Double loop electrochemical potentiokinetic reactivation test of Nickel-base Alloy 600 surface-melted by a CO2 laser beam

  • Lim Y
  • Kim H
  • Kim J
 et al. 
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Abstract

Ni-base Alloy 600 was widely used as a steam generator (S/G) tubing material in nuclear power plants because of its good mech. and corrosion properties at high temps. However, degrdns. of S/G tubes due to intergranular attack (IGA) and intergranular stress corrosion cracking (IGSCC) during normal operation were frequently reported. In particular, Alloy 600 can be very susceptible to IGA/IGSCC in some sulfur-bearing environments by sensitization. The beneficial effects of laser surface melting (LSM) on intergranular corrosion of the sensitized Alloy 600 is presented from the results of the double loop electrochem. potentiokinetic reactivation (DL-EPR) test. The DL-EPR test was performed in de-aerated 0.01M H2SO4+20 ppm KSCN at a scan rate of 0.5 mV/s at room temp. The degree of sensitization (DOS) of the sensitized Alloy 600 measured from the DL-EPR test was considerably reduced by LSM. The sensitized Alloy 600 after LSM also exhibited a relatively low DOS, compared with that of the sensitized but not laser treated Alloy 600. From the microscopic observation, the microstructural changes brought about by the LSM process, esp. changes in the pptn. behavior of grain boundary Cr-rich carbides, caused the improvement of resistance to intergranular corrosion of the laser treated Alloy 600. The resistance to IGSCC of the laser treated Alloy 600 in sulfur-bearing environments is also discussed from the results of measured DOS and microstructural examn. [on SciFinder(R)]

Author-supplied keywords

  • alloy 600
  • dl-epr test
  • intergranular corrosion
  • laser surface melting
  • sensitization

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Authors

  • Y. S. Lim

  • H. P. Kim

  • J. S. Kim

  • H. S. Kwon

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