natural drainage—current drainage from an underground or submerged metallic structure to a more negative(more anodic) structure, such as the negative bus of a trolley substation.
near-white metal blast cleaned surface—an abrasive blast cleaned steel surface that isfree of all visible contaminants and foreign matter, but may have some random staining on no more than 5 percent of the surface area. [See NACE No. 2/SSPC-SP10 for detailed specification.]
negative return—a point of connection between the cathodic protection negative cable and the protected structure.
Nernst equation—an equation that expresses the potential of an electro-chemical reaction in terms of the activities of its products and reactants.
Nernst layer—the diffusion layer at the surface of an electrode in which the concentration of a chemical species is assumed to vary linearly from the value in the bulk solution to the value at the electrode surface.
nitriding—the absorption and diffusion of nitrogen in metallic materials (most commonly ferrous alloys).(Typical processes for intentional nitriding include, but are not limited to,liquid nitriding, gas nitriding, and ion or plasma nitriding.)
noble—the positive (increasingly oxidizing) direction of electrode potential.
noble metal—a metal with a standard electrode potential more positive than that of hydrogen.
noble potential—a potential more positive than the standard hydrogen potential.
nodular cast iron—see ductile cast iron.
normalizing—heating a ferrous alloy to a suitable temperature above the transformation range (austenitizing), holding at temperature for a suitable time, and then cooling in still air to a temperature substantially below the transformation range.