2023. Vol. 18. Issue 1, Pp. 17–26

URL: http://mfs.uimech.org/mfs2023.1.003

DOI: 10.21662/mfs2023.1.003

URL: http://mfs.uimech.org/mfs2023.1.003

DOI: 10.21662/mfs2023.1.003

Stress-strain state of an underwater offshore oil pipeline taking into account changes in ground conditions and operating parameters

Zaripov R.M.^{∗}, Masalimov R.B.^{∗∗}

The article briefly describes the construction of concreted pipes used in recent years in the construction of offshore gas and oil pipelines. In the formulation of the problem of the stress-strain state of an underwater offshore oil pipeline, the calculated section is conditionally divided into three parts: the middle blurred bare part and the underground parts adjacent to it on the left and right. A brief description of the solution of the problem is given. The results of calculations of the main characteristics of the stress-strain state of the underwater section of the offshore oil pipeline are presented in the form of a diagram of the pipeline deflection and bending stresses, as well as in tables through extreme values of deflection and bending stresses from span and support bending moments for various values of operating parameters and soil conditions in adjacent underground parts. By analyzing the stress- strain state of the calculated section of the offshore oil pipeline, the critical values of the operation parameters and the corresponding critical values of the equivalent longitudinal axial force were determined.

oil pipeline,

concreted pipe,

ground,

deflection,

stress,

drop,

ascent

**Purpose:** Numerical study of the stress-strain state of an underwater offshore oil pipeline, taking into account changes in ground conditions and operating parameters.

**Solution methods:** In the mathematical model, a concreted pipe, consisting of a steel pipe, an insulating layer and a concrete weight coating, is represented as a three-layer hollow tubular rod. In it, the stress-strain state of an underwater section of an offshore pipeline is described using a differential equation for longitudinal-transverse bending of a tubular rod in an elastic medium.

**Results:** A technique for joint integration of a differential equation is developed taking into account the boundary conditions. In it, the substitution of the obtained solutions of differential equations in finite analytical expressions into the boundary conditions leads to a system of linear algebraic equations. Computation programs for a computer were compiled, in which integration constants were found, diagrams of the main characteristics of the stress-strain state along the entire length of the calculated underwater section of the offshore oil pipeline were constructed. The tables present the extreme values of deflection in the middle of the span, as well as the values of bending stresses from span and support bending moments in the eroded bare part for two types of ground.

**Conclusions:** The possibility of emplacement of concreted pipes on the underwater section of the offshore oil pipeline, similar to gas pipelines at the Nord Stream 2 crossing through the Baidaratskaya Guba in Yamal, has been established by calculation. The influence of the length of the eroded bare part, operating parameters, weakening of soil stiffness due to their liquefaction in the underground parts on the ascent of concreted pipes in the underwater section of the offshore oil pipeline is revealed, and recommendations are given to identify the possible causes of its ascent. The critical values of the operating parameters and the corresponding value of the critical value of the equivalent longitudinal axial force are found depending on the length of the eroded bare part, the stiffness of the soil in the underground part. The description of the method of returning the oil pipeline to the design position is given. It has been calculated by calculation that the emptied oil pipeline, which is deformed together with the soil in the underground part, is in the design position and there are no prerequisites for its ascent.

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