Non-destructive testing (NDT)
Ultrasonic test allows to detect and measure internal flaws in the material such porosity, inclusions, cracks. This done using sound waves of ultra-high frequency. The receiver generates high voltage electrical pulses which are transformed by transducer into high-energy sound waves and introduced into material. If the wave comes across any discontinuity on its path, it will be reflected back to the transducer which re-transforms it into an electrical signal. The time after which the echo comes back to the transducer is directly related to the distance from the flaw to the material’s surface.
Magnetic particle inspection is a easy and fast method of detecting surface flaws such as cracks. It involves magnetic field and small particles that exhibit magnetic properties. Firstly, the inspected material is magnetized, so that there is a south pole on one end and north pole on the another. Then iron particles are sprinkled over the material or applied as a wet suspension. If there is any discontinuity on the metal surface, south and north pole will form on its edges. This will cause the particles to be attracted to that area and form clusters, which are detected visually by the inspector. A big advantage of this method is that it does not require special surface preparation prior to test and can be performed on a forged surface.
Dye penetrant inspection is another effective method used for detecting surface cracks. It is based on capillary action, prior to the inspection the examined surface must be thoroughly cleaned and dried. Then penetrant liquid is applied and left for sufficient time, allowing the liquid to be drawn into the defects. Once penetrant is removed from the surface, developer is applied. The developer draws the dye back to the surface, where it can be detected by the inspector.