The good news is that if you properly understand how galvanic corrosion works, it is very easy to avoid or at least, minimize.
Galvanic corrosion takes place when: a. We have two metals in contact b. They are immersed or surrounded (totally or partially) by an electrolyte (in AC applications the most common would be humidity and salt).
We also know: a. The further these metals are in the galvanic series, the stronger the reaction b. The anode will be the sacrifice material whereas the cathode will get stronger. Learn more
Climetal’s MCHEx are so resistant to corrosion due to the best alloy combination design.
Climetal’s 15-year experience in the manufacturing of Microchannel Heat Exchangers assures the highest quality materials and alloy combinations in the market.
Microchannel heat exchangers are made of headers, tubes and fins. These three are basically aluminum but because each of them is manufactured with a different process (lamination and extrusion) they require different alloys suited for each of them. Again, because of dissimilar aluminum alloys, we encounter – although very limited compared to traditional copper and aluminum coils – a potential risk of galvanic corrosion.
At Climetal we did a careful selection of our alloys in order to control and minimize the risk of corrosion.
The key elements we took into consideration were the following:
Material compatibility for correct temperature homogeneity during brazing. If brazing temperatures of the different alloys are too different it can complicate the brazing process causing diffusion in some of the alloys and eventually leading to pitting corrosion.
Refrigerant must not leak from the heat exchanger, therefore corrosion has to be kept away from the microchannel tubes, which have extremely thin walls and contain the refrigerant at high pressure.
Corrosion attack must be directed to the least important element of the heat exchanger.
Ideally the corrosion attack should follow this sequence:
Fin: The fin should be the first component to corrode as it does not contain any refrigerant.
Header: The header walls are normally very thick (1,2mm-1,5mm), so very unlikely to corrode to a critical level that might cause a leak.
Microchannel tubes (MP tubes): MP tube wall thickness can be as thin as 0,3mm and working pressure inside can be as high as 45bars, so this is the most critical element to protect.
As we know, in a galvanic process the anode or sacrificial element is the one with the lower galvanic (electric) potential. Therefore as shown on the following experiment the galvanic potential order of each element should be as follows – from lower to higher potential: fin, brazed joint (fillet), header and microchannel tube. Schematically:
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