The Holding Power and Hydraulic Tightness of Expanded Tube Joints: Analysis of the Stress and Deformation

Abstract

The expanding process used for making the tubes of boilers tight and in other applications is idealized to form a problem in the theory of plasticity. This problem is solved in order to find out how far the factors taken into account in this theory are adequate to explain the results obtained in tests, mainly those reported in the companion paper of Grimison and Lee (19). The pressure left between the tube and plate or seat, which gives it tightness and contributes to its strength, is the principal object of calculation. Its variations with the yield stresses of tube and plate material, with degree of expanding, and with the thickness of the plate, are obtained in graphical form. Numerical comparison with tests is made for six joints, with fair agreement in five, the theoretical values being within 12 per cent. All are on the low side, and this is to be expected from the fact that the theory disregards strain-hardening, stress in the direction of the tube axis, and possible differences between expanding by a three-roller tool and expanding by uniform pressure within the tube.

Electrohydraulic Crimping of Tubes within Rings

“…Merah [5] explored the effect of initial radial clearance between the tube and the ring while Oppenheimer [6] and Maxwell [7] recommended to use a much higher yield stress for the material of the ring compared to that of the tube. Others works concern the evaluation of the residual contact pressure by analytical models in order to avoid often costly experimental campaigns [8][9][10][11]. To improve the strenght of crimped joints, researchers have also tried to implement a groove inside the ring, as shown by Marré and Wang's works [1,12].…”

Lean-and-Green Strength Performance Optimization of a Tube-to-Tubesheet Joint for a Shell-and-Tube Heat Exchanger Using Taguchi Methods and Random Forests

“…The strength and reliability of the tube-to-tubesheet joints heavily depend on the geometry of their components, their fabrication process, and their operating conditions [16][17][18][19]. The persisting issue of controlling the expansion pressure and operating temperature differentials on the connection capacity of hydraulically expanded joints still remains a puzzle in heat-exchanger fabrication [20][21][22][23]. The basic techniques for tube expansion are: (1) rolling, (2) explosive forming, and (3) hydraulic forming.…”