2017 Volume 66 Issue 10 Pages 738-745
Creep damage assessment of high temperature components in aged thermal power plants is necessary to maintain reliable operation. Although an accurate creep damage assessment result is obtained by a destructive assessment method in which creep tests are performed, it is difficult to cut a standard size specimen from actual components. Therefore, development of testing and damage assessment methods by using a miniature specimen are expected. In this study, creep tests of a CrMoV forging steel were conducted by using a solid bar tensile type miniature creep specimen with 1mm diameter at 600℃. It was demonstrated that equivalent creep deformation and rupture properties to those obtained from the standard size specimen are obtained by the miniature specimen under stress level below 200MPa. Creep damage materials were produced by interrupting creep tests performed by using a standard sized smooth bar specimen and two types of round notch bar specimen with radiuses at notch root of 0.5mm(R0.5) and 2.0mm(R2.0). Uniaxial tensile creep tests were performed by using the miniature creep specimens taken from the plain specimens and the notch roots of the notch specimens. Although accurate creep damage assessment results were obtained from the creep tests with the miniature creep specimens taken from the plain specimens, it should be noted that the results may give under estimation for higher creep damaged condition. Creep damage assessment results based on the creep tests with miniature specimens also gave under estimation for the creep damaged material of R0.5 due to lower axial creep strain accumulation under multiaxial stress states before interrupting the creep tests. On the other hand, accurate creep damage assessment results were obtained for the creep damage materials of R2.0 indicating that creep tests with the miniature specimens may be applicable to creep damage assessment of components under certain range of stress multiaxiality.
