Numerical Modeling of the Stress-Strain State of an Underwater Offshore Gas Pipeline, Taking into Account Soil Liquefaction and Operating Parameters

The brief information presented on the unexpected resurfacing of two lines at the underwater crossing through the Baidaratskaya Bay in Yamal indicates that in the course of the development of projects, full studies were not carried out on the issues of ensuring the strength and stability and maintaining the gas pipelines in the design position. To identify one of the main reasons for the ascent, the problem of the stress-strain state of the underwater section of the offshore gas pipeline was posed and solved, taking into account partial and complete flooding of the soil in separate underground parts. The considered underwater section of the underwater gas pipeline in the design scheme is conditionally divided into three parts. In its middle part there is a blurred bare part, which is formed due to liquefaction and erosion of the soil. Underground parts adjoin it on the left and right. A one-dimensional rod system in an elastic medium, consisting of curvilinear and straight three-layer rods of a tubular section and their junctions, is taken as a mathematical model of the calculated section of the gas pipeline. The stress-strain state of the rod element is described by a system of differential equations, which consists of geometric and physical nonlinear relationships, nonlinear differential equilibrium equations. The solution of the problem is carried out by the method of finite elements in displacements. A numerical experiment has found the critical values of the operation parameters and the shape of the bend of the gas pipeline preceding its ascent for different lengths of the washed-out bare part, changes in the state of the soil in the underground parts and various values of the gas pipeline operation parameters.