Analytical Evaluation of the Hydraulic Expansion of Steam Generator Tubing into Tubesheets

Abstract

Hydraulic expansion is the process used by Westinghouse for expanding heat transfer tubes through the full thickness of tubesheets in recirculating nuclear steam generators. The aims of the process are: (i) to expand the tube tightly against the tubesheet, (ii) to leave the smallest possible secondary side crevice depth with no tube bulge above the tubesheet, and (iii) to minimize residual stresses in the expanded tube - all for the purpose of mitigating the effects of corrosion phenomena. Several analytical techniques have been used to provide quantitative evaluation of the effects of the various expansion variables on the quality of the tube-to-tubesheet joint. Following the description of the expansion process and the analytical models, results are presented relating to joint tightness (interfacial contact pressure), crevice depth control, and expanded-to-unexpanded tube transition zone residual stresses.