Figure 9a: Comparison of the experimental and predicted values of mean time to reach a specified damage state by both Bogdanoff model and CDM approach with relative Confidence Interval (CI) at 870oC/56 MPa: (a) top and (b) bottom portion of service exposed reformer tube. Probability distribution of void area fraction at 870°C/56 MPa: (c) top and (d) bottom portion of service exposed reformer tube.