Overview of French Proposal of Updated Austenitic SS Fatigue Curves and of a Methodology to Account for EAF

Abstract

Environmentally Assisted Fatigue is receiving nowadays an increased level of attention not only for new builds but also for the installed bases which are currently having their lives extended to 60 years in various countries. To formally integrate these effects, some international codes have already proposed code cases. More specifically, the ASME code has used the NUREG/CR-6909 [1] as the basis for Code Case N-792 [2] and suggests a modification of the austenitic stainless steels fatigue curve combined with a calculation of an environmental penalty factor, namely Fen, which is to be multiplied by the usual fatigue usage factor. The various methodologies proposed are not finalized and there is still a significant level of discussion as can be illustrated by the recent update of NUREG/CR-6909 [3]. In this context, EDF, AREVA and the CEA have also submitted two RCC-M Rules in Probatory Phase (RPP) (equivalent to ASME code-cases) to AFCEN to propose respectively an update of the fatigue curve for austenitic stainless steels and a methodology to incorporate EAF in fatigue evaluations. The approach is globally similar to the one in the ASME code: it consists in an update of the mean air and design fatigue curves as well as the calculation of an environmental penalty factor. Nevertheless, the methodologies differ in their detailed implementation by especially introducing the Fen-integrated which accounts for the environmental effects already covered by the fatigue curves. This paper is the sequel to the proposal already described in [4] [6].

Environmental Fatigue Analysis of Nuclear Structural Components: Assessment Procedures, Loads, and a Case Study

“…The mean air curve specified in this document is identical to the one in NUREG/CR-6909. This conclusion was reached [23] based on a statistical comparison of the air data available and the NUREG/CR-6909.…”

Influence of mean stress and pressurized water reactor environment on the fatigue behavior of a 304L austenitic stainless steel

“…Thereafter, different factors are applied to the strain amplitude and to the number of cycles to failure, in order to account for the degradation in fatigue strength induced by various parameters, such as the stress multiaxiality, the size, the surface finishing of the component, or the material variability and the scatter in data. It is worth noticing that when applying these factors, it is assumed that these parameters influence the fatigue behavior independently from each other, which may lead to a substantial over‐ or under‐conservatism in the life prediction in presence of interactions (synergy or attenuation) 3 . Therefore, the investigation of the effect of these parameters and their interactions is of high interest to improve the accuracy of the fatigue life assessment of nuclear power‐plant components.…”

“…It is worth noticing that when applying these factors, it is assumed that these parameters influence the fatigue behavior independently from each other, which may lead to a substantial over-or under-conservatism in the life prediction in presence of interactions (synergy or attenuation). 3 Therefore, the investigation of the effect of these parameters and their interactions is of high interest to improve the accuracy of the fatigue life assessment of nuclear power-plant components.…”