material selection of wet air chiller exchanger 1

[gopalsankar]

We have a chiller mainly used to cool the ambient air. Tube side medium is FREON(Operating temp is 5 Deg.C) and shell side is Air(Inlet-40 Deg.C & O/L is 10 Deg.C).The tube metallurgy is carbon steel A179.Due to continuous presence of moisture the tubes are getting corroded externally and severe scale formation was noticed at the shell side.
Is there better metallurgy available to combat the tube external corrosion by moist air.Your valuable suggestion is highly appreciated.

 

[metengr]

Brass or Aluminum tubing. These materials also have excellent formability and thermal conductivity.

 

[EdStainless]

Copper alloys are the most common. There are dozens of different alloys used.

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[gopalsankar]

Thanks for the reply.The problem is we have Carbon Steel tube sheet with limited space available to provide sacrifical anodes.Galvanic corrosion is a main problem if we choose either aluminium or copper base alloys.Will coating work to avoid galvanic corrosion.Can you specify the equiv.ASTM Grade material for the above service.

regards,

 

[metengr]

gopalsankar;
I would use brass tubes with the carbon steel tubesheet. You can coat the tubesheet on the side exposed to the Freon; for the moist air side of the Hx, the carbon steel tubesheet can be left as is.

ASTM B 135 UNS C2300 or
ASTM B 395 Alloys UNS C23000
UNS C44300
UNS C44400 or C44500