In order to develop and validate a procedure of creep rupture tests using miniature specimens in estimating the remaining life of fossil power plant parts, a method to make the miniature specimens was investigated first. Then the accelerated stress-rupture tests were performed on the miniature specimens to predict the remaining creep life of Cr-Mo-V, 21/4Cr-Mo and 11/4-1/2Mo steels.
The results obtained are summarized as follows:
(1) The miniature specimens could be produced by either only machining, or welding the grips at the ends of specimen and then machining them. The miniature specimen sized into 2mm dia.×30mm was suitable as a reduced size specimen.
(2) The creep curve and rupture life of the miniature specimens tested in argon were similar to those of the conventional size specimens in air. The fracture mode of the miniature specimens was also consistent with that of the conventional size specimens.
(3) On a graph of temperature vs. logtr, the creep rupture data of Cr-Mo-V, 21/4Cr-Mo and 11/4Cr-Mo steels were represented with an iso-stress line, respectively. Each iso-stress line moved parallel with the stress level. It was found that the miniature specimens could be used in the short time iso-stress creep line extrapolation method to predict the remaining creep life.
(4) The present method was found to be applicable to the parts subjected to long-term service. It is considered that the creep life evaluation based on this method is very useful because of its convenience and reliability.
