Corrosion of Alde Convectors

rh5555

The best material for corrosion resistance is titanium, which you can get in 7/8" diameter tubes.  This is a sample vendor, there will be others maybe with thinner walls, which would be cheaper.  Anodized aluminum is a very good second best.  Preferably go with "hard" anodizing, and select the appropriate grade of aluminum for best results.  I learned all this the hard way when I made oceanographic instruments. 

grassgd

rh5555 said:

Look out!  Stainless Steel is notorious for crevice corrosion - just as bad as aluminum.  It needs constant access to oxygen to stay stainless.  

Glad to have your comments. 

I know stainless comes in various grades and I don't know the grade used in the Alde heater tank but thankfully the connections to the tank which are under the same EPDM rubber hose and same type clamps on my trailer showed no signs of corrosion.

I believe/assume the corrosion on the aluminum components under the EPDM rubber hose is related to the trapped glycol corrosion inhibitor and oxygen being consumed and cannot be replaced creating a differential in oxygenated glycol which apparently can cause a corrosion cell to set up.  If this is correct, the same oxygen deprived crevice would have been created on the stainless steel Adle tank connections.

Could this be due to the grade stainless steel used in the Alde tank?

I was thinking of making the glycol system a closed system and purging all air/oxygen out.  Based on your comment this could be a bad idea unless the corrosion inhibitor can protect the stainless, especially in the crevice, right?

rh5555

I should probably back off on my blanket statement about stainless.  It is true that generally stainless needs an oxygen supply to prevent pitting, but maybe there are alloys that are less problematic.  We had a ferry here in Washington that was built using stainless steel for the salt-water fed sprinkler system.  It was quite expensive to change it all out once it rusted through.  Titanium is a safe bet, though.  Also the clamp position is probably the primary source of all our problems - are the tubes on the Alde tank shorter than the tubes on the radiators? In which case the clamps would be close to the tube ends (where they should be), thereby alleviating the problem.  Best not to have any crevices.

grassgd

rh5555 said:

I should probably back off on my blanket statement about stainless.  It is true that generally stainless needs an oxygen supply to prevent pitting, but maybe there are alloys that are less problematic.  We had a ferry here in Washington that was built using stainless steel for the salt-water fed sprinkler system.  It was quite expensive to change it all out once it rusted through.  Titanium is a safe bet, though.  Also the clamp position is probably the primary source of all our problems - are the tubes on the Alde tank shorter than the tubes on the radiators? In which case the clamps would be close to the tube ends (where they should be), thereby alleviating the problem.  Best not to have any crevices.

I did not measure the stubs on the Alde tank but seemed to be about the same, maybe a little shorter.  

Corrosion on the aluminum is not only in the crevice but extends underneath the clamp too.  Maybe it starts in the unclamped crevice then progresses under the clamp,  don't know.

It could be you experience with stainless problems stem from use in salt water.  The glycol/water we are using may be less severe service for stainless steel.

kproctor

I have a completely naive question, is there an issue replacing the aluminum tubing with copper.  I am not knowledgeable about the interaction of copper with this type of glycol.

pthomas745

@kproctor Copper has come up in this reeeaalllly long thread a few times.  This mention on page 4 of the thread back in 2021.

https://tab-rv.vanillacommunity.com/discussion/13226/corrosion-of-alde-convectors/p4

I'm sure there are more mentions of various metals, but they are a bit difficult to search for.

cafyrman

rh5555 said:

The best material for corrosion resistance is titanium, which you can get in 7/8" diameter tubes.  This is a sample vendor, there will be others maybe with thinner walls, which would be cheaper.  Anodized aluminum is a very good second best.  Preferably go with "hard" anodizing, and select the appropriate grade of aluminum for best results.  I learned all this the hard way when I made oceanographic instruments. 

Do we know if the convectors from Alde are anodized at all, no less hard anodized?  I just received a new set yesterday.  Seems like if they aren't anodized, or aren't anodized well, it would behoove me to have that done to protect them inside and out.

Then maybe use magic paint for double protection.

rh5555

Unless something has changed, they are not anodized at all.  If you can get the tubes anodized inside and out before installing, my opinion is that you'd be golden.  No need to do anything else, including worry!

Robermcm

I visited Truma this spring to get my boiler replaced (water froze). Met some nice techs and customer service folks. I had questions about principles of operation. Mostly heat and hot water and how things flowed. No pun intended. Recap attached. Posted here due to glycol corrosion discussion and what I heard from Truma directly. …….

Talked to a Truma Alde senior customer support tech with lots of interactions with engineers,  in Elkhart today. Madi(?) She called me to discuss my emailed Alde questions. They are so darn helpful. 

Hot water without heat, flow tank installed
- the flow pump, combined with the one-way valves on the flow tank and boiler creates a short loop for water heating. 

- this pump runs for both 120 degree and 149 degree controller selections. 

- the only difference between regular and turbo is water temperature. 

Hot water without a flow tank
- some systems used a water tank, but she didn’t know of any nu_camps doing that 
- water pressure moves the water through the boiler, heating without its pump running

glycol corrosion
- rhomar is what they use, but she can’t say that. (She winked)
- the current blue/green fluid is ‘best on the market’ to reduce corrosion
- cheaper alternatives and un-refreshed glycol cause worse corrosion
- early Alde installs had issues due to poor grounding and thus electrolysis in the aluminum pipes 
- if ph gets below 8, it’s time to change it (maybe related to the anti corrosion elements being acidic?)

cafyrman

Robermcm said:

glycol corrosion
- rhomar is what they use, but she can’t say that. (She winked)
- the current blue/green fluid is ‘best on the market’ to reduce corrosion
- cheaper alternatives and un-refreshed glycol cause worse corrosion
- early Alde installs had issues due to poor grounding and thus electrolysis in the aluminum pipes 
- if ph gets below 8, it’s time to change it (maybe related to the anti corrosion elements being acidic?)

There were some other discussions about grounding here -- and I believe that's what those shiny aluminum trailer people were doing.  But grounding of what?  The main unit?  Each convector?

I'm planning to anodize my convectors when they all get here, but I could certainly scrape some off and figure out a ground if that's what it takes. 

Sharon_is_SAM

@cafyrman - they ground the Alde unit directly to the battery.

https://tab-rv.vanillacommunity.com/discussion/17013/alde-ground

StepheninDen

Robermcm said: 

- if ph gets below 8, it’s time to change it (maybe related to the anti corrosion elements being acidic?)

Thanks for this intel @Robermcm. Do folks think we can interpret this to mean that ph testing our rhomar glycol is a safe way to determine when to change it, instead of the every 2 years routine?

Sharon_is_SAM

No.  There has been corrosion noted with minimal pH change.  Stick to the 2 year cycle.

Freespirit

Follow-up: I had a lab do an analysis on the “sludge” found in my Alde system after a complete flush and Rhomar replacement 2 years ago. I also had them do an analysis on a sample of fresh/unused Rhomar I put in the system 2 years ago. 

2 year old Unused Rhomar analysis:

Sludge Analysis:

For the second time, I have replaced all parts and filled with Rhomar. Will update in 2 years. 

BridgerSunset

@Freespirit,

The lab findings seem like they make sense, being aluminum makes up the biggest chunk of solids.  I assume the volatiles are glycol....is that your guess?  

The lab's explanation of the carbonate portion is probably right, even though I've always believed the glycol was blended using distilled water, and your flushes appeared to be with distilled water.  Might be another source of carbonate in the blend.   Headscratcher, but probably not a big concern.

In the end, it seems to be as simple as corrosion of aluminum, with a lot of variables as to where, when, & whom it affects.

Thanks for making the extra effort to diagnose things & share with us.  Hope this next cycle treats you much better.

And thanks for the lab check on the 2-yr old unused Rhomar - as I have a similar jug for incidental top-offs & this gives me confidence to use it.

barbarella20722

Morning all. Sorry I'm late to this discussion. I have a 2020, 400, BL and have just begun the process of tracking down and repairing the corrosion issues with the Alde. I've gone through the 400 thread but not a lot there that I could see. In terms of "coating" the stubs. Does anyone have any info on the longevity of 'magic paint'? It's pricey so I wanted to see if anyone here has some feedback on its efficacy. In addition, while I haven't inspected the convector under the bathroom floor yet. Given the likelihood it will also need attention. Has anyone had luck DIYing the repair, and how? I'll post pics of the convector under the bed. Full disclosure, I was a year late on changing out the fluid (yellow with yellow) the damage seems excessive, though I'm no expert. This leads me to presume all the convectors are likely in some state of needing repair. This is a first for me. I'd appreciate any information you may have that could help me navigate through this. Thank you!

ScottG

@barbarella20722, sorry you are experiencing this. I don't have any wisdom about the magic paint or access to the bathroom convector, but thank you for your post and photos. The corrosion on your convectors looks much further along than what I experienced in my 2015, and I was four years overdue for my glycol change. 

Although many owners have attributed this issue to deferred glycol changes, I maintain there are other (possibly multiple) factors at play. Whether the relatively recent switch to the new Rohmer product make a difference remains to be seem. Unfortunately, there have been some recent reports of convector issues in those units as well.

pthomas745

@barbarella20722 Here is the thread with the locations of the convectors for a 2021 400.  Yours, of course, may vary. https://tab-rv.vanillacommunity.com/discussion/18266/t-b-400-convector-locations

barbarella20722

@ScottG thank you for your response. I agree that there is more going on here than the glycol controversy. I did get an email back from Truma. Aside from them agreeing to sell me a few parts, there wasn't much else of note. For the rear, I cut two fins off either side, pushed the brackets in, and cleaned the convector stubs. I am quite happy with the results. Just figuring out the hose situation since it's slightly shorter now. I did end up ordering the paint. Mostly out of desperation, I think.

  I was able to get the left hose off of the convector under the wetbath and clean it. I'll need to try the other side at some point. I say this because even though the hoses showed no swelling or leaking, there were the beginnings of corrosion. @pthomas745 has been a huge help for me in the FB group. Given that the 400 has more than a few convectors in extremely inconvenient places. I see this being a long and frustrating process. I'll probably be asking for guidance again at some point. Here are some new pictures.

1 and 2 are under the wetbath. 3 is a before and after of the one from under the bed.

cafyrman

rh5555 said:

Unless something has changed, they are not anodized at all.  If you can get the tubes anodized inside and out before installing, my opinion is that you'd be golden.  No need to do anything else, including worry!

Finally finding time to finish this project.  I had the new convectors anodized.  That should help protect them inside and out.  Only cost $150 for all of them, so I was pretty happy to do it versus the PITA and expense of replacing all.

Now the next question -- anodization alone?  Or paint with magic paint over the anodization on the ends?

glesieutre

I have a 2015 Max-S and, now retired, finally had time to take on the question of potential convector corrosion in my Alde system. (I first noticed slight bulging at a couple of hose-convector connections in 2021.) I did find corrosion and did my best to remediate it. This wouldn't have been possible without all the information and advice that others posted in this thread and elsewhere -- thanks to all for that assistance. 

I basically disassembled the entire fluid circulation system and examined all the aluminum parts. 

Several convector ends had evident corrosion. The levels seemed to be worst on the flow input side of the convectors and to depend on how much the hose had to be bent to align with the convector connection. The worst one was on the passenger-side top convector, on the input side towards the rear of the trailer -- I had to cut off about a 1/4" of that convector tube. 

I cleaned all convector ends with very rough scotchbrite pads, wiped them down with alcohol, and painted with Miracle Paint. I replaced all aluminum hose connectors with plastic ones ("stubs") from Alde: https://www.alde.us/our-products/stub/?from-filters=heating-systems,assembly-parts-pipes,22mm.

I added two hose elbows to reduce the stress associated with hose bending at connectors. One was a 90-degree bend at the rear lower convector (passenger side) and the other was at the bottom of the reservoir on the hose (it was kinked!) that leads to the drain and circulator pump at the bottom of the Alde unit. I used stock hose clamps everywhere, except on the added elbows -- which had a larger diameter -- where I used worm-gear clamps. In general, I tried to clamp towards the ends of the connectors, not the ends of the hoses. 

I tried to straighten and align the hose-convector connections, adding a couple of cable clamps to support the hoses leading to/from the passenger-side convectors to the rear of the T@B. 

A few pictures follow. 

I definitely earned the T@B yoga merit badge for this activity, and I plan to never have to do it again! 

[rear convector, passenger side, looking forward (you can see the manual bleed valve)]




[passenger-side top convector, input (rear) side]




[cable clamps to support/align hoses on passenger-side convectors]

pthomas745

Nicely done!