Corrosion behaviour of IN625 in superheated steam at 800°C

Abstract

Concerns with greenhouse gas emissions and the uncertainty of long-term supply of fossil fuels have resulted in renewed interest in nuclear energy as an essential part of the energy mix for the future. Canada is currently undertaking the design of Generation IV supercritical water-cooled reactor (SCWR) with improved higher thermodynamic efficiency and considerable plant simplification. The identification of appropriate materials for in-core and out-of-core components to contain the SCWR coolant is one of the major challenges for the design of Canadian SCWR. This study is carried out to evaluate the oxidation/corrosion behaviours of Inconel 625 (IN625) under superheated steam (SHS) at a temperature of 800°C (0.1 MPa) for up to 3000 hours. The results show that chromium-based oxide forms on the surface after exposure in SHS for 800, 2000 and 3000 hours. The oxide formation leads to initial weight increase followed by weight loss after extended exposure, likely due to chromium oxide dissolution. No localised oxide spallation was observed on all samples examined. Despite the slight weight reduction, a dense and adhered oxide layer, consisting primarily of Cr₂O₃ with some spinel (Ni(Cr,Fe)₂O₄), remained on IN625 after 3000 hours in SHS.

Keywords:

• Canadian SCWR
• Superheated steam
• IN625
• Weight change
• Microstructure evaluation
• XRD

Acknowledgement

We thank Mr Fred Barrett and Rainier Garcia Sanchez for testing the samples in the SHS rig. Financial support for this research is provided by NSERC/NRCan/AECL under a Collaborative Research Development fund.