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!