Influence of Strain Rate and Waveshape on Environmentally-Assisted Cracking during Low-Cycle Fatigue of a 304L Austenitic Stainless Steel in a PWR Water Environment

Thibault Poulain,Laurent De Baglion,Gilbert Hénaff,Jose Mendez

doi:10.3390/met9020197

Abstract

In this paper, the low cycle fatigue resistance of a 304L austenitic stainless steel in a simulated pressurized water reactor (PWR) primary water environment has been investigated by paying a special attention to the interplay between environmentally-assisted cracking mechanisms, strain rate, and loading waveshape. More precisely, one of the prime interests of this research work is related to the consideration of complex waveshape signals that are more representative of solicitations encountered by real components. A detailed analysis of stress-strain relation, surface damage, and crack growth provides a preliminary ranking of the severity of complex, variable strain rate signals with respect to triangular, constant strain-rate signals associated with environmental effects in air or in PWR water. Furthermore, as the fatigue lives in PWR water environment are mainly controlled by crack propagation, the crack growth rates derived from striation spacing measurement and estimated from interrupted tests have been carefully examined and analyzed using the strain intensity factor range ΔKε. It is confirmed that the most severe signal with regards to fatigue life also induces the highest crack growth enhancement. Additionally two characteristic parameters, namely a threshold strain εth* and a time T*, corresponding to the duration of the effective exposure of the open cracks to PWR environment have been introduced. It is shown that the T* parameter properly accounts for the differences in environmentally-assisted growth rates as a function of waveshape.

Highlights

The aging management of nuclear power plants is one of the main challenges for the energy stakeholders worldwide in the coming years
It is worth noticing that the estimated duration of tests to failure using complex signals with a long period was so high in this environmental condition that it was decided to interrupt the tests after 1350 cycles
Concerning the tests using standard triangular waveshape, those performed at the intermediate and the highest strain rates were conducted until failure while the one carried out at the slowest strain rate was stopped before failure, after 2500 cycles, because of the very long duration of the test in such condition

Summary

Introduction

The aging management of nuclear power plants is one of the main challenges for the energy stakeholders worldwide in the coming years. In the case of pressurized water reactors (PWR), water is used both as a nuclear reaction moderator and as a heat carrier medium. In order to maintain the water in a liquid state throughout the entire primary circuit, a pressure of about 140 bars is applied while its temperature varies between 290 and 350 ◦ C. This water, with a definite and controlled chemistry, represents the PWR medium. The primary circuit pipings, commonly made of austenitic stainless steel, are subjected to complex thermomechanical loadings in the low-cycle

Results

Discussion

Conclusion