Thermal Stresses and Initial Deformation of Heated Condenser Tubes

A condenser tube bank with individual tubes axially and laterally restrained at the ends by tube sheets, and laterally restrained at intermediate locations by support plates is subjected to a uniform temperature rise. In the interior of the bank, the tube sheet flexibility is sufficient to allow absorption of the thermal growth without buildup of high compressive loads in the tube. Around the periphery of the tube bank the tube sheet is attached to a massive fixed water box; hence, in this vicinity, axial growth of the tubes is prevented and high tube compressive loadings can ensue. Accompanying such high tube loadings are two potentially severe problems: (1) buckling of the tube with attendant lateral growth and large bending stresses; and (2) failure of the tube-tube sheet attachment due to the high compressive loading. In this work we develop relations to predict the build-up of tube load and deformation as a function of initial deformation parameters. We show that the presence of initial deformation serves to reduce the magnitude of the direct compression load in the tube, but does so at the expense of building up large tube bending stresses. Thus, tube design to minimize the occurrence of tube failure at the tube sheet connection point may lead to severe tube bending between support plates. Typical tube geometries are investigated and numerical results presented; the results of these investigations suggest certain directions for tube design for particular operating configurations.