In order to improve the accuracy of remaining life evaluation for high-temperature bolts of 12Cr-Mo-W-V steel in long-time use, creep tests on its notched specimens were carried out and non-destructive evaluation of creep damage for the bolt threads were investigated. Bending creep rupture tests were also made for the bolt threads used for a long-time. The results obtained are as follows:
(1) A bending creep rupture test equipment was developed to obtain directly the creep life expenditure of bolts. Specimens were taken from a bolt used over a long period and bending creep tests were carried out using this equipment. The results showed that the creep life expenditure of this bolt was small.
(2) The creep void observation, hardness, eddy current and X-ray diffraction methods were applied to creep damage evaluation. In these methods except for the eddy current method, a good correlation was confirmed between the detected values and creep life expenditure. The creep void observation is considered as the most suitable method from the viewpoint of evaluation accuracy and applicability to the bolt threads.
