Optimum Expansion and Residual Contact Pressure Levels of Hydraulically Expanded Tube-to-Tubesheet Joints

Abstract

Tube-to-tubesheet joints in steam generators and other heat exchangers are now often assembled by means of a hydraulic expansion process that plastically deforms the tubes against the tubesheet and thus creates an interference residual contact pressure between the tube and the tubesheet as well as tensile residual stresses in the tube. A good understanding of both the residual contact pressure and the residual stresses is important for establishing the integrity of the expanded joint. The propose of this paper is to investigate the effect of the level of the expansion pressure on both the residual contact pressure an the maximum tensile residual stresses. A comparison between the 3-D and the axisymmetric Finite Element models for a triangular array tube patterns is presented. An analytical equation is proposed for determining the optimum expansion pressure that provides an acceptable level of residual contact pressure and maximum tensile residual stresses. A statistical technique is also carried out to confirm the validity of the proposed approach.

Cold hydraulic expansion of oil well tubulars

“…The cold expansion of tubes has been used for many decades in the assembly and leak repair of heat exchangers in power generation, nuclear and process industries, see for example Middlebrooks et al [1] and Allam et al [2]. In the assembly of many shell and tube heat exchangers, holes are drilled in the tube-sheet and a tube is placed in each of the holes.…”