Caustic stress corrosion cracking of alloys 600 and 690 with NaOH concentrations |
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Authors: | In-Gyu Park Chang-Soon Lee Seong-Sik Hwang Hong-Pyo Kim Joung-Soo Kim |
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Affiliation: | (1) Dept. of Materials System Engineering, Sun Moon University, 100 Kalsan-ri, Tangjeong-myeon, 336-708 Asan, Korea;(2) Steam Generator Materials Development Team, Korea Atomic Energy Research Institute, Yuseong, P.O. Box 105, 305-600 Daejeon, Korea |
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Abstract: | In order to evaluate the stress corrosion cracking resistance for commercial alloys (C600MA, C600TT, C690TT) and Korean-made
alloys (K600MA, K690TT), C-ring tests were performed in a caustic environment of 4, 10, 20, 30, and 50% NaOH solution at 315°C,
for 480 h with an applied potential of 125 mV vs. OCP. Different stress corrosion cracking phenomena were observed according
to the NaOH concentration. The rate of caustic IGSCC attack did not appear to increase monotonically with caustic concentrations,
but peaked at a concentration between 4 and 50% caustic, or approximately 30% NaOH. Intergranular stress corrosion cracking
was found for C600MA in 10, 20, and 30% NaOH solutions, while no cracking was observed in the 4 and 50% NaOH solutions. In
30% NaOH solution, transgrnular stress corrosion cracking was detected in C690TT, which may be related with the large amount
of plastic strain (150% yield) and the applied potential (125 mV vs. OCP). The overall data clearly indicate that C600MA has
the worst SCC resistance while K690TT offers the best resistance. There is also fairly good correlation between the caustic
SCC susceptibility and some metallurgical parameters, particularly the grain size and the yield strength at room temperature.
Specifically, materials having larger grain size and lower yield strength exhibited higher caustic SCC resistance. |
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Keywords: | stress corrosion cracking alloy 600 alloy 690 steam generator tube |
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