Eddy Current (ET)
Eddy Current testing is a nondestructive test which compares the condition of a test to that of a reference standard of sound material with known defects. When the test coil is placed next to an electrically conductive part, the primary magnetic field causes eddy currents to flow in the part (Faraday's law). This flow of eddy currents induced in a material generates a second magnetic field in the part called a secondary field. If there is an interruption in the field, such as a flaw, then the change in the current flow is represented on the instrument’s screen in a presentation similar to the test standard.
A series of electrical pulses is applied to a transducer which converts these pulses to mechanical energy in the form of pulsed waves at a selected nominal frequency. The transducer transmits the waves into the material through the surface of the part and couplant. Pulsed energy is transmitted into the material and is reflected back to the search unit by a discontinuity or boundary which is parallel or near parallel to the contacted surface. By comparison of the displayed signal amplitudes to those from a reference standard, both location and estimated discontinuity size may be determined.
The X-ray technique is a non-destructive method of detecting surface and subsurface defects in a part or assembly. X-rays are produced when electrons traveling at a high speed in a vacuum are stopped by matter. Some of the radiation will be absorbed and scattered as it passes through the part. When the beam of penetrating radiation is directed through the part then the amount of radiation passing through the part is observed or recorded on a photographic type film called X-ray film, or the image can be recorded on an Imaging Plate (Computed Radiography). After the film or plate is processed, a shadow picture of the internal structure of the part is obtained. This technique is used to inspect castings, welds, wrought structures, adhesive bonds / composites, aircraft structure and instruments.
Fluorescent Penetrant (PT)
A nondestructive test method used to detect discontinuities open to the surface. The principle of the test consists of applying penetrant to the surface being examined then allowing it sufficient time to enter the discontinuities by capillary action. The excess penetrant is then removed from the surface in such a manner as to leave the penetrant in the discontinuity cavities undisturbed. A developer is applied. The developer acts as an absorbent blotter to draw the penetrant out of the discontinuity cavity. The bleeding penetrant back to the surface into the developer causes an indication in the form of a penetrant stain in the developer coating. The amount and type of indication bleed-out is then interpreted and evaluated to the appropriate acceptance criteria.
Magnetic Particle (MT)
A nondestructive test method used to detect discontinuities at or near the surface of ferromagnetic materials. The principle of the examination consists of magnetizing an article and applying magnetic particles to the magnetized surface of the test article, then the test surface is examined for any accumulation of particles (indications) at points causing magnetic field leakage caused by discontinuities and the indications are evaluated to an acceptance standard.