CS267351B1 - Method of non-destructive inspection of stressed welded joints of welded metal structures - Google Patents

Abstract

The solution concerns non-destructive inspection of extremely stressed weld joints of welded metal structures. The critical point of the weld joint, especially the heat-affected area with a size of 500 to 5,000 mm2, is polished to a metallic luster surface, which is provided with an anti-corrosion coating and a layer against mechanical damage, then when inspecting the weld joint, the layer is removed and the metallic luster surface is cleaned, on which the degree of plastic deformation of the weld joint in the form of slip bands or microcracks is monitored.

Description

(57) The solution concerns the non-destructive control of extremely stressed welded joints of welded metal structures. The critical weld joint site, the most heat-affected area of 500 to 5,000 mm 2, is polished onto a metal-coated surface which is provided with a corrosion coating and a mechanical damage pad, then when the weld seam is checked, the pad is removed and the metal surface cleansed on monitors the degree of plastic deformation of the weld joint in the form of slip belts or microcracks. CS 267351 Bl CS 267 351 Bl

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BACKGROUND OF THE INVENTION The invention relates to a method for the non-destructive inspection of stressed welded joints on a welded structure by observing the sliding strips of welded joints after operation of the same structure.

So far known methods for monitoring the damage of welded joints of extremely stressed welding structures, such as pressure vessels, bridges, storage containers and the like, are relatively limited. They are demanding in terms of technical equipment and personnel, such as the tensometric method, the Moiré method, or the holographic method. The strain gauge method can only be used to monitor the stress of the structure into the yield strength of the material. Once the yield strength has been exceeded, the method no longer allows the plastic deformation to be measured. Moiré and holographic can only be used with the current photographic record and can only be used for short-term trials. Other non-destructive tests used in practice are tests to monitor the development and development of cracks, such as ultrasonic, magnetic dip fluorescence, rontgenographic and capillary tests.

Methods such as strain gauge, Moiré, and holographic cannot be used in the operation of, for example, pressure vessels because they need direct contact with the site of interest. Indeed, the trials already follow defects that may have occurred either during the production of the welded structure or during operation. However, they do not allow monitoring of the defect-activating conditions, especially cracks.

The above-mentioned disadvantages are largely eliminated by the method according to the invention, the principle of which is that the predetermined critical point of the welded joint, the most heat-sealed area of 500 to 5000 mm 2, is polished onto a metal-coated surface which is provided with a corrosion coating and a blanket against mechanical damage, then, when checking the weld joint, the liner is removed and the metal-wiped surface is cleaned and the degree of plastic deformation of the weld joint in the form of slip belts or microcracks is monitored on the surface thus prepared.

The method of non-destructive inspection according to the invention is suitable from the point of view of very simple application in practice, does not require demanding technical equipment. The method according to the invention can be applied in the control of several critical points of a welded construction where the yield stress limit in both the operating and experimental conditions is assumed to be exceeded. The evaluation of the control is advantageous in practice because it allows the degree of plastic deformation or micro-cracks in the weld joint to be detected on the wearer as well as in the laboratory. In the critically stressed area of the weld joint, which is usually a temperature-controlled area, the metallographic paper is ground and mechanically polished to a surface of 500 to 5,000 mm 2, which is protected from corrosion and mechanical damage. Corrosion protection is done with silicone paste or translucent varnish. Prior to mechanical damage, an anti-corrosion coating is placed on the anti-corrosion coating, which may be plastic or steel sheet due to the circumstances and the welded construction. The plastic pad is glued to the metal with a glue, and the steel pad is supported by a low-melting solder.

When checking or prescribing a welded design revision, the mechanical protection of the polished area is removed as well as the anti-corrosion coating and thus the polished surface is ready for observation. If the critical point has been plastically deformed, slippery bands or microcracks can be observed directly in the light microscope. After etching the structure, the interaction of the sliding strips with the structure can also be observed. If necessary, a print, for example celluloid, can be taken from the observed spot, which is coated with a carbon shielding substance and the canopy is observed with a light or electron scanning microscope. After steaming the celluloid imprint with carbon and dissolving the celluloid in acetone, a two-step imprint on the transmission electron microscope was possible. The method of non-destructive inspection of the welded structure according to the invention is suitable for all welded structures stressed in the yield point, preferably under low cycle fatigue conditions.

Claims (1)

Method of non-destructive inspection of stressed welded joints of welded metal structures, characterized in that the presumed critical point of the welded joint, the heat-affected area of 500-5000 mm, is polished to a metal-coated surface, provided with a corrosion coating and a sheath against mechanical damage. then, during inspection of the weld joint, the liner is removed and the metal-gloss surface is cleaned and the degree of plastic deformation of the weld joint in the form of slip strips or micro-cracks is monitored on the surface thus prepared.