In the study, experimental and theoretical studies were carried out to assess the influence of the shapes of dents in the tank wall on the stress-strain state of the defect zone. By testing fragments of a cylindrical tank, it was found that the most appropriate expression is (5), which could take into account the leaching of the tank wall, resulting in a decrease in the stress concentration index. At the same time, during theoretical studies in this paper, it was found that polynomials determined the stress concentration coefficient, where the obtained analytical expression data were compared with the data determined numerically in the ANSYS program, and it was found that the spread was from 2% to 10%. According to the results of a numerical study of the stress-strain state of the dent zone in the tank wall, graphical dependences of the stress concentration coefficient on the dimensionless depth of the dent for various values of the dimensionless radius of the dents and do not exceed 2% of the indicators that are obtained. At the conclusion of the experimental and numerical studies, a conclusion was made about the degree of influence of the geometric dimensions of the dents on the stress concentration index.

In the study, experimental and theoretical studies were carried out to assess the influence of the vertical mounting joint zone of the tank on the stress-strain state of the defect zone. Thus, experimental tests of models of a tank wall fragment with an imperfection of the mounting joint evaluated the stress-strain state of the mounting joint zone and established the dependence of the stress concentration in the joint zone on the deflection, the width of the zone and the thickness of the tank wall. It is shown that with a 50 mm bending boom, the annular stresses increase by 1.3 times than with a 30 mm bending boom and the meridional stresses increase by 1.16 times. The same nature of the increase is observed with the stress concentration indicator. By numerical analysis of the stress-strain state of tanks with joint imperfections in the ANSYS medium, the stress-strain state of the tank is estimated for various values of the joint bending parameters ς and ξ. The dependences of the stress concentration coefficient on the geometric dimensions of the imperfection, radius and thickness of the tank wall are also obtained. From the results of calculating the stress concentration coefficient, with an increase in the dimensionless parameters ς and ξ, the values of the stress concentration coefficient K_σ increase by 1.35 times. As a result of the calculations, an interpolation polynomial (5), approximating the stress concentration coefficient K_σ, is obtained, which can be used to estimate the strength, durability and residual resource of the tank. In addition, the obtained results can be used to normalize the limiting dimensions of the imperfection of the joint and to establish the values of the coefficient, taking into account the peculiarities of the work of structures at stress concentrations.

This article presents one part of a study on the dynamic deformation and fracture of sections of steel gas pipelines with an external crack-like defect under the action of internal pressure. This work was performed on the basis of finite-element simulations using a cylindrical shell model executed by ANSYS-19.2 on the example of the section of the steel gas pipeline “Beineu–Bozoy–Shymkent” in the Republic of Kazakhstan. The propagation of the incipient crack-like defect along the pipeline and the resulting dynamic fracture in its tip area were investigated. The options of pipeline loading by working and critical internal pressure were both considered. It was found that, within the time of 1.0 ms, the formed crack expanded in the circumferential direction up to the maximum value, which depended on the value of the internal pressure. A further growth of cracks occurred along the longitudinal direction. At the operating pressure, the initial length of the crack increased by a factor of 5.6, while the equivalent stresses increased by a factor of 1.53 within 3.5 ms. Within the time of 3.75 ms, the equivalent stresses stopped growing due to the gas decompression. Specifically, there was a stop to the crack growth along the longitudinal direction. Vice versa, at the maximum pressure, the pipeline fracture did not change qualitatively, while at the time of the process, it decreased up to 3.5 ms. The finite-element results of the stress–strain state and pipeline fracture in the crack tip area at the working pressure showed that, within the time of 1.0 ms, the distance between the crack walls reached 23 mm at the free edge. Conversely, within the time periods of 2.25 and 3.5 ms, it increased two and three times, respectively. The crack elongation in the longitudinal direction occurred 5.8 times with time. Together, within the time of 3.5 ms, the equivalent stresses increased twice, after which the growth of the crack stopped due to the gas decompression. Moreover, studies on the growth of the crack-like defect in its tip area at the maximum pressure showed that additional considerations on the pressure on the crack edges led to an increment of 3.6% of the crack length. The results of this work can be used for the development of measurements for operating gas pipelines in the field of structural reinforcement.