Development of a Fatigue Design Curve for Austenitic Stainless Steels in LWR Environments: A Review

Abstract

The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components and specifies fatigue design curves for structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. Existing fatigue strain–vs.–life (ε–N) data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. This paper reviews the existing fatigue ε–N data for austenitic stainless steels in LWR coolant environments. The effects of key material, loading, and environmental parameters, such as steel type, strain amplitude, strain rate, temperature, dissolved oxygen level in water, and flow rate, on the fatigue lives of these steels are summarized. Statistical models are presented for estimating the fatigue ε–N curves for austenitic stainless steels as a function of the material, loading, and environmental parameters. Two methods for incorporating environmental effects into the ASME Code fatigue evaluations are presented. Data available in the literature have been reviewed to evaluate the conservatism in the existing ASME Code fatigue design curves.

Review of the margins for ASME code fatigue design curve - effects of surface roughness and material variability.

“…40 In water, the existing data include the tests performed by GE at the Dresden 1 reactor, 33 the JNUFAD database, studies at MHI, 18,[21][22][23] IHI, 19 and Hitachi 41,42 in Japan, and the present work at ANL. [24][25][26][27][28] In air, the fatigue e-N database for austenitic SSs is composed of 500 tests: 240 on 26 heats of Type 304 SS, 170 on 15 heats of Type 316 SS, and 90 on 4 heats of Type 316NG. Most of the tests have been conducted on cylindrical gauge specimens with fully reversed axial loading; ª75 tests were on hourglass specimens, and ª40 data points were from bending tests on flat-sheet specimens with rectangular cross section.…”

“…The magnitude of this reduction depends on strain amplitude, strain rate, temperature, DO level in the water, and, possibly, the composition and heat treatment of the steel. [16][17][18][19][20][21][22][23][24][25][26][27][28] The effects of LWR environments on the fatigue lives of wrought materials are comparable for Types 304, 316, and 316NG SSs; effects on cast materials differ somewhat. As in the case of the carbon and low-alloy steels, fatigue life is reduced significantly only when certain critical parameters meet certain threshold values.…”

“…14,17,26,28 In room-temperature air, the fatigue life N of carbon steels is represented by ln(N) = 6.564 -1.975 ln(e a -0.113) (3) and that of low-alloy steels, by ln(N) = 6.627 -1.808 ln(e a -0.151),…”

“…In one case, new, environmentally adjusted fatigue design curves are developed; [14][15][16][17]26,28 in the other, fatigue life correction factors F en are used to adjust the fatigue usage values for environmental effects. 11,28,54,55 Estimates of fatigue life based on the two approaches can differ somewhat because of differences between the ASME mean curves used to develop the current design curves and the best-fit curves to the current data that are used to develop the environmentally adjusted curves. However, both methods provide an acceptable approach to account for environmental effects.…”

“…Existing fatigue strain-vs.-life (e-N) data illustrate potentially significant effects of light water reactor (LWR) coolant environments on the fatigue resistance of carbon and low-alloy steels [4][5][6][7][8][9][10][11][12][13][14][15][16][17] and austenitic stainless steels (SSs) [16][17][18][19][20][21][22][23][24][25][26][27][28] (Fig. 1).…”