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Old 17-08-2014, 23:06   #31
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Re: Re-Welding Stainless Tanks?

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Originally Posted by Terra Nova View Post
The plastic tanks are not baffled.
You can get them with baffles. Baffled Water Tanks | Water Tanks | Car Valeting Water Tanks | Window Cleaning Water Tanks If he has 2 100 gallon tanks he would need to look at the 400 liter sizes.
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Old 18-08-2014, 07:53   #32
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Re: Re-Welding Stainless Tanks?

I realize the plastic tanks are not baffled, but then I see no indication that the stainless ones are, either. I presently have four 50 gallon tanks, but am planning on changing that to a 50 and a 30 in each hull. I'll be giving up 40 gallons storage but I'm okay with that. we'll make that up in packaged drinking water. Going to the smaller tanks in the aft positions gains me some other stuff.

As for sloshing, these tanks are only 14.5" wide I don't think there's room in there for a tsunami with enough force to do much, other than in a fore and aft motion and these are below the waterline anyhow, in a catamaran. My gut feeling is that they wouldn't be able to affect the boat motion much at their worst slosh.

I looked at those baffled ones, but a.) none of them come close to fitting my boat and b.) I'd have to import them from UK. That's sea freight from UK to Miami, then sea freight from Miami to Providenciales. That pretty much takes them out of any competitive price contention in itself. I need something that essentially drops in. I plan to put the boat on a cruising permit somewhere and import the tanks to that location, OR just boogie on down to Puerto Rico where I don't have to pay any import duties for US made tanks.
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Old 18-08-2014, 08:12   #33
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Re: Re-Welding Stainless Tanks?

If you can remove the tank that is the best option for both welding and leak testing.

Tig weld only. Filler selection is based on ending up with the weld being slightly more noble than the tank. During welding certain constituents in the parent material migrate to the weld area. Typically use 308 wire for 316 parent material.

Ideally you want to be able to pickle the tank after welding to remove the heat coloring from welding. The passive oxide film will then reform in air. This will be the most reliable and long lasting. Also never use contaminated grinding media. Nothing that has been used on non stainless.

Cleanliness, lack of voids and correct filler selection are the key to success.

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Old 19-08-2014, 16:39   #34
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Re: Re-Welding Stainless Tanks?

[QUOTE=Canibul;1608304]I realize the plastic tanks are not baffled, but then I see no indication that the stainless ones are, either. /QUOTE]

Canibul, If your having stainless tanks made, you can have them made up how ever you want. In any case, my 35 gallon tanks have two baffles per tank, dividing each one into 3 compartments.
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Old 20-08-2014, 05:45   #35
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Re: Re-Welding Stainless Tanks?

Thanks for all the input. There's absolutely no chance we would have new stainless tanks made. That would be crazy expensive.
We've pretty much decided to replace the four stainless tanks with plastic. Now we're just deciding where would be the best place to do it, since we're in the Turks and Caicos. This is NOT a good place to buy things for boats. Way too expensive to import stuff here. We'll either take the boat up north to the Bahamas and order the tanks on a cruising permit, or go south to Puerto Rico or St. Martin where we can get them shipped in without paying duty. I'm going to try to put a temporary patch on the leak using the epoxy plumbers putty stuff that cures underwater.
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Old 20-08-2014, 11:45   #36
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Re: Re-Welding Stainless Tanks?

Canibul-
This is a real kludge, but it follows common hurricane preparedness & civil defense guides. Both tell you to fill a bathtub full of water if you expect utilities to go down (no electric, no water for most) and in order to "seal" the drain and keep out the grunge, they tell you to buy a cheap plastic tarp and line the tub with it. The water pressure will keep it full against the tub, the plastic is clean and leakproof.
So if you've got a reasonably sized inspection port...you take an oversize thin plastic tarp, tuck it in to line the tank, either use some tape or glue or bunch the excess up and out of the port to keep it in place. Voila, cheap liner. I wouldn't do it "forever" and whatever water is between the plastic and the steel will either weep out the leaks or get grungy...but it will keep your water in the tank, until you get those replacements. And at what, two bucks a sheet? It is a cheap enough kludge, ergh, solution to try.
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Old 06-11-2014, 15:44   #37
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Re: Re-Welding Stainless Tanks?

Well, we're back after a two month trip to the good old USA. Now it's time to take on that tank patch. First step will be to launch the boat.
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Old 06-11-2014, 16:35   #38
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Re: Re-Welding Stainless Tanks?

I haven't read the whole thread, but I thought I would comment, as I am a tig welder and have been welding stainless steel for many years.

Stainless steel is not a good choice for tank material in a boat. In the heat effected zone of the weld there will develope very small stress cracks which will eventually leak.






 


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Old 06-11-2014, 17:57   #39
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Re: Re-Welding Stainless Tanks?

[QUOTE=Zai;1671988]
Stainless steel is not a good choice for tank material in a boat. In the heat effected zone of the weld there will develope very small stress cracks which will eventually leak.





That is crazy talk. By "eventually" you must mean at least 50 years from new for a well made and installed tank. Lets not get into jet engines and space ships.





 

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Old 06-11-2014, 18:26   #40
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Re: Re-Welding Stainless Tanks?

No, he means stainless tanks will fail early in a boat's life, like 15-20 years or less. Monel is fine.

You're not going to find much stainless steel on a space ship--too heavy. Instead you'll find alloys including aluminum and titanium; roughly 1/3 and 1/2 the weight of stainless steel, respectively.
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Old 07-11-2014, 00:36   #41
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Re: Re-Welding Stainless Tanks?

I know it is hard to believe and there are quite a few making them.
However the problems could show up in a few years (2-4).
Read the US Coast Guard boating safety circular 79.
The American Boat and Yacht Counsil standards ANSI/ABYCH-24, ABYCH-33 and ANSI/NFPA 302 all require stainless steel fuel tanks to be less than 20 gallons and with domed heads, to limit the wall stress experienced in service.
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Old 07-11-2014, 09:51   #42
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Re: Re-Welding Stainless Tanks?

[QUOTE=Guy;1672031]
Quote:
Originally Posted by Zai View Post
Stainless steel is not a good choice for tank material in a boat. In the heat effected zone of the weld there will develope very small stress cracks which will eventually leak.





That is crazy talk. By "eventually" you must mean at least 50 years from new for a well made and installed tank. Lets not get into jet engines and space ships.




actually it's not crazy at all. My 1985 boat had a SS tank in the keel under the floor. It did not sit on the bottom but did get and stay damp as it was above the bilge drain/keel. By 1992 that tank had two holes in it, one about the size of a pencil eraser.. The holes were no where near a weld. That's a seven year life in that environment. The two other tanks under the setees were fine for many years.
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Old 07-11-2014, 10:59   #43
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Re: Re-Welding Stainless Tanks?

[QUOTE=Terra Nova;

You're not going to find much stainless steel on a space ship--too heavy. Instead you'll find alloys including aluminum and titanium; roughly 1/3 and 1/2 the weight of stainless steel, respectively.[/QUOTE]

I believe Inconel is the metal of choice for lots if not most of turbine and rocket engine parts. It's a stainless steel alloy too, just like 304/316.
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Old 07-11-2014, 12:29   #44
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Re: Re-Welding Stainless Tanks?

So,
What corrodes water tanks on a boat? Is it primarily from the outside, or from the inside?
What about fuel tanks?

My aluminum tanks are 27 yrs old, look good from the outside, can't tell about the inside
Will they fail tomorrow? Which one is most likely to go, the water tank?
I've got a 1946 airplane with very thin aluminum fuel tanks, they are in great shape, why should a boat aluminum fuel tank not last as long if it's not corroding from the outside?
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Old 07-11-2014, 12:34   #45
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Re: Re-Welding Stainless Tanks?

Not a spaceship, but I think the MIg-25 was mostly Stainless Steel
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