Keiji Sonoya

EVALUATION OF CREEP RUPTURE PROPERTIES WITH MINIATURE TEST PIECE

ABSTRACT As much as about 60 % of Japanese thermal power plants have been in service for over 100, 000 hours, so that many of them are time-worn. To maintain a high level of safety for these plants, a highly refined maintenance system is called for. For these plants, development of methods of evaluating the remaining service lifetime for the aged equipment is indubitebly an importantr task, for which various diagnostic methods, including the one shown in Fig. 1 that comprises three steps 1) , have been proposed. Now, it has been shown that the lifetime of a part or member of an equipment can be predicted with satisfactory accuracy if the degradation in the mechanical properties, that in the creep chracteristics, in particular, of that part is known 2) . Although several non-destructive methods of evaluating such degradation on the basis of changes in the physical properties are available, correlations between physical properties and mechanical properties remain unclarified. All in all, therefore, higher accuracy in lifetime prediction can only attained by performing destuctive mechanical tests on speciments that have been sampled directly from the part in question. In reality, however, taking large specimens from an operating equipment is a highly difficult proposition, even if such an undertaking is allowed. It is for these reasons that we have been examining a number of testing methods that may be donducted with a small quantity of sample. In the present communication, we intend to discuss an experimental creep machine we have devised so as to make use of miniature-size test pieces and the results obtained with it.