Effects of LOMI (low oxidation state metal ion) decontamination and preoxidation processes on stainless steel-clad low-alloy steel

Technical Report · Thu Mar 01 04:00:00 EST 1990

OSTI ID:7014382

Wang, M T ^[1]

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1. General Electric Co., San Jose, CA (USA). Nuclear Energy Div.

Standard 1T WOL (wedge opening load) bolt-loaded specimens were fabricated from a heat of SA302 Gr B low alloy steel and clad with 308L stainless steel. This quenched and tempered SA302 Gr B steel possesses a bainitic microstructure and is one of the key steels for boiling water reactor (BWR) pressure vessel fabrication. Fatigue precracks were produced which passed through the 308L clad layer into low alloy steel. This through-clad precracking, together with the galvanic coupling of austenitic and ferritic steels, is considered to be the worst condition for the stress corrosion cracking of the reactor pressure vessel (RPV) wall. The precracked specimens were loaded to an applied stress intensity of approximately 45 ksi (in.){sup 1/2}. Scanning electron microscopy (SEM) and optical metallographic examinations revealed both intergranular (IGSCC) and transgranular (TGSCC) branched stress corrosion cracks beyond the tip of fatigue precracks in the Peach Bottom 3 in-plant LOMI/NP/LOMI exposed specimens. The low temperature BWR water autoclave immersion test was performed to simulate the time/temperature cycle of the Peach Bottom 3 in-plant decontamination process but without addition of any decontamination solvents. Results of this study also indicated that the NP/LOMI process tended to promote stress corrosion crack propagation in the pressure vessel low alloy steel. Although the degree of susceptibility and crack morphology may depend on process time, temperature, and solvent concentration, it appears that nitric acid is the key ingredient for the promotion of both IGSCC and TGSCC.

• Research Organization: Electric Power Research Inst., Palo Alto, CA (USA); General Electric Co., San Jose, CA (USA). Nuclear Energy Div.
• Sponsoring Organization: EPRI
• OSTI ID: 7014382
• Report Number(s): EPRI-NP-6730
• Country of Publication: United States
• Language: English

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