Abstract
AISI 347 austenitic steel is, as an example, used in nuclear energy piping systems. Piping filled with superheated steam or cooled water is particularly exposed to high stresses, whereupon local material properties in the pipes can change significantly, especially in the case of additional corrosive influences, leading to aging of the material. In the absence of appropriate information, such local material property variations are currently covered rather blanketly by safety factors set during the design of those components. An increase in qualified information could improve the assessment of the condition of such aged components. As part of the collaborative project “Microstructure-based assessment of the maximum service life of core materials and components subjected to corrosion and fatigue (MiBaLeB)”, the short-time procedure, StrainLife, was developed and validated by several fatigue tests. With this procedure, a complete S–N curve of a material can be determined on the basis of three fatigue tests only, which reduces the effort compared to a conventional approach significantly and is thus ideal for assessing the condition of aged material, where the material is often rare, and a cost-effective answer is often very needed. The procedure described is not just limited to traditional parameters, such as stress and strain, considered in destructive testing but rather extends into parameters derived from non-destructive testing, which may allow further insight into what may be happening within a material’s microstructure. To evaluate the non-destructive quantities measured within the StrainLife procedure and to correlate them with the aging process in a material, several fatigue tests were performed on unnotched and notched specimens under cyclic loading at room and elevated temperatures, as well as under various media conditions, such as distilled water and reactor pressure vessel boiling water (BWR) conditions.
Highlights
AISI 347 steel is used in pipes, volume control, reactor water purification, feed water system and other components of German nuclear power plants (e.g., in current light–water reactors (LWR) plants) in a temperature range up to 350 ◦ C
Non-destructive testing (NDT) techniques offer great potential for detecting the microstructural degradation that precedes micro crack formation. This potential has not been sufficiently explored when it comes to the fundamentals of quantitatively characterizing the material behavior under static, cyclic, as well as any combinations of thermal and corrosive loading using NDT, which might provide an insight into the interactions between an NDT-based measurement signal and a material0 s microstructure
Etchant and subsequent optical microscopy examinations, as well as crystallographic analyses using electron backscatter diffraction (EBSD) measurements (Figure 2a) on the unetched sample, a square region consisting of an inhomogeneous multiphase structure of coarser-grained austenite and deformation-induced α0 -martensite with mechanical twins was detected in the center of the cross-section
Summary
Tobias Bill 1, * , Ruth Acosta 2 , Christian Boller 2 , Kai Donnerbauer 3 , Lukas Lücker 3 , Frank Walther 3 , Klaus Heckmann 4 , Jürgen Sievers 4 , Tim Schopf 5 , Stefan Weihe 5 and Peter Starke 1. Evaluation of AISI 347 Steel for Nuclear Power Energy Applications
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