Abstract
The assessment of metallic materials used in power plants’ piping represents a big challenge due to the thermal transients and the environmental conditions to which they are exposed. At present, a lack of information related to degradation mechanisms in structures and materials is covered by safety factors in its design, and in some cases, the replacement of components is prescribed after a determined period of time without knowledge of the true degree of degradation. In the collaborative project “Microstructure-based assessment of maximum service life of nuclear materials and components exposed to corrosion and fatigue (MibaLeb)”, a methodology for the assessment of materials’ degradation is being developed, which combines the use of NDT techniques for materials characterization, an optimized fatigue lifetime analysis using short time evaluation procedures (STEPs) and numerical simulations. In this investigation, the AISI 347 (X6CrNiNb18-10) is being analyzed at different conditions in order to validate the methodology. Besides microstructural analysis, tensile and fatigue tests, all to characterize the material, a pressurized hot water pipe exposed to a series of flow conditions will be evaluated in terms of full-scale testing as well as prognostic evaluation, where the latter will be based on the materials’ data generated, which should prognose changes in the material’s condition, specifically in a pre-cracked stage. This paper provides an overview of the program, while the more material’s related aspects are presented in the subsequent paper.
Highlights
Damage is an expression generally used when a material is exposed to loading
A series of constant amplitude fatigue tests (CAT), as well as load and strain increase fatigue tests (LIT and SIT), were performed under various loading, temperature and environmental conditions, where load and deformation had been recorded and parameters associated with non-destructive testing (NDT), taken as a material response for the description of the material’s damaging behavior
These fatigue tests were performed following short time evaluation procedures (STEP), that allow a complete S-N curve of a material to be determined with three tests only
Summary
Damage is an expression generally used when a material is exposed to loading. its meaning is extremely wide, and the mechanisms damage is based upon are versatile. A series of constant amplitude fatigue tests (CAT), as well as load and strain increase fatigue tests (LIT and SIT), were performed under various loading, temperature and environmental conditions, where load and deformation had been recorded and parameters associated with non-destructive testing (NDT), taken as a material response for the description of the material’s damaging behavior. It has been shown in [5] after analyzing stress amplitude, mean stress and plastic strain amplitude curves of strain-controlled fatigue tests conducted at different strain amplitudes in the HCF regime (εa,t = 0.165 to 0.220%), that at the beginning of the test, cyclic softening occurs, followed by cyclic hardening For both LCF and HCF regimes, there is an incubation period where no α’-martensite transformation takes place, followed by a continuous increase in the α’-martensite volume fraction. The plasticity model-based notch root strain and the Neuber approach represent two complementary approaches, allowing local stresses and strains in notched specimens to be assessed
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