PSI - Issue 30

A.A. Antonov et al. / Procedia Structural Integrity 30 (2020) 11–16 A.A. Antonov et al. / Structural Integrity Procedia 00 (2020) 000–000

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1. Introduction The problems of ensuring the operational reliability of underwater crossings for the main transmission of oil and gas are of great importance since failures and accidents on them far exceed similar incidents on the linear part by their economic and environmental consequences. The main gas pipelines of the Russian Federation the length of which is 153 thousand km (179 thousand km in 2016) include 1,620 underwater crossings, or 2,529 lines with a total extent of 1,445 km in the channel part, and specifically 253 passages (483 lines) that cross navigable rivers. According to the results of 2016, the share of pipeline transportation makes more than 48% of the freight turnover of the entire transportation system in Russia, slightly exceeding the share of railway transport. There are gas pipelines that are not connected with the unified transport system of Russia. For example, AO “Sakhatransneftegaz” operates main and distribution gas pipelines in Yakutia with a length of 7041.0 km, as pointed by Ivanov et al. (2000). In the North, the route of the main gas pipeline undergoes negative geocryological processes. According to studies did by Markov et al. (2015) and Aleskerova et al. (2015), the interaction of the main gas pipeline with the surrounding soil, reconstruction of the main gas pipeline system, as well as the formation of ice jams during an ice drift on the river Lena, are the technogenic factors that increase thawing depth by raising the soil temperature and activates thermal erosion and thermokarst processes. The formation of ice jams is followed by flooding of lower sections of the river valley. Burrel et al. (2015) and Takakura et al. (2015) described the nature of ice jams, its physical-mechanical, hydrological, and hydromorphological basis, and effect on facilities. The underwater crossing of the main gas pipeline (MGL) across the river Lena is intended for gasification of regions on the eastern side of the Lena river (Zarechny regions) of the Republic of Sakha (Yakutia). It is an extension of the main gas pipeline of Hatassy GDS-2 (project 0371.00.03.TGPL.000.000.000.PZO). The starting point of the mainline of the gas pipeline is PK 1 + 00 (10.5 km) of the DN 500 main gas pipeline of Hatassy GDS-2. The terminal point is the junction point on the right bank of the Lena River at Pavlovsk. The line extent is 16.96 km; pipeline transmission capacity is 528 million m 3 /year; the nominal pipe size is DN 500; the maximum tubing pressure is 55 kgf/cm 2 . As it is noted by Ammosov A.P. and Kornilova Z.G (2008), the structure of the underwater crossing of MGL across the river Lena includes DN = 500 mainline, DN = 500 reserve line, pig launcher, receiving station, and gas valve sites. One of the stages of technical diagnostics necessary for trouble-free operation of the underwater crossing of MGL across the river Lena is the determination of its actual planned-high-altitude position. The stress-strain state is calculated based on it.

Nomenclature MGL

the main gas pipeline the gas distribution station

GDS-2

RD-8000 the line locator Dn

the passage diameter

2. Research materials and methods The planned-high-altitude position of two lines in the floodplain section of the underwater gas pipeline was determined using the RD-8000 line locator. It detected the position of the pipeline axis for setting the control point. The control point is fixed with a surveying rod on the ground and numbered. After fixing all the control points in the area, the line locator was installed at the control points alternately, and the depth of the pipeline axis was measured. At each control point, the depth was measured at least three times. An electronic tacheometer was used to determine the planned-high-altitude position of the control points. The tacheometer, which is centered, leveled, and oriented towards the adjacent temporary control station, was installed on one of the permanent control stations. To determine the tacheometer's height, the height of the device to the center of the station was measured with a tape measure. The accuracy of centering the device in terms of the benchmark center is 1 mm.