Technology of Welding of Annular Joints of the Trunk Pipelines from the Pipes of Strength Class K56 at Low Ambient Temperatures

N.G. Goncharov, Cand. Sci. (Eng.), Lead Researcher G.V. Nesterov, Cand. Sci. (Eng.), Lead Researcher, A.A. Yushin, Cand. Sci. (Eng.), Laboratory Head OOO NII Transneft, Moscow, Russia


The key element in forming the reliability and safety of the trunk pipelines is the quality of making butt welded joints.
When welding under conditions of negative temperatures as a result of increasing the cooling rate of the weld pool, the metal loses its plastic and viscous properties and becomes prone to the formation of hot and cold cracks. When welding from the molten metal the output of gases and oxides is hampered that increases the content of hydrogen, oxygen, nitrogen of nonmetallic inclusions in the metal weld and can lead to the formation of poor penetration, pores, and hot cracks. The possibility of formation of the hot cracks is further enhanced with an increase in the rate of elastoplastic deformation in the critical temperature range, when the heated metal is already in the brittle state. After welding, the probability of cold cracks is high. To give the welded joints metal properties meeting the regulatory requirements, it is required to conduct additional technological activities that ensure optimal heat input to the metal during welding operations.
Selection of the optimum thermal cycle of welding determines the nature of the metallurgical processes running at the welded joint crystallization, mechanical properties of the weld metal and the weld zone, and the quality of the weld joint as a whole.
The complex of carried out researches made it possible to determine the most rational parameters of thermal welding cycles when performing work at low temperatures for pipes of steel of strength class K56 applied to the technology of manual arc welding and the combined technology with the welding of the root layer by STT method and filling and facing layers by the automatic welding with welding heads M-300S. The metal of welded joints had the satisfactory complex of the mechanical properties and resistance to the formation of cold cracks. This allowed to recommend the parameters of the thermal cycle when making butt welded joints from pipes of strength class K56 in the Arctic zone of the Russian Federation at temperatures up to –40 °C.


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DOI: 10.24000/0409-2961-2018-8-42-47
Year: 2018
Issue num: August
Keywords : trunk pipeline welding welded joint heat-affected zone low temperatures Arctic zone of the Russian Federation preheating thermal welding cycle mechanical properties deformation capacity