Stainless water tank...

[B_C]

I got a job from my aviation business customer today that has me stumped.......It's a water storage tank from a passenger jet plane and it got a leak in it that was pretty much impossible to locate.....(under a brace that is spot welded to the main Tank)....I'll take a couple pics ...







He wanted me to weld a bead all the way around both sides of ALL the reinforcement bands to try and seal the leak that was coming from under the straps.......I explained to him that the straps were going to burn up before the tank itself would start to flow a bead since it was way thinner material than the tank plus there was an air gap between them making it even harder to weld like he wanted.......I purged the tank and started to run a bead (with .035 316L) and it welded so bad that I gave up after a few inches.......The stuff just was terrible to weld.....I have welded Stainless for years so it was very disappointing.....Should I feel bad that I can't fix this tank? Or was I DONE before I started?

[old blue]

I'd try to find the leak and surgically deal with it instead of welding circles around the whole thing.

If the problem is under one of those beaded bands, cut the spot welds out so you can slide the band out of the way to find and fix it. Then put the band back. Find out if it matters where the band goes.. you might be able to just reattach it right next to the repair area.

[Rocky D]

First, you need to tack the seam .25" apart all the way round, then use a heavier rod, lay it in there, .045" or larger, and melt right up the rod...rod should contact the joint tightly, and remain in the puddle...I know ya know how to do that. The larger rod will take the heat from the thin side. Taking a section of the band off may be easier, as ol blue suggests, but you better be sure where the leak is first...DPM won't help much, here either, uless you remove the entire band.

[B_C]

I called the customer and explained what was going on and he said to just stop and let him make a decision....I really don't want to remove those bands since they will most likely become JUNK after dealing with the spot welds......Remembering that this is super thin stainless and needs a ton of gas backup to stay "Food Safe" I don't know that I want to get involved with this deal the more I think of the possible results.....The thought of having to replace this tank makes me very nervous..

[012LDY]

Could you fab the customer a new, and more serviceable tank than he could reasonably purchase on his own, without either of you losing money on your effort ??? Just my 35 cents worth BC. Take Care - Shawn

[Rocky D]

How about cutting that bad boy all the way round remove the leaky seam altogether, and weld it back up again, using the purge dam technique ,so that you are only purging the back side of the weld area, and not the whole tank.

[B_C]

It's not a seam that's leaking...It's a spot weld that is on one of the straps and it is leaking from under the strap...Making it tough to locate......As far as cutting the tank in half........HA HA HA YEAH RIGHT

[B_C]

I'd try to find the leak and surgically deal with it instead of welding circles around the whole thing.

If the problem is under one of those beaded bands, cut the spot welds out so you can slide the band out of the way to find and fix it. Then put the band back. Find out if it matters where the band goes.. you might be able to just reattach it right next to the repair area.

How would you suggest I cut the spot weld out since there are like 25 on each band....Without damaging the tank itself? It can't have any holes drilled in it......

[Roger]

Looks like over engineered throw away tank with to many sections made to be light regardless of cost. Are there baffles at some sections? Maybe bands increase rigidity?

[B_C]

Nope no baffles. I just talked with the customer and he hasn't figured what to do with it yet. Like you said "Throw away tank" I really don't see me or anyone doing a "Welding repair" on this tank unless I can figure out which spot weld is leaking and carefully grind the area away covering it and then weld it up....Still doubtful.
But I will talk to the customer this morning and see what he has to offer....If it didn't have to be Food Vessel I wouldn't be so concerned but since it is so thin I'm worried about SUGARING even with the ARGON PURGE...

[fjk]

hmm, proverbial rock and hard place....
it sounds like you've all but ruled out welding.
instead of welding, can the tank be lined with something
like an epoxy? (obviously, it would have to be food-grade, and
liquidy enough to flow around and coat the inside....)

alternatively, can stainless be brazed? if so, you could try to
heat each band and sweat the joint, just like copper plumbing pipe.

frank

[old blue]

How would you suggest I cut the spot weld out since there are like 25 on each band....Without damaging the tank itself? It can't have any holes drilled in it......

With one of these

[Roger]

Place silver solder rod in bands with flux. flux and ring of solder around other spots. Place in oven until solder flows which could be timed production line event. Clean with circulated 200 degree tsp solution.

[B_C]

Sounds good except the tank is 6 feet long and I don't have an oven except for Lynda's and she probably wouldn't like that tank in there

[Rocky D]

Why not just try to DPM it...die on the inside and developer on the outside...it could identify the leak right on for ya.