Use of the program SYSWELD to analyze residual stresses and strains after the welding of pressure vessels
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OF THE PROGRAM SYSWELD TO ANALYZE RESIDUAL STRESSES AND STRAINS AFTER THE WELDING OF PRESSURE VESSELS G. A. Bilenko
There are many different design methods and tools that can be used to quickly find engineering solutions to a wide range of problems, but the most efficient method and tool is numerical modeling. Discrete mathematics makes it possible to solve problems of the most diverse nature and, most importantly, to obtain an exact value for the quantities that are of interest. This is approach that was realized in the software product SYSWELD. We will look at an example of the use of this program to solve a model problem – developing a technology for welding a tank car. Finding the solution will make it possible to obtain answers to engineering problems that determine the quality of the final product: minimizing warpage and determining the microstructure of the welds and the heat-affected zone. Achieving these goals will require the solution of a coupled heat-transfer problem – a problem of metallurgy and mechanics. Figure 1 shows a CAD model of a tank car designed to store petroleum products. The car is made of structural steel having the following composition, wt.%: 0.2 C; 1.6 Mn; 0.55 Si; 0.035 S; 0.035 P. The car is made with the use of semiautomatic welding in protective gases. The thermal problem is solved based on the thermal welding cycle in the region of the weld (Fig. 2). The numbers of the welds in the structure are shown in Fig. 3. The welding operation is performed in stages: the hemisphere and inlet orifice are welded first, this then being followed by the welding of the supports. Several support variants were used to minimize warpage (Fig. 4). No fixtures are used when the welding operation is performed in accordance with variant No. 1, in which the structure is pre-assembled on clamps. Variant No. 2 entails the use of constricting rings that are placed inside the product. Table 1 shows the sequence of steps performed in the welding operation. Since the steel used to make the tank car is a multiphase material, certain structural transformations take place during its heating and rapid cooling. This fact is also considered by SYSWELD, it being accounted for through the use of models – in particular, the Leblon and Koistinen–Marburger models – that were integrated into the program. The Koistinen–Marburger equation: P(T) = 1 – exp(–b(Ms – T)), where P is the amount of martensite that is formed; T is temperature; Ms is the temperature at which the martensite transformation begins; and b is a constant. The Leblon equation: Peq (T ) − P(T ) dP(T ) = f (T ) , dt τ(T ) where Peq is the initial amount of the metallurgical phase; P is the fraction of the phase that undergoes transformation; τ(T) and ƒ(T) are constants of the reaction. PLM Ural Company Group. Translated from Metallurg, No. 8, pp. 32–34, August, 2012.
0026-0894/12/0708-0565 ©2012 Springer Science+Business Media New York
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Fig. 1. CAD model of tank car (red denotes the welds in the structure of the car).
Fig. 2. Thermal cycle in the weldi
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