Thermal Stresses at Dissimilar Pipe-Stanchion Interfaces

Abstract

High temperature steam lines in power plant piping systems are often supported by the use of pipe support stanchions welded to the steam pipe. The end of the pipe stanchion has a steel plate welded to it, which typically slides on rack steel. The temperature of the stanchion drops from the process pipe interface along the length of the stanchion. The material for the process pipe carrying high temperature steam can be stainless steel, alloy steel, or carbon steel. The material for the stanchion can also be stainless steel, alloy steel, or carbon steel. It is of course cheaper to use carbon or low alloy steel for the stanchion as there is no steam flow in to the stanchion, when the process pipe is made of stainless steel, or other high alloy steel such A335 Gr. P91. In this paper, finite element thermal analysis is utilized first to obtain steady state temperature distribution due to decay or attenuation from the steam line surface along the stanchion. Conduction of heat from process pipe to stanchion, and convection from stanchion surface are considered. Then finite element structural analysis was performed to obtain steady state thermal stresses at the pipe-stanchion interface utilizing the temperature distribution obtained from thermal analysis as an input. The current industrial practice is to use similar materials for both process pipe and stanchion materials conservatively. Normally encountered pipe materials were considered. The materials studied include 304 & 316 Grade stainless steels, A335 Grades P91, P22, & P11 alloy steels, and A106 Grade B carbon steel. The temperature and stress results are presented. Guidelines are provided for the acceptability of pipe-stanchion dissimilar interfaces.