The NDTs - Non-Destructive Testing
Non Destructive Testing (NDT) are tests performed on finished or semi-finished materials to verify the existence (or not) of discontinuities and/or defects, without altering their physical, chemical, mechanical or dimensional characteristics and without interfering in their subsequent use. In other words, tests are carried out to certify the quality of a certain part, without it being damaged or rendered useless. These tests are one of the main tools for quality control of materials and products, helping to ensure quality, reduce costs and prevent accidents. They are used in manufacturing, construction, assembly, inspection and maintenance, being widely applied in welding, castings, forgings, laminates, plastics, concrete and others, in Oil & Gas, Power Generation, Petrochemical, Automotive, Aeronautical, Railway, Naval, Steel, Civil Construction and others
The NDT Non-Destructive Testing include methods capable of providing information about the defect content of a given product, the technological characteristics of a material, or even the monitoring of degradation in service of components, equipment and structures.
Os métodos de NDT are: ACFM (Alternating Current Field Measurement), Vibration Analysis, Calibration and Measurement Reliability, Dimensional Control, Eddy Currents, Acoustic Emission, Visual Test, Leakage, Liquid Penetrant, Electrochemical Potential Measurement, MFL (Magnetic Flux Leakage), Guided Waves, Magnetic Particles In addition, the company offers a wide range of services, such as, Instrumentation Pig, Thermography, Spot Testing, and Ultrasound.
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To obtain satisfactory and valid results, the following items must be considered as fundamental elements of these tests:
- Trained and qualified personnel;
- Qualified test execution procedure based on standards and perfectly defined acceptance criteria;
- Duly calibrated equipment.
Besides the industrial use, the application of NDTs in Agriculture and Civil Construction has grown significantly.
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Non-destructive testing by Liquid Penetrant
The Penetrant test is considered one of the best test methods to detect surface discontinuities of non-porous materials, such as: ferrous and non-ferrous metals, aluminium, metallic alloys, ceramics, glass, certain types of plastics or organo-synthetic materials
The Penetrant is applied with a brush, by spraying using a spray gun or an aerosol dispenser, or even by immersion of the piece in the tank containing the product, and then a certain period of time is allowed for infiltration into the discontinuities. This method is based on the phenomenon of capillarity, which is the power of a liquid to flow in extremely small areas due to its low surface tension. The penetrating power is a very important characteristic since the sensitivity of the test is extremely dependent on it.
The application of a developer (fine white powder with absorbing power) should be made in the form of a uniform film, which will absorb the penetrant of the defects showing their location with precision and great simplicity, although their dimensions are slightly enlarged.Discontinuities in cast materials such as cold drop and stress cracking caused by quenching or tempering processes are easily detected by the liquid penetrant method. Also manufacturing discontinuities or process discontinuities such as seams, double lamination or material overlap. Welding cracks and cracks caused by machining, material fatigue or even stress corrosion can also be detected by penetrant method.
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Non-destructive testing by Magnetic Particles
Magnetic particle testing is used to detect surface and subsurface discontinuities in ferromagnetic materials. Defects such as cracks, weld cracks, cold joints, inclusions, cold drop, double lamination, lack of penetration, bends, segregations, etc. are detected. The test method is based on the generation of a magnetic field that runs over the entire surface of the ferromagnetic material. The magnetic lines of the flux induced in the material deviate from their path when they encounter a surface or subsurface discontinuity, thus creating a region with magnetic polarity highly attractive to Magnetic Particles. At the moment this magnetization is caused, the Magnetic Particles are applied to the part, which in turn will be attracted to the location of the surface that contains a discontinuity, thus forming a clear indication of a defect.
Some typical examples of applications are ferritic steel castings, forgings, laminates, extruded parts, weldments, parts that have undergone machining or heat treatment (nuts and bolts), cracks from grinding and many other applications in ferrous materials. For the discontinuities to be detected it is important that they are in such a way that they are "intercepted" or "crossed" by the induced magnetic flux lines; consequently, the piece must be magnetized in at least two 90° offset directions. To perform this test, electromagnets are used, the well-known yokes - portable machines - or stationary magnetizing equipment for serial or standardized tests.
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We will list here some links for further study material on the subject of non-destructive testing.