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Magnetic Particle Testing

Focus NDT Ltd

Established in July 1993, Focus NDT is a recognized leader in Non-Destructive Testing (NDT) and inspection activities. With Offices in Rotherham, Wolverhampton and Aberdeen we provide quality services for Engineering, Transport, Petrochemical, Gas, Nuclear, Manufacturing and Aerospace. With a full-time staff of qualified technicians and inspectors, Focus NDT prides itself on its Rapid Response and is committed to providing complete customer satisfaction, through the utilization of some of the most advanced NDE methods available including : Magnetic Particle Inspection (MPI), Ultrasonic Inspection (UT), Liquid Penetrant Inspection (LPI) Radiography (RT) & Eddy Current (EC).


Ultrasonic Inspection

This method of testing for flaws utilises sound waves which are introduced into the component via an ultrasonic source, as the sound travels through material reflections or echoes occur from the back surface. In addition any internal discontinuity will reflect the sound wave and generate a signal into the receiver. The time lags of the echoes are measured to determine the thickness of the material and the distance to the discontinuity.

Magnetic Particle Testing

Magnetic particle inspection (MPI) and magnetic particle testing can be used for the detection of surface and near-surface flaws in ferromagnetic materials. Using a permanent magnet, electromagnet, flexible cables or hand-held prods a magnetic field is applied to the item under test. If a flaw is present the magnetic flux is distorted and 'leaks'. Fine magnetic particles, (normally in spray form in carrier fluid) can be applied to the surface of the specimen, are attracted to the area of flux leakage creating a visible flaw indication. It is recommended that the inspection surface is magnetised in at least two perpendicular directions at 90° to each other, due to lack of disturbance to the magnetic field if the crack runs parallel to the magnetic field.

Liquid Penetrant Inspection

This method involves applying a visible or fluorescent dye to the surface. After application by immersion or spray the dye enters any discontinuities via capillary action. The component is wiped dry and any subsequent seepage from fissures is detected by drawing the liquid out into a white absorbent coating applied after drying off (See Diagrams Below). This method is suitable for any non ferrous components or material that is non absorbent. Typical applications are forged, cast or welded products.

Eddy Current Inspection

Eddy Current can be used in two different manners, Firstly for finding surface and subsurface flaws, and Secondly for determining different metallurgical characteristics. Eddy current is based on the principle of measuring changes in the impedance of an electromagnetic coil as it is scanned over a surface of conductive material. An alternating current in the coil produces a magnetic field that is induced in the material. To counter the coil's primary magnetic field, eddy currents are produced in the material. Eddy currents produce a secondary magnetic field H'B to oppose the coil's primary magnetic field HB. When the coil is scanned over a discontinuity, the secondary magnetic field is distorted, thereby changing the loading on the coil. Changes in coil loading directly affect the coil impedance, these changes are signified on the trace as a (possible) flaw.

Radiographic Inspection

A source of ionising radiation positioned at on one side of item to be inspected, and a photographic film placed in close proximity to the other side. The radiation is partly absorbed during transmission and differences in material thickness or absorption qualities are recorded on the film giving a full-size image showing internal detail. The higher the Material density more radiation absorbtion will occur. Processed films are called radiographs, Industrial radiography requires X-rays or gamma rays to reveal hidden flaws in solid objects. X-ray radiography is generated electrically by means of a high voltage X-ray tube. Gamma rays are produced by the natural disintegration of nuclei in a radioactive isotope. Common types being Iridium 192 and Cobalt 60. Radiography's main benefits are that it provides a non-destructive method of detecting hidden flaws in materials and fabrications and provides a permanent record. Radiography is particularly good at detecting volumetric flaws such as voids, gas pores and solid inclusions, It is also good at determining the nature and dimensions (length and width) of flaws - however it cannot be used to measure through-thickness of defects.

Hardness Testing

A modular construction allowing the user to replace components on site and featuring a 4.6M armoured cable, steel bodied microscope unit with military style connectors, free standard software upgrades, and simple change over of a

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