Ultrasonic Test
Ultrasonic methods of NDT use beams of sound waves (vibrations) of short wavelength and high frequency, transmitted from a probe and detected by the same or other probes. Usually, pulsed beams of ultrasound are used and in the simplest instruments a single probe, hand held, is placed on the specimen surface. An oscilloscope display with a time base shows the time it takes for an ultrasonic pulse to travel to a reflector (a flaw, the back surface or other free surface) in terms of distance traveled across the oscilloscope screen. The height of the reflected pulse is related to the flaw size as seen from the transmitter probe. The relationship of flaw size, distance and reflectivity are complex, and a considerable skill is required to interpret the display. Complex mutiprobe systems are also used with mechanical probe movement and digitization of signals, followed by computer interpretation are developing rapidly.
Radiography Test
Radiography is a Non-Destructive Examination method that uses X-ray and Gamma-ray for detecting internal imperfections, for measuring wall-thickness and for detection of corrosion. Conventional Radiography involves the process where radioactive rays are directed at the object to be inspected, to pass through it and the resulting image is captured on a film. This film is in-turn processed and image displayed as a sequence of grey shades between black and white. With radiographic examination the material is exposed to a homogenous ray from a radioactive isotope or an X-ray tube, while a negative film is positioned behind the material to be examined. After development of the film, thickness and density differences (i.e. material imperfections) will show as blackness differences. Acceptance criteria define whether or not the indication is non-acceptable (a defect) or not.
Penetration Test
This method employs a penetrating liquid, which is applied over the surface of the component and enters the discontinuity or crack. Subsequently, after the excess penetrant has been cleared from the surface, the penetrant exudes or is drawn back out of the crack is observed. Liquid penetrant testing can be applied to any non-porous clean material, metallic or non-metallic, but is unsuitable for dirty or very rough surfaces. Penetrants can contain a dye to make the indication visible under white light, or a fluorescent material that fluoresces under suitable ultra-violet light. Fluorescent penetrants are usually used when the maximum flaw sensitivity is required. Cracks as narrow as 150 nanometers can be detected.
Magnetic Test
The Magnetic Particle Inspection method of Non-Destructive testing is a method for locating surface and sub-surface discontinuities in ferromagnetic material. It depends for its operation on the face that when the material or part under test is magnetized, discontinuities that lie in a direction generally transverse to the direction of the magnetic field, will cause a leakage field, and therefore, the presence of the discontinuity, is detected by use of finely divided ferromagnetic particles applied over the surface, some of these particles being gathered and held by the leakage field, this magnetically held collection of particles forms an outline of the discontinuity and indicates its location, size, shape and extent.
Eddy Current Testing (ET)
Eddy current testing is a rapid and accurate technique used to detect discontinuities in tubing, heat exchangers, condensers, wires, plates, etc. Eddy current testing is also performed for alloy separation and for the determination of treatment conditions. The location of repair welds, girth welds and seam welds may also be detected on ground machined surfaces.
Moody Everbright provides the correct NDT techniques to locate and size defects in your assets, offering a fully integrated service pack combining NDT and technical inspection etc. Whether it is in fabrication, pipe manufacturing, pipeline, plant construction, chemical, petrochemical plants, shipyards or offshore industry
