Corrosion Glossary - R

Rabbit ears: a Spray pattern often seen with airless spray. The edge of the pattern separates to form a single stream.
Radiation damage: a general term for the alteration of properties of a material arising from exposure to ionizing radiation (penetrating radiation), such as x-rays, gamma rays. neutrons, heavy-particle radiation, or fission fragments in nuclear fuel material.
Radiography: use of ionizing radiation to produce shadow images on a photographic film. Some of the gamma or X-rays pass through an item being evaluated while others are partially or completely absorbed by more opaque parts of the item and cast a shadow on the photographic film.
Radon: heavy, natural, radioactive gas formed by the radioactive decay of radium, a decay product of uranium. Its atomic number is 86 and its atomic weight is 222. Its symbol is Rn.
Rate of blowdown: a rate normally expressed as a percentage of the water fed.
Raw water: untreated water, or any water before it reaches a specific water treatment device or process.
Reaction: a chemical transformation or change brought about by the interaction of two substances.
Reactive metal: a metal that readily combines with oxygen at elevated temperatures to form very stable oxides, for example, titanium, zirconium, and beryllium.
Reassociation: the recombination of the products of dissociation.
Recirculation: the reintroduction of part of the flowing fluid to repeat the cycle of circulation.
Recrystallization: a) formation of a new, strain free grain structure from that existing in cold worked metal, usually accomplished by heating. b) the change from one crystal structure to another, as occurs on heating or cooling through a critical temperature.
Red water: water which has a reddish or brownish appearance due to the presence of precipitated iron and/or iron bacteria.
Redox potential: the potential of a reversible oxidation-reduction electrode measured with respect to a reference electrode, corrected to the hydrogen electrode, in a given electrolyte.
Reducing agent: a compound that causes reduction, thereby itself becoming oxidized.
Reducing atmosphere: an atmosphere which tends to 1) promote the removal of oxygen from a chemical compound; 2) promote the reduction of immersed materials.
Reduction: the gain of electrons by a constituent of a chemical reaction.
Reference electrode: a nonpolarizable electrode with a known and highly reproducible potential.
Refractory: a ceramic material that can resist great heat and is therefore suitable for lining furnaces. Fireclay, dolomite, magnesite and silica are examples. This is not to be confused with refractory metals, such as columbium and tantalum.
Refractory: brickwork or castable used in boilers to protect metal surfaces and for boiler baffles.
Refractory metal: a metal having an extremely high melting point, for example, tungsten, molybdenum, tantalum, niobium, chromium, vanadium, and rhenium. In the broad sense, this term refers to metals having melting points above the range for iron, cobalt, and nickel.
Regenerant: a solution of a chemical compound used to restore the capacity of an ion exchange system. Sodium chloride brine is used as a regenerant for ion exchange water softeners, and acids and bases are used as regenerants for the cation and anion resins used in demineralization.
Regeneration: the process of restoring an ion exchange medium to a usable state after exhaustion. In general, it includes the backwash, regenerant introduction and fresh water rinse steps necessary to prepare a water softener exchange bed for service. Specifically, the term may be applied to the step in which the regenerant solution is passed through the exchanger bed (salt brine for softeners, acid and bases for deionizers.
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.
Relief valve (safety relief valve): an automatic pressure relieving device actuated by the pressure upstream of the valve and characterized by opening pop action with further increase in lift with an increase in pressure over popping pressure.
Residual: the amount of a specific material remaining in the water following a water treatment process; may refer to material remaining as a result of incomplete removal, or to material meant to remain in the treated water.
Residual chlorine: chlorine remaining in a treated water after a specified period of contact time to provide continuing protection throughout a distribution system; the difference between the total chlorine added, and that consumed by oxidizable matter.
Residual stress: stresses that remain within a body as a result of plastic deformation.
Resilience: The ability of a material to absorb energy when deformed elastically and to return it when unloaded. This is usually measured by the modulus of resilience, which is the strain energy per unit volume required to stress the material from, zero stress to the yield stress.
Resin: synthetic organic ion exchange material, such as the high capacity cation exchange resin widely used in water softeners.
Rest potential: see open-circuit potential.
Retarders: a solvent added to a paint to slow down its evaporation rate.
Reverse osmosis: a process that reverses, by the application of pressure, the natural process of osmosis so that water passed from the more concentrated to the more dilute solution through a semipermeable membrane, thus producing a stream of water up to 98% free of dissolved solids.
Reversing mill: any rolling mill in which the direction of rotation of the rolls can be reversed at will. Heavy primary mills for bloom and slab rolling are the most common, but others, including some cold-rolling mills, are also made to reverse.
Rhodium plating: the electro-deposition of rhodium for oxidation resistance combined with surface hardness.
Ringworm corrosion: localized corrosion frequently observed in oilwell tubing in which a circumferential attack is observed near a region of metal "upset".
Riser: a) that section of pipeline extending from the ocean floor up the platform. also, the vertical tube in a steam generator convection bank that circulates water and steam upward. b) a reservoir of molten metal connected to a casting to provide additional metal to the casting, required as the result of shrinkage before and during solidification.
Rockwell hardness test: an indentation hardness test using a calibrated machine that utilizes the depth of indentation, under constant load, as a measure of hardness.
Rod: rolled steel or steel with a circular cross section can be a bar, a rod or a round, and there is no generally accepted firm dividing line. Broadly, a rod is from 3/16 to 1/2 inch in diameter. Rods today are usually rolled in long lengths and coiled.
Rosin: natural resin obtained from living pine trees or from dead tree stumps and knots.
Rust: a corrosion product consisting primarily of hydrated iron oxide. (A term properly applied only to ferrous alloys.)

Link to glossary of corrosion and materials maintenance terms