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Old 15-08-2014, 08:18   #1
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Re-Welding Stainless Tanks?

We're starting to see little drips and cracks in welds on our stainless steel fresh water tanks. I think that the welds must eventually fail due to their stiffness and the flex of the tanks as water sloshes in them over the years. Or maybe it's metallurgical, I don't know.

My question is whether or not I could just pull these tanks out and run another stainless weld over the cracked ones, or grind them down and patch or something like that. I've had some good experiences using a small dc arc welder and stainless rod lately, repairing a Force 10 stove grill. Any reason I couldn't patch 28 year old stainless welds?
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Old 15-08-2014, 08:21   #2
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Re: re-welding stainless tanks?

Yes no problem rewelding. Typically the cracks are ground out. Stick welding is not ideal for ss as you are likely to blow tru but if you feel comfortable, go for it
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Old 15-08-2014, 08:31   #3
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Re: re-welding stainless tanks?

You are going to need to get a TIG welder for thin stuff. You need to be able to control the heat.
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Old 15-08-2014, 09:25   #4
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Re: re-welding stainless tanks?

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You are going to need to get a TIG welder for thin stuff. You need to be able to control the heat.
You need someone that with a Tig, if your not comfortable Tig welding, this is not the job to learn on.

I've never stick welded SS, but can only imagine the weld quality due to oxidized filler can't be that good?
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Old 15-08-2014, 09:54   #5
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Re: re-welding stainless tanks?

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You need someone that with a Tig, if your not comfortable Tig welding, this is not the job to learn on.
Not some people on this forum. They learn it in just a few hours. Piece of cake. Those of us who have had to practice for years with TIG and gas welding are just slow.
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Old 15-08-2014, 11:28   #6
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Re: re-welding stainless tanks?

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Originally Posted by Canibul View Post
We're starting to see little drips and cracks in welds on our stainless steel fresh water tanks. I think that the welds must eventually fail due to their stiffness and the flex of the tanks as water sloshes in them over the years. Or maybe it's metallurgical, I don't know.

My question is whether or not I could just pull these tanks out and run another stainless weld over the cracked ones, or grind them down and patch or something like that. I've had some good experiences using a small dc arc welder and stainless rod lately, repairing a Force 10 stove grill. Any reason I couldn't patch 28 year old stainless welds?
Yes you can repair the tanks by welding them back up. That being said you will need to grind down the old weld before proceeding. I would not recommend using an arc stick welder for what you are doing, too easy to miss a bit of slag and cause a leak. You will can use a Heli-Arc type Tig welder which requires allot of skill to use but if you know how to steel weld not just braise with an Oxygen-Acetylene torch it is not that big of a jump to learn how to use. I wouldn't want you to be learning to use a Tig on your tanks though. The easiest way to weld it up and find someone that could do it would be with a Mig welder. The Mig is similar to the Tig welder but self feeds the welding wire to fill in the joint of the welded pieces. The Tig welder can weld much thinner metal than ether a Mig or Arc welder can do. Back in High School our final test with the Heli-Arc Tig welder was to weld two aluminum cans that were sitting on top of one another together without burning a hole through them, we had a test can to use to setup the welder, then off to weld the cans. If you got a full bead all the way around the can and the two were welded together without any holes burned through you got a 100%. You lost 10 point for every hole you burned through the can. If you do use a stick welder make sure you use the proper type rod for the job. Some stick type rods the weld is porous and fluid will leak through the weld. Just pick up a welding guide book to find the proper type welding rod for what you are welding on. Good luck with your welds.

P.S. Using a stick welder has one other disadvantage that the other types of welds don't have. The metal nearest the weld will be weaker than the weld or the other metal around the weld that was not subject to the heat of the welders arc. This is why most of the time when you see a crack form at a welded joint done with a Arc welded joint it cracks beside the old weld not in the middle of the weld. This is why you have to re-temper the joined metal to make it back to the original strength. On a tank that big it is pert near impossible to do even out of the boat and in a shop.
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Old 15-08-2014, 12:12   #7
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Re: re-welding stainless tanks?

Yes, clean the old weld well and Tig weld it. or have someone Tig it. I believe 309 wire is the wire of choice for corrosion resistance... but may be remembering that wrong. 321 or 347 would work well also.
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Old 15-08-2014, 12:19   #8
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Re: re-welding stainless tanks?

If you know the aloy of the tank you should use that aloy of filler as there will be moisture preasent with dissimilar metals and all. Failing that, then 309 will be more noble and a better than the other way around.
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Old 15-08-2014, 12:24   #9
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Re: re-welding stainless tanks?

The tanks are probably 304, and my understanding is you should not use 304 wire unless the assembly will be solution heat treated after, otherwise corrosion will be likely.
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Old 15-08-2014, 12:26   #10
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Re: re-welding stainless tanks?

Canibul-
In theory, a proper weld makes two pieces of metal (three including the stick) into one homogenous piece, so stress on the weld shouldn't crack it any faster than it would crack the surrounding metal.
In practice, the welding rod was probably a different alloy, or the weld wasn't really clean, or something like that contaminated the weld so it is failing now.

Unless you grind out all the old weld (which would mean cutting apart the tank and rebuilding it) the old stuff is still there and if it is the wrong metal, it will come back to come apart again. In practice, I would think a generous new bead inside and out would bury it well enough to get 20 more years out of it.

But personally, I think I'd try to lap some "L" stock over the bad welds, and either drop a liner into the tank, or have it sprayed with a food-grade plastic lining. The "L" stock would be a structural repair, the bladder or liner would ensure there's no leakage. Between the two? "Forever".

And it might even be quicker and cheaper to do it that way.
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Old 15-08-2014, 12:32   #11
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Re: re-welding stainless tanks?

thanks for the info. That's kind of what I was expecting to hear. I'm a shade tree welder, I understand the penetration and polarity aspects of this little stick welder, and can stick stuff together solidly but it's not pretty. A cracker box is what I have, so if that's not the tool then I need to find a Plan B. Doesn't sound worth buying and importing a TIG welder for this one job.

If I can't do it with what I have, I'm thinking it might be cheaper and smarter to just see if I can import plastic tanks. I can hire someone here, but it would cost me a fortune and once I delivered the tanks the timing would be out of my control. Might be a week. Might be a month.
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Old 15-08-2014, 12:35   #12
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Re: re-welding stainless tanks?

My understanding has been 316L is the aloy of choice for these sorts of things so that's what I built my water tank from using mig and 316L wire. But unless the op knows what aloy the tank is it's a crap shoot and best to err on the High side.
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Old 15-08-2014, 13:03   #13
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Re: re-welding stainless tanks?

I have the same problem with one of my stainless tanks. Anyone ever tried this:
Microseal, metal sealant, seal castings
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Old 15-08-2014, 13:19   #14
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Re: re-welding stainless tanks?

Some good welding info here.

I have weeping going on from a foamed- and glassed-in 316 tank. I have always suspected that the glass against the bottom seam of the tank deprived the SS of oxygen, which resulted in corrosion. If I understand correctly when SS is deprived of oxygen it is unable to repair the protective oxide layer on top and corrosion results. For this reason I am also very suspicious of any coatings.

Any thoughts?

Greg
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Old 15-08-2014, 13:32   #15
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Re: re-welding stainless tanks?

Forget welding! Just remove tanks, clean them up very good (use sno-bowl toilet acid----and epoxy repair them. first brush on a coat of epoxy,then another, then use thickened epoxy glue to make a rounded edge on all external edges-say a 5/8 diameter one. Sand smooth. Then apply a 4inch wide FG tape 8oz embedded in epoxy liquid. Let set and sand burrs----then final coat. No need to paint. Will never leak or break.The 5/8 rounding is so you can bend the tape around the edge without it lifting before epoxy is set.(no Bubbles)> PS a heat gun will speed work.
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