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Old 02-09-2016, 11:46 AM   #15
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1998 30' Excella 1000
Livingston , Texas
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Maybe you have a very benign water chemistry where you are or travel? Or the heater gets limited use?

I posted this on a related thread, so you may have already read it:

I've always chalked up variable tank life to differing amounts of use, and water chemistry. Now I am wondering.

I've had three tanks with pinhole leaks over 17 years of full-timing. Not one leaked from the flue. Atwood states:

"The aluminum tank is the anode and the metals in the water serve as the cathode. Consequently, the aluminum gradually sacrifices itself and aluminum particles are carried away with the water flow. A white scaly material (aluminum oxide) often is formed around the points where the heaviest action is taking place and heat accelerates the process."

It makes sense that heat would accelerate this reaction. The flue should be the hottest portion of the assembly. Most reports are of pinhole leaks in the tank body, not the flue.

Atwood states:

"The interior of the tank consists of a 15% thickness of type 7072 aluminum (pure aluminum and zinc) that is fused to the core during the rolling process."

Now I do not know what they mean by the "rolling process". Is is creating a laminated flat stock, or the forming of the tank body? If it is the latter, are they pouring the molten alloy into the tank to yield a bonded coating? If we speculate (a dangerous thing to do) that this is the case, could their protective alloy coating be thinner in some places, and on some tanks? Could this be why some tanks last 30 years+, and others only 3 years?

I had a pinhole leak, that I presumed meant the tank was toast, and soon to fail in other locations. I fixed it with epoxy, and the tank lasted another 6 years of full-time use. Go figure.
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Old 02-09-2016, 12:01 PM   #16
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Originally Posted by Piggy Bank View Post
So my friend with an SOB keeps insisting that I need to change out the anode on my water heater so it won't go out at an inconvenient time.
I pulled out the owners manual on my water heater and there is no mention about this. Just talk of flushing out sediment.

So is this something that needs to be done? If so what's the story?
As noted upthread, recent production Airstreams all use Atwood water heaters. They have an aluminum lined tank, and are not ordinarily equipped with an anode. Recent production Airstreams use PEX (polyethylene) tubing to carry water to and from the water heater, with nonmetallic fittings.

Anodes are not a cure-all for corrosion problems. They provide protection against electrochemical corrosion when dissimilar metals are used in the water distribution system when the water has certain properties. The absence of anything more than a trivial amount of other metal (other than the water heater) in contact with the freshwater system, means there is no cathode, and electrochemical corrosion cannot take place.

There are other causes of corrosion, but an anode won't help with those. Extremely acidic water, for example, will gradually dissolve metal components in the plumbing, anode or no anode.

There are a handful of situations where the anode will make water problems worse, though these are not common.

Any water heater made of metal will eventually corrode and fail. Maintenance, at best, helps a little bit.
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Old 02-10-2016, 08:58 AM   #17
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1996 25' Excella
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Quote:
Originally Posted by Siegmann View Post

Atwood states:

"The interior of the tank consists of a 15% thickness of type 7072 aluminum (pure aluminum and zinc) that is fused to the core during the rolling process."

Now I do not know what they mean by the "rolling process". Is is creating a laminated flat stock, or the forming of the tank body? If it is the latter, are they pouring the molten alloy into the tank to yield a bonded coating? If we speculate (a dangerous thing to do) that this is the case, could their protective alloy coating be thinner in some places, and on some tanks? Could this be why some tanks last 30 years+, and others only 3 years?

I had a pinhole leak, that I presumed meant the tank was toast, and soon to fail in other locations. I fixed it with epoxy, and the tank lasted another 6 years of full-time use. Go figure.
The rolled coating is actually put on as they roll the sheet of aluminum out from the ingot. Since it is a hot rolled process there is good bonding of the interior layer to the tank body. Their fabrication requires welding which means they have to get good weld penetration all the way through the tank wall; wonder what that does to the rolled coating at the seams. Was your pinhole leak on the seam?
Interesting that they use an alloy containing zinc. Presume it is to protect the main tank body, but then if zinc is dissolving over time then the coating would become porous.
Certainly your comments about time of use and corrosiveness of the water are valid. My current trailer has been extensively used over its 20 years of life. New to me, so we'll see whether the Atwood can last another 5 or 6 years.
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Old 02-10-2016, 10:18 AM   #18
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Interesting.... one leaked at a seam, another leaked at the juncture of the water out fitting. You may be on to something.
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Old 02-10-2016, 10:49 AM   #19
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It's my opinion, and it may conflict with some of the opinions above, that the aluminum/zinc rolled-on cladding acts as the anode against the main tank stucture which is aluminum. The aluminum/zinc alloy would be a protective coating that would eventually corrode away leaving the tank unprotected after X years where X depends on the corrosivity of the local water.

Under this theory, if you use a magnesium anode in an Atwood water heater it would corrode before the aluminum/zinc alloy, and therefore extend the life of the water heater, especially if the local water is corrosive.

Depending on water quality, you could extend the life of the water heater by using a magnesium rod. Whether the extension is worth the cost of the rods and the labor rquired to periodically replace the rod depends on local water quality.

As a test, I would install a magnesium rod and check it after one year. If there was significant loss of material that would indicate to me that it was useful. You must look at the magnesium rod as protecting the aluminum/zinc cladding, rather than protecting the tank itself.

This belt, then suspenders, approach might not work for you. As I have said above, it depends a lot on your local conditions.
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Old 02-11-2016, 11:52 AM   #20
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Quote by markdoane; "As a test, I would install a magnesium rod and check it after one year. If there was significant loss of material that would indicate to me that it was useful. You must look at the magnesium rod as protecting the aluminum/zinc cladding, rather than protecting the tank itself.

This belt, then suspenders, approach might not work for you. As I have said above, it depends a lot on your local conditions." Endquote

Sensible, practical ....nothing wrong with this idea!

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Old 02-12-2016, 02:11 PM   #21
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2014 30' Flying Cloud
Black Creek , British Columbia
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Hard water

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Originally Posted by AnnArborBob View Post
Our HW tank does not have an anode. Since we have similar aged units, I suspect your HW tank does not have an anode. Assuming that's the case, a periodic draining and flush as suggested above should be fine. If you travel extensively in areas known for hard water (i.e., the desert SW) you might want to do this a few times a year (we are basically full timers.) If you are a weekend warrior, once a year is probably fine.
We are currently in Yuma and our neighbor at the park we are in, told us not to drink the water. We can buy water at the park 25cents/ gal. I assume the water is hard and we are here for a month so will I need to clean/flush the tank when we get back to a soft water supply. Are there any tank cleaning products recommended for the Atwood water heater

thanks
Norrie
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Old 02-13-2016, 11:41 AM   #22
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You simply 1/2 fill your fresh water tank with water at home, add 1/2 cup of bleach through the fill nozzle (use a pop bottle) and flush the hot water heater with the fresh chlorinated water. Drain everything after letting it sit for 30 minutes and refill with fresh water. You at least need to get the bleach out of the aluminum tank by flushing if you are planning to store the trailer.
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