PSI - Issue 65

D.S. Ivanov et al. / Procedia Structural Integrity 65 (2024) 102–108 D.S. Ivanov, G.S. Ammosov, Z.G. Kornilova, A.A. Antonov / Structural Integrity Procedia 00 (2024) 000–000

107

6

Equation (12) determines the maximum normal tensile and compressive stresses in a beam bending by Iktin V.A. (2004). The maximum normal stresses arise at the upper and lower edges of the cross-section of a beam bent in a vertical plane. According to Zhuravsky's formula, the shear stresses are zero at the edges of the cross-section. The shear stresses of a bent beam are maximum at the center. In the present paper, we do not consider these stresses. Assessment of the stresses in the pipeline overlaid on the graph of the vertical position function is given in Figure 3.

Fig. 3. Stress in underground pipeline: —— ‒ stress, ‒‒‒‒‒ ‒ pipeline position, ------ ‒ daylight surface of the ground.

6. Discussion

The yield strength of 13G1SU (13Mn1C-C) pipes used in the underwater pipeline crossing through the Lena River is 390 MPa. However, the study reveals values exceeding this limit in sections of 120-150 m from the reference point (Fig. 3). This result can be explained by the fact that the pipeline was considered as a solid beam when deriving equation (4). Its thin-walled structure was not taken into account. When the bending reaches the level at which a solid beam experiences plastic deformations, a thin-walled cylindrical beam will have an oval cross section and function in the elastic region. When a certain stress threshold is exceeded, the dependence of the moment of force on the bending radius for a thin-walled pipe will differ from the equation (3). The proposed stress assessment method is not applicable to stresses close to the yield strength. A method for assessing stresses in a pipeline subjected to complex deformation in the form of several successive arches has been developed based on data obtained from planned-high-altitude measurements. Existing methods can only be used in the case of deformation in the form of a single arch by Ainbinder A.B. et al (1982); The proposed assessment method encounters significant errors at stresses close to the yield point. This is due to the fact that the pipeline is modeled as a solid cross-section beam. An equation for modeling an underground pipeline as a thin-walled cylindrical beam is currently under development. It is designed to reduce errors and improve the accuracy of stress assessment; Studies on experimental assessment of stresses in a deformed underground pipeline are in progress. We expect they will verify the methodology we have developed. Acknowledgements 7. Conclusions