Lamellar failures in state-of-the-art welded structures is rather rare phenomenon, although as far back as 40-50 years ago such defects in thick-wall structures in the area of tee, and especially cruciform joints occurred rather frequently. Substantial studies carried out in 1970-1980s of the previous century enabled establishment of more strict requirements to thick-wall steel rolled stock in regard to the content of impurities (in particular sulfur) and ductility of the material in z-direction, which enabled successful overcoming of the problem of lamellar failures in structures made of these materials. Nevertheless, it is difficult to completely exclude occurrence of lamellar defects, that's why it is necessary to take this threat into account. It should be mentioned that in a number of cases an attempt is made to place responsibility for technological or design miscalculations on insufficiently high resistance of the material to formation of mentioned defects. From this viewpoint the considered case of welding of shells of manholes from steel 09G2S 16 mm thick into body of the reservoir RVS 75,000 m~3 in town of Brody is rather indicative. This steel, the content of sulfur in which is ～0.045%, has reduced resistance to lamellar failure (KCV = 28 J/cm~2 and δ_c = 0.02 cm in Z-direction at KCV = = 134 J/cm~2 and δ_c = 0.024 cm in plain of the sheet), that's why observed during hydrostatic tests of the reservoir leakiness of welded joints, by which the shells of the manholes were welded to the reservoir wall using cover plates, was connected with lamellar defects in the shell. Carried out numerical study of stressed state (residual welding stresses, and total stresses allowing for stresses from the test pressure) showed that at considered thicknesses and radii of curvature in structures of protection manholes risk of occurrence of lamellar failures is very low. Change of the welded joint design made it possible to avoid leakiness in welded joints during hydraulic tests and confirmed results of numerical estimations, which showed rather low risk of lamellar failure occurrence in the considered welded assembly.
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