On the basis of the crack initiation and growth control parameterJT integral estimation, a time-dependent failure
assessment
diagram (TDFAD) for the steady creep condition of defective structure at elevated
temperature was investigated in this work. The definition and calculation approach of parameters Kr, Lr, Lrmax, s0.2c as well as isochronous stress-strain curve, related to the TDFAD, were presented. Three methods for determining the material creep fracture toughness Kmatc, i.e., experimental measuring method, parameter estimating approach and graphic solution, were discussed in detail. Several families of failure
assessment curves (FAC) for 2.25Cr1Mo at elevated temperature were constructed according to the presented procedure. The research results indicate that the effect of serve-time on the FAC is not much evident under the condition of environmental temperature lower than the material creep temperature, and the general FAC offered in R6 at ambient temperature can be applied in the engineering practices to give a rough assessment for high temperature structure. Whilst for the structure operated at temperature higher than the material creep temperature, the changes of the FACs compared to the general FAC in R6 will increase with serve-time prolonging and operating temperature elevating, and the TDFAD should be adopted in this case. The effect of service-time and environmental temperature on structure failure can be imaged rationally by the TDFAD proposed in this work.