Investigation About Classification of Stresses due to Radial Deformation Induced by Design Pressure Applied to the Tubes of Square Pitch Multi-Perforated Portion of Thick Plates

Abstract The design of thick Tube Sheets (TS) of a level 1 heat exchangers in the nuclear industry is a precise and complicated process, and one needs to consider the effects of numerous perforations. It must be noted that the residual stresses from the tube welding and expansion processes are not considered in this study. The present paper focuses on the stresses induced by the radial deformation due to internal design pressure applied on the inner skin of the tubes expanded into the multi-perforated portion of plates. It is assumed that the stresses due to welding, hydraulic expansion and/or roller expansion have no impact. Indeed, pressure in the perforations tends to expand the multi-perforated portion of the plate. This radial deformation is resisted by the unperforated rim, the surrounding components and by the ligaments themselves. The present paper studies the radial effect of the pressure in the tube expanded in the Tube Sheet in order to suggest a classification of the induced stress as either primary or secondary. The multi-perforated portion of plate is often represented by a homogenous equivalent material model, developed to replicate the mechanical behavior of the multi-perforated plate while being far less computationally expensive. These methods consider only the primary to secondary pressure differential across the Tube Sheet in the numerical calculation and not the internal pressure in the tubes expanded in the multi-perforated portion of plate. It can be introduced in the stress results by additional post-processing, usually conservatively or excluded if considered as secondary stresses. During the Tube Sheet service life, primary stresses, together with, to a lesser extent, secondary stresses, should be limited to avoid the risks of excessive deformation. To assess the risk of excessive deformation, a limit load analyses is performed. The Finite Element Method (FEM) used is an explicitly modeled perforated zone of a square pitch Tube Sheet with its surrounding components. The tubes having not been explicitly modeled, two approaches are considered to represent the radial load applied to the holes of the Tube Sheet without considering the stiffness of the expanded tubes.