Cathodic protection of tubes in Shell & Tube Heat Exchanger
Cathodic protection requires an electrolyte to work. You could just pass current through the tubes but how is it going to return to the power supply? If there is no electrolyte to conduct ions it cannot provide any protection to your system. Have you considered replacing your heat exchanger with glass or glass-coated metal? If the capital costs of this are prohibitive, I would think your best bet would be to try drying the gas some more, as you mentioned. Do you happen to know the water content of the gas going into the exchanger now?