Corrosion of Alde Convectors

ScottG · April 2021

FWIW, here is a quick cross-section schematic of the boiler chambers. The photos below (from a U.K. forum) show the innermost cylinder (the green ring in my diagram). You can see one of the electric immersion heaters still attached just below the cylinder.

This component is definitely aluminum. It's outside surface acts as a heat exchanger to warm the glycol when the propane burner is on. The one in the upper photo has some corrosion evident. The one in the lower photo is a new replacement.

What is not clear is the composition of the middle (blue) ring. It is part of both the glycol and the HW tank, so is it aluminum like the inner ring, stainless like the outer ring, or a layer of both?

pak · April 2021

Thanks, Scott. I called Century and was told if the ph was between 8 and 10 the corrosion protection is still effective. I also was told any ph strips used for hot tubs or swimming pools work fine.

Bayliss · April 2021

I previously copied the below info from a few resources online. It helps put things into perspective when assessing the pH of a substance:

pH is a scale of acidity from 0 to 14. It tells how acidic or alkaline a substance is. More acidic solutions have lower pH. More alkaline solutions have higher pH. Substances that aren't acidic or alkaline (i.e., neutral solutions, such as pure water) usually have a pH of 7. Anything below 7.0 is acidic, and anything above 7.0 is alkaline. Thus, 0 is very acidic. 14 is very alkaline.

gulfarea · April 2021

Sure would be great if instead of antifreeze and water they used oil like some of the small home room electric heaters do. Art

ScottG · April 2021

pak said:

Thanks, Scott. I called Century and was told if the ph was between 8 and 10 the corrosion protection is still effective. I also was told any ph strips used for hot tubs or swimming pools work fine.

That has been my impression as well, and what most of us have been working with given the available information to date. Mine was in that range when last checked, and it sounds like @fstop32's was as well. While I can't be certain of the condition of my convectors without dismantling them, it's pretty clear fstop32's were toast, so something is going on that pH alone is not clueing us into.

Again, I'm not fully convinced that that something isn't some interaction with the rubber/aluminum connections in the heating loop. I'm actually hoping that is the case as it would suggest that the boiler innards are still spiffy. The convectors are comparatively cheap and easy enough to replace if need be.

fstop32 · April 2021

Way to go @pak, keep that system clean! Unfortunately by the time you see bulges I'm afraid there is no easy fix...I was talking about my waistline but the same goes for the glycol system.

Good refresher course @Bayliss, I always need those!

@ScottG, I agree with you that maybe we'll hear more feedback on other systems as the "spring-izing" gets into full swing. Great info you gave at top of this page.

The big corrosion question still bouncing around in my mind is why the corrosion started in the space between the pipe and the hose and didn't just go after any aluminum it could come in contact with???

Surely we have a PhD in chemistry out there T@b'ing around who could break it all down for us! From what I've found in mine I'd have to say you can't JUST count on the pH being in the comfort range.

Updated pic below...I've discovered lots of new storage space once I get all that "unnecessary stuff" out of the way

As you can see my Alde is MIA, it's on the shelf in my garage and I guess i'll be pulling it apart to see what that innermost cylinder looks like in mine soon...news at 11.

Image: https://us.v-cdn.net/5021717/uploads/editor/42/kifsgjqze0qz.jpg

Denny16 · April 2021

@ScottG, There is no conductivity between aluminum tubes and rubber hoses. Rubber is an insulation material, and is mostly inherit, it doesn’t give up or take electrons from another material. Aluminum on the other hand is a very good conductor of both heat and electrons. Stainless steel is only a fair electrical conductor, but will conduct heat, though not as well as aluminum does.
cheers

Sharon_is_SAM · April 2021

In this thread lisadbricker and TAOSMAC both had white flecks in their new TaB glycol: pg 2-3
https://tab-rv.vanillacommunity.com/discussion/12778/alde-3020-heat-only-from-bed-vents/p3

BridgerSunset · April 2021

Not a ChemE, but did spend many years chasing corrosion & scaling in industry.

FWIW, I asked Century to send me the MSDS sheet to see what's in the TF-1 fluid. They did; but it didn't disclose anything beyond propylene glycol. Everything else is deemed a "trade secret"; not uncommon to see.

Was hoping to find what corrosion inhibitor they use, in case there's a rubber swelling/ compatibility issue.
Was hoping to find if a scale inhibitor is present, which often is a phosphonate - a white substance.
Was hoping to find out if any salts or other substances are present in solution, which could dry out between the hose & tube and cause "under deposit attack" of the aluminum - a common occurrence in the corrosion world.

Sorry not much help. But I do know that inhibitors get consumed with time/contact/heat & must be replenished.

Verna · April 2021

@Ratkity, any input from you?

Sharon_is_SAM · April 2021

It would be nice to know why Alde has changed to the Rhomar glycol. (I found out - see next post.)

I found another result of corrosion: https://m.facebook.com/caravanalia/videos/often-asked-about-alde-fluid-change-and-if-its-worth-the-money-well-this-is-what/687217025267475/

Sharon_is_SAM · April 2021

Here is a YouTube video with Paul Beckley interviewing an Alde/Truman rep. He discusses the change of the glycol formula at 12:35.
https://youtu.be/drdxGky_Xo0

Although a little vague, he reports that the Rhomar is a better quality formulation for the aluminum system and it is better for the Alde system. So, did they discover problems using the Century brand and if the Rhomar is “better” why aren’t they telling owners to change over to Rhomar?

Next is a little off topic but still important...

Also, at 6:00 he clarified the issue with placing RV antifreeze in the Alde hot water tank. It has nothing to do with damage to the stainless steel tank. The issue is if the boiling point of the antifreeze is lower than the 180 F temperature that the Alde reaches, you will hear the antifreeze boil and bubble within the hot water tank. So, they noted that the Camco brand RV AF has a boiling point of 220 F and you can winterize the TaB and Alde with that product and run the Alde for cabin heat without problem.

ChanW · April 2021

Well, isn't that enlightening!?!

When we first heard about this "hot antifreeze in contact with the Alde hot water tank" limitation, it was because the rubber seals might be damaged by the hot antifreeze.... This was reportedly from Alde too.

This makes a bit more sense, but I'm beginning to wonder now if anyone really knows....

Sharon_is_SAM said:

Here is a YouTube video with Paul Beckley interviewing an Alde/Truman rep.

.......

Also, at 6:00 he clarified the issue with placing RV antifreeze in the Alde hot water tank. It has nothing to do with damage to the stainless steel tank. The issue is if the boiling point of the antifreeze is lower than the 180 F temperature that the Alde reaches, you will hear the antifreeze boil and bubble within the hot water tank. So, they noted that the Camco brand RV AF has a boiling point of 220 F and you can winterize the TaB and Alde with that product and run the Alde for cabin heat without problem.

Ratkity · April 2021

@Verna Long time, so see! Biochem person here with some organic and inorganic chem in Masters (PhD was Microbiology - all of that chem in action!). @Denny16 's comment was correct. No interaction between metal and rubber. The interaction is between metals with the sitting fluid, glycol. The formulations of the glycol will more than likely have a buffer. That is something that keeps the glycol at a neutral pH no matter if it's sat for a winter or a little bitty microbe has infected your glycol and is trying to change the pH. Some buffers are better than others. They all function the same. What is proprietary is how stable they are over time and how they respond to any metal corrosion.

First, I was under the impression the glycol had to be changed every 2-3 years. There's a reason for this. It loses its buffering capacity and will get rid of any contaminants.

If i was an engineer (I'm not even close to one), I would have a filter in the expansion tank as the glycol comes from the Alde unit to test to see if there seems to be metal corrosion happening. No matter what precautions are taken, two metals will eventually react and cause some sort of corrosion.

If you've reached this far, remember the Alde Unit has been used in Europe for a long time in their caravans. Are they having issues? Is there a way to contact the original manufacturer to ask your questions about corrosion?

I know many of you have not seen me around, I have a Retro 820R tiny toy hauler now, but sorely miss my T@B. Especially since I got a leak that needed to be fixed. The floor was saved, overkill repairs have been done, garage quality mat has been put in the back (all black), and it looks like a 3 yo did the caulking around the taillight that was the leaking culprit. On a good note, I did install a backup camera that was a Xmas present. Because of all the aluminum in a bigger camper, I had to get one with an extra-long antenna that runs the length of the roof. It gave me a chance to check out the roof too. Good thing no one can see the caulk job I did to keep the clips holding the antenna cable stuck to the roof. I didn't trust the 3M adhesive, so I added lapseal

Sharon_is_SAM · April 2021

For the record, I have been reading the Airstream forum and they changed to Rhomar in 2020. They also sent out a service bulletin to flush and refill some Aldes. https://static.nhtsa.gov/odi/tsbs/2020/MC-10170838-0001.pdf

In another AS thread they discussed adding a ground wire to the Alde to help with galvanic corrosion and yet another discussed filtering the old glycol for corrosion flakes. Hmmm...

ScottG · April 2021

Wow, lot's happening here since I last had a look!

@fstop32, you are boldly going where no T@B owner (I'm aware of) has gone before. I look forward to your continuing reports. Please be sure to take lots of photos, particularly of the inside of the boiler body and the outer wall of the glycol chamber (the blue ring in my schematic). Photos of Alde guts are pretty scarce and I've only been able to find images of the inner core such as those I posted earlier.

@Sharon_is_SAM, good sleuthing re: the recent glycol switch. I'm not surprised there is more to that story. The ground issue is also interesting--that was mentioned in one of the communications fstop32 reported from nuCamp.

@Denny16 and others, I use the term "interaction" very loosely and I'm not suggesting there is a conductivity issue between rubber and aluminum. I just find it curious that fstop32's convector corrosion seems to begin at that interface and progress inward to where the glycol is actually circulating. It's more about asking questions than offering answers.

On a related note, @BridgerSunset, thanks for scouring the MSDS. Seems I ran across that at some point in the past I vaguely recall it wasn't all that informative. I'm wondering if your last question about salt deposits drying out at those junctions might be a clue. If that's the case, it suggests that once the deposits are established the corrosion will likely continue even after the glycol is replaced. Do you concur?

@Ratkity, it's good to hear from you--@Verna's power's apparently extend to summoning the departed! ;-) Sorry about the issues with your toy hauler, but I hope you've enjoyed being able to take your hog along for the ride.

To be continued...

Ratkity · April 2021

@ScottG @Verna does have much power. Never underestimate her persuasiveness! Well, my new Harley is an inch too long to go in straight. I can get it in if I take the ramp at an angle. In the meantime, I'm enjoying the backroads of MD and the Eastern Shore of MD/DE with the Harley. As for the the Mini toy hauler (the unicorn of Retro), my service dog's crate fits perfectly as well as a scooter I use while camping. I have a foot that is getting worse for walking (riding the bike = not an issue

)

I have found the main vinyl floor that is checkered black and white is starting to yellow, no matter how much bleach or magic eraser I use. Replacing the small area in the back was hard enough. I have no inclination to replace the entire floor!

Verna · April 2021

Thank you, @Ratkity! It is marvelous to have your extremely technical views gracing our modest forum again👏👏

mona · April 2021

To answer a question previously asked by @Sharon_is_SAM, I have a 2015 320s, manufactured in March 2015. I have religiously had the glycol exchanged at the recommended intervals by NuCamp. After reading this tread, I lifted the wood shelf to check my hoses, and low and behold, the black hose entering the convector from the drivers side, has a bulge, but no visible corrosion. I spoke to Austin, and he has seen bulges on the hoses from older T@Bs, that have not had the glycol exchanged, but mine is the first he had heard of it happening to a T@B, that has had the glycol exchanged at the recommended intervals.

Jeannie

ScottG · April 2021

@mona, thank you for your detailed report--I'm sorry to hear that you have the same issue. Hopefully we will come to find that this is peculiar to the convectors and does not extend into the boiler. FWIW, that first connection one of the places I found a bulge. It was small but probably the largest of all of them. The pipe underneath still felt solid and there was no visible corrosion.

How much use does your Alde get?

ScottG · April 2021

@ChanW, I see you have weighed in here. IIRC you have an older Alde that has gotten a fair amount use, and you've changed your glycol at least once. How do your convectors look?

mona · April 2021

Please keep in mind these figures are my best guesstimates give or take. I do camp year round.

20 days heat only
30 days hot water only as needed. Shut off otherwise.

Jeannie

mona · April 2021

I forgot to add, that’s per year.

Jeannie

fstop32 · April 2021

@ScottG - “Aye, the haggis is in the fire now for sure”! I noticed in one of the manuals you put me onto it says “Never leave the glycol jacket empty”…so I’m headed to Ace to pick up a couple of rubber pipe caps so I can fill mine with fresh glycol while my boiler is out of the camper. It seems I can't get into anything without seeing other things that also require attention. The Alde issue led me to see some old water damage where water got past the outside receptacle so I'm rebuilding/replacing the rear bench supports with some new stuff (pic will follow at a later date). And thank you all for all the great info you've been sending my way!

@Ratkity - That yellowing in the vinyl could be the glue used to put it down, bleeding through, part of my JOAT/MON (jack of all trades/master of none) complex coming through there. Also, I LOVE your “overkill repairs”, we’re like lost twins as I’m ALWAYS overkilling my solutions!

@BridgerSunset - “trade secret” - a) something you don’t want your competitors to know and be able to copy, or b) something you don’t want the world to know and it become a liability Kudos on your really smart hopes! I knew it wasn’t going to be hard to find people smarter than me!

@Sharon_is_SAM - that vid reminds me of my former part-time life as an auto mechanic, white “smoke” exiting the tailpipe is almost always a blown head gasket between the water cooling jacket and the combustion chamber…but I digress.

@mona - You’re breaking my heart, I was so hoping no one who did the suggested glycol maintenance would be cursed with a bulge. I'm sorry to hear that.

To all concerned: @mona ’s recent find does tweak my brain again when I wondered what would happen if perhaps the convector pipe tailpieces had been “cleaned” prior to hooking the heater hoses up to them. Aluminums natural protective oxide would have been removed and not given time for it to rebuild before being covered over by the hose…?

On a personal note: I am approaching this corrosion issue I have by trying to find out why it happened so I can make sure to fix it right and not repeat the sins of the fathers. I am in no way “looking for a culprit” or someone to blame for what I have, there are no warranty claims because I have no warranty. I’m just looking for an answer so I can only do this repair job once before I die 8^ D

Denny16 · April 2021

I think the manual warning about keeping the boiler glycol chamber full, is for a unit still in service, or that could be turned on. Since yiur boiler has been removed, caping the inlet and outlets should keep the tank clean, air in the tank should not be an issue as long as it is not heated up. I would refill it before installing it to help refill the system.

Interesting thought about the nipple to hose connection having a localized corrosion issue due to over cleaning and natural protective aluminum oxide off. You could use an aluminum specific anodizing material to coat and protect the outside of the nipples under the river hose connections from localized corrosion. I did this in the heat exchanger in my boat heat exchanger aluminum bits. The anodizing material goes on like a thin stain, not a thick emulsion like paint. It reacts with the aluminum to create an air seal on the aluminum surface.

The Inger view Paul had with the Alde rep was very informative, he stated the water tank is a stainless steel jacket, which would indicate is wraps all round the water compartment, so only the glycol jacket tank is aluminum, which makes sense to me. Now the question is do the water jacket and glycol chamber share a common wall, or are they separate?

Cheers

fstop32 · April 2021

@Denny16, good idea, i had wondered about something like that at assembly time. Do you have any suggestions for what to use? I'm only familiar with stuff like NoAlox that's used on electrical connections in panels to block the oxidation process that will loosen connections over time if not used. But that application might not even be the process you are talking about.
After I get done making dinner for the other losers living here while my wife is at work I'll sit down and watch that interview.

Denny16 · April 2021

I used some special aerospace anodizing a friend of mine got from work (NASA) that was left over from a job they did. It was a two part mixture, thst had a limited shelf life once mixed. I would avoid using Zinc Chromate, which was a popular primer coating for aluminum. It was used primarily in the aircraft industry.

Here is a site thst shows various systems used https://techmetals.com/aluminum-anodizing/
cheers

ChanW · April 2021

I'm dreading taking the Tab's cover off, @ScottG!
I'll be sure to let you know!

It's not sounding too promising...

ScottG said:

@ChanW, I see you have weighed in here. IIRC you have an older Alde that has gotten a fair amount use, and you've changed your glycol at least once. How do your convectors look?

ScottG · April 2021

Thanks, @ChanW. For some reason I thought you used yours in the winter so would be in there running the heat on occasion. Good luck!

ChanW · April 2021

@ScottG, we're not shy about using the Tab in winter, in the dead of winter only once though.

I'd say we're 'medium use' winter campers, mainly just doing off-season, thus cooler weather, camping.

And I've done only two glycol changes (more accurately 1½), but have kept track of ph. I see from the info in this thread though that the ph is possibly not the big reason to change the glycol, that the problem is more likely to be the degradation of the buffering corrosion-inhibitor. Too bad there's no way to measure that!.

I expect to open up the Tab today, to see what I need to see....

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