PSI - Issue 40

Z.G. Kornilova et al. / Procedia Structural Integrity 40 (2022) 245–250 Z.G. Kornilova at al./ Structural Integrity Procedia 00 (2021) 000 – 000

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Figure 3 shows the pipeline stress values calculated from the obtained solution to the equation of the underground pipeline. The pipeline is made of steel of 13G1SU grade, the yield point of which is 390 MPa. At levels above 390 MPa, the stresses exceed the yield point and cause plastic deformations.

Fig. 3.Stresses in the underground pipeline

The differential equation is derived using an elastic deformation model. Values of stress above the yield point are high. In these areas, the stress values are approximate, and they show only the presence of plastic deformations. 3. Discussion The results of our measurements of the planned-high-altitude position of the underwater crossing of TGL across the river Lena have detected a section with significant seasonal deformations. The deformation values exceed the soil shear from frost heaving. A hypothesis is proposed that significant vertical transverse displacements of the pipeline in the ground are associated with the preliminary stresses of the pipe obtained during construction, incorporated into the project for crossing across uneven terrain with an insignificant difference in levels. There is a limit for preliminary elastic stress, after which deformations arise in the pipeline from small heaving shears (heaving). 4. Conclusion The uneven distribution of the planned-high-altitude positions of the I-st and II-nd lines of the underwater gas pipeline was detected on the floodplain areas from the right and left banks of the river, which is most likely due to the uneven heaving, ground thawing, and freezing processes, as well as pipeline sinking and floating-up due to the heterogeneity of soil composition, moisture distribution, density, freezing conditions, etc. along the underwater crossing of TGL route across the river Lena. A mathematical model of an underground pipeline has been developed based on point measurements of the planned-high-altitude position of the underground pipeline. The model has served for the development of a computer program for calculating stress. The program was tested using the planned-high-altitude measurements of the underwater crossing of TGL across the Hatasskaya channel of the river Lena. The obtained values show the presence of plastic deformations in certain places. Calculation of stresses of an underground pipeline is relevant for evaluating the service life, especially under permafrost conditions. Our methodology for assessing the stress-strain state will allow predicting the damages in