Crack growth rates of nickel alloy welds in a PWR environment.

Abstract

In light water reactors (LWRs), vessel internal components made of nickel-base alloys are susceptible to environmentally assisted cracking. A better understanding of the causes and mechanisms of this cracking may permit less conservative estimates of damage accumulation and requirements on inspection intervals. A program is being conducted at Argonne National Laboratory to evaluate the resistance of Ni alloys and their welds to environmentally assisted cracking in simulated LWR coolant environments. This report presents crack growth rate (CGR) results for Alloy 182 shielded-metal-arc weld metal in a simulated pressurized water reactor (PWR) environment at 320°C. Crack growth tests were conducted on 1-T compact tension specimens with different weld orientations from both double-J and deep-groove welds. The results indicate little or no environmental enhancement of fatigue CGRs of Alloy 182 weld metal in the PWR environment. The CGRs of Alloy 182 in the PWR environment are a factor of ≈5 higher than those of Alloy 600 in air under the same loading conditions. The stress corrosion cracking for the Alloy 182 weld is close to the average behavior of Alloy 600 in the PWR environment. The weld orientation was found to have a profound effect on the magnitude of crack growth: cracking was found to propagate faster along the dendrites than across them. The existing CGR data for Ni-alloy weld metals have been compiled and evaluated to establish the effects of key material, loading, and environmental parameters on CGRs in PWR environments. The results from the present study are compared with the existing CGR data for Ni-alloy welds to determine the relative susceptibility of the specific Ni-alloy weld to environmentally enhanced cracking. iv Intentionally Left BlankForeword v This report presents crack growth rate data and the results of the corresponding fracture surface and metallographic examinations from cyclic loading and primary water stress-corrosion cracking (PWSCC) tests of two nickel-base Alloy 182 (A182) weldments, which are typical of those used in vessel penetrations and piping butt welds in nuclear power plants. The effect of crack orientation with respect to dendrite orientation is the most significant variable investigated in this study. However, this report also includes a review of data from several laboratories, which describes the effects of material composition, loading characteristics, and chemistry of the aqueous environment. The main conclusion is that the PWSCC growth rates described for A182 specimens in this report are comparable to the crack growth rates that characterize the performance of Alloy 600 (A600).This report is the first in a series documenting the results of crack growth rate testing in vessel head penetration materials, focusing on the weld metals, A182 and A152, and including results of some tests of the base metals, A600 and (eventually) A690. The results presented in this report were obtained in tests of a laboratory-fabricated, shielded metal arc welding deposit of A182. ...

Crack growth rates and metallographic examinations of Alloy 600 and Alloy 82/182 from field components and laboratory materials tested in PWR environments.

“…33 Under similar loading conditions, the CGRs of Ni-alloy welds are a factor of 2-3 higher than those of Alloy 600. The analysis 33 …”

“…In an earlier report, 33 experimental CGR data were obtained at ANL on field Alloy 600 and weld Alloys 82 and 182. In that report, K values were calculated using the correlations for a disc-shaped specimen instead of a standard CT specimen.…”

“…The results were presented in detail in previous reports. 32,33 This section summarizes the most important findings for laboratory-prepared alloys and for field components from the Davis-Besse and V. C. Summer reactors.…”

“…The results from the present study and data available in the literature have been reviewed to determine the effects of material and environmental parameters on the cyclic and constant-load CGRs in these alloys. The alloys being investigated include laboratory-procured Alloys 600 and 690, [26][27][28][29][30][31] laboratory-prepared deep-groove and double-J welds of Alloy 182, 32 Alloy 600 from Davis-Besse CRDM nozzle #3, Alloy 182 from a J-groove weld in Davis-Besse nozzle #11, and Alloys 182 and 82 from a hot-leg nozzle-to-pipe weld in the V.C. Summer reactor coolant system.…”

“…Summer reactor coolant system. 33 The results have been compared with the existing CGR data to determine the relative susceptibility of these alloys to PWSCC and to determine whether the crack growth data in the field materials are consistent with our general understanding of CGRs in Ni-base alloys.…”