Because of their importance for the integrity of heat exchangers, the strength of tube-to-tubesheet joints, and particularly their axial strength, is of special interest. A finite element model of an expanded tube-to-tubesheet joint is proposed and examined experimentally with the objective of determining numerically its axial strength. Simplified analytical methods that were previously proposed by many authors to predict the joint axial strength are also used in this investigation. Experimental testing shows that the finite element model is highly accurate for calculating the joint axial strength. The experimental investigation also proves that the pull-out strength is overestimated when calculated using a simple analytical solution. A parametric analysis using the finite element results indicates that the pull-out force is normally lower than the push-out load and that both are lower than the estimations of the analytical solution. The results indicate that the pull-out force as given by the finite element model is generally 35 percent lower than that evaluated by the analytical solution. A difference of as much as 10 percent is also found between the push-out and pull-out loads.

The knowledge of residual stresses introduced in the tubes of heat exchangers during their expansion in the tubesheet holes is important because of their effect on the structural integrity of components. This paper presents a simplified theoretical method to calculate the maximum residual stresses introduced in the transition zone of expanded tube-to-tubesheet joint. The higher positive values of tensile residual stresses and their corresponding axial locations are determined by using a standard deviation analysis. The validation of the proposed equations was accomplished by comparing their results to those obtained by the finite element method for some arbitrary cases. An upper limit has been imposed on the expansion pressure level, depending on the combination of the geometrical and material parameters that are involved in the design of the tube-to-tubesheet joints.

The mechanical behavior of friction stir welded joints made of aluminum alloy 5083-H111 was studied in this investigation. Different welding processes parameters (rotational speeds, travelling speeds and tool pin shapes) were used to investigate the effect of process parameters on the strength and fracture properties of the joint. Scanning electron microscopy and optical microscopy analysis were conducted to study the effect of friction stir welding FSW process on the grain size in the welding zones. In general, the results illustrated that tool profile, the rotation speed and the traveling speed has great effect on the strength of the welded joint. Scanning electron microscopy and optical microscopy investigations showed that the grains inside the welding zone was refined and equiaxed resulting in higher hardness inside the nugget.

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.

Service reliability and durability of tubular heat exchangers and steam generators are much dependent on the proper response of the tube-to-tubesheet joints to the operating conditions. In this paper a 2-D axisymmetric finite element model is proposed and compared to a 3-D finite element solution for the purpose of predicting the temperature effect on the residual contact pressure and maximum tensile residual stresses of such joints. A parametric study using the finite element results shows that, although thermal loading and temperature cycling have a negligible effect on the maximum tensile residual stresses, the room-temperature initial residual contact pressure may be completely relieved following the initiation of plastic deformation in either the tube or the tubesheet during thermal loading. A comparison between the results of the proposed finite element model and those obtained from the literature shows good agreement. A simplified analytical approach, which may be used for the design of tube-to-tubesheet joints, is also proposed to predict the joint behavior at the operating conditions.