PSI - Issue 30
A.A. Antonov et al. / Procedia Structural Integrity 30 (2020) 6–10 A.A. Antonov et al. / Structural Integrity Procedia 00 (2020) 000–000
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oil per year. The construction is done in a trench manner. Herewith, it was found that the process of construction and operation of the underwater crossing strongly depends on the climatic, hydrological, and hydromorphological factors of the northern rivers. Moreover, all underwater crossings of the oil pipeline across medium and large rivers were built and put into operation in a single-line design. Consequently, ensuring the operational strength, reliability, and environmental safety of the underwater crossing of the pipeline system is a top-priority objective. In case of emergency spills along the route and the underwater crossing of the pipeline system, oil directly enters the main river system. According to Lebedev et al. (2012), the contingency of such oil spills is considerably high. Teplinskij et al. (2007), Andrijashin et al. (2006), Sitenkov and Perevozchenko (2004) noted that the operational strength and reliability of the underwater crossing of MP are affected by the damage intensity of welded joints of siphon pipes, which, in turn, depends on the welding technology. This paper investigates the welded joints of the siphon pipes of the underwater crossing of the pipeline system manufactured from 09G2 steel. The diameter of the welded pipes is 1220 mm, and the wall thickness is 29 mm. The manufacturing of steel pipes involves thermal strengthening during accelerated cooling as noted by Makarov (1981). Welding was performed at ambient temperature from -2 °C to -21 °C.
Nomenclature LB-52U brand of electrode 09G2 steel grade RWS residual welding stress HAZ heat affected zone
2. Materials and methods The root weld was applied with LB-52U electrodes 3 mm in diameter at a current strength of 90-110 A, filling. The cap weld was applied with LB-52U electrodes with a diameter of 4.0 mm and the amperage of 180-200 A. Alignment of the pipe length joints for welding was accomplished on an external centralizer with tacks 130-180 mm long in at least four places. The distances between the lower and upper edges of the bevels were 1.5 mm and 32.1 mm, respectively. After the tack-weld and removal of the external centralizer, the area to be welded was heated with a thermal insulation belt. When the temperature of the pipe joint metal reached 100 ... 110 C, the root pass was applied from the inside. After processing with a grinding wheel and inspecting the root weld from the inside, the filling run in a hot pass was accomplished by two welders at both ends of the pipe joint. The filling run consisted of 5-6 passes (depending on the welding heat input and the qualifications of the welder). After that the cap weld was performed, followed by cleaning from slags and splashes. The weld was then polished to the required size. For the elaboration of the welding technology, similar pipes were butt-welded by automated and manual electric arc welding. Then two test coils were cut and delivered to Yakutsk. Hardness was measured on a TDM-2 dynamic hardness tester in the field. The same hardness distribution measurements were accomplished in the laboratory using a TR2041 hardness tester in the area of the welded joint of the manual arc welding on a sample cut from an imported coil. The measurements were carried out according to the following scheme: eight horizontal lines from the first to the eighth were drawn from a hypothetical vertical Y-axis passing through the center of the weld with a spacing of 3.0 mm. Afterwards the hardness was measured along horizontal lines with about 3.0 mm spacing from the Y-axis to the edge of sample. The distribution of RWS in the pipe welded joint was determined using a portable X-ray device for determining mechanical stresses developed at the Department of Metal Physics, St. Petersburg Technical University. Golikov and Ammosov (2012) described the RWS measurement technique in detail. To determine the resistance of the weld metal and the heat-affected zone to small plastic deformations, tensile tests were performed according to GOST 6996-66 (Russian national standards). According to the test results the following mechanical characteristics were determined: Rm is a tensile strength, Rp 0,2 is a relative yield strength, and A is a relative elongation. Samples made from a coil were subjected to tensile testing on an Instron-8802 tensile machine at room temperature.
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