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What is NDT : NDT means Non Destructive Test. NDTs allows to verify the condition of material, construction, mashine etc. and performed in a manner that does not affect the future usefulness of the object or material. They are implement tests that locate and characterize material conditions and flaws that might otherwise cause planes to crash, reactors to fail, trains to derail, pipelines to burst, and a variety of less visible, but equally troubling events. NDT provides an excellent balance between quality control and cost-effectiveness. NDT applies to industrial inspections and is relevant to medical technology but subjects here are non living objects.The number of inspection methods, as (VT) Visual Testing, (RT) Radiography, (MT) Magnetic Particle Testing, (PT) Penetrant Testing, (UT) Ultrasonic Testing, (ET) Electromagnetic Testing, (LT) Liquid testing and (AE) Acoustic Emission are, seems to grow. An overview of each method given below:

Visual and Optical Testing (VT) : The most basic NDT method is visual examination. Visual examiners follow procedures that range from simply looking at a part to see if surface imperfections are visible, to using computer controlled camera systems to automatically recognize and measure features of component.                                                                                                                                                                                                                  Radiography (RT) : RT involves the use of penetrating gamma- or X-radiation to examine material's and product's defects and internal features. An X-ray machine or radioactive isotope is used as a source of radiation. Radiation is directed through a part and onto film or other media. The resulting shadowgraph shows the internal features and soundness of the part. Material thickness and density changes are indicated as lighter or darker areas on the film.           

Magnetic Particle Testing (MT) : This NDT method is accomplished by inducing a magnetic field in a ferromagnetic material and then dusting the surface with iron particles (either dry or suspended in liquid). Surface and near-surface flaws produce magnetic poles or distort the magnetic field in such a way that the iron particles are attracted and concentrated. This produces a visible indication of defect on the surface of the material.                        

Ultrasonic Testing (UT) : In ultrasonic testing, high-frequency sound waves are transmitted into a material to detect imperfections or to locate changes in material properties. The most commonly used ultrasonic testing technique is pulse echo, whereby sound is introduced into a test object and reflections (echoes) from internal imperfections or the part's geometrical surfaces are returned to a receiver. New UT equipment represent imperfections, their location, shape etc.                                                                                                                                                                                                            

Penetrant Testing (PT) : The test object is coated with a solution that contains a visible or fluorescent dye. Excess solution is then removed from the surface of the object but leaving it in surface breaking defects. A developer is then applied to draw the penetrant out of the defects. With fluorescent dyes, ultraviolet light is used to make the bleedout fluoresce brightly, thus allowing imperfections to be readily seen . With visible dyes, vivid color contrasts between the penetrant and developer make "bleedout" easy to see.                                                                                                                                  

Electromagnetic Testing (ET) : Electrical currents (eddy currents) are generated in a conductive material by a changing magnetic field. The strength of these eddy currents can be measured. Material defects cause interruptions in the flow of the eddy currents which alert the inspector to the presence of a defect. Eddy currents are also affected by the electrical conductivity and magnetic permeability of a material, which makes it possible to sort some materials based on these properties.        

Leak Testing (LT) : Several techniques are used to detect and locate leaks in pressure containment parts, pressure vessels, and structures. Leaks can be detected by using electronic listening devices, pressure gauge measurements, liquid and gas penetrant techniques, and/or a simple soap-bubble test.         

Acoustic Emission Testing (AE) : When a solid material is stressed, imperfections within the material emit short bursts of acoustic energy called "emissions." As in ultrasonic testing, acoustic emissions can be detected by special receivers. Emission sources can be evaluated through the study of their intensity and arrival time to collect information about the sources of the energy, such as their location.

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