Creep-fatigue life prediction for ligament of boiler headers by strain range partitioning method

摘要

Strain range partitioning method was applied to creep-fatigue life prediction for ligaments of high temperature boiler headers. Typical operating transient data was used to conduct thermal transient analysis and elastic-plastic-creep stressanalysis with three dimensional FEM models simulating ligament parts of headers. Creep-fatigue life was predicted by strain range partitioning method based on the analytical results and creep-fatigue properties of a header material. The results obtainedwere as follows.(1) Cracking was expected in ligament parts with inelastic strain produced by thermal transient during start-up and shut-down operation.(2) The points where ligament crack was predicted to initiate coincided with ones reported in actual plants failure cases.(3) The effects of operational condition and size of header on ligament crack initiation life were evaluated by this analysis. It was found that the ligament crack initiation life tends to be shorter in the case of the faster ramp rate and the largerheader diameter.