aluminum anode in hot water with copper?

jerbear

Our boiler system includes a ordinary glass lined DHW 40 gal tank into which I have installed two copper heat exchangers ( 4 foot "wand" type, double wall, inserted into hot and cold water ports). One wand is for solar DHW preheat and one is for indirect preheat from the boiler. I also inserted a new aluminum anode and now am wondering if this might cause corrrosion rather than prevent it? I thought copper and aluminum react together but I don't really understand the processes involved here? Should I get a magnesium anode or maybe take it out altogether? The other concern is the tank is in the attic and to replace or even check the anode would involve tipping over the tank after removing all the solar, boiler, pressure valve expansion tank, etc plumbing. Tanks, I mean Thanks

gerry gill

aluminium is fine as an anode rod.

i prefer magnesium tho..aluminum rods seem to cause this jelly like deposit to form with the sediment..the magnesium rods don't seem to generate this..you can buy segmented anode rods when its time to replace them..much easier when ther is no headroom.

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Larry Weingarten

Hmmm...

Thar's trouble on the horizon! Copper is noble to steel which is noble to both aluminum and magnesium. Copper in a glass lined steel tank will make the steel play anode to the nobler metal. Unless you have electrically isolated the copper, this will be a problem. Possibly, putting two magnesium anodes in the tank and checking them at six months will slow damage to the steel tank. Once you know how quickly the anodes are being consumed, you can fine tune the service schedule. I'd certainly put the tank in a drain pan, plumbed to a safe place. I'm not fond of aluminum in water that may get taken internally. Magnesium however is considered good for health.

If your tank is electric, a plastic tank might work better.

Yours, Larry

Perry_3

Gee.... Now apply that to a boiler...

This "jelly like deposit" sounds exactly like the "slime" that I read about aluminum block boiler HX's leaving in a heating system in Europe.

Immagine: Aluminum is used as a sacrifical anode for hot water... Commonly available - commonly used.

Now tell me again how Aluminum is a good material to make a boiler HX from?

This is one of two of the galvanic issues I was concerned about the instant I heard about Al Block HX's.

The value of cheap construction last long after the initial bill is paid... (or becomes apparent long after)...

Perry

[Deleted User]

Big difference...

A DHW system is an OPEN system. A properly designed CLOSED loop system doesn't have to contend with the same oxygen issues.

One of my old solar professors (George Lof) use to tell a story about failing solar lines. Seems the installation crew was using 5 gallon buckets as saw horses whenever they were cutting the aluminum legs of the collector supports. Later, these buckets were uses as mixing buckets for the glycol/water mix. He had a whole bunch of copper pipe that swiss cheesed on him, and when investigated, they found that there were particles of aluminum floating freely in the closed loop, and wherever it came into contact with the copper, it set off an electrolysis process that eventually ate its way through the pipe.

I've also heard stories of water treatment plants getting out of control with their Alum (sister of aluminum) and THAT causing water line pitting in new construction.

If your house has plastic tubing, its OK. If it has OLD copper water tubing, which has run in hard water, you probably have a protective patina. If its new, or has had a sodium exchange water softener, I'd be concerned.

If it has galvanized steel, you've got a WHOLE lot of other problems regardless of anode type:-)

ME

Perry_3

Your story indicates No Difference

Mark:

This issue is not oxygen in the water. Its about galvanic issues.

The very story you cite about the Aluminum particles in the copper solar heat system causing problems - even in a gylcol system exactly indicates the galvanic issues.

How much oxygen is in the water really has no bearing on this issue.

Also, I would not count too much on the protective hard water scale on the existing copper or steel piping - all that will do is slow the process down a bit.

Only by the use of proper corrosion inhibitors can the issue possibly be contained - and they have to be monitored and adjusted on a frequent basis to maintain proper chemical control (if you get ones that work - and this is much more than a PH test). I am not aware of any home heating contractors who are doing this kind of chemical monitoring and adjustment (you would have to send a sample into a lab for analysis - then add a very specific amount of corrective chemicals on a follow-up visit, let the system stablize and resample).

I am dealing with a similar issue at work right now that had galvanic corrosion of part of the HX assembly in a corrosion inhibited system. We are spending $50,000 - $100,000 for a series of lab test on different materials to come up with a new series of materials that will work without galvanically corroding each other on our replacement HX's (all told this is about a $2.6 Million dollar project to replace some HX's due to galvanic corrosion).

It's all great to say that Aluminum block HXs will work problem free on a plastic system. That may indeed be true as long as the connectors materials are compatable. Installing an Aluminim block boiler on an existing copper or steel piped system.... Well all the evidence I found on a number of European websites (presented here on the wall several time in past postings) indicates problems and a fairly short boiler HX life.

I just think it is so funny that the plumbing industry has used Aluminum Anodes for corrsion control for years.... (something I did not know before)...and then claims that Alumimum block HX's won't have any galvanic problems.

Perry

[Deleted User]

Main difference...

These closed loop heating systems had no means of oxygen removal. They were closed loop, but had no air seperators or auto vents.

Correct me if I'm wrong, but I've always been taught that in order to have electrolysis that you needed an aqueous solution, oxygen and dissimilar metals directly connected within the electrolyte.

In the case of a closed loop system with air elimnation, the O2 is removed, hence the battery stopped.

But, it wouldn't be the first thing I've found out that I've been lied to all these years... You speak of glavanics. Is that substantially different from electrolytics? I thought they were one in the same.

BTW, after reading all your information on aluminum HXers, I've fallen out of love with them. And this post was not intended to be in defense of said HXers, but wondering what the long term affect on copper water ways will be that are connected to Aluminum HXer boilers...

Boilers are EASY to replace. Pipes hidden behind sheet rock, that's a whole different story.

ME

Perry_3

Galvanic Corrosion

Electrolysis is the generation of hydrogen and oxegen by electically breaking down water. It has nothing to do with galvanic corrosion.

Galvanic Corrosion occurs when three conditions are present:

1) Galvanically disimilar metals (typically over 1/4 volt difference).

2) Electrically conductive solution (the more conductive the faster the corrosion).

3) NO Alternate "preferential" corrosin path available (i.e: installation of a properely sized and placed sacrificial anode); or NO electical galvanic suppression field (these are tricky, and can cause reverse corrosion if the field is set to high - it's happened, and you should see how fast its possible to destry a titanium tubed power plant condenser by having too high a field voltage).

In addition there is another factor at play that will determine the rate of corrosion.

4) Distance & Relative areas. Galvanic corrosion is most pronounced when the metals are joined or in close contact; and the amount of corrosion is driven by area factors of the items involved. As an example: A small sacrificial anode rod compared to the area of a hot water tank corrodes away relatively fast.

The problem with retrofitting an aluminum block HX into a steel or copper system... is that the almuminum block is relatively far apart on the galvanic scale from steel and copper and it will act as if it were just a sacrificial anode for the system (just like an aluminum, or zinc, rod acts as a sacrificial element for a steel hot water tank).

Those kinds of failurs have occured in Europe based on the descriptions I found late last summer when I was researching European Websites relating to Aluminum Block HXs).

There are ways to electrically isolate the metals; but those are harder to implement effectively than a lot of people imagine (and I did not see any attempt to do so on home heating boilers in the pictures I studied of Aluminum block boiler HX's).

There are also chemical methods to control this (corrosion inhibitors) - but that is also tough to do (this is the reason that automotive antifreeze must be reconditioned or replaced every several years - to replace the corrosion inhibitors). Again, I have seen no real indication that this is being done for home heating systems.

I do note that chemical inhibitation can be off as well... Why do you think I'm involved with a $2.6 million dollar replacemnt project for 4 heat exchangers at work right now. That was an inhibited system that had constant monitoring by an onsite chemistry staff with a fully equiped chemical laboratory. Opps ! "We" forgot something about the metals in the system... Well... Now I'm going to find metals that will work within our inhibitor system for the new HXs.

I do note that now you can get aluminum radiators in Euorpe. I wonder is that was so you could have essentially a all aluminum/plastic system to eliminate the galvanic issues (and I wonder what they make the fittings out of...).

From an engineering standpoint Aluminum block HX's have only one advantagous feature... They are cheap to fabricate.

Aluminim requires even without galvanic issues a fairly tight control of water PH and basid inhibitors. You just can't fill it and forget it.

Acid disolves it easily (and the designers intentionally make the mod/con boiler HX's thicker so that the condensation will take a while to eat through them).

Thick aluminum has a much worse heat transfer than thin stainless steel (It is not just the heat transfer coefficient that is important - it is the combination of the heat transfer coeficient and the thickness of the material that is important).

I will admit that your story above concerning the Aluminum flakes was probably affected by free oxygen in the system. Under a pure galvanic reaction the aluminum flakes would have just dissolved into some kind of aluminum ions or sludge. However, due to trace elements and available oxygen they created a pitting cell enviroment - which then perferentially attacked the copper where the flake was. That scenerio does not apply to an Aluminum Block HX as long as no free flakes are formed and circulate through the system (Threading chips might be an issue).

Hope this helps. Feel free to research galvanic corrosion on the Web. Tons of information out there.

Oh yeh... Explosively welded aluminum to steel will not galvanically corrode. The explosive weld bond has some really unique properties... But, it is an expensive joint and I doubt you would ever see it on a household heating boiler.

Perry

[Deleted User]

Explosive weld bonding...

No thanks, my customers wouldn't stand for the noise...

As usual, thanks for the enlightenment and education.

So, in your experience as an engineer, got any suggestions for us wet heads that have installed a lot of these aluminum HXers in closed loop applications, like a lesser noble anode within the fluid stream???

You've raised a LOT of concern here...

ME

Perry_3

Some Recomendations...

To bad you didn't want to fund my getting back into exlposive welding as that is one of my two areas of expetise in explosive work, and the reason I have maintained my blasters license was so I could get back into it. Fascinating field of work. Great for stress relief too... "Fire in the hole" - Ka BOOM;}

Onto the subject of modern boilers.

I understand the situation the Mfrs are in. Old cast iron boilers with black iron pipe systems last many many decades (often 50 years easy).

The problem is that once you try to extract more energy - or run them at theoretically more heating system efficient temperatures or for radiant floors they no longer work well due to the corrosion issues.

So new boiler materials are introduced; and few people have any understanding of all the issues involved with those new metals.

Another problem is that "low cost" wins market share. Far to many heating contractors only know how to sell on price. They don't know how to sell a more expensive product based on the features that make it great. Thus, most of the Mfr's are under pressure to produce low cost units.

It does not escape my attention that one of the ways to lower cost is to reduce the cost of design. That usually means getting rid of the "expensive" people and going with less costly people. If I were not in the Nuclear industry I'm the perfect canidate to be "riffed" and the company to hire someone at about half of my "cost" to do the same job... Of course those people do not have my knowledge and may make some really interesting and very costly mistakes.

The US Tubeular Heat Exchanger industry has seen this over and over the last several decades with the results that old name companies can no longer produce high quality large heat exchangers and are either getting sued due to problems with their current products or not getting the business at all because people with half a clue won't include them on the bid list.

Along a similar line home boiler Mfr's are probably not worried about lawsuits from homeowners about misdesign of their boilers if they fail down the road (who is more likely to be named and loose in a homeowner lawsuit... The heating contrator who recomeneded and installed the boiler). Industrial customers would sue instantly over some of the problems I see down the road on Aluminum block heating boiler HXs, and potentially on one problem with the SS HXs; and would focus on the Mfr.

The two common materials of choice for modern mod/con boilers are 300 series SS and Aluminum.

Last week there was a thread about problems with a 300 series SS boiler HX weaping. I opinioned that it was probably chloride related. Perfect environment for chloride problems and most of these boilers are exposed to some form of chloride. While it could be something else - most likely chlorides

My recomendations as an engineer with lots of metal failure analysis experience... 1) Put in a simple carbon filter along with the backflow preventer and makeup pressure control valve. City water levels of chlorine will be romoved by a simple carbon filter. 2) ensure that you only use an approved "chloride free" leak check compound (Snoop) and industrial cleaning compound for any cleaning of the boiler HX (ask at your industrial supply house - redily available).

For the Aluminum Block Boiler HX's. I still really scratch my head on why the Mfrs ever went there (OK its cheap - and they should last at least a few years even in the worst case). The galvanic issues of Aluminum/steel and Aluminum/Copper is well known. The issue that the combustion condensation slowly eats away at it is also well known.

I am just not sure what to say if the boiler companies engineers did not know this - or did not tell managment... This is basic college level textbook stuff and as far as I know every engineer has to take a basic metals course where they teach about these kinds of issues and tell "great" failure stories about certain metal combinations (guess which ones I remember from my college days...).

Considering the experiences in Europe that I uncovered with a day of internet searching - I am surprised that the Mfr's did not know that and provide very specific instructions on how and where to use these boilers.

Certainly, on a new system properely constructed of PEX and other materials there will probably not be a galvanic problem. Proper PH control will minimize other potetial issues.

On retrofits to existing systems.... Ugg.

Probably the best thing you can do is to create an electrical separation of the metal from most of the system. Can you install a large diameter piece of PEX between the boiler and the rest of the system? It would not need to be that long, and it would reduce the galvanic currents to what could travel on the scale that will line the PEX which should be enough to do the trick (at least until the HX fails for another reason).

If I were installing a new installation (assuming I was a field installer) I would try to put in this type of electrical break between the very near boiler piping and the headers. Idealy, the Mfr would have a properely engineered and impossible to incorrectly install electrically insulating connection to the Aluminum boiler block and the boiler connection piping for the system. As I noted above - this is often far more difficult than it appears up front. Great new elecrically insulating joints when new have problems down the line - or are taken apart and improperly assembled.

I would still install the carbon filter on boiler fill. No reason to add any chlorine to the mix of issues (I actually think that is a good recomendation for any boiler - water or steam - of any metal).

Even with that - I wonder how many service people are going to properly control PH and other boiler additives to keep an Aluminum Block HX from degrading down the years due to other chemical control issues....

In the end, if you do adequately control the internal system chemistry and galvanic issues... the HX will be eaten out by the acidic combustion condensation.

I found no information on what the Mfr's expected these boilers to last from that perspective. However, i have heard some people discuss the concept that boilers should be replaced periodically just like kitchen appliances... every 8 - 10 years. I wonder if that is an indication of the expected life of condensate corrosion of the Aluminum Block. Don't know - just wonder.

The concept of regular and somwhat freequent boiler replacment is very scarry considering the price of a boiler + installation. Any overall cost efficiency of hot water heat goes out the window under that scenerio. At least the appliance dealers will deliver, install, and remove your old appliance for free.

Since I also have a sales background; and I know that some people want to see the cheapest.. I could see the concept of - with the right exclusions printed as part of the option - to list an Aluminum Block Boiler as "Cheapest mod/con options" in a 3 part bid (low, middle, best) that included the customer specifically accepting which option and stating that they read and understood the tradeoffs (and I would be somewhat upfront and blunt about possible issues with Aluminum Block boiler HX's - keep in mind that others will probably offer them one and at least they should know).

Not everyone will buy a Vitodens or another premium boiler (of course, I beileve that if presented on a regular basis a lot more would buy than some would believe).

Hope that helps,

Perry

hr

Clean and maintain the system fluid

As you know I use, and like the Rhomar multi metal products They do have a test kit specfic to their product. As Perry mentined ph is not enough info.

Getting a coating on the surfaces is important.

Aluminum does rust to protect itself, although it is called oxidize. Anodized aluminum is one way they treat aluminum to make it more tolerant. It's basically a forced "rust" concept. As in outdoor yard furniture

I think the plating agents in the Rhomar are going to prove to be the key component.

Finding one, or a group of chemicals to handle all the metals found in modern hydronics is the challange.

I believe Rnomar 922 has 35 different ingrediants. Hense the sticker price It's in all my Ultra installs.

hot rod

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Perry_3

If it were only that simple

Hot Rod:

There is no doubt that a good corrosion inhibitor package can do a lot of good. But even it has its limits - and must be maintained.

Why do you think I am spending $50,000 - $100,000 at work to research different material combinations for the one set of HXs we are replacing. The tubes being used are too far away from carbon steel for the kind of inhibitor we are using.

What we are using for an inhibitor is one of those great products that has virtually been banned from use because it is a carcinigen (chromate based). We can get away with using it because we have a full time chemistry staff - proper protective gear - and all drains go into a special waste drain system that would process it out and dispose of it as a hazardous waste.

When we told the corrosion lab what we were using they were shocked with surprise. Chromate based... they had only heard of one other place that was still using it (another nuclear unit). Their next comment was - well I guess we can't improve your corrosion inhibitor. Thus we are experimenting in the lab with different metal combinations to find a series of metals that as a series of one metal against another: Tube to support plate - support plate to shell - shell to nozzle - Nozzle to Carbon Steel Pipe - that won't have any significant galvanic corrosion between any metal to metal junction.

Changing the tube material might seem simple; but would cost us at least another half a million dollars in future testing to prove that the new tubes worked good enough (I have a series of baseline test on the existing tube material that the regulator has accepted). It would also open us up to other degradatio of the tubes - and we know that the current tubes do not degrade (even if they cause the rest of the HX to degrade).

Back to home boiler HX's.

Copper is a long long way galvanically from aluminum. I doubt that a corrosion inhibitor package will do the job if an Aluminum Block Boiler HX is connected to a copper based heating system (the fact that sacrifial aluminum anodes are used to protect copper systems ought to give a clue).

I will agree that a good corrosion inhibitor package might work for an old steel system with an Aluminum Block boler HX as they are closer toghether on the galvanic series - but it must be properely maintained. How are you maintaining your Rhomer. How do you test the concentrations - and how do you replenish just the right amount?

I hope it works out for you. Time will tell.

Perry

Cosmo_3

This thread is an eye opener

This is why I love the Wall.

Cosmo