Assessment and Test of the Creep-Fatigue Crack Behavior for a High Temperature Component

An assessment of creep-fatigue crack initiation and growth is of key importance for the evaluation of a high temperature structural integrity of a reactor structure such as the liquid metal reactor KALIMER Korea advanced liquid metal reactor1, operating in a creep regime. The high temperature design codes, ASME Section III Subsection NH 2 and RCC-MR 3, provide design guidelines for a defect-free body while the RCC-MR A16 Technical Appendix4 provides assessment procedures for creepfatigue crack initiation and propagation. The A16 guide provides an assessment procedure for creepfatigue crack initiation and propagation only for austenitic stainless steel because it does not provide the essential coefficients and material properties for other materials. The current A16 guide does not provide a procedure for Mod. 9Cr‐Mo ASME Grade 91 steel. In this study, the assessment of creep-fatigue crack initiation with an extended d approach has been carried out as a case study for a Grade 91 structure based on a proposed d value, a material specific characteristic distance from a defect tip, as d=36 m 5 and on a d value of d=50 m. The assessment results with the two different d values were compared with the observed images. The creep-fatigue crack propagation behavior of the austenitic stainless steel part of a specimen was examined with the results by an assessment according to the A16 guide and a test. Comparison of the two results should be useful for quantifying the conservatism of the A16 guide. Similar research on creep-fatigue damage and creep-fatigue crack behavior has been carried out for an austenitic stainless steel structure with weldments 6‐8.