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TIG welding both sides of corner joint, legit?

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bryanmartin

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Discussion starter · #1 ·
Hi. I'm building a tank, and I'm concerned about penetration in a few areas of my joints. I'm TIG welding 1/8" 5052 H32 aluminum with 3/32 5356, and as you can see from the photo, I have no back side penetration in some areas. The weld on the front side looks good, my question is, can I just run another bead on the inside of the corner joint? I ask because I don't know if there's some metallurgical reason why I shouldn't (e.g. it will make the weld more brittle or something). What about the area where it looks like I did get penetration, can I run another bead on the inside of that area, or will problems arise from re-melting that area?
 
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#2 ·
Yes. This is the proper technique to build a tank.

We custom fabricate all of our tanks, fuel and otherwise, in the shop. They are all MIG welded 100% on the inside, then we clean up the outside edges for a nice corner to corner joint, and then TIG weld 100%. Then they are pressure tested, and gone over with a fine tooth comb multiple times to ensure there are no pinhole leaks.

You've done it backwards, however. TIGing the outer edges should come last; this is your way of finalizing the aesthetics of the tank. If you happen to burn through when MIG welding the back side, you have little recourse to make an adequate repair and maintain the aesthetics of the TIG weld.
 
Discussion starter · #3 ·
Hillbilly Welder said:
You've done it backwards, however.
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Awesome, thanks for the reply. Since I'm only building it for myself, I suppose I'll continue to finish this side backwards, but I'll weld the other side on in the order you recommend. It makes sense, thanks again.
 
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Discussion starter · #4 ·
Hillbilly Welder said:
all of our tanks... are all MIG welded 100% on the inside.
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Ok, I tried welding on the inside. It's going great. I could use some advice though. How to you get into these areas where corners meet? Any tips? Oh, and ignore the black :laugh:
 
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#5 ·
We use MIG for the inside of the tank. Way faster than TIG, and because it will never be seen again, you don't need the aesthetic qualities that TIG offers.

If you're limited to TIG for the inside, I would switch to the biggest cup you have. Preferably, a gas lens. This will allow you to use a longer stickout; the fact that you're welding in a corner like that will also help trap your argon shield. If your machine has a pre-flow feature, use it. If not, just bump the pedal for a moment to get the post-flow running, displace the atmosphere really quick, and then start your arc. That way you won't risk contaminating your tungsten, considering so much of it will be exposed.
 
Discussion starter · #6 ·
Hillbilly Welder said:
We use MIG for the inside of the tank. Way faster than TIG, and because it will never be seen again, you don't need the aesthetic qualities that TIG offers.

If you're limited to TIG for the inside, I would switch to the biggest cup you have. Preferably, a gas lens. This will allow you to use a longer stickout; the fact that you're welding in a corner like that will also help trap your argon shield. If your machine has a pre-flow feature, use it. If not, just bump the pedal for a moment to get the post-flow running, displace the atmosphere really quick, and then start your arc. That way you won't risk contaminating your tungsten, considering so much of it will be exposed.
Click to expand...
You're awesome. I do have pre-flow, and a monster pyrex cup. I'll go try it now. Thanks!
 
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#8 ·
You could probably leave those corners. But if it bugs you try backfeeding(backhand) into the corner. You could point the tungsten towards the corner and feed from behind. I do that to minimize distortion or on joints that are like yours.
 
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#9 ·
bryanmartin said:
How to you get into these areas where corners meet?
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Not sure if this helps, but when I did these I started in the corner, and worked my way out and ran for like an inch - stopped, and finished the weld (or tried too..) Also, you're going to have to switch hands for one side.. Isn't REAL welding fun? I also had a tack there, and it's 1/2" steel... (maybe use a backing bar/corner so you don't blow thru?) It was done for fun at work on a personal project.

IMG_0528 by Los Pantelones!, on Flickr
 
#12 ·
shovelon said:
You could probably leave those corners. But if it bugs you try backfeeding(backhand) into the corner. You could point the tungsten towards the corner and feed from behind. I do that to minimize distortion or on joints that are like yours.
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Not a good idea. The corners are already the most likely to have pinholes, due to the fact that most people begin and terminate their outside corner welds here. The only way to properly construct a tank is to weld every seam possible both inside and out. Obviously you can't do this with the lid, but that's not as big of a deal as the sides and bottom.
 
#13 ·
Hillbilly Welder said:
Not a good idea. The corners are already the most likely to have pinholes, due to the fact that most people begin and terminate their outside corner welds here. The only way to properly construct a tank is to weld every seam possible both inside and out. Obviously you can't do this with the lid, but that's not as big of a deal as the sides and bottom.
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You leave pinholes? :nono:

I am not saying not to weld on the inside. I am saying his skills are probably good enough not to have leaks if he leaves the inside corners unwelded. In any case he could back into the corners if he wanted.
 
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#14 ·
shovelon said:
You leave pinholes? :nono:

I am not saying not to weld on the inside. I am saying his skills are probably good enough not to have leaks if he leaves the inside corners unwelded. In any case he could back into the corners if he wanted.
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No. I'm saying that that is where pinholes are commonly found when people build tanks. Most people who don't do this kind of work for a living, and even many who do, will find pinholes when they pressure test something like this. Every halfway decent welder knows that stops and starts are the weakest part of the weld, and that includes pinholes. It's just something that happens. You find it, repair it, and move on.

A perfect TIG weld will have no pinholes. A good one very well might. How many people produce "perfect" aluminum TIG welds, and how many produce "good" ones? A lot more "good" than "perfect," and probably even more "acceptable" than "good" would be my guess. There are many ways to skin a cat; sure. But, that's the difference between a $200,000 custom aluminum sport boat, and a $75,000 off the assembly line sport boat for example (though the concept applies to nearly everything, not just boats). Little details, like how you weld out your fuel tanks.
 
#15 ·
My procedure when building tanks (and cabinets or toolboxes) was to fit everything up using TIG (no filler) on the outside, then switch to MIG spoolgun and add some more substantial tack welds on the inside. Then continue to use the spool gun to weld up the corners and other higher stress areas; then at the end continuous TIG weld the outer joints.

Would then pressure up the tank, (just a couple psi needed) and spray all the welds with Windex or soapy water.


When you control each ripple of the weld, a TIG joint isn't likely to leak, and the MIG inside is there to add strength so vibrations and flexing won't cause a leak in the future.
 
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#17 ·
motolife313 said:
What is your tank for? If it's only 1/8" think I don't see why it can't be done with just 1 pass and be done with it
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Because the chances of a leak being discovered in the weld don't change based on the thickness of the material. Whether it's 1/8" or 1", it should still be welded on both sides to ensure adequate strength and leak protection.

When you're building any kind of a tank, especially a fuel tank, whether it's in a race car, or a boat, or an aircraft, you absolutely cannot afford to be leaking fuel. In fact, just recently a boat in the local harbor, a boat built on an assembly line, blew up when it developed a fuel leak and caught a spark. It's a wonder that the owner, who was in the cabin at the time, was uninjured.

Gambling on one weld being "good enough" is absolutely not worth the few minutes you save by not welding out both sides.
 
#20 ·
motolife313 said:
I could see it being stronger but that's a lot of extra welding.
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I think it depends on the size of the tank, and whether the baffles reinforce the sides from canning in and out. Of course filler is essential to be high strength 5000 series.
 
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