ボイラ管寄スタブのクリープ疲労損傷計測のための基礎的検討

Abstract

To confirm the safety and reliability of the long-term operating thermal power plants, various non-destructive residual life assessment methods of component materials have been developed in the past. In this paper, in order to develop a non-destructive creep-fatigue damage assessment method, a series of fundamental experiments were carried out. The experimental condition was as follows: Test material was 2.25Cr-1Mo simulated HAZ. Low cycle fatigue tests and creep-fatigue tests with tensile strain hold were carried out using smooth specimens at 570°C. The strain range employed was from 0.4% to 1.6% and the length of strain hold-time was 10 minutes. To observe the small crack growth behavior during the test, the tests were interrupted and replicas were taken from the specimen surface.The following results were obtained.(1) The creep-fatigue life was smaller than the low cycle fatigue life. Transgranular cracking was observed in the low cycle fatigue specimen, while intergranular cracking and creep voids were observed in the creep-fatigue specimen. The significant life reduction caused by the strain hold resulted from the accumulation of creep damage at grain boundaries.(2) Many small cracks were observed on the specimen surface in the creep-fatigue test. These small cracks grew and joined to make large cracks. If the creep-fatigue life was defined as the cycle when the maximum crack length reached about 2mm, the creep-fatigue life was predictable by the maximum crack length.