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Understanding the Effect of Water Chemistry and Surface Grinding on the Stress Corrosion Cracking Initiation of Filler Metal 82

SCC of Ni-base filler metal (FM) 82 has been reported in the nozzles and other components in Light Water Reactors (LWRs). The typical characteristics of stress corrosion cracking (SCC) of Ni-base alloys are a long incubation time followed by slow propagation, which can suddenly transition to fast propagation. Whilst there has been considerable effort expended to develop an SCC mechanism that can explain and predict SCC in Alloy 600, fewer studies have investigated SCC of FM 82. The Preferential Intergranular Oxidation (PIO) SCC mechanism of Alloy 600 proposed by Bertali et al.  which is an evolution of the Selective Internal Oxidation SCC mechanism proposed by Scott and Le Calvar is considered one of the most representative primary water SCC mechanisms for Alloy 600.

Product Number: ED22-17143-SG
Author: N.SUPORNPAIBUL, M.G. BURKE, J. DUFF, F. SCENINI, Y.WANG
Publication Date: 2022
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Stress corrosion cracking (SCC) initiation of specimens extracted from filler metal (FM) 82 weldments was investigated in high purity 288˚C water. Accelerated autoclave slow strain rate tensile (SSRT) tests were conducted at different electrochemical corrosion potentials (ECPs) by varying the water chemistry through adjusting the concentration of dissolved hydrogen and oxygen in the recirculating water. The effect of surface preparation was also investigated. Statistical characterization of SCC initiation results showed that the ground surfaces (using P600 grit) of FM 82 appeared to be more resistant to SCC initiation than the surfaces polished via oxide polishing suspension (OPS). The effect of ECP on the SCC initiation susceptibility is also discussed through statistical characterization of the observed IG cracks.

Stress corrosion cracking (SCC) initiation of specimens extracted from filler metal (FM) 82 weldments was investigated in high purity 288˚C water. Accelerated autoclave slow strain rate tensile (SSRT) tests were conducted at different electrochemical corrosion potentials (ECPs) by varying the water chemistry through adjusting the concentration of dissolved hydrogen and oxygen in the recirculating water. The effect of surface preparation was also investigated. Statistical characterization of SCC initiation results showed that the ground surfaces (using P600 grit) of FM 82 appeared to be more resistant to SCC initiation than the surfaces polished via oxide polishing suspension (OPS). The effect of ECP on the SCC initiation susceptibility is also discussed through statistical characterization of the observed IG cracks.