NUMERICAL ANALYSIS OF LINEAR THERMAL EXPANSION OF PIPES DURING THE THERMAL TRANSIENT

Luis Fernando Silva Moura¹; Jorge Luis Baliño¹

¹ Universidade de São Paulo

doi:10.20906/CPS/COB-2015-2660

Resumo

Thermal expansion is a problem the pipe engineers often have to deal with, since it is important to control the total linear thermal expansion and minimize stresses and forces associated with this physical phenomenon. The design of pipe systems is guided by standards, being ASME B.31.3 certainly the most used in Brazil and the United States. For this standard the pipe system, from the thermal standpoint, is always evaluated based on a constant and uniform design temperature, being this normally the steady state value. These criteria are sufficient to ensure the pipe structural integrity due to the way the admissible and acting stresses are established; however, the standard is silent regarding the thermal transient and the pipe linear thermal expansion during this period. Such thermal expansion may be associated with forces transmitted by the pipe to equipment and structures, neglected by ASME B.31.3 and the literature. This paper presents the equations involved in the pipe thermal transient problem. Based on the results of numerical simulations and the procedures normally used by Pipeline Engineering to compute forces, a discussion is made about the forces associated with the thermal expansion in the period of the thermal transient. It was found that the higher the flow velocity, the Nusselt number and the thermal diffusivity of the pipe material, the higher the pipe heating rate. Besides, it was found that the higher the heating rate and the thermal expansion coefficient, the higher the linear thermal expansion rate of the pipe. Moreover, the force associated with the linear thermal expansion starts to be transmitted to the pipe fixed point (anchor or stop) in an abrupt way and increases intermittently until its maximum value, then falls to its minimum value in an extremely abrupt way, being this minimum value the load obtained in the usual pipe load analysis.

Palavras-chave: Thermal transient; Pipe; Thermal expansion ; Loads