Ultrasonic testing of pressure vessel steel plates

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This is because raw steel plates are prone to internal defects such as folding, delamination, inclusions, and cracks during the production process (such as rolling). For steels used in special applications like pressure vessels, manufacturers can use ultrasonic testing to carry out quality grading; steel plates that do not meet the required standards are handled in accordance with relevant material management regulations. Folding (double skin) refers to the formation of a folded metal layer on the surface or near the surface of the steel plate during rolling. Layering is caused by defects such as residual shrinkage cavities in slabs, non-metallic inclusions, or metal oxides and sulfides. These defects fail to fuse during rolling and mostly appear in the middle or slightly off-center portion of the steel plate, running essentially parallel to its surface. Inclusions are caused by the failure to weld together during rolling due to a low compression ratio, and their locations are distributed in a random manner. Among them, internal inclusions refer to central carbon-manganese segregation that results in a high number of low-melting-point inclusions in the molten steel, whereas external non-metallic inclusions are formed by impurities that enter as a result of things such as the shedding of furnace wall refractory materials. Cracks are mainly white spots or heat treatment cracks. White spots are small cracks that form due to the insufficient time for hydrogen to diffuse during rolling cooling; they pose a significant risk (refining furnaces can help prevent such defects effectively). Slab heat treatment cracks are caused by improper heat treatment, or by thermal stresses in the heat-affected zone during cutting, resulting in cracks that are perpendicular to the rolling direction of the steel plate; they generally occur on the surface of the steel plate, but occasionally also inside it.