Published: Jan 1979
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A high-temperature slow strain-rate facility was developed to evaluate the stress corrosion resistance of alloys considered for the construction of liquid metal fast breeder reactor (LMFBR) steam generators. The primary concern was stress corrosion that might occur on the water side during steam generator operation in locally faulted caustic environments. Most of the studies were performed at 316°C in 5 or 10 percent sodium hydroxide (NaOH) solutions with 2¼Cr-1Mo steel and Incoloy-800.
With minor modification, the slow strain-rate test was converted to a straining electrode test. Experiments conducted by the straining electrode test permitted the study of stress corrosion behavior in the high temperature caustic solutions over a range of oxidizing potentials.
It was found that 2¼Cr-1Mo steel was extremely resistant to caustic cracking at 316°C in all metallurgical conditions tested by the slow strain-rate test and the straining electrode test. A few slow strain-rate tests performed at 232 °C in 5 to 10 percent NaOH resulted in intergranular and transgranular stress corrosion failures of 2¼Cr-1Mo steel.
Unlike 2¼Cr-1Mo, Incoloy-800 was susceptible to caustic cracking at 316°C. The susceptibility depended on the metallurgical condition and to some extent, the oxidizing potential. The cold-worked and Grade 1 conditions exhibited excellent resistance to caustic cracking in the slow strain-rate test. However, limited studies in the straining electrode test showed the Grade 1 condition could be readily cracked at anodic oxidizing potentials.
stress corrosion cracking, slow strain-rate test, straining electrode test, caustic cracking, high temperature, high pressure, liquid metal fast breeder reactor, boilers, 2¼Cr-1Mo steel, Incoloy-800, metallurgical condition, alloys
Principal engineer, General Electric Company, San Jose, Calif.