A CrMoV turbine rotor retired after long service operation (22 years at 500°C) was investigated to characterize the material degradation due to temper embrittlement by use of three different kinds of techniques ; the electrochemical polarization curve (EPC) method, the electrochemical noise analysis (ENA) and the small punch (SP) test. Grain boundary embrittlement due to phosphorous segregation can be detected as a change in repassivation behavior in the EPC method ; a significant difference in corrosion potential fluctuation in ENA ; and a shift of SP transition temperature. Diagrams for evaluating the temper embrittlement of a CrMoV turbine rotor were also proposed. Furthermore, a realistic and rational procedure for evaluating material degradation during service operation has been also discussed by combined EPC, ENA and SP methods.