Copper finned heat exchanger turning green in boiler 1

[skbutler]

On several low mass copper finned boilers, the heat exchanger corrodes with a green exfoliate. Is this due to over heating or what other mechanism?

Thanks

 

[imok2]

The rate of patina formation and the proportion of the components depend upon humidity and the amount of "air pollution" such as malachite or brochantite from sulpher in the air.

 

[willard3]

Copper oxidizes to green. The green oxide layer is very thin and protects the rest of the copper from further oxidation.

Next time you see a copper roof of any age at all, note that it is green.

 

[skbutler]

Let me revise my question.
With most low mass copper finned tube boilers and water heaters, the copper finned tubes do not corrode to an exfoliated green flaky 'stuff.' Of course all copper like aluminum, reacts on the surface with atmospheric oxygen to form an oxide, which is technically corrosion, but this is not what I'm concerned with.

One look at the corroded tubes I'm talking about and you would know instantly that there was a serious problem with the boiler. The question is: Has low stack temperature / condensation caused this condition, or has low flow / over heated tubes caused the problem?

And thanks for the response to my question. I love this forum. I need to visit it every day.

 

[ChrisConley]

Not enough info to guess. Besides the two failure modes you propose we can also have issues with boiler water treatment and combustion air pollution. You can upload pictures if you have any...

 

[skbutler]

I've never uploaded a photo before but that's a great suggestion. I'll try now.

 

[skbutler]

I should have identified the pictures.

The top pic is what a copper finned tube from a boiler heat exchanger should look like.

The middle pic shows what a typical 'green' tube looks like,

The bottom is interesting and I see it a lot. The heat exchanger is a 2 pass. Water flows to the right in the first 6 tubes, turns around and flows to the left and out of the boiler. The metal temp in the first 6 tubes will be lower than the back 6 tubes.

Steve

 

[SAK9]

If copper tube boilers operate in a condensing mode accelerated corrosion is possible.So check if return temperature(say less than 60C) is low enough to cause condensation.

Typically condensing boiler heat exchanger is therefore of stainless steel construction.

I hope the reason why the first pass is green(third photo) is clear now

 

[skbutler]

How about a chlorofluorocarbons, ie Freon leak? Would the resultant corrosion be more severe in the presence of flue gas condensation?

As to the return water temperature... it varies but is usually less than 140°F (60°C) so there is likely some condensation taking place.

 

[SAK9]

Freon has no effect on copper.Air conditioning equipment have a lot of copper components that are in constant touch with Freon.Moreover Freon is non flammable and not likely to burn if accidentally drawn into the boiler.

The quality of natural gas also can be a cause for tube corrosion for eg high sulphur content or presence of H2S

 

[skbutler]

Actually SAK9, while freon is not corrosion to copper, freon drawn into a boiler's combustion chamber along with combustion air, breaks down and releases chlorine compounds that are extremely corrosive to copper. In many jurisdictions in the states, mechanical codes do not permit refrigeration equipment using chlorofluorocarbons to be located in the same room as boilers.

My question is, 'would flue gas condensation' accelerate such corrosion.

Steve