Non-Destructive Testing (Non-destructive testing, in short: NDT) is a type of inspection performed without damaging the integrity of the material or part to be examined. The validity of this inspection is based on the results of the destructive inspections that have been made before.
Non-destructive testing methods are used to detect invisible discontinuities in materials or open discontinuities on the material surface. Apart from detecting errors and defects, it is used to measure the amount of another material in a closed material, to measure the paint thickness on metal surfaces, to determine the status of mounted parts, and in radar systems. In Ultrasonic Examination and Industrial Radiography, tests are carried out by sending high-energy rays with very small wavelengths such as ultrasonic sound waves, X or gamma rays to the area to be examined in general.
METHODS
1. Visual Inspection (VT)
1. The part surface with an invisible crack.
2. Penetrant is applied to the surface.
3. Excess penetrant is wiped off.
4. The crack is made visible by applying the developer.
It is an examination with the naked eye. It is the examination of the parameters affecting the quality such as discontinuities on the surface of a product, structural defects, surface condition, with or without the use of an optical aid (such as a magnifying glass).
Although visual inspection seems to be a very simple method, it has its own subtleties. It is usually a study that should be done before applying another non-destructive testing method.
2. Penetrant Inspection
It is an intrusive paint inspection. Only faults opened on the outer surface of the material can be detected. Only porous materials are not subject to this inspection.
a) Pre-cleaning: It is done to clean the foreign materials, oil, dirt and rust on the surface of the material.
b) Penetrant application: Penetrant liquid is sprayed on the surface and fills the crack. 15 min wait
c) 2nd cleaning: It is the cleaning process of the red liquid (penetrant) on the material surface.
d) Developer application: It can be applied with water, solvent or spraying. It absorbs the liquid from the crack and expels it.
e) Inspection: It is examined visually or under fluorescent light, depending on whether fluorescent liquid is used.
3. Inspection with Magnetic Particles
Only ferromagnetic (magnetizable) material can be inspected. The part is made magnetized. If the magnetic field is pulled over the soft iron, it will return to its original state. Even if the magnetic field is removed from C steels, if there is a crack in the material, polarization may continue for a while. Transverse faults can be detected with magnetic field and longitudinal faults with electric field.
It can flow easily. The resistance to the field is great. If a coil with alternating current is brought close to a conductive material, eddy uptakes are induced in this material. Induced eddy currents create an additional magnetic field. This field can be detected either by the coil itself or by a separate coil. The imperfections, geometrical and metallurgical changes present in the material cause local changes in electrical conductivity and permeability, thus in induced eddy currents. These changes in eddy currents are sent to a suitable device by the detector coil. The reading device can be a pointer device, scope, pen recorder, light or audible alarm, counter, automatic imprinter or separator device. Thus, electrical, magnetic and geometric discontinuities of the material can be measured indirectly.
Not applicable to non-conductive materials. However, there is an exception to this; The thickness of a non-conductive coating on a conductive material can be measured by eddy currents.
4. Ultrasonic Inspection
With the central frequency between 0.1-15 MHz and sometimes 50 MHz, very short ultrasonic pulse-waves are initiated to stimulate the material or material to detect internal problems. This technique also frequently determines the thickness of the test object, eg pipework corrosion used to monitor.
Ultrasonic testing, which can be used in wood and composite concrete, however, is often done on steel and other metals and their alloys, though less resolution.
5. Radiographic Examination
Radiographic Inspection (RT) or industrial x-ray, a nondestructive (NDT) method of inspecting materials using short wavelength electromagnetic radiation (high energy photons) general ability to manipulate various materials, is testing for latent defects.
Either an X-ray machine or a radioactive source (IR-192, Co-60 or, in rare cases, Cs-137 in) photons can be used as a source. Neutron radiological testing (NR) is a variant of radiological testing that uses photons instead of neutrons to manipulate the material. Because neutrons can pass through lead and steel easily but plastic, water and oil stopped by this, you can see many different things from X rays.
Since the amount of radiation emanating from the opposite side of the material can be detected and measured, this amount of radiation (or variations in intensity) is used to determine the thickness or composition of the material.
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