redox potential—see oxidation-reduction potential.
reduction—gain of electrons by a constituent of a chemical reaction.
reference electrode—an electrode having a stable and reproducible potential, which is used in the measurement of other electrode potentials.
reference half-cell—see reference electrode.
reinforcement—(1) glass cloth, chopped fibers, or mat used to provide additional tensile and flexural strength and other properties to a coating or lining. (2) bars or fibers added to concrete to enhance its mechanical properties.
relative humidity—the ratio, expressed as a percentage, of the amount of water vapor present in a given volume of air at a given temperature to the amount required to saturate the air at that temperature.
remote earth—a location on the earth far enough from the affected structure that the soil potential gradients associated with currents entering the earth from the affected structure are insignificant.
residual stress—stress present in a component free of external forces or thermal gradients.
resin—a clear to translucent, solid or semisolid, viscous organic substance, often of relatively high molecular mass, which exhibits a tendency to flow when subjected to stress and usually has a softening or melting range. (Natural resins originate from secretions of certain plants and insects. Synthetic resins are physically similar polymerized synthetic materials, either thermoplastic or thermosetting,which are used to form plastics. Resins are commonly used as the binder invarious paints, coatings, adhesives, and synthetic plastics.)
resistivity—the electrical resistance between opposite faces of a unit cube of material.
rest potential—corrosion potential after time transients have subsided.
reversible potential—see equilibrium potential.
rimmed steel—an incompletely deoxidized steel. [also called rimming steel]
rimming steel—see rimmed steel.
riser—(1) that section of pipeline extending from the ocean floor up to an offshore structure. (2) the vertical tube in a steam generator convection bank that circulates water and steam upward. (3)a large-diameter pipe or duct in a fluidized catalytic cracking unit into which the hydrocarbon feed is injected to mix with a stream of hot catalyst and steam and through which the resulting reaction mixture flows upward.
RockwellC hardness—hardness value, measured in accordance with ISO 6508-1 or Test Methods E18, obtained using a diamond cone indenter and a force of approximately 1.471 N (150 kgf).
rouge—a reddish-brown fine powder consisting primarily of iron oxide particles.
run—See sag.
rust—corrosion product consisting of various iron oxides and hydrated iron oxides. (This term properly applies only to iron and ferrous alloys.)
rust bloom—discoloration indicating the beginning of rusting.