Defectoscopy – non-destructive testing of welds:
Defectoscopic weld testing a wide group cost- effective and acceptable methods that allow you to examine the quality of the product without damaging it. In the event that the product meets the quality requirements and is found satisfactory, it can be used immediately. Non-destructive testing is very important especially in welds where the presence of defects is a major problem in the usability of the product.
Non-destructive testing – methods
VT – visual welds testing
Visual testing method is considered to be the basic and most cost-effective method non-destructive welds testing. Visual method can be performed during the welding and after welding.
Visual inspection of the weld can detect a wide range of surface defects, including cracks, porosity and burnt offerings. Furthermore, controls the size of the weld, the weld root cant etc .. Visual method can be used as a standalone method or a method which is before another NDT method. It focuses on evaluation of the surface condition of product with eye or using a magnifying glass, microscope or special devices, such as endoscopes, fiberscopes and videoscopes.
PT – penetrant welds testing
Another method non-destructive weld testing is penetration (capillary) method. That method is based based on capillary action, wherein the low surface tension of the liquid penetrates into the clean and dry surface discontinuities. The penetrant may be applied to the test surface by dipping, spraying or brushing. After the penetrant was allowed sufficient time for penetration of discontinuities, remove the excess and applied developer. Developer helps wick penetrant from defects, then the defect is visible on the surface and can be evaluated. Checking is performed in the ultraviolet or white light, depending on the type of dyes.
- Cleaning surface: The test surface must be free from all impurities, paints, oils and grease, which could degrade during the test. The ultimate goal of this step is a clean surface.
- Application of penetrant: The penetrant is applied on the surface of the weld to be tested. The penetrant is left on the surface 5 to 30 minutes. During this time the penetrant gets all the defects on the surface.
- Removal of penetrant: The penetrant is removed from the surface. Removal method is controlled by the type of penetrant.
Application developer: After being removed penetrant is applied on the surface of the test material developer.
- Evaluation: Developer helps wick penetrant, defects that become visible and can be recorded and evaluated.
- Final cleaning: Test surface is needed after checking and recording defects cleaned.
MT – magnetic particle welds testing
Magnetic particle method evaluation of welds is one of the most common methods of non-destructive welds testing.
Magnetic particle method is a method of locating and defining discontinuities in magnetic materials. It is excellent for detection of surface defects in the weld, including discontinuities, which are too small to be seen with the naked eye. Magnetic method can also find defects that are located just beneath the surface of the weld. MT method is a suitable method for the detection of surface
With this method, the electromagnet is placed on each side of the area to be inspected. This will saturate the magnetic material and whereas the detected defect has different magnetic properties, and at the point defects leads to a deformation of the magnetic field, the field lines extend to the surface after application of the magnetic powder, these defects become visible. Indications are assessed based on visual perception of color and luminance contrast. The detection capability of the method begins with the width of the defect units of thousandths of a millimeter.
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