The authors proposed an NDE method of detecting the crack developed in the turbine blade by means of digital holographic microscopy (DHM). UT procedures sometimes have limitations in particular cases of in-service-inspections such as the detection and sizing of a creep crack developed in the air-cooled casting blade of the combined cycle gas turbine. The local displacement at the blade surface near the crack during a mechanical loading is different from that of a non-cracked blade. This small different can be detected by DHM. The authors discussed whether this difference affected by the mechanical load between the cracked blade and the non-cracked is detectable by means of DHM or not. In this paper, the authors verified the practical validity of the proposed NDE method using the finite element analyses.
The development of uncooled ceramic vanes for a 20MW class gas turbine with the firing temperature of 1300°C is progressing.The 1st stage ceramic vanes were made of sintered SiC or sintered Si3N4 , and the 2nd stage ceramic vanes were made of sintered Si 3N 4 . These vanes were tested by means of hot and high pressure cascade testing simulating actual gas turbines operation.After minor modifications, we have succeeded in developing sound ceramic vanes which are durable against high thermal stress which occurs during the transient of trip (emergency shutdowns or fuel tripouts), and obtained great results for the practical application.In this paper, details of the ceramic vanes' structure and cascade testing are described and the results of the tests are discussed.
In this study, the way to enhance the sensitivity of evaluating deep surface cracks by DCPD technique using four probes is considered. The potential drops across two-dimensional cracks having different depths are analyzed by the three-dimensional finite-element method. The effect of the distance between current input and output probes and the distance between measuring probes on the change in potential drops are analyzed for a wide range of crack depths. By extending the distance between current input and output probes, the change in potential drop with the change in the depth of deeper crack becomes large. But the voltage of potential drop becomes small to measure. Finally, the way to select the appropriate distances between the probes for the measuring sensor is shown from the viewpoints of sensitivity and the required current.
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