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 per decade).
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 be extracted.
TDS: The 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 done.
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 strength.
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 elongation.
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.
Thermal 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.
Thermography: 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 process.
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 8.3).
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, and bicarbonates.
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 dish.
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 analytical methods.
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 or grains.
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 material.
Tribology: the science and technology concerned with interacting surfaces in relative motion.
Tube: a hollow cylinder for conveying fluids.
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 energy.
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 pressure drops.

Link to glossary of corrosion and materials maintenance terms