Contribution of High Mechanical Fatigue to Gas Turbine Blade Lifetime during Steady-State Operation

Abstract

In this study, the contribution of high thermomechanical fatigue to the gas turbine lifetime during a steady-state operation is evaluated for the first time. An evolution of the roughness on the surface between the thermal barrier coating and bond coating is addressed to elucidate the correlation between operating conditions and the degradation of a gas turbine. Specifically, three factors affecting coating failure are characterized, namely isothermal operation, low-cycle fatigue, and high thermomechanical fatigue, using laboratory experiments and actual service-exposed blades in a power plant. The results indicate that, although isothermal heat exposure during a steady-state operation contributes to creep, it does not contribute to failure caused by coating fatigue. Low-cycle fatigue during a transient operation cannot fully describe the evolution of the roughness between the thermal barrier coating and the bond coating of the gas turbine. High thermomechanical fatigue during a steady-state operation plays a critical role in coating failure because the temperature of hot gas pass components fluctuates up to 140 °C at high operating temperatures. Hence, high thermomechanical fatigue must be accounted for to accurately predict the remaining useful lifetime of a gas turbine because the current method of predicting the remaining useful lifetime only accounts for creep during a steady-state operation and for low-cycle fatigue during a transient operation.

Test-Rig Simulation on Hybrid Thermal Barrier Coating Assisted with Cooling Air System for Advanced Gas Turbine under Prolonged Exposures—A Review

“…Not only 1100 • C, but 1000 • C also has become a popular choice as the test temperature for TBC isothermal oxidation. Chang et al in their study used real gas turbine material that was cut from the after-service blades from thermal power plants in Korea [93]. The scrapped specimens were then TBC coated and heat treated prior to a prolonged 8000 h exposure using a furnace.…”

“…The above-mentioned articles [80][81][82] do not consider the addition of cooling systems in their work. Studies that have been conducted using typical commercial furnace [32,72,77,[83][84][85][86][87][88][89][90][91][92][93][94][95][96][97][98][99] have also proven to not be capable of simulating the cooling air effect on TBC in advanced gas turbine operating condition. The developed custom-made test rigs are also limited to short test duration under cyclic condition and no cooling air effect under prolonged steady-state operating conditions.…”

Structural and Thermal Analysis of F Class Gas Turbine Compressor Blade

“…The analyses are made to determine the positive or negative situation that may occur in the part due to external factors such as force, angular or radial velocity, and temperature acting on the part. ANSYS program is used for thermal and structural analyses [7][8][9][10][11][12][13][14][15][16][17][18].…”

“…In these studies, researchers worked on many different analysis methods. Some of them used the Matrix Method, and some of them used the Finite Difference Method and the Finite Element Method (FEM) [16][17][18][19][20][21]. In their study, Meng and Zhangqi tried an analytical procedure by making simplifications in large-scale wind turbine structure.…”

“…This program is calculating all requests easily and gives the exact solution. That is why it is used by many design companies and gas turbine manufacturers [16][17][18][19][20][21][22]. This study has been performed to protect and verify the engineering value of AEN 94.3A F-type gas turbine side running conditions.…”