Analysis Of High Temperature Strength For A High Pressure Rotor Of A Ultra Supercritical Steam Turbine

The new-design ultra-supercritical steam turbine with increased parameters(35MPa/600℃) has advantages such as high efficiency, low carbon dioxide emissions and low pollution characteristics. The increase of the steam parameters for the high pressure module exceeds the present limitation. In order to satisfy the improvement of the steam parameters, the rotor structure is updated again, and this would significantly influence the transient thermal stress and fatigue life. Therefore, it is necessary to analyze the high temperature strength and calculate the damage for the new-design rotor. Based on the results, the startup phase is optimized to improve the fatigue life by adjusting the temperature rise rate, which guarantees the safe operation within the service period.In this paper, the new-design rotor is modeled by using finite element method. In addition, an in-service rotor of a 1000 MW ultra-supercritical steam turbine is compared to evaluate the strength of the new-design rotor in terms of creep behavior, transient thermal stress, and damage. Further opinion on the fatigue life improvement is specified.In the present study, Norton-Bailey constitutive equation is applied to simulate the creep behavior. Additionally, Cocks-Ashby multiaxial factor is taken into consideration to demonstrate the multiaxial creep behavior. Comparison of the new-design and the in-service rotors are performed in terms of temperature field, stress field, C-A equivalent strain distribution. The results disclosed that the maximum deformation appears at the first and second blade slots. Combination of the highest temperature and centrifugal force induces the larger creep deformation. Comparison of the results between the new-design and the in-service rotors demonstrates that the structure of the new-design rotor is reasonable and satisfy the working requirement.Transient stress during startup and shutdown phases is carried out based on the provided startup and shutdown curves. Evaluation on the fatigue is performed based on Manson-Coffin strain-life law and Miner’s rule. Comparing the results of the new-design and the in-service rotors finds that the damage of the new-design rotor is greater than that of the in-service rotor. Optimization on the original startup phase is put forward to improve the fatigue life, and four cases are given in the present thesis. The damage of four cases is calculated to compare the results based on the original startup phase, and the optimal case is presented.Finally, continuum damage mechanics is applied to study the creep-fatigue damage behavior. Python based code is used in ABAQUS to calculated the CDM results and evaluate the life time.