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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
- 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
- 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
- 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.
electrode: a nonpolarizable electrode with a known and highly
- 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,
- 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
- 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
- Resin: synthetic organic ion exchange
material, such as the high capacity cation exchange resin widely used in water
- Rest potential: see
- Retarders: a solvent added to a
paint to slow down its evaporation
- 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.
a corrosion product consisting primarily of hydrated iron oxide. (A term properly
applied only to ferrous alloys.)