Determination of damage functions for the pitting of AISI type 403 blade alloy and ASTM A470/471 dis pdf epub mobi txt 电子书 下载 2026

The prediction of pitting accumulation on turbine blades and disks is of particular importance to predict localized corrosion damages in low pressure (LP) steam turbines. Damage Function Analysis (DFA) and Deterministic Extreme Value Statistics (DEVS) have been employed to predict the pitting damage on AISI Type 403 stainless steel (SS) blade alloy and ASTM A470/471 disk steel in simulated LP steam turbine environments within the phase transition zone. The passivity properties of Type 403 SS and A470/471 steel in the passive regions, including defect type, defect concentration in the barrier film, barrier film thickness, and the steady-state current density, agree with the predictions of the Point Defect Model (PDM) for an n-type semiconductor. Optimization of the PDM based impedance model on the experimental electrochemical impedance data has yielded a set of parameter values that can be used to predict the barrier film growth on Type 403 SS in deaerated borate buffer solution (<italic> pH</italic> = 8.2) at ambient temperature. Experimental relationships between the breakdown potential and chloride activity, <italic>pH</italic>, temperature, and potential scan rate have demonstrated the applicability of the PDM for describing passivity breakdown on Type 403 SS and A470/471 steel. The obtained parameter values were used to calculate the breakdown potential, induction time, and their distributions, via the PDM, which represents the first quantitative characterization of the passivity breakdown behavior on Type 403 SS. Pitting damage functions for Type 403 SS have been experimentally determined for the first time. However, low pit density on A470/471 steel led to insufficient pit numbers on the 1.27 cm<super>2</super> surface for the effective determination of damage functions. DEVS has been demonstrated by predicting the average maximum pit depth for 750 hours from short-term (24 hours and 240 hours) maximum pit depth data on Type 403 SS in deaerated buffer solution with 0.10 M NaCl at an applied potential of 0.090 V_SCE and on A470/471 steel in the solution with 0.028 M NaCl at 0.058 V_SCE. To the author's knowledge, the work reported in this dissertation represents the first instance in which DEVS has been used to predict the accumulation of pitting damage on LP steam turbine alloys, thereby heralding a new era in the prediction of corrosion damage in these systems.