Research On Modeling And Validation Of Stress Corrosion Cracking For Nickel-Based Alloys In Supercritical Water Environment

This paper focuses on the potential issue of stress corrosion cracking(SCC)in high-temperature critical components made of nickel-based alloys for advanced ultra-supercritical units.Based on the Fracture and Reliability Research Institute(FRI)model for stress corrosion under subcritical water conditions,this research proposes an enhanced version,namely the Stress Enhanced Oxidation(SEO)modified FRI model.The original electrochemical corrosion mechanism of the model is replaced with the high-temperature oxidation corrosion mechanism specific to supercritical water,while also accounting for the stress-enhanced oxidation effect.Through parameter trend analysis and sensitivity analysis of crack growth rate(CGR)results,this paper thoroughly discusses the changes in the impact of parameters in the corrected model on SCC prediction results.The analysis shows that the introduction of the stress-enhanced oxidation factor changes the trend of the impact of yield strength and hardening index on SCC in the original model,and changes the degree of impact of the oxidation decay index,yield strength,hardening index,and stress intensity factor on SCC.The calculation of the comprehensive sensitivity coefficient of model parameters shows that the SEO correction weakens the influence of environmental corrosion factors in the original FRI model,enhances the influence of mechanical factors and material factors,but does not change the dominant position of environmental corrosion factors in the model.Combined with SCC experimental data of nickel-based alloy Inconel 625 under steam conditions at 700 and 750℃,the predictive ability of the SEOcorrected FRI model for stress corrosion cracking is demonstrated.The results show that the use of SEO correction can improve the accuracy of the prediction results,and the calculated results of the theoretical model are in good agreement with the experimental results.Based on the analysis of experimental data and model parameters,this paper decouples and analyzes the differences in crack propagation life of components under single mechanical,single corrosion,and stress corrosion effects,and provides an application method of the model in ultra-supercritical units for future stress corrosion safety evaluation and health management of high-temperature components.