2021 Volume 70 Issue 2 Pages 147-153
In order to avoid troubles caused by damage of steam piping of thermal power plants, it is strongly required to improve accuracy to predict Type IV creep damage of Mod.9Cr-1Mo steel. Although Type IV creep damage occurs at the heat affected zone, it is recognized that the creep strengths between the welded joint and the base metal have correlation. So, evaluation of remaining life of the base metal is very important. In this report, the method for estimating the change in hardness due to creep was applied to unused and serviced Mod.9Cr-1Mo steel, and from the results, a method for estimating the creep life equation for the serviced material was proposed. A thermal aging estimation equation that expresses the change in hardness due to thermal aging, and ΔG and ΔGServiced parameters to express the acceleration of softening of unused and serviced materials were formulated. Based on the ΔGServiced parameter and the creep life equation of unused materials, the creep life equation for the serviced materials was constructed, too. It was shown that this equation can accurately estimate the rupture time in short and long-term regions.
