Study of Residual Stresses and Surface Hardening in Tubes for Nuclear Steam Generators

摘要

The quality of heat-exchange tubes is one of the most important factors affecting the technical condition and the durability of steam generators at nuclear power plants. The combined influence of the aggressive environment and stresses in heat-exchange tubes during the exploitation of steam generators leads to corrosive cracking of tubes. This results from the residual stresses (RS) stretching tube walls. The production of heat-exchange tubes involves the following operations: boring and grinding hot-rolled pipe billet, cold rolling middle-sized pipes, heating, rolling final-sized pipes, straightening, electro-polishing the inner surface and burnishing the outer surface, checking the final quality. The operation modes of straightening and burnishing predetermine the residual stresses in pipes in the delivery state. The paper presents the results of the studies on the residual stresses and surface hardening caused by the finishing operations. The paper also shows the need for exceptions to the production techniques for heat-exchange pipes, i.e. a series of operations increasing tensile residual stresses.