Acta Phys. -Chim. Sin. ›› 2015, Vol. 31 ›› Issue (3): 467-475.doi: 10.3866/PKU.WHXB201501053

• ELECTROCHEMISTRY AND NEW ENERGY • Previous Articles     Next Articles

Corrosion Behavior of Alloy 690 in Simulated Alkaline Water Chemistries Containing Sulfur at 300 ℃

XIA Da-Hai1,2,3, LUO Jing-Li2   

  1. 1. School of Materials Science and Engineering, Tianjin University, Tianjin 300072, P. R. China;
    2. Department of Chemical and Materials Engineering, University of Alberta, Edmonton T6G 2V4, Alberta, Canada;
    3. Tianjin Key Laboratory of Composite and Functional Materials, Tianjin University, Tianjin 300072, P. R. China
  • Received:2014-11-21 Revised:2014-12-31 Published:2015-03-06
  • Contact: XIA Da-Hai, LUO Jing-Li E-mail:dahaixia@tju.edu.cn;luoj@ualberta.ca
  • Supported by:

    The project was supported by the Atomic Energy of Canada Limited (AECL).

Abstract:

Alloy 690 is one of the steam generator (SG) tubing materials in pressurized water reactors (PWR). The degradation of this alloy in alkaline solutions containing reduced sulfur is one of the main causes of stress corrosion cracking. In this study, the corrosion behavior of Alloy 690 in simulated alkaline crevice chemistry at 300 ℃ was investigated using polarization curves, scanning electron microscopy (SEM), Auger electron spectroscopy (AES), and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Studying the effect of thiosulfate and sulfate on the properties of the passive film formed on Alloy 690 showed that the film formed at 300 ℃ was composed of an outer porous layer and an inner compact layer, and that the ion species presented in chloride solutions had a significant impact on the corrosion behavior of the alloy. The addition of thiosulfate increased the passive current density, decreased the transpassive potential, and therefore lowered the corrosion resistance. The presence of thiosulfate also led to a decrease in Cr levels and an increase in Ni levels in the passive layer. The thiosulfate can reduce sulfur at the film surface and enter into the film, causing an increased sulfide content in the film which decreases the corrosion resistance. However, experiments using sulfate had no obvious effect on film degradation as the ion had minimal interaction with the film.

Key words: Alloy 690, Passive film, Alkaline, Thiosulfate, Sulfate

MSC2000: 

  • O646