PSI - Issue 40

A.G. Khakimov et al. / Procedia Structural Integrity 40 (2022) 214–222 A.G. Khakimov / StructuralIntegrity Procedia 00 (2022) 000 – 000

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1. Introduction In hydrostatic systems, the interaction between elastic and hydrodynamic instabilities occurs simultaneously. External impacts can be both independent and associated to each other (Ilgamov, 2018). An overview of similar research articles is also given here. Many articles deal with studying the longitudinal stability of pipelines. Let us note fundamental works (Dimov and Bogushevskaya, 2010; Yasin and Chernikin, 1968; Aynbinder and Kamershteyn, 1982) that describe the most important cases related to a possible loss of the pipeline stability in mineral grounds and present-day analytical and experimental investigations in this area. In the works listed below and in some others, the authors treat the loss of the pipeline stability in a somewhat different manner, attaches not one and the same meaning to this notion and explain the fact of its possible occurrence from different standpoints both qualitatively and quantitatively (Dimov and Bogushevskaya, 2010). For example, paper (Gumerov and Silvestrov, 2017) performs an analysis of literary sources, from which it follows that in some works (Babin et. al., 1979; Borodavkin and Berezin, 1977; Mugallimov et. al., 2015; Chuchkalov and Gumerov, 2014) the equation of length-cross pipeline bending has the form other than the equation presented in (Korobkov et. al., 2009; Petrov and Spiridonov, 1973). According to Gazprom Transgaz Surgut LLC that operates the Urengoy-Surgut-Chelyabinsk trunk pipeline, a considerable length of the pipeline (10%) has segments under non-project conditions such as their uncovering, floating-up and arched ejection formation. In most cases of the outage of pipeline segments in need of major overhaul, it is precisely the non project conditions that confront the company. Gazprom has disclosed information on the disruption of project conditions in already two of the four threads of the undersea crossing through the Baydarata Bay on the Yamal Peninsula: in 2018 it became known about the floating-up of the first thread and in 2019 the same happened with the fourth reserve thread. According to information published on the website of Gazprom, the Bovanenkovo-Ukhta 2 and the Bovenenkovo-Ukhta routes have crossed through the Baydarata Bay (the Kara Sea) ice-covered during most of the year. Here concrete-coated steel pipes of diameter 1219 mm are designed to be used at pressure of 120 atm. The laying of gas pipelines with such technical parameters in extreme-weather scenarios was carried out for the first time in the world. Once the pipeline had been laid, it suddenly floated up to the surface, which necessitated immediate decisions made by the Company to restore the pipeline project conditions ( INTERFAX ). In terms of the major overhaul, Gazprom Transgaz Ikhta planned to deepen a pipeline segment 2.2 km long. The process of modifying the project conditions is dictated by an intricate combination of hydro-geotechnical characteristics, and their prediction at the design stage is almost impossible. Causes for the loss of longitudinal stability in the subsurface pipeline are as follows: effect of temperature gradient in the delivered product on the pipeline material; decrease in internal gas pressure (incorrect assertion, remark by A.G. Khakimov); seasonal changes in ground characteristics associated with route flooding; derogation from the pipeline trenching technology (Sysoev et. al., 2012). The solution to a number of major problems, for example, gas pipeline stability under non-project conditions, is shown in (Kharionovsky, 2019). Researchers have faced two main challenges, one of which is connected to the development of improved methods for calculating stability in newly designed gas pipelines, and the solution to the second problem would give an answer to the question about the possibility of exploiting buoyant segments and the development of criteria that determine the outage of a pipeline segment in need of repair. The problem regarding gas pipeline stability (Bolshakov and Burnashev, 2015) should be tackled not only at the stage of construction, but also, as practice shows, during the period of exploitation in case of disrupting project conditions of gas pipeline segments or during their repeated installation on boggy and wet sites of the route. As a rule, gas pipelines are laid in trenches by means of material-intensive and stiff ballasting devices, most often by concrete weight coatings unreliable in operation in wet and weak grounds subjected to periodic freeze-thaw cycles. As a consequence, pipeline buckling and bending occur quite often. Following the assumption about the initial deformed pipeline shape without initial stresses, we have clarified critical compressive load (Khakimov, 2018; 2019; 2020). The pipeline is subject to internal and external pressures and also the compression force. Fluid flows along the pipeline with the exact pre assigned density [15]. Account is taken for axisymmetric expansion of the pipe and its longitudinal contraction, change in the temperature of the pipe wall and formation of arched ejections (Khakimov, 2019; 2020). Research is carried out on the static interaction of instabilities under the effect of the aforesaid factors. This research is aimed at determining the pipeline parameters during the formation of arched ejections.