QUALITY CONTROL OF MATERIALS AND PRODUCTS
Non-destructive testing (NDT) is the quality control of materials and products performed without compromising the integrity of the material or product. Defects in materials and products can occur either during production depending on the production technology used (cracks, pores, shrinkage...) but also during operation and are caused by corrosion or wear. At present, NDT has higher goals than just detecting defects in materials and products. It is a means of improving the quality of production processes, preventing industrial accidents.
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NDT - METHODS OFFERED
Testing by visual methods VT
It represents a very effective and inexpensive way of detecting obvious surface defects of inspected objects. VT can reveal surface cracks, welds, significant changes in the shape (deformation) of the controlled material, etc. The resolution of VT for failures (cracks) is about 0.1 mm. Before performing the VT, the object or part of it must be cleaned of slag, corrosive paints, grease and other impurities (mechanically, chemically or electrochemically) that would interfere with the inspection, and the visibility of errors, if inspection conditions allow, can be easily found by etching the surface. Lighting of inspected areas must be necessary for reliable detection of errors. Visual inspection is the basic inspection method, which is always performed first. It therefore precedes a sufficiently different NDT control.
Testing by capillary methods PT
They are used to detect fine surface defects - defects that result in the surface of the inspected object. The essence of PT is the use of liquids with low surface tension, i. j. those which wet the surface of the material under investigation well, as a result of which they penetrate even the smallest pores. The implementation of PT consists in covering the controlled surface with a penetrating liquid so that it can penetrate the defects protruding on the surface. After removing its excess from the controlled surface, the penetrating liquid (penetrant) from the defects (capillaries) erupts on the surface into the applied developer, on which it creates either a color or fluorescent error indication according to the penetrant and developer used.
Magnetic powder testing method MT
It is used to control ferromagnetic materials (alpha iron, nickel, cobalt and their alloys). MT uses changes in magnetic conductivity in materials in the surface layer. The homogeneity of magnetic field lines in the volume of an object depends on the homogeneity of its magnetic conductivity. If there are any obstacles in the path of the magnetic flux that have a different permeability than the base material, a scattering magnetic field is created at the defect. The scattering magnetic field on the surface of the tested component is indicated by a ferromagnetic powder applied to the surface (by sputtering, spraying, etc.), which is captured in the scattering magnetic on the surface of the component. The size of the indication is larger than the size of the defect, which makes the defects very visible. Either dry ferromagnetic powder, ferromagnetic powder suspended in a liquid (dilute oil or kerosene) or ferromagnetic powder covered with a phosphor are used. A necessary condition for error indication is the magnetization of the tested component.
Ultrasound testing UT
It uses the laws of propagation of individual types of ultrasonic waves (reflection, refraction, transformation, absorption, bending, etc.) to detect errors in the test object. The error will cause either an echo from the error or a reduction of the transient echo, depending on the testing technique used. Ultrasound are mechanical oscillations of ambient particles around an equilibrium position with a frequency higher than 20 kHz. The evaluation of errors is based on the evaluation of the size and area of the fault echo on the echograms.