PSI - Issue 20

A.A. Antonov et al. / Procedia Structural Integrity 20 (2019) 270–277

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A.A. Antonov et al. / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction The underwater crossing of the trunk gas pipeline across the river Lena is intended for gasification of regions on the eastern side of the river Lena (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), through which natural gas will be supplied in the village of Pavlovsk at the second stage of construction. It will reach the village Maya at the third stage. In the next stages of construction, gasification of all settlements of Zarechny regions is envisaged with the development of the TGPL, a network of gas pipeline branches and gas distribution stations: Churapchinsky, Amginsky, Ust-Aldansky, Megino-Kangalassky, Tattinsky. The underwater gas pipeline across the river Lena for the gasification of Zarechny regions of the Republic of Sakha (Yakutia) is laid across the lands of the Hatassky production-agricultural cooperative, Pavlovsk, the water resource of the river Lena and Pavlovsky production-agricultural cooperative. The structure of the underwater crossing of the trunk gas pipeline across the river Lena includes DN = 500 mainline, DN = 530 reserve line, pig launcher, and receiver station, gas valve sites. The main pipeline extent is 16.26 km; the reserve line is 16.26 km. The pipe diameter is 530mm, the wall thickness varies from 8 to 14 mm. Pipes are made of 13Mn1C-C steel according to TU 14-3-1573-99, the maximum tubing pressure is 55 kgf/cm2. The starting point of the main line of the gas pipeline is PK 1 + 00 (10.5 km) of the DN 500 trunk gas pipeline of Hatassy GDS-2. The terminal point is the junction point on the right bank of the Lena River at Pavlovsk. The underwater passage was laid by the cut-and-cover method by underwater trenching. This traditional method of pipe laying through the watercourse involves excavation of formidable volumes of soil, depends on the climatic conditions and requires additional materials for ballasting the pipeline, which leads to a significant increase in the construction costs in VNiR BI3-2. (1987). Scours of the pipeline in the trench and its sagging are common phenomena during operation. This leads to stresses in the pipe wall, the level of which increases with the increasing length of the scoured section. In addition to static stress, dynamic stress arises from pipeline sagging caused by fluctuations of the scoured section in the water flow. One of the stages of technical diagnostics necessary for trouble-free operation of the underwater crossing of TGPL across the river Lena is the determination of its planned-high-altitude position, on the basis of which the stress-strain state of its elements by Sapsay et al. (2017) is calculated and the decision is made about the need for repair. 2. Research materials and methods The following instrumental examination methods are used to obtain the most complete information about the actual planned-high-altitude position of the underwater crossing of TGPL across the river Lena: • profile sounding using the OKO-2 GPR with the AB-150 antenna with a central frequency of 150 MHz. The depth of penetration is 12 m, the resolution is 0.35 m; • the Hydra 500E side-scan sonar with the following characteristics is used for examination of the bottom of the river Lena in the area of the underwater crossing of TGPL: average frequency is 500 kHz, resolution is not less than 0.94 cm, the maximum slant range is not less than 60 m, the operating depth is up to 20 m with a built-in echo sounder; • determination of the actual planned-high-altitude position of the floodplain part of the pipeline is performed by the RD-8000 line locator. Profile sounding was accomplished at the place of the underwater gas pipeline across the river Lena with the help of the OKO-2 GPR with an open-type AB-150 antenna unit with the central frequency of 150 MHz located on the boat (Fig.1a). The coordinates of the beginning and end of the profile were recorded on the GPS receiver so that all profiles have GPS receiver binding. Coordinates obtained during operation are calculated according to the Baltic system. For tasks that require the highest quality of the display, information, or sounding at greater depths, the number of points in depth is 511, accumulation is set to 32, which makes it possible to identify weaker signals and improves