Creep Life Assessment of In-Service Components by Testing Sub-Standard Sized Samples in Bending: An Example Case of X22CrMoV12-1 Ferritic Steel Used in Steam Turbines

The residual life assessment of a 9–12% Cr tempered martensitic ferritic steel, used in steam turbine blades and rotors, has been carried out using samples extracted from a turbine blade-root in bending, a novel small-scale testing method. Bending creep specimens (2 × 2 × 10 mm 3 ) and miniaturized cylindrical compression creep specimens (5 × 7.6 mm 2 ) were tested at 550 °C by applying effective stresses of 200–500 MPa, which mimics the near operating conditions. The alloy microstructure showed lath boundaries and prior austenitic grain boundaries decorated with M 23 C 6 carbides pinning low-angle boundaries. An excellent equivalence between uniaxial and bending creep was observed in the alloy with a creep stress exponent, n, of 8, thereby suggesting bending creep can be a viable method for creep testing sub-standard-sized specimens extracted from the in-service components.