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Corrosion Glossary - T
- Tafel slope: the slope of the straight
line portion of a polarization curve, usually occurring at more than 50 mV from
the open-circuit potential, when presented in a semi-logarithmic plot in terms
of volts per logarithmic cycle of current density (commonly referred to as volts
- Tailings: the end-product or waste of
ore mining, usually piled up in close proximity of a mining area. Some will
often contain some metal that can
abbreviation for "total dissolved solids".
- Telegraphing: the revealing of the substrate
surface profile through the coating after cure. Commonly caused by not using
a surfacer or filler.
- Tempering: also known as drawing, the
process by which steel or
iron is softened by reheating it at
a considerably lower temperature than that at which its previous hardening was
- Temporary hardness: water
hardness due to the presence of
calcium and magnesium carbonates and bicarbonates, which can be precipitated
by heating the water. Now largely replaced by the term "carbonate hardness".
- Tensile strength: in tensile testing,
the ratio of maximum load to original cross-sectional area. also called ultimate
- Tensile stress: a stress that causes
two parts of an elastic body. on either side of a typical stress plane, to pull
apart. contrast with compressive stress.
- Tension: the force or load that produces
- Terne: an alloy of lead containing 3
to l5% tin (Sn), used as a hot dip coating
for steel sheet or plate. Terne coatings, which are smooth and dull in appearance,
give the steel better corrosion resistance and enhance its ability to be formed,
soldered, or painted.
- Therm: a unit of heat applied especially
to gas. one therm = 100,000 btu.
- Thermal barrier coating: a coating forming
an insulating barrier to a heat source to protect the substrate.
- Thermal shock: a cycle of temperature
swings that result in failure of metal due to expansion and contraction.
spraying: a group of processes wherein finely divided metallic
or nonmetallic materials are deposited in a molten or semi-molten condition
to form a coating. (The coating material may be in the form of powder, ceramic
rod, wire, or molten materials.)
- Thermochemically formed coatings: a
painted, dipped or sprayed chromium oxide based coating consolidated by repeated
deposition and curing cycles (about 500oC).
- Thermocouple: a device for measuring
temperatures, consisting of lengths of two dissimilar metals or alloys that
are electrically joined at one end and connected to a voltage-measuring instrument
at the other end. When one junction is hotter than the other, a thermal electromotive
force is produced that is roughly proportional to the difference in temperature
between the hot and cold junctions.
- Thermogalvanic corrosion: the corrosive
effect resulting from the galvanic
cell caused by a thermal gradient across the metal surface.
an NDE technique in which the
coating is flash heated and then viewed with an infra red camera. "Hot spots"
indicate areas of poor bonding or greater coating thickness.
- Thermosetting resin (thermoset): a resin
designed to undergo an irreversible chemical and physical change when undergoing
a heat-cure schedule, i.e., A plastic resin that cross links during cure so
that it does not soften when reheated.
- Thixotropy: the tendency for the viscosity
of a liquid to be shear rate dependent. When the liquid is rapidly shaken, brushed,
or otherwise mechanically disturbed, the viscosity decreases rapidly.
- Threshold: a very low concentration
of a substance in water. The term is sometimes used to indicate the concentration
which can just be detected.
- Threshold stress: threshold stress for
stress-corrosion-cracking. the critical gross section stress at the onset of
stress-corrosion cracking under specified conditions.
- Throughput volume: the amount of solution
passed through an ion exchange bed before the ion exchanger is exhausted.
- Throwing power: the relationship between
the current density at a point on a surface and its distance from the counter
electrode. The greater the ratio of the surface resistivity shown by the electrode
reaction to the volume resistivity of the electrolyte, the better is the throwing
power of the process tinning.
- TIG: the tungsten inert gas welding
- Tile: a preformed refractory, usually
applied to shapes other than standard brick.
- Time between coats: a time range given
to apply a second coat of topcoat
without any film defects.
- Tinplate: thin
steel sheet with a very thin coating
of metallic tin. Used primarily in can-making.
- Tool steels: steels that are hardened
for the use in the manufacture of tools and dies.
- Titanium dioxide:
white pigment in virtually all
white paints. Prime hiding pigment
in most paints.
- Titration: an analytical process in
which a standard solution in a calibrated vessel is added to a measured volume
of sample until an endpoint, such as a color change, is reached. From the volume
of the sample and the volume of standard solution used, the concentration of
a specific material may be calculated.
- Tinplate: thin steel sheet with a very
thin coating of metallic tin. Used primarily in can-making.
- Tool steels:
steels that are hardened for the use
in the manufacture of tools and dies.
- Topcoat: usually the final paint film
applied to a surface.
- Total acidity: the total of all forms
of acidity, including mineral acidity, carbon dioxide, and acid salts. Total
acidity is usually determined by titration with a standard base solution to
the phenolphthalein endpoint (pH
- Total alkalinity: The alkalinity of
a water as determined by titration with standard acid solution to the methyl
orange endpoint (pH approximately 4.5); sometimes abbreviated as "M" alkalinity".
Total alkalinity includes many alkalinity components, such as hydroxides, carbonates,
- Total carbon: the sum of the free carbon
and combined carbon (including carbon in solution) in a ferrous alloy.
- Total chlorine: the total concentration
of chlorine in a water, including combined and free chlorine.
Total dissolved solids
(TDS): The weight of solids per unit volume of water which are
in true solution, usually determined by the evaporation of a measured volume
of filtered water, and determination of the residue weight.
- Total hardness:
the sum of all hardness constituents in a water, expressed as their equivalent
concentration of calcium carbonate. Primarily due to calcium and magnesium in
solution, but may include small amounts of metals such as iron, which can act
like calcium and magnesium in certain reactions.
- Total pressure: the sum of the static
and velocity pressures.
- Total solids: the weight of all solids,
dissolved and suspended, organic and inorganic, per unit volume of water; usually
determined by the evaporation of a measured volume of water at 105oC in a pre-weighted
- Total solids concentration: the weight
of dissolved and suspended impurities in a unit weight of boiler water, usually
expressed in ppm.
- Toughness: the ability of a metal to
absorb energy and deform plastically before fracturing.
- Trace: a very small concentration of
a material, high enough to be detected but too low to be measured by standard
- Transcrystalline: see transgranular.
- Transference: the movement of ions through
the electrolyte associated with the passage of the electric current. also called
transport or migration.
- Transferred arc: in a plasma torch the
plasma jet is emitted from the torch and the current flows from the internal
cathode to the internal anode represented by the nozzle of the torch. When the
jet is carried to another anode with it being electrically favourable to do
so the current will then transfer to the second anode, usually the workpiece
and the arc is said to be transferred.
- Transgranular: through or across crystals
- Transgranular cracking:
cracking or fracturing that occurs through or across a crystal or grain. also
called transcrystalline cracking.
- Transgranular fracture: fracture through
or across the crystals or grains of a metal.
- Transition metal: a metal in which the
available electron energy levels are occupied in such away that the d-band contains
less than its maximum number of ten electrons per atom, for example, iron, cobalt,
nickel, and tungsten. The distinctive properties of the transition metals result
from the incompletely filled d-levels.
- Transpassive region: the region of an
anodic polarization curve, noble to and above the passive potential range, in
which there is a significant increase in current density (increased metal dissolution)
as the potential becomes more positive (noble).
- Transpassive state: state of anodically
passivated metal characterized by a considerable increase of the corrosion current,
in the absence of pitting, when the potential is increased.
- Trap: a receptacle for the collection
of undesirable material.
- Treated water: water which has been
chemically treated to make it suitable for boiler feed.
- Tribo charging: the process of creating
a static electric charge on powder particles by action against a nonconductive
- Tribology: the science and technology
concerned with interacting surfaces in relative motion.
- Tube: a hollow cylinder for conveying
- Tube hole: a hole in a drum, heater,
or tube sheet to accommodate a tube.
- Tuberculation: the process in which
blister-like growths of metal oxides develop in pipes as a result of the corrosion
of the pipe metal. Iron oxide tubercles often develop over pits in iron or steel
pipe, and can seriously restrict the flow of water.
- Turbidity: a measure of the cloudiness
in water, the result of finely divided particulate matter suspended in water;
usually reported in arbitrary units determined by measurements of light scattering.
- Turbine: wheel with many blades that
is spun when steam pushes the blades. A turbine converts heat energy into mechanical
- Turbulent flow: a type of flow characterized
by cross currents and eddies, as opposed to laminar or streamlined flow. Turbulence
may be caused by surface roughness or protrusions in pipes, bends and fittings,
changes in channel size, or excessive flow rates; turbulence significantly increases