Effect of Creep on the Residual Stresses in Tube-to-Tubesheet Joints

Steam generators are the subject of major concern in nuclear power plant safety. Within these generators, the tightness barrier, which separates the primary and secondary circuits, is ensured by the existence of a residual contact pressure at the tube-to-tubesheet joint interface. Any leakage is unacceptable, and its consequences are very heavy in terms of the human and environmental safety as well as maintenance cost. Some studies have been conducted to understand the main reasons for such failure. However, no analytical model able to predict the attenuation of the residual contact pressure under the effect of material creep relaxation behavior. The development of a simple analytical model able to predict the change in the residual contact pressure as a function of time is laid out in this paper. The results from the analytical model are checked and compared with those of finite elements. A simulation conducted on a high temperature tube-to-tubesheet joint has shown that relaxation of the contact stress due to creep can be significant and should be considered in the design.