4.2.2 Trend of creep fracture lifetime coefficient U<sup>0</sup>

Based creep data sheets of creep fracture time under different stress and temperature on typical ASME Grade 91(9Cr-1Mo-V-Nb) steel [14], the value of U<sup>0</sup> was calculated and graphically shown in Figure 7. Furthermore, the inverse U<sup>0</sup> and stress level for P91 is obtained and shown in Figures 8 and 9, respectively.
