日本機械学会維持規格における弾塑性破壊力学評価法に用いる割増し係数（Z係数）の開発

概要

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Appendix E-9, “Elastic-Plastic Fracture Mechanics Evaluation,” in the JSME Rules on Fitness-for-Service for Nuclear Power Plants (Codes for Nuclear Power Generation Facilities) uses the load multiplier Z-factor that is applied to elastic-plastic fracture mechanics evaluation for a pipe circumferential flaw of austenitic stainless steel piping and ferritic steel piping. The Z-factor is defined as the ratio of the limit load to the load at tearing instability. Here, the Z-factor of the current JSME Rules on Fitness-for-Service for Nuclear Power Plants was developed for a through-wall pipe circumferential flaw with the angle of 60°. In Code Case JSME S NA-CC-002, ”Alternative Rule of Criteria on Allowable Flaw Angle for Circumferential Crack” published in 2005, the Z-factor equations are applicable to a circumferential surface flaw including the angle of greater than 60°, but the Z-factor equations of the Code Case were conservatively formulated as upper-bounded those Z-factors for through-wall pipe circumferential cracks including the angle of greater than 60°. However, the original purpose of the Code Case was to eliminate the limitation of flaw angle and evaluate non-through-wall flaws. Accordingly, Z-factors for non-through-wall flaws should be developed to have the consistency. Therefore, Z-factor equations of austenitic stainless steel piping and ferritic steel piping have been developed for non-through-wall flaws.