06-11-2017, 11:07 AM
Non-destructive testing (NDT) is a broad group of analysis techniques used in the science and technology industry to evaluate the properties of a material component or system without causing damage. The terms non-destructive examination (NDE) non-destructive inspection (NDI) and non-destructive evaluation (NDE) are also commonly used to describe this technology. Because NDT does not permanently alter the item being inspected, it is a very valuable technique that can save both money and time in product evaluation, problem solving and research. The six most commonly used methods of NDT are Foucault current, magnetic particles, penetrating liquids, radio-graphic, ultrasonic and visual tests. NDT is commonly used in forensic engineering, mechanical engineering, petroleum engineering, electrical engineering, civil engineering, systems engineering, aeronautical engineering, medicine and art. Innovations in the field of non-destructive testing have had a profound impact on medical images, including echocardiography, medical ultrasound and digital radiography.
NDT methods are based on the use of electromagnetic radiation, sound and other signal conversions to examine a wide variety of items (metallic and non-metallic, food products, artifacts and antiques, infrastructure) for integrity, composition or condition without alteration of the article under review. Visual inspection (VT), the most commonly applied NDT method, is often improved by the use of magnifications, borescopes, cameras or other optical arrangements for direct or remote viewing. The internal structure of a sample can be examined for a volumetric inspection with penetrating radiation (RT), such as X-rays, neutrons or gamma radiation. The sound waves are used in the case of the ultrasonic test (UT) another volumetric NDT method: the mechanical signal (sound) is reflected by the conditions in the test article and the amplitude and distance of the search unit is evaluated ( transducer). Another NDT method commonly used in ferrous materials involves the application of fine iron particles (either suspended in liquid or dry powder - fluorescent or colored) that are applied to a part while it is magnetised, either continuously or remotely. The particles will be attracted to the fields of leak magnetism in or on the test object, and will form indications (particle collection) on the surface of the objects, which are evaluated visually. The contrast and the probability of detection for a visual examination with the naked eye are often improved by the use of liquids to penetrate the surface of the test article, allowing visualization of defects or other surface conditions. This method (penetrating liquid test) (PT) involves the use of dyes, fluorescent or colored (typically red), suspended in fluids and used for non-magnetic materials, usually metals.