Session: CS-16-01 Fatigue and Ratcheting Issues in Pressure Vessel and Piping Design

Paper Number: 121778

121778 - Investigation of the Very High Cycle Fatigue (Vhcf) Behavior of Aisi 347 and 304 Austenitic Stainless Steels Including Their Welds for Reactor Internals at Ambient and Operating Temperature 

Reactor internals are subjected to thermo-mechanical fatigue induced by operational temperature transients and to flow induced vibrations. The resulting complex loading collectives induce low cycle (LCF), high cycle (HCF) and even very high cycle (VHCF) fatigue and their interaction. Austenitic stainless steels, like AISI 304 and AISI 347 as well as weld material  ER 347, are often used for reactor internals due to their favorable properties such as strength and corrosion resistance. To ensure save operation the fatigue behavior of components must be assessed. Particularly, the VHCF fatigue behavior has not yet been sufficiently investigated, e.g.  the existing data base for load cycles equal to or above 10⁷ is still highly insufficient. The mean data curves used for the derivation of design fatigue curves in existing design codes (e.g. ASME code , German KTA Safety Standard) are based on extrapolation procedures at very high number of cycles rather than on experimental data. The methodological gaps within the current fatigue assessment approach are addressed in the framework of an on-going cooperative R&D project (MPA Stuttgart, Framatome GmbH, RTU Kaiserslautern) “Investigations concerning the fatigue behavior of austenitic stainless steels and their welds for reactor internals in the HCF and VHCF region”. After the successful finalization of the joint R&D project VHCF-I (see e.g. reference below) - obtaining knowledge of the fatigue behavior of AISI 347 and its weld material ER 347, used in German nuclear power plants, particularly in the VHCF regime - the follow-up project VHCF-II is intended to extend the existing knowledge and to obtain expertise on the internationally used AISI 304L austenitic stainless steel. It is intended to provide further findings for the design and fatigue evaluation of components and their welded joints with focus on loading conditions in the VHCF regime.

Therefore, the project partners investigate the following aspects: MPA and Framatome study the threshold behavior of AISI 304 and ER 347 under influence of high temperature water both for BWR and PWR conditions. Furthermore, the cyclic deformation behavior of AISI 304 is analyzed in order to obtain a material model for numerical calculations. Technical University of Kaiserslautern tackles the fatigue behavior of AISI 304 up to 2x10⁹ cycles, AISI 347 loaded with measurement intervals and non-constant load collectives (LCF/VHCF, HCF/VHCF), and investigates both austenitic stainless steels systematically regarding the possible frequency influence in air at operational relevant temperatures (RT and 300 °C) on the fatigue and alpha´-martensite formation. Moreover, the fatigue behavior of ER 347 transverse to the weld direction is investigated in the VHCF regime. Finally, it should be possible to transfer the data to components and specimens similar to components (welded joints). An engineering calculation concept in terms of the development of a fatigue assessment methodology for reactor internals - including the welds - under consideration of the transient endurance limit and damage accumulation effects is part of the project. This includes the multiaxial extension of a damage parameter based approach developed in the framework of VHCF-I.

The foreseen and on-going work of VHCF-II is presented in this paper in order to give a detailed overview of obtained results and upcoming studies.

Reference to VHCF-I:

Smaga, M., et al. (2022).  VERY HIGH CYCLE FATIGUE (VHCF) BEHAVIOR OF AUSTENITC STAINLESS STEELS AND THEIR WELDS FOR REACTOR INTERNALS AT AMBIENT AND OPERATING RELEVANT TEMPERATURE, Transactions, SMiRT-26, Berlin, Germany

Presenting Author: Juergen Rudolph Framatome GmbH

Presenting Author Biography: Dr. Jürgen Rudolph - Framatome Senior Expert / Senior Advisor with the Lifetime Management Department of Framatome GmbH (Erlangen, Germany) - More than 20 years of experience in design and analysis of pressure vessel and power plant components with special interest in fatigue, aging and lifetime issues, > 100 publications - Graduation at the Technical University of Magdeburg (1992), PhD (1996) and post doctorate (2004) at Dortmund University - Framatome since 2007, before German Technical Supervision Associa¬tion TÜV NORD AG in Hannover - Active participation in different design code working groups,e.g. ASME IWG, KTA and EN 13445-3 - Licensed project manager for customer projects on aging and lifetime topics.

Authors:

Juergen Rudolph Framatome GmbH
Georg Veile Materialprüfungsanstalt Universität Stuttgart (MPA)
Elen Regitz RPTU Rheinland-Pfälzische Technische Universität Kaiserslautern Landau
Marek Smaga Rheinland-Pfälzische Technische Universität Kaiserslautern Landau (RPTU)
Udo Fischer Framatome GmbH
Michael Grimm Framatome GmbH
Stefan Weihe Materialprüfungsanstalt Universität Stuttgart (MPA)
Tilman Beck Rheinland-Pfälzische Technische Universität Kaiserslautern Landau (RPTU)