A comprehensive comparison of creep-fatigue life assessment through leading industrial codes

Creep-fatigue damage has been recognised as a critical failure mode for high-temperature structures. In fusion power reactors, plasma-facing components endure complex loading conditions, resulting in high thermomechanical stresses. These components, often made from 316L material, joined to ferritic-martensitic steels, face significant challenges due to the interaction of various loads affecting their material properties and structural integrity. This paper compares internationally recognized methods for creep-fatigue assessment: the R5 procedure and the RCC-MRx code. The study evaluates the differences and similarities in creep-fatigue assessments between these procedures, providing a global overview and a detailed comparison. The conservatism of both approaches are assessed by comparing the material properties dataset, total strain calculations, and lifetime estimates for 316L at 550 °C. Additionally, the welding assessment approaches of RCC-MRx and R5 are compared and applied to similar metal welds (316L-to-316L). Further, dissimilar Electron Beam Welded metals (316L-to-10CrMo9-10) are prepared, investigated and characterized using creep-fatigue experiments to compare the predicted service life using RCC-MRx. • This paper presents a comparative analysis of creep-fatigue assessment procedures of R5 and RCC-MRx, used for ensuring the safe and reliable design of DEMO components in fusion applications, underlining their differences and similarities. • A comparison is conducted by analyzing the material properties of 316L under identical conditions used in R5 and RCC-MRx, exploring the impact of varying factors on the assessment, and comparing the calculated total strain required for creep-fatigue assessment at 550°C. The results indicate that RCC-MRx exhibits greater conservatism under these conditions. The experimental creep-fatigue tests validate the conservatism of the RCC-MRx assessment. • The main sources of conservatism observed are: o Differences in material properties used in R5 assessment (R66) and RCC-MRx for the same materials under identical conditions. o The calculation of fatigue damage per cycle in R5 relates to crack nucleation and can be adjusted for defect initiation, whereas RCC-MRx uses endurance curves based on a specific load drop, which corresponds to a relatively large crack size.