Piping Systems
Piping systems are essential components in many industries such as refineries, power plants, and chemical plants, where their prime purpose is the transport of fluid from one piece of equipment to another. Normally, the content fluid of the pipe is hot, a
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Piping Systems
Piping systems are essential components in many industries such as refineries, power plants, and chemical plants, where their prime purpose is the transport of fluid from one piece of equipment to another. Normally, the content fluid of the pipe is hot, and since the piping system is initially designed at reference temperature, the temperature change causes thermal expansion. If the ends of the piping system are restricted, which is usually the case, forces and moments are produced through the pipe system and at the supports of the pipes causing thermal stresses in the system. The art of piping flexibility analysis is to give enough flexibility to the piping system so that the resulting stresses at all points of the system remain under a safe limit. Usually, this flexibility is designed with a loop in the system or flexible joints at the ends. Therefore, the design procedure of a piping system is to consider the isometric of the piping system at the reference temperature. Then, by means of analytical or numerical methods the restrained forces and moments at the support of the piping system are calculated and, finally, by sketching the free body diagram of each piping member using the appropriate codes and standards, the stresses are computed and compared with the safe limit. If the calculated stresses are above the allowable limit, a loop for the piping system at a proper location may be considered and the calculation procedure is repeated.
25.1 Thermal Expansion of Piping Systems There are many methods for the calculation of the restrained forces and moments of a piping system under thermal expansion. In this chapter we discuss an analytical technique based on the elastic center method. The stiffness approach or the finite element method may also be employed for pipeline analysis. The stiffness approach is essentially derived from the structural analysis under mechanical loads. Since thermal loads behave similarly to mechanical loads, they may be included in the stiffness method of analysis of structures. In the following sections the elastic center method is described. M. Reza Eslami et al., Theory of Elasticity and Thermal Stresses, Solid Mechanics and Its Applications 197, DOI: 10.1007/978-94-007-6356-2_25, © Springer Science+Business Media Dordrecht 2013
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25 Piping Systems
25.1.1 Definition of the Elastic Center Consider a piping system in two-dimensions with clamped ends A and B. The isometric lines of the piping system are shown in Fig. 25.1. The piping system is assumed to be under a uniform reference temperature T0 . If we ignore the weight of the pipes, the reaction forces and moments at ends A and B at the reference temperature T0 are zero. Now, a hot fluid is passed through the piping system and the temperature of the piping system is raised to T . It is again assumed that the temperature T is constant through the length of the piping system. If the end B is considered free, due to thermal expansion of the piping system, it travels to point B , as seen from Fig. 25.1 To bri
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