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Old 09-11-2014, 09:22   #61
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Re: Re-Welding Stainless Tanks?

Quote:
Originally Posted by Canibul View Post
...The manufacturer does not advertise this product for this purpose...
How about emailing the manufacturer with your plan?

Tell them the depth of the tank, so they'll know how much pressure will be trying to push the coating off.
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Old 09-11-2014, 09:32   #62
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Re: Re-Welding Stainless Tanks?

Minimal, with a tank depth of about 18" max. Location of leak most likely higher than that by a couple inches.
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Old 09-11-2014, 12:17   #63
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Re: Re-Welding Stainless Tanks?

Just as an aside, here is a link to the rubber sloshing compound.

PR-1005-L BUNA-N-SLOSH COATING from Aircraft Spruce
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Old 09-11-2014, 12:54   #64
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Re: Re-Welding Stainless Tanks?

Says for aircraft fuel. Nothing about potable water supply.
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Old 09-11-2014, 13:17   #65
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Re: Re-Welding Stainless Tanks?

I've never done this for a marine application, but I have gas brazed stainless steel tanks, both with hi temp silver brazing alloy and also "back in the day" with regular flux coated bronze brazing rods.

The nice thing about brazing pinholes closed is you can put a large puddle around the hole so it supports the adjacent metal if there are any other pinholes in close proximity.

The issue is that once brazed, it most likely can never be welded again without tedious cleaning, and initial weld and then going over the inevitable holes from poor weld coverage. However, it is an option to keep in the memory banks. I was once told that stainless can be soldered using lead-free plumbing solder but have never tried that myself.
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Old 09-11-2014, 13:29   #66
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Re: Re-Welding Stainless Tanks?

I bought some stainless steel welding rods, and played around with trying to fix a Force 10 stove grill. Using a cheap "cracker-box" dc welding machine with a manual written in Chinese. It does work, though. But the results are ugly with a lot of splatter.

I'll have to get the tank out to fix it. If the leak includes a loss of structural support It may well be a combination of my poor welding and rubber bed liner.
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Old 09-11-2014, 13:56   #67
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Re: Re-Welding Stainless Tanks?

I'm suspicious that your approach may build new problems in for the future. Sanding the stainless creates crevices which allow corrosion to start quickly - that's why it is best to use polished stainless steel on a boat. Then overcoating with a sealant will deprive the stainless of oxygen, which is also questionable. Simplistically, the shiny protective surface on SS is made of oxides of chrome and nickel and possibly other metals in the alloy; when new metal is exposed to air these oxides naturally form - without oxygen the protective oxides don't form (which explains why once corrosion starts it tends to spread into the metal instead of along the surface). If somewhere along the line a flaw develops in the seal and moisture gets between the sealant and SS, corrosion can start and spread quickly in the anoxic environment. (For the same reason a too tight stuffing box can cause a SS shaft to corrode). It is actually a bit worse than this, as the unprotected stainless has a different galvanic potential to stainless with the oxides intact and so can become self-galvanic. It is for similar reasons that SS screws should never be used to fasten wooden hulls below the waterline (although they can also be damaging to the wood).

I would leave the sandpaper and sealant for something else...

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Old 09-11-2014, 14:00   #68
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Re: Re-Welding Stainless Tanks?

and just give up on the idea of carrying fresh water?

seriously, though, I don't really care if it starts corroding elsewhere. I'm just trying to make it serviceable until I can get someplace else to import big plastic tanks. 46% import duty here, plus fees plus surtax, plus plus plus.

If I can make it last another year or two I'll be fine. I can nip up to the Bahamas and go on a cruising permit and order some, or head down to Puerto Rico and fly some in without paying import duties. I'm just trying to stop this leak for now.

And as stated, I already have discovered that the coating sticks to the unsanded steel just as well as it does to the scratched stuff. No need to sand it. Just clean it with solvents and get any residue from being under water for 28 years off of it.
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Old 09-11-2014, 14:21   #69
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Re: Re-Welding Stainless Tanks?

Skipping the sanding sounds like a good idea. Extending the life of the tanks a few years with a sealant sounds like it should work. My fear is that it will also hasten their ultimate demise but that isn't a concern for you.

As for plastic tanks, polyethylene welders are not all that rare. I remember that there was a small shop in the marina in Turkey that could weld custom tanks. I wouldn't hold my breath looking for them in T&C, but I would expect that they exist in Puerto Rico.

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Old 09-11-2014, 14:26   #70
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Re: Re-Welding Stainless Tanks?

Just to temporarily fix one small leak, slap some fiberglass and epoxy resin over the hole.
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Old 09-11-2014, 16:25   #71
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Re: Re-Welding Stainless Tanks?

I the to be conventional, but why not just clean the stainless with some metal wool or sandpaper, then apply plain epoxy over the leak areas? Or some bandage gauze or t-shirt soaked in epoxy, if there's no glass fiber to be found?

Epoxy bonds well to most clean stainless. And there are so many ways to thicken or reinforce it. Surely, for a long-term-temporary solution, old fashioned epoxy would do?
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Old 10-11-2014, 08:39   #72
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Re: Re-Welding Stainless Tanks?

I've been reading about Devcon stainless epoxy and putty. it's possible I can find a similar two part epoxy for steel here. I know I can get JB Weld.
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Old 10-11-2014, 08:57   #73
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Re: Re-Welding Stainless Tanks?

The Devcon SS is just a two-part epoxy with SS dust added to it - I guess for additional strength?. In your application, a plain epoxy will work just as well. JB weld will do.

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Old 10-11-2014, 09:02   #74
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Re: Re-Welding Stainless Tanks?

I have had stainless tanks fail over time at their welds. It was not worth the hassle to try to patch them only to have them fail again in a different place.

I replaced my stainless tanks with High Density Polyurethane (HDPE) plastic. They of course will never oxidize.

If you cannot find the size you need then you can have the them custom made to fit exactly.
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Old 10-11-2014, 09:04   #75
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Re: Re-Welding Stainless Tanks?

This works good.



Amazon.com: Permatex 84209 PermaPoxy 4 Minute Multi-Metal Epoxy, Two 1 oz. Tubes: Automotive



I've also posted links to potable tank coating systems when this has come up in the past. A search should find it.


Prep with Roloc scotch brite pads. You can use a Roloc fitting in a cordless if you don't have something better.
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