METHODS OF ANODIZING THE INTERNAL SURFACE OF HEAT TRANSFER TUBES

Disclosed is a method of anodizing the interior surface of a heat transfer tube comprising placing a plurality of contact electrodes in electrical communication with, and along, an exterior surface of the heat transfer tube, inserting a counter electrode into an interior space of the heat transfer tube, providing an electrolytic solution to the interior space of the heat transfer tube, passing an electric current between the plurality of contact electrodes and the counter electrode through the electrolytic solution, forming an oxidation layer along the interior surface of the heat transfer tube, wherein the oxidation layer has an oxidation layer thickness that decreases along a length of the heat transfer tube, stopping the passage of the electric current, removing the electrolytic solution, and applying a sealing solution to a surface of the oxidation layer to form a sealed oxidation layer along the interior surface of the heat transfer tube.