The paper considers standard methods for determining the corrosion and mechanical characteristics of pipes and their welded joints, steel shell structures for water supply to consumers. It was found that sharp fluctuations in the values of microhardness in the zone of thermal influence of the welded joint exceed the baseline values in the middle part of the weld and the base metal of the pipe. The obtained results can be used to test the performance of carbon steel steels designed for the construction of water towers of long service life in corrosive environments. Under the action of the temperature gradient on the outer surfaces of the walls of the water tank tensile stresses occur, and on the inner surfaces-compressive, which is a favorable factor that reduces the risk of corrosion. Temperature stresses that occur in the case of temperature inhomogeneity along the contour of the cylindrical tank are unfavorable. Stresses from the weight load are small and do not have a significant effect on the destruction of the steel tank, because they are compressive. The value of technological final stresses was determined experimentally by mechanical strain gauge according to the classical method, as well as with the help of electric strain gauges and ultrasonic method according to the method of E. O. Paton Electric Welding Institute (PWI). It has been experimentally established that the most dangerous final welding stresses in assembly seams, the value of which for the longitudinal stress component is close to or exceeds the yield strength , and for the transverse – close to the yield strength , while on steel plates VSt3 of the same thickness . It is likely that welding during installation in conditions of rigid compression of the metal causes an increased level of final stresses. The magnitude and sign of the final stresses  significantly depends on the method of installation. Even during block installation, when the water tower is mounted from several pre-annealed blocks, the connection between the mounting ring seams in some areas of the base metal near these seams during fitting creates significant stresses (up to 17.6 kgf / mm2), in some areas – up to 6 kgf / mm2. When sheet assembly stresses can reach a level close to the yield strength.

The durability and reliability of operation of steel pipelines of water supply and sewage systems is determined in particular by the quality of their welded joints, which in turn depends both on the composition of the materials used in their manufacture and on the observance of welding technology. The composition of impurities of transported liquids, which can cause corrosive destruction of materials, also has a significant impact on the reliability of pipeline systems. These phenomena are especially important in hot water supply and industrial drainage systems, where the destructive influence of physical factors and the chemical composition of the environment can be decisive. It was found that the loss of strength of the pipeline is caused in particular by improper operation, under the conditions of which micro-flaws of welded joints of pipelines appear, which leads to their destruction. The results of examinations and experimental studies of the strength of welds of steel process pipelines are presented. An external inspection was carried out, determination of the structure and strength parameters of pipeline welds, layer-by-layer analysis of corrosion damage on their inner surface. It was found that premature destruction of welded joints of hot water supply pipelines and industrial sewage is caused by long-term operation in a stressed state. Under such circumstances, the uneven coarse-grained structure of the seam, the presence of non-metallic inclusions in the metal structure, and violations of the welding technology had a critical impact on the loss of strength. In order to increase the corrosion-mechanical resistance of welded joints of industrial pipelines, it is necessary to modify the surfacing metal of the weld to break down the structure and significantly reduce non-metallic inclusions, as well as to improve the technology of manual arc welding with coated electrodes, in particular, the root layers of welding seams.

No abstract

It is known that the fatigue process begins with the plastic deformation of the surface layers of the metal fittings. Moreover, the displacement of dislocations under conditions of re-alternating loads is observed at loads below the elastic limit of the metal. The rate of local plastic deformation during cyclic deformation is several orders of magnitude higher than the rate of deformation under static loading. Dislocation slip begins in grains with a favorable orientation near stress concentrators. As the number of cycles in the surface layers increases, the density of dislocations and the number of vacancies increases. When the base number of NR cycles is reached, a surface reinforced layer of metal with a large number of germinal cracks is formed, the size of which does not reach a critical value. Increasing the number of cycles cannot cause further development of fracture in such a layer. Only when the stresses exceed the endurance limit of the crack reach a critical length, after which the process of their discharge into the main crack begins with the spread of the latter. The results of experimental studies indicate a strong effect of diffusion hydrogen on static and cyclic parameters of crack resistance. It was found that with increasing flooding, especially when the hydrogen content exceeds 5 cm3/100g, both static strength and long-term strength (fatigue) decrease sharply. Moreover, for these areas of hydrogen solution in reinforcing steel is characterized by a viscous nature of fracture, while for heavily flooded reinforcement (from 5 to 12 cm3/100g is characterized by brittle fracture by the mechanism of microfission in the hardened (martensite or troostite structure). allowed to determine the optimal hydrogen content in reinforcing steel (3…5 cm3 /100g), the excess of which will reduce the crack resistance of reinforcement during long-term operation, especially in corrosive environments. The results of the research confirm the above data. bainite structure y sharply reduces the crack resistance of reinforcing steel, which makes it impossible to use in the manufacture of reinforcement involved in reinforced concrete structures designed for long-term operation (more than 50…60 years). Thus, the obtained diagram can be recommended to designers of reinforced concrete structures for hydraulic purposes, as it greatly facilitates the reasonable choice of reinforcement in the development of reinforced concrete structures for responsible and long-term use.

The process of carbonization of concrete with different ratio of water to cement (W/C) was studied, and the influence of the environment on corrosion damage of reinforced concrete reinforcement was studied. The results of the study of carbonization of concrete on specially prepared model samples of concrete with a size of 250x250x250 mm with an exposure period in NACE solution for 500 days without external load are presented. Measurements of corrosion damage of reinforcing rods, which were placed inside concrete cubes, were performed. The method of estimating the amount of carbonization of concrete and corrosion of reinforcement is described in detail in known scientific papers. The obtained data testify to the active carbonization of concrete during the whole exposure period of the samples in NACE solution, however, concrete prepared at the ratio W/C = 0.5 and 0.6 is particularly significant in terms of carbonization intensity. Concrete with a ratio of W/C = 0.7 is less susceptible to damage. Moreover, a similar trend is observed for corrosion of fittings. This is due to the fact that the increase of the aqueous medium in the concrete mass facilitates diffusion processes of delivery to the reactive zone of chemically aggressive ingredients such as carbon dioxide, chloride ions, hydrogen, sulfur, sulfate ions, various types of bacteria and the like. The kinetics of concrete carbonization and corrosion of reinforcing bars in chemically aggressive NACE medium depending on the exposure period of the samples in the model solution was experimentally studied. It is established that with the increase of the water-cement ratio W/C from 0.5 to 0.7, the depth of carbonization and the layer thickness of corrosion products increase sharply. The flooding of the surface layers of the reinforcement and their strong embrittlement in the process of long-term operation of the reinforcement in the structure of reinforced concrete, which causes a decrease in crack resistance in general of reinforced concrete structures. The degradation of reinforcing steel during long-term operation in aggressive environments, which leads to premature corrosion damage to the reinforcement with subsequent destruction of the structure, was investigated experimentally with the involvement of high-precision metallographic equipment.