a part of migging alum. I'd like to know if this job is doable with MIG or if anyone has similar experience. Also, what would be the best method for pressure testing the thing? Any advice anyone can offer would be appreciated.
Reply:You can definitely weld 3/16" aluminum with the spool gun.  I like to heat the part with a torch to get the aluminum warm.  Of course, after a few beads, it's going to be pretty warm anyway.  Best way to test for leaks is to pressurize it with air ( it only takes 5 psi to test) and brush soapy water on all the welds.  I would be tempted to do this with stainless rather than aluminum.Miller Syncrowave 350Millermatic 252/ 30A spoolgunMiller Bobcat 225g w/ 3545 spoolgunLincoln PowerArc4000Lincoln 175 Mig  Lincoln 135 Mig Everlast 250EX TigCentury ac/dc 230 amp stickVictor O/AHypertherm 1000 plasma
Reply:I prefer stainless (316) over alum. too. This monday i'm gonna fax a sketch to the sheet metal place & i'm asking them to quote  prices for both materials. I figure 10 gauge in stainless would be fine, maybe even a little lighter gauge. Maybe they'll have some advice. They've been in business a long time.
Reply:anneal 5000 series al?   use 4000 series al instead?   substitute 316l/ 10ga?  don't worry about those cold starts, no problem there. lolgood luck,  hope i don't  read about you later.
Reply:Originally Posted by fdcmiamianneal 5000 series al?   use 4000 series al instead?   substitute 316l/ 10ga?  don't worry about those cold starts, no problem there. lolgood luck,  hope i don't  read about you later.
Reply:I believe you are going to need at least one baffle inside the tank to prevent sloshing, if not 2. The fuel moving back and forth in a 1/2 full tank will beat the cr@p out of it like a battering ram in heavy seas/ high speeds. With the space constraints inside with a spoolgun, you'll probably want to rethink how this will all go together and maybe consider leaving off the top so you can reach down inside to weld the baffles in place..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:I believe there's at least two baffles inside the original tank. I plan on cutting into it to see what they look like. I'm just copying the tank that came in the boat which is a Boston Whaler.
Reply:no more than 30 in's or 3 cu ft on baffles.5052 h32 or 5086 aluminum sheet   you don't  need to anneal anything.don't know what's with the 4000 aluminum unless you're talking about the wire your going to use to  weld it  up.i would suggest you give it to someone else to weld up.bend u channel and cut end plates and top.   some people plug weld baffles from top, they also  need  air  and limber holes.since you are copying an existing whaler you should be ok.no need to go to the extra expense of the 316L  ss.  in fact you could do it in .125 al instead of  .187.cold starts = leaks...not  good.
Reply:.I would agree with fdcmiami.  5052 or 5086 is very common for marine tanks. Most tank builders  don't recommend bending 90 degrees, rather shear and weld a full open corner. 3 or 4 psi for testing if good and soapy water works well. As far as baffles go, I like to bend 90 degrees on all four sides of baffle, removing the corners and welding the sheared end only, not the bent side. Install cover last and plug weld several places through cover to baffles. .I would also recommend it be tig welded and proper MFG tag be installed. There is much more to building a USCG approved tank than building a box with a filler neck.Tons of rules and regulations plus lots of engineering and a solid understanding of stress points.  Please read and research before you get in over your head.Just my thoughts.....
Reply:I agree with 5052, I also believe in preheating the pieces to about 150 to 200 degree, that way your cold start isnt so cold.
Reply:Originally Posted by astaindsoul5446I agree with 5052, I also believe in preheating the pieces to about 150 to 200 degree, that way your cold start isnt so cold.
Reply:pirana, what your question(s) seem to indicate is that some of the basics of #1 aluminum alloys, #2 welding aluminum alloys & #3 your current tank building knowledge seem to be less than could be useful?That would indicate to more experienced people that you may want to take time to upgrade your knowledge of some of these basics before jumping off on a tank project?If you don't 'know' that annealing 50(52/86/83) series alloys to bend/brake is is not (either) needed or recommended then it would indicate you would be more effective helping your friend by gathering more information before building this tank?  [yes you can anneal it and it will reduce strain cracks along the bends; but at a cost to the entire project's integrity.]Further, 4000 series material is not used for marine tanks and this tends to make others skeptical of you and your friend relying on your current levels of judgement to make this project successful?I'd suggest you consider reading more thoroughly about welded tanks and research more about the alloys used, forming methods from a wide(r) group of fabricators and then consider a few practice 'boxes' that were smaller that you 'pressure tested' before you begin this work.Once you have done more research into common practices and maybe done some small box tests (?) then I'm confident  you'd build a fine tank using a spool gun.Answers; Yes, MIG can be used to make a fully functional tank.Air testing is most common and ranges from 2-5 psi are common.  3/16" is thick enough and 5052 will bend to a thickness radius but steel nose bars may crack it if too tight and deep a die are used.  5086 is stiffer and a better overall choice but more expensive and will crack much worse than 5052 along the same radius; so its most often bent (in press brakes) with a three or four 'shot' corner of 4T=r or more. Pressure gauges that measure <10psi are (usually) not that accurate, unless 'Test' quality or 4" dial face, so a simple Tygon tube manometer is easiest to build.  27.4 inches of H2O column ~ 1psi so a difference of 80" between the levels will 'test' the tank's welds. The open end of the manometer will also act as a PSV so that tank can't get overpressured and deformed if something happens at the pressure regulator.good luck with your projectCheersKevin Morin
Reply:pirana,Just read the post and you've gotten good advice from fdc, psl, Kevin, etc.  What you do with it now is what's important.When an experienced guy reads your post, the first thought that comes to mind is Oh Oh, here comes trouble.  Sure the tank can be mig welded with a spoolgun BY A VERY EXPERIENCED WELDER.  This is not a job to be learning to weld aluminum on.Your comments about materials, etc,  further raised doubts.You didn't mention whether this tank is installed above deck (say under a seat) or is installed below decks (most likely) which would make it even more difficult to inspect regularly.  Personally, I wouldn't want a non-certified tank installed in my bilge.Also, be aware that if something happened to that tank and the boat caught fire/exploded, you could be held responsible.  Do you have insurance to cover that?  Also, your buddy's insurance may not pay because he used a non-approved tank.Also, if your buddy goes to sell the boat and the buyer brings in a marine surveyor, he will (if he's decent) note that non-approved tank has been installed and could cause problems.  I've had sales go south for similar reasons.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:I'll be the first to admit I don't have much experience or knowledge of aluminum. That's why i'm asking for advice here. If it was stainless or mild steel I would not even be asking. It's not like i'm a complete newbie to welding. That said, i'm leaning towards possibly fitting the thing up & taking it to someone who can TIG weld it. Plus, I know the various fittings in the top of the tank would be a bitch to do with MIG. Overall, thanks for the advice & the humility in which it was given in (some) of the replies.