Corrosion of Alde Convectors

fstop32

Mine was well used and Alde was used in winter when sub-freezing temps were threatening.

ScottG

@Dalehelman, I've moved your comment and associated responses over here as they are more related to this topic.

Thanks for reporting in on your 2015. I'm glad to hear you are bulge free but have no explanation. There was a suggestion within our small sample that greater use was related to increased bulging, deposits, and convector corrosion, but your preliminary findings seems to contradict that. At this point I'm inclined to say there is no predictable pattern here, but don't take my word for it--go back and carefully review the posts of the others who have checked their systems and draw your own conclusion.

Lastly, at the risk of throwing a bit of cold water, note that deposits and corrosion may still be occurring in the absence of obvious bulges. I only had bulges (small ones at that) on some of my fittings, but once I took things apart, deposits were evident to some degree on every single one. 

Dalehelman

Please don’t get me wrong. In the past 6 years there have been months at a time when our Alde is not in use. Especially the last year and a half. Mush as I would like to I just can’t afford to travel all of the time. Although use or lack of use maybe a factor.

ScottG

@Dalehelman, either way--like with that frame crack issue--it's always good to add another point of data.

Still hoping to hear from more owners on this matter, particularly those of 2014-2015 vintage T@Bs.

Denny16

Well, that kills my idea, of it being use related.  I guess periodic inspection is going to be the best preventative measure.
cheers

DougH

Deleted

ChanW

I think Dale's report here, of having no corrosion at all, with no glycol changes, is confounding.

I wonder if Alde had a bad batch of convectors, or if 'Little Guy' used a bad batch of glycol. Or maybe they had a bad batch of distilled water...

It seems pretty odd that only some of these Tabs have this problem!

ScottG

@ChanW, I moved your second comment (and my response) over to this discussion. It's becoming increasingly hard to keep topics from fragmenting as we now have several different but related discussions ongoing about Alde glycol. 

The one consistent factor (so far) does seem to be age. The reports of bulges are from 2014 and 2015 models (and maybe one 2016?)

Notice I said "bulges" as opposed to corrosion. The bulges occur when deposits (associated with underlying corrosion) build up to a certain point. The rate of build-up seems to be variable, even within a single system, and the lack of a bulge does not necessarily mean deposits have not begun to form. I believe only three of us thusfar (@fstop32, @db_cooper, and me) have disassembled our convector loop and we have all found deposits and corrosion at every aluminum fitting (bulge or not)  

So, while it is possible that this traces some defect in materials in a specific run of trailers, my hunch is that it is more a factor of time confounded by other variables such as use, maintenance, and maybe even climate. 

Sharon_is_SAM

@Dalehelman - how about checking for corrosion under the hoses at the converter loops?

Dalehelman

@Sharon_is_SAM
I plan to when we get home next week

ScottG

Following up on my comment of April 7 I contacted Truma/Alde to inquire about the specific composition of the different components of the boiler core. I included this graphic and was very specific in how I asked the question. 

Here is the response I received:

"While the combustion chamber is made from aluminum, the glycol chamber and the water tank are both made from stainless steel."

While this is still a bit vague, it is a bit more informative than that previously offered by the Alde literature. I interpret this response to refer to the three rings in my diagram--the green ring (combustion chamber) is aluminum, and the blue (glycol chamber) and black (water tank) rings are stainless steel. This would be consistent with observations that the "glycol in" and "glycol out" appear to be stainless rather than aluminum.

If my interpretation is correct, this leaves unresolved the issue of having a relatively large surface of cathodic stainless steel in galvanic contact with a smaller area of anodic aluminum. I assume that Alde engineers who (hopefully) understand the science better than I did something to mitigate any potential for corrosive reaction between these surfaces.

I'm also curious as to what sort of metal the electric heating elements are made from. 

Denny16

See my post below.

ScottG

@Denny16, see the photos I included in my April 7th post (link above). I'm pretty certain the component shown is the "combustion chamber"--it appears to be one piece and made of aluminum, with a solid convoluted surface for maximizing heat exchange between the burner and the glycol. It's also the component that typically corrodes on the side exposed to the glycol.

I'm only interpreting based on what is pretty limited information, and not claiming to have definitive knowledge. If you have additional resources (photos, images, documents, or links) to support your understanding of the construction, please pass them along.

fstop32

I've still got my money riding on the outside of the aluminum combustion chamber is the green circle on the depiction above and that it comes into direct contact with the glycol.  Back on page 3 below the diagram (same as above) there is a pic of a corroded aluminum combustion chamber.  In that pic one can see the electric heating elements which are shown in diagram above to be inside the glycol chamber.  I can see a gasket outside of the electric coils but not one inside closer to the combustion chamber.  There is very little space between the coils and the aluminum flame chamber for another wall of stainless, plus I would think an air gap, even a small one would limit the heat transfer from the flame chamber through a stainless tank wall to get to the glycol to heat it.
If I get really bored after doing a bunch of other mods while I resource parts maybe I'll rip my boiler apart for the definitive answer 

Denny16

OK, Scot I missed that one, and after looking at it, I agree, the green ring, around the combustion camber (inner ring) bit is aluminum and is also the inner wall of the glycol chamber, the blue wall next separating the glycol from the water chamber in your cutaway diagram is stainless steel, as is the outer water chamber ring around the outside of the water chamber (black ring in the diagram).  So the Alde hot water/glycol heater is actually a manifold cap type, construction, with end caps providing the seal between the chambers, and not an actual one piece tank.  I think this is the bit that is causing all the confusion, including with me.  

This is similar to the construction of a model fire tube steam boiler, with a propane burner in the single inner fire tube inserted in the center of a cylindrical water tank, with soldered end caps, to create a seal.  The center of the end caps on each end has a hole opening into the fore tube, one end with the burner and an air intake and the other end opening into the smoke box at the end of the boiler to draw out the exhaust gases.  Water flows around the fire tube as it is heated by the single wall separating the fire tube from the water tank.  Aside from the choice of materials, it is the same principle the Alde tanks is based, a single flue, fire tube boiler, with electrical heating elements inserted in the glycol chamber as an alternative heating method.  

Once you realize the Alde tank is actually a multi-compartment boiler, with separate end cap and inner ring construction, it all makes sense.  The boiler can be disassembled, as the ends come off, and the inner aluminum ring can be replaced, as can the heating elements.  The stainless rings will probably last the lifetime of the unit.  Spot in Scott, thanks for the feedback.

Now keeping the glycol changed to prevent corrosion in both the boiler and heat exchanger convectors, which are made from aluminum.  Without the corrosion inhibitors in the glycol, galvanic corrosion can occur between the aluminum  inner wall and the stainless outer wall of the glycol chamber, as shown in Scott’s photo on his April 7 post, I previously missed or did not pick up on. :b:blush:

Perhaps the white crystal like substance corrosion creates on aluminum in the boiler is circulated in the glycol to the aluminum convectors, and deposits are accumulated in the tube to hose connections, resulting in more corrosion and the tube bulging others have experienced in their older Alde units.

Now, everything is as clear as mud.  
cheers

ScottG

@Denny16 and @fstop32, I'm not sure if it has been posted previously, but I find this image helpful. It's from the U.K. version of the Alde service manual, but the parts as depicted should be the same over here.

What Alde calls the "boiler body" (#33) appears to be two parts: the stainless steel water tank and the aluminum combustion chamber. (#29 is a gasket, not a separate part.)

This "boiler body" can apparently be replaced, but in the U.K. the part is only available as some sort of premium Alde service that I interpret as meaning they will only sell you the part if they install it. The service manual does not include any instructions for the removal or replacement of the boiler body.

As a piece of equipment, this doesn't really look all that complicated to work on if you could easily source the parts like you can for pretty much every other appliance on the planet.  :-/

Sharon_is_SAM

@ScottG - to me it looks like the electric elements are attached to the rim of the combustion chamber and that unit slides into it’s own “dry” chamber that is then surrounded by a glycol tank.  I think we have been assuming that the electric elements are bathed in the glycol.  What do you think?

ScottG

@Sharon_is_SAM, I think you are correct about the attachment of the electric heating elements, but once the combustion chamber is inserted and sealed to the other half of the boiler body, they would be within the glycol chamber and bathed in glycol. 

This diagram is a little blurry, but it shows the three walls (red arrows) of the boiler body. If you follow the glycol IN and OUT pipes, you can see (sort of...) that they empty into the middle chamber that contains the electric elements.

  
 

Sharon_is_SAM

Thanks @Scott.  Is that typically how an electric hot water tank works - bathed in the water?

ScottG

I believe it is. Air is a pretty good insulator so I would expect that having elements (or other heat exchangers) not in direct contact with the fluid would dramatically cut efficiency. As fstop32 pointed out above, that is why having the aluminum walls of the Alde's propane combustion chamber in contact with the fluid is important. 

Interestingly enough, domestic hot water heaters usually have a sacrificial anode--often made of aluminum--to help prevent against galvanic corrosion in the tank.

rh5555

I'm late to this party, but I may have some insight regarding aluminum corrosion gained from decades of making undersea instrumentation:  The inside of the aluminum pipe that runs the length of the radiators HAS to be anodized.  If it wasn't, you'd have a horrific mess once glycol/water came into contact with it.  Anodizing is a process by which a comparatively thick layer of aluminum oxide is formed on the aluminum surface.  This oxide is very, very corrosion resistant.  Coloring is also frequently added to make products pretty, too.  In a well-manufactured radiator, the outside of the aluminum tube should be anodized too (at least the ends, where the rubber pipes clamp on).  What would happen if the outside wasn't anodized (or was badly anodized)?  Exactly what is being seen - crevice corrosion that causes the rubber hoses to swell as the corrosion builds up.

Why is this happening in some radiators and not others?  There may have been a change of supplier to one who cut corners on the anodizing process (the eternal problem of the low-bidder), there may have been a change of manufacturing procedure, it's impossible to tell.

The solution:  First determine if the outside of the aluminum tube is anodized.  A properly anodized surface will not conduct electricity whereas untreated aluminum will conduct electricity really well. You can check this with an multimeter set to read resistance.  If the surface is not anodized you need to keep the glycol away from it.  Wrapping with self-amalgamating tape (like @db_cooper did) is one option, applying a sealant is another, using heat-shrink tubing (the kind with the meltable lining) would be very effective (if it doesn't get too thick).  Then double up the hose clamps, ensuring one is right at the end of the aluminum pipe to stop any glycol from seeping past.

I think the frequency of changing the glycol is a bit of a red herring.  It probably is mostly to do with replacing corrosion inhibitors, which shouldn't have been needed in the first place!

ScottG

Good info, @rh5555. I'm not sure what exactly anodizing might look like, but when I dismantled my convector loop it seemed to me there was some sort of coating on the inside of the pipes that was different in appearance from the outside of the pipes. (There are photos in my post of April 11 though I'm not sure the differences will be obvious. @fstop32 described something similar on April 6.) 

Regardless, I agree that everything else falls nicely into place behind this explanation. The corrosion reported to date all seems to originate on the outside of the convector tube, underneath what appears to be dried crystalline glycol deposits that form between the rubber hose and the convector pipe. Damage to the inside of the pipe (as reported by fstop32 and db_cooper) only occurs when the corrosion makes its way entirely through the aluminum. In my case, the deposits were limited so the corrosion was still quite superficial.

I also agree that adhering (or not) to the strict glycol change regimen may be a red herring. It certainly doesn't seem to correlate neatly with current reports of bulging/corrosion. As to whether early corrosion of the external convector pipes is limited to certain units remains to be seen. We know bulges are not evident in all cases, but by the time the telltale bulges become obvious it seems the damage has already advanced a level.

If the convector pipes are indeed anodized, it's reasonable to assume the aluminum combustion chamber in the boiler core would be, too, and therefore should be protected from damage as well.

It's unfortunate that we have to spend so much time trying to deduce this stuff on our own. Quick answers to all these questions exist somewhere, but finding a reliable source of those answers seems elusive. 

Dalehelman

rh5555 said:

I'm late to this party, but I may have some insight regarding aluminum corrosion gained from decades of making undersea instrumentation:  The inside of the aluminum pipe that runs the length of the radiators HAS to be anodized.  If it wasn't, you'd have a horrific mess once glycol/water came into contact with it.  Anodizing is a process by which a comparatively thick layer of aluminum oxide is formed on the aluminum surface.  This oxide is very, very corrosion resistant.  Coloring is also frequently added to make products pretty, too.  In a well-manufactured radiator, the outside of the aluminum tube should be anodized too (at least the ends, where the rubber pipes clamp on).  What would happen if the outside wasn't anodized (or was badly anodized)?  Exactly what is being seen - crevice corrosion that causes the rubber hoses to swell as the corrosion builds up.

Why is this happening in some radiators and not others?  There may have been a change of supplier to one who cut corners on the anodizing process (the eternal problem of the low-bidder), there may have been a change of manufacturing procedure, it's impossible to tell.

The solution:  First determine if the outside of the aluminum tube is anodized.  A properly anodized surface will not conduct electricity whereas untreated aluminum will conduct electricity really well. You can check this with an multimeter set to read resistance.  If the surface is not anodized you need to keep the glycol away from it.  Wrapping with self-amalgamating tape (like @db_cooper did) is one option, applying a sealant is another, using heat-shrink tubing (the kind with the meltable lining) would be very effective (if it doesn't get too thick).  Then double up the hose clamps, ensuring one is right at the end of the aluminum pipe to stop any glycol from seeping past.

I think the frequency of changing the glycol is a bit of a red herring.  It probably is mostly to do with replacing corrosion inhibitors, which shouldn't have been needed in the first place!

Some of the best information I have seen so far 
Thank You very much

ScottG

Agreed, @Dalehelman. I wish I had known this when I had my system apart in early April, as it would have been easy to test all those surfaces with a multimeter as rh5555 described. Maybe next year.

Denny16

Sharon, the electric elements wire connection (28/29) comes through the end cap of the combustion chamber and is sealed in the end plate and part 32 is the seal for the end plate and the glycol chamber/tank.  The rest of the glycol tank and water tank (part 33 is made of stainless steel per Alde, so the aluminum combustion chamber is inserted in the glycol tank and the end of the combustion chamber is the end cab manifold to create a water tight seal of the tank.

So the outer cylinder of the combustion chamber is the inner wall of the glycol tank, so the inner wall of the glycol tank is the aluminum bit, and the rest of the tank stainless steel.  The end of the combustion chamber we can not see, that goes into the glycol tank first must be an aluminum sealed end also.  So basically the aluminum combustion chamber is inserted into the glycol tank, along with the electrical heating elements.  The glycol is then in contact with the aluminum cylinder and end of the combustion chamber.

This, as Scott stated, allow the complete combustion chamber to be withdrawn and replaced.  Given the seals involved, and electrical connections, I can see where Alde would require a qualified Alde technician to work on the boiler itself.
Cheers

tybladesmith

@ScottG, I agree with your description of the outside of the aluminum combustion chamber in contact with the glycol. I anticipate inserting a borescope into the glycol in port of the boiler to inspect for corrosion probably next week. I will also inspect hose/convector connections then, and take ohm readings on convector ends. I should have the reservoir drain/fill kit together by then.
@Denny16, The Airstream recall electrical bonding only refers to 12VDC connections not AC as in the Alde heating elements. Curious!

db_cooper

That is great information @rh5555

I can confirm that the outside of my connections were shiny, and the inside of all pipes had a flat patina look that was very consistent.  If what you are saying is correct, that it was glycol in contact with non-anodized aluminum,  that is probably good news for me as far as the boiler condition.   I did not know if the look of the inside of the pipes was good or bad.  If they're just anodized, then it's all good.

I've done what I can to stop the contact on the outside of the connections, so now we'll wait and see how it looks in 2 years.  

fstop32

Great stuff @rh5555, thank you for your input!
I've made a mental note to examine the outside of the new convector pipe stubs when/if I ever get them...humm, I'd better make that a post-it note, my mental notes keep getting lost.   
It makes me wonder if the corrosion inhibitors could be added to the system every couple of years and push the full flush out to every 5 or 6 years.  It seems like we've not seen much indication of the glycol itself breaking down.

Dalehelman

Just removed the old Century fluid. Looks  pretty bad. I am going to strain it through a paint filter to see what I find. Very cloudy. Probably an indication of corrosion. I used a shop vac because I prefer not to loosen any of the hose connections since none are showing signs of leaking. I placed the hose end through the fill cap and directly onto the return line which is directly below. If interested. Stay tuned for the next step.
The flush.

Denny16

How old is your TaB Dale, and has the glycol ever been replaced?
cheers