NDT Glossary

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T

• Tangential - See circumferential.
  
• Target - A material bombarded by any radiation, as the target is bombarded by electrons in an x-ray tube.
  
• Temporary Magnet - A body of a soft steel or piece of iron which is readily magnetized but retains only a very small field after the active power of the external magnet field is removed.
  
• Tensile - Pertaining to forces on a body that tend to stretch, or elongate, the body. A rope or wire under load is subject to tensile forces.
  
• Tensile Strength - In tensile testing, the ratio of maximum load to the original cross-sectional area.
  
• Tenth Value Layer - That thickness of any material which will reduce radiation intensity by a factor of 10.
  
• Test Coil - Coil coupled to test material. It senses geometric, electric and magnetic changes in test material.
  
• Test Frequency - The frequency f vibration of the ultrasonic transducer employed for ultrasonic testing.
  
• Test Surface - That surface of the test object at which the ultrasonic energy enters or leaves.
  
• Thermal Cycles - Repetitive changes in temperature, that is, from a low temperature to a high temperature, and back again.
  
• Thompson-Gray Model - A model that allows the approximate prediction of ultrasonic scattering measurements made through liquid-solid interfaces.
  
• Thomson Scattering (R) - When an x-ray photon interacts with the whole atom so that the photon is scattered with no change in internal energy to the scattering atom, nor to the x-ray photon.
  
• Three Phase Alternating Current - commercial electricity is commonly transmitted as three single-phase currents, that is, these separate currents following separate sine curves, each at 60 cycles (or other frequency) per second, but with the peaks of their individual curves one-third of a cycle apart. At least three (sometimes four) conductors are required for three phase alternating current.
  
• Threshold - In reference to current or magnetic fields, the minimum strength necessary to create a looked-for effect is called the threshold value. For example, the minimum current necessary to produce a readable indication of a given defect is the threshold value of current for the purpose.
  
• Threshold Dose - The minimum dose that will produce a detectable degree of any given effect.
  
• Through Hardening - Hardening of a metal part, usually steel, in which the hardness across a section of the part is essentially uniform; that is, the center of the section is only slightly lower in hardness than the surface.
  
• Through-Transmission - A test method in which ultrasonic energy is transmitted through the test object and received by a second transducer on the opposite side. Changes in received signal amplitude are taken as indications of variations in material continuity.
  
• 3-2T Radiography - Quality level of radiography in which the finished radiograph displays a discernible image of a penetrameter hole that has a diameter equal to twice the penetrameter thickness. The penetrameter thickness equals 3 percent of the material thickness.
  
• Thulium 170 - A radioisotope of the element thulium.
  
• Time Base - See sweep.
  
• Time Delay - See sweep delay.
  
• Time of Flight - The time for an acoustic wave to travel between two points, Fro example, the time required for a pulse to travel from the transmitter to the receiver via diffraction at a discontinuity edge or along the surface of the test object.
  
• Time Response - A means for describing radio frequency (RF) response of the waveform.
  
• Toe Crack - a base-metal crack at the toe of the weld.
  
• Toe of Weld - the junction between the face of a weld and the base metal.
  
• Tolerance Dose - For industrial safety guidelines. 100 mr/week. (The word "tolerance" should not be understood to have the meaning "allowable," e.g. tolerance on machined parts.)
  
• Tone - The distinctive property of a complex sound.
  
• Tone Burst - A wave train consisting of several cycles of the same frequency.
  
• Torque - A measure of the twisting moment applied to a part under a torsional stress. Usually expressed in terms of inch pounds or foot pounds, although the terms “pound inches” and “pound feet” are technically more accurate for torsional moments.
  
• Torsion - A twisting action applied to a generally shaft-like, cylindrical, or tubular member. The twisting may be either reversed (back and forth) or unidirectional (one way).
  
• Toughness - Ability of a material to absorb, energy and deform plastically before fracturing. Toughness is proportional to the area under the stress-strain curve from the origin to the breaking point. In metals, toughness is usually measured by the energy absorbed in a notch impact test.
  
• Tracers - A radioactive element whose pathway through which a chemical reaction can be followed.
  
• Transducer - An electroacoustic or magnetoacoustic device containing an element for converting electrical energy into acoustical energy and vice versa. See search unit.
  
• Transducer Element - The component in a transducer that actually converts the electrical energy into acoustical energy and vice versa. The transducer element is often made of a piezoelectric material or a magnetostrictive material.
  
• Transformer - A transformer is simple a device that transforms electricity form one voltage to another.
  
• Transgranular Fracture - Through, or across, the crystals or grains of a metal. Same as transcrystalline and intracrystalline. Contrasted to intergranular fracture. The most common type of transgranular fracture are fatigue fractures. Cleavage fractures, dimpled rupture fractures, and shear fractures.
  
• Transient Currents - These currents are of short duration, generated by sudden changed in the electrical or magnetic conditions existing in an electrical or magnetic circuit.
  
• Transmission Angle - The incident angle of a transmitted ultrasonic beam. It is zero degrees when the beam is perpendicular (normal) to the test surface.
  
• Transmission Characteristics - Test object characteristics that influence the passage of ultrasonic energy, including scattering, attenuation or surface conditions.
  
• Transmission Technique - See through-transmission.
  
• Transmitter - The transducer that emits ultrasonic energy.
  - The electrical circuits that generate the signals emitted by the transducer.
  
• Transmutation - The change of one element into another as a result of changes within the nucleus.
  
• Transverse - Literally “across,” usually signifying a direction or plane perpendicular to the axis of a part.
  
• Tritium - A radioactive isotope of hydrogen with two neutrons and one proton in the nucleus. It is heavier than deuterium (heavy hydrogen). Tritium is used in industrial thickness gages, as a label in tracer experiments and in controlled fusion experiments.
  
• Tungsten - A metal commonly used to make the plugs used for connecting metal wires to one another or to the devices in integrated circuits.
  
• Two-crystal Method - Use of 2 crystals for sending and receiving. May be pulse-echo or through transmission method.
  
• Two-Film Technique - A procedure wherein two films of different relative speeds are used simultaneously to radiograph both the thick and the thin sections of an item.
  
• 2.2 T Radiography - Quality level of radiography displays a discernible image of a penetrameter hole that has a diameter equal to twice the penetrameter thickness. The penetramenter thickness equals 2 percent of the material thickness.

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