Enhancing retaining ring durability of high-speed generators using autofrettage process

Retaining ring in rotating machineries such as turbo-generators is to resist centrifugal forces of the field end winding of rotors. Retaining ring is one of the high stressed parts of a turbo-generator and its failure may cause catastrophe. Inducing compressive residual stresses into retaining ring can raise resistance to stress cracking and also decrease the effect of high inner pressure imposed by the rotating internal parts. Autofrettage is a metal manufacturing method in which a pressure cylinder is subjected to a huge internal pressure, leading to compressive residual hoop stresses in the internal layer. The aim of autofrettage is to enhance the durability of the final product. In the present paper, a Variable Material Property (VMP) code for the solution of the autofrettage process of the retaining rings of high-speed generators is developed. The results revealed that the magnitude of calculated tangential residual stress at the inner radius of the retaining ring strongly depends on the employed autofrettage pressure. Moreover, the pressure of MPa was chosen as a best possible autofrettage pressure.