PSI - Issue 20

Oleg Naumov et al. / Procedia Structural Integrity 20 (2019) 53–56 Oleg Naumov et al. / Structural Integrity Procedia 00 (2019) 000 – 00

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Fig.4. Pipeline SSS under the soil sag.

Fig.5. SSS under the pipeline sag and heave

The maximum SSS values occur under the sag and combined heave and sag effect. The maximum stresses are 401 and 395 MPa that is higher that minimum yield point (275 MPa). These values make assertions about the presence of the permanent deformations. At these types of the seasonal change in the soils, the large travels from the initial geometric position occurs along with the bends, which increase the stresses in the pipe walls. In the conditions of the permafrost soils, a great difference in the temperatures of the fluid pumped and wall (protective envelope), and the large bend radius can result in the crack appearance and propagation. The sag and heave effect upon SSS below the yield point (98.4 MPa and 260.2 MPa). The travel under thermokarst is insignificant compared with the sag and combined effect. The travel under heave is 2 times more than the thermokarst, and propagates in other direction than that under the thermokarst and heave (under the thermokarst in the gravity force direction, under the heave – at the angle from the gravity direction). The modelling of the oil pipeline section with the length of 35 m and more has demonstrated the higher SSS values (the higher than minimum strength – 470 MPa). It makes assertions about the higher risks of the wall fracture in the oil pipeline within the zones of the maximum bend and necessity to develop the measures to decrease the effect of the freeze-thaw processes in the permafrost soils. The maximum travels occur when the length of contact with the soil freeze-thaw processes is 10 m and more. The monitoring of a state of 10 – 15 m sections of the oil pipeline route depending on the season and soil composition, diverting of the ground water and use of the seasonal cooling units by Permyakov et al. (2017) to decrease the probable travel will allow to decrease the probability of the facility destruction. 4. Summary The main changes in the geometric oil pipeline position on the route are attributed to the stresses occurred due to the seasonal changes. The stresses in the wall exceeding the yield point make assumptions about the presence of the afterflow and probable microcrack initiation that will cause the crack formation in the oil pipeline wall in the future. The results of modelling the oil pipeline of the underground route allows to draw the following conclusions: The effect of the factors associated with the seasonal change in the permafrost soils causes the pipeline to change its position against the initial one;

2452-3216 © 2019 The Author(s). Published by Elsevier B.V. Peer-review under responsibility of the ILEE-2019 organizers