During the past 30 years many fatigue tests and fatigue analysis improvements have been developed in France in order to improve Codified Fatigue Rules of RCC-M and ASME Codes [1, 2].
This paper will present the major technical improvements to obtain reasonable evaluation of potential fatigue damage through EDF road map. Recently new results [3] confirm possible un-conservative fatigue material data:
- High cycle fatigue in air for stainless steel,
- Environmental effects on fatigue S-N curve for all materials
- Fatigue Crack Growth law under PWR environment for stainless steel.
In front of these new results, EDF has developed a “Fatigue Road Map” to improve the different steps of Codified fatigue rules.
A periodic up-dating of proposed rules in the different French Codes: RCC-M, RCC-MRx and RSE-M with research of harmonization with other Code rules developed in USA, Japan and Germany in particular, will be done on a yearly basis. During the past 15 years, many results have been obtained through fatigue tests of stainless steel materials:
- mean and design fatigue curve in air,
- environmental effects on fatigue curves,
- plasticity effects,
- bi-axial load effects,
- mean stress effects,
- stress indices,
- transferability from small to large specimen,
- weld versus base metal.
In parallel, many new developments have been made in non-nuclear pressure equipment industry: like the reference stress of ASME Section VIII or the structural stress of EN 13445. These methods are mainly well adapted to fatigue pressure cycling.
In front of that situation, the French nuclear code organization needs to propose reliable rules for new design and for operating plants. Different proposals are under discussion and the status of the EDF proposals are presented in the paper.
The consequences could be important for the utilities because a large part of the in-service inspection program is connected to some fatigue usage factor level between 0.5 and 1.