[Objective] In the background of China’s national “dual carbon” (carbon peak and carbon neutrality) strategy, thermal power plants are increasingly tas ked with providing flexible, deep -load-following services. Frequent and pronounced load variations induce substantial transients in key thermal parameters , such as steam temperature, pressure, and metal wall temperature, thereby perturbing the thermo-mechanical equilibrium of high2 temperature, pressure-bearing components, particularly thick-walled headers. To quantitatively characterize stress redistribution and cumulative fatigue damage in the final superheater outlet header under deep load regulation, and to enhance operational integrity during flexible dispatch, this study focuses on a 1000 MW ultra -supercritical unit capable of stable operation down to 15% of rated power (Pe) at a domestic power plant. The lowest peak -load reduction capacity of this power plant reached 15% of the peak load. The peak-load reduction process recorded the relevant thermal parameter changes. 

[Methods] Transient thermo -mechanical simulations rigorously calibrated against high-fidelity DCS-recorded operational data across the full 15%Pe~100%Pe load range are employed to resolve the spatiotemporal evolution of temperature and stress fields during four representative transient phases: 40%Pe~100%Pe (ramp -up), 100%Pe ~40%Pe (ramp -down), 15%Pe ~40%Pe (low -load recovery), and 40%Pe~15%Pe ( deep ramp -down). The thesis mainly studied the transient temperature field changes during different load variations, as well as the stress field changes considering both thermal stress and mechanical stress. By extracting the characteristic temperatures and stresses in the transient temperature field and transient stress field during the variable load process, the relevant fatigue parameters are calculated. Life consumption in each phase is quantified using a fatigue model. 

[Results] Simulation results reve al a critical load -dependent transition in stress dominance: above 40%Pe, pressure -induced mechanical stress governs total equivalent stress, whereas below 40%Pe, thermally induced stress becomes predominant -exhibiting near -identical temporal variation wit h total stress. During ramp-up transients, thermal and mechanical stresses predominantly oppose one another, resulting in partial cancellation and reduced net stress amplitude; conversely, during ramp -down transients, both components generally act in conce rt, producing additive stress effects and higher cyclic loading severity. The 40%Pe ~15%Pe transition exhibits the largest thermal gradient, highest stress rate, and most accelerated life depletion. The lifespan loss of the container can be calculated using the Manson-Coffin equation. 

[Conclusion] This work delivers stageresolved, quantitative life consumption metrics for the final superheater outlet header under deep load regulation. Based on the degree of fatigue life loss in a single instance, the life loss during long-term operation can be calculated. The findings provide a technical foundation for condition-based life assessment, risk-informed inspection planning, and design optimization of thick-walled components in flexibly operated ultra-supercritical units.