Study of the Structure and Mechanical Properties of a Weld in a Heat Exchanger by Computer Modeling
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Y OF THE STRUCTURE AND MECHANICAL PROPERTIES OF A WELD IN A HEAT EXCHANGER BY COMPUTER MODELING
G. A. Bilenko and A. F. Tynyanyi
UDC 519.876.5:621.791.05
This article examines the effect of the welding of steel 15Kh5M on the formation of local thermal stresses in a weld formed between a tube and the tube array of a shell-and-tube heat exchanger. The study was performed by computer modeling of the welding operation with the use of the finite-elements method. Keywords: welding of heat exchanger, heat-exchanger array, welds in heat engines, structural transformations during the welding of martensitic steels.
Power engineering has always presented engineers involved in the design and manufacture of power generation equipment with the most diverse range of problems. As regards the design of heat machines and heated structures, it is necessary to assess their performance at elevated temperatures by determining the stresses which develop under the loads encountered in tests and during service. It often turns out that stresses which are purely of an operational nature are augmented by processing-induced stresses that are created during the fabrication of a product. The range of the types of processes that can cause such stresses is extremely broad. They are often processes or phenomena that are associated with a specific manufacturing operation. One such process is welding. We will use computer modeling to examine the effect that welding has on the creation of processing-induced stresses in the fabrication of a shell-and-tube heat exchanger (Fig. 1). Computer modeling makes it possible to obtain accurate results for any region of the object being studied. We chose a local weld in a steel 15Kh5M tube and tube array (see the right side of Fig. 1) as the computer model. Figure 2 shows the geometry of the weld and the preparation of the edges. The given computer model describes the rapid heating and cooling of the structure by the welding source, structural changes – phase transformations in the weld zone – and the changes that take place in the mechanical properties of the material in connection with the structural changes. The model was constructed in the programming-computing complex SYSWELD 2013, which is based on the finite-elements method. The modeling was performed for the following welding regime: • welding current 110–115 A; • arc voltage 25 V; • welding speed 2 mm/sec • wire diameter 3 mm; • preheat temperature 350°C. The region being studied was subdivided into finite elements for the purposes of the modeling operation. The number of elements was increased in the weld zone, since large temperature gradients and high stresses develop in that region along with structural transformations. The model is shown in Fig. 3, and the weld is shown in Fig. 4. PLM Ural – Delkam Ural Company Group, Ekaterinburg, Russia; e-mail: [email protected], [email protected]. Translated from Metallurg, No. 7, pp. 20–23, July, 2013. Original article submitted July 10, 2013. 0026-0894/13/0708-0573 ©2013 Springer Science+Business Media New
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