Creep fatigue life prediction for ligament of boiler headers by strain range partitioning method
Hayakawa Hiroyuki; Miyahara Mituo; Kanaya Akihiro; Okamura Kazuo
Abstract: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 stress analysis 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 obtained were 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 larger header diameter. Key Words:creep-fatigue, life prediction, boiler, stress analysis, strain range partitioning method