HVAC corrosion in an air marine environment

[PagoMitch]

I originally posted this over in HVAC. but it was suggested that this might be a more applicapable forum.

Corrosion between Cu tubes and Al fins is accellorated in coastal areas. Military HVAC units (on buildings) are usually specified with Cu/Cu tubes/fins for that reason. While I can find a reference (sort of) to air salinity (

http://www.arl.noaa.gov/faq_ac18.php),

I cannot find a reference indicating how the values would be applicable to Al corrosion when mechanicaly bonded to a copper coil. Has anybody ever seen a study that measures the galvanic potential between Cu tubes and Al fins, at various distances from the shore? It would probably vary with temperature, and be influenced by wind and humidity, but it would be a useful criteria to use as a basis for justifying the expense of an all copper coil. This sounds like a great project for a Masters Thesis. I can make an educated(?) guess...say, 0 to 5 miles (or 10, or ?)from the coast is all copper in order to eliminate the problem. But it would be nice to find something a little more authoritative. This can't be the first time someone has posed this question...

 

[EdStainless]

I have seen the units being tested at LaQue. I figured that the data was proprietary.
There are a lot of published studies on the Cl levels vs distance from the shore. This is a lot more complicated than that. If the region gets a lot of rain and the coils are exposed then you can handle higher cl levels. If the coils are protected from rain or it is a dry area then even small Cl amounts are an issue.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[fdac]

The potential difference between copper and aluminium is pretty much constant. What changes with distance from the shoreline is the presence of an electrolyte (salt) at the interface.

There are a number of standards around the world (ISO, Australian are the ones I use) which identify atmospheric corrosivity categories related to distance from coastline. Relevant factors are time of wetness and salt deposition rate.

As EdStainless states, sheltering from rain exacerbates the situation because salts do not get washed off and tend to build up.

I would probably look at establishing a blanket criteria (i.e. within x km of a surf beach or y km of a calm coastline, use all copper and no Al), or refer to the various studies and standards out there.

 

[strider6]

This reference can help u:

CORROSION OF ALUMINUM-FIN, COPPER-TUBE HEAT EXCHANGE COILS

https://txspace.tamu.edu/bitstream/...d=27AD6D419B8F664E1BF0142324947512?sequence=1

S

Corrosion Prevention & Corrosion Control