Control
Errors in welded joints occur like any technological procedure, because they carry a constant risk of the occurrence of certain errors. Considering the large number of influencing factors on the quality of welded joints, special attention must be paid to this danger both during the construction of the welded structure and in its application.
Penetrant testing or penetrant testing is used when testing welded joints on structures as a non-destructive test. A penetrant is applied to the previously cleaned and degreased surface. After penetrating into any crack, the penetrant is removed in an appropriate way (water or a dry cloth). With penetrants that are removed with water, you should be careful and direct the water jet parallel to the surface of the sheet, so that the water jet does not push the penetrant out of the crack. After drying the surface of the sheet (dry cloth), a developer (usually white) is applied, which draws the penetrant from the crack, so a red line from the penetrant from the crack is easily visible on the white surface of the sheet. For thinner sheets, a penetrant is applied on one side and a developer on the other. If there is a crack through the full thickness of the sheet, then the developer will draw the penetrant to its side, which will be detected as an easily visible red line of penetrant from the crack on the white (from the developer) surface of the sheet. With this method, it is possible to detect cracks with a length of 0.1 mm and a width of 0.03 mm. [1]
Testing with liquid penetrants is not applied to welded joints of welded products for the food industry,nor with welded joints where there is a tendency towards corrosion (especially stress corrosion). The disadvantages of this method are the high dependence of the quality of error detection on the method of preparation and the condition of the tested surface, usability only in a limited temperature range, unsuitability for outdoor application without protection from atmospheric conditions.
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