A Short-Time Approach for Fatigue Life Evaluation of AISI 347 Steel for Nuclear Power Energy Applications

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.

A nonlinear lifetime prediction method for un‐ and low alloyed steels by damage determination based on non‐destructive measurement techniques

“…These enable the generation of a trend S-N curve in the High Cycle Fatigue (HCF) regime. 38,39 These methods allow a reliable prediction of the fatigue life, based on one load increase test (LIT)/ strain increase test (SIT) and two constant amplitude tests (CAT). By using a stepped specimen geometry, the method SteBLife enables the determination of a trend S-N curve with only one specimen.…”

“…A number of LPM has already been developed at the Department of Materials Science and Materials Testing at the University of Applied Sciences Kaiserslautern. These enable the generation of a trend S‐N curve in the High Cycle Fatigue (HCF) regime 38,39 . These methods allow a reliable prediction of the fatigue life, based on one load increase test (LIT)/strain increase test (SIT) and two constant amplitude tests (CAT).…”

StressLife: A Short-Time Approach for the Determination of a Trend S-N Curve in and beyond the HCF Regime for the Steels 20MnMoNi5-5 and SAE 1045

“…The aim of these methods was to improve the representation of the transition areas of the S-N curve. The department of materials science and materials testing at the University of Applied Sciences Kaiserslautern has already developed a number of short-time procedures over recent years, such as SteBLife, StrainLife, and MiDAc-Life, which can be found in [20][21][22][23][24]. The StressLife method described in this paper differs from the other methods because the fatigue properties are described by an elastic-plastic approach, whereas SteBLife and MiDAc-Life are only based on an elastic and linear approach, respectively.…”