Data Quality, Issues, and Guidelines for Electrochemical Corrosion Potential Measurement in High-Temperature Water

• Published in: Corrosion (Houston, Tex.) Tex.), 2003-07, Vol.59 (7), p.584-596
• Main Authors: Kim, Y.-J., Andresen, P.L.
• Format: Article
• Language: English
• Subjects: Applied sciences; Boiling water reactors; Corrosion; Corrosion environments; Corrosion mechanisms; Corrosion potential; Dissolved gases; Electrochemical corrosion; Electrochemistry; Electrodes; Exact sciences and technology; High temperature; Hydrodynamics; Hydrogen peroxide; Impurities; Metals; Metals. Metallurgy; Nuclear energy; Pressurized water reactors; Reactors; Surface chemistry; Temperature; Water; Water chemistry; Water temperature
• ISSN: 0010-9312; 1938-159X
• DOI: 10.5006/1.3277589

ABSTRACTThe electrochemical corrosion potential (ECP) of a metal is influenced by a large number of variables, such as oxygen, hydrogen, and hydrogen peroxide (H2O2) concentrations, the surface chemistry, impurities, hydrodynamic flow conditions, type of reference electrode, etc. The state of reference electrode development and qualification, water chemistry conditioning procedures, surface history, etc. is such that achieving total agreement from all international investigators is difficult. However, identification of key factors, preferred techniques, and sensible ranges in potentials for several standard conditions is possible. The purpose of this paper is to identify factors that influence ECP measurements in hightemperature water, propose recommended techniques, and characterize the expected range of corrosion potentials for specific materials, dissolved gas chemistries, water chemistry/ pH, and temperature associated with boiling water reactor (BWR), pressurized water reactor (PWR), and related high-temperature water environments. INTRODUCTION The degradation of structural materials in nuclear power plants has been well addressed in previous papers.1-2 It is well understood that when the electrochemical corrosion potential (ECP) of stainless steel (SS) to high-temperature water is decreased, the intergranular stress corrosion cracking (IGSCC) susceptibility of sensitized SS in boiling water reactors (BWR) can be decreased (Figure 1). By lowering the ECP of SS below a critical potential (?230 mV vs the standard hydrogen electrode [SHE]), the susceptibility to IGSCC in BWR is markedly reduced. The ECP is controlled by the amounts of oxidizing and reducing species and the hydrodynamic water flow conditions and can also be affected by the electronic/ionic conductivity of oxide films formed on metal surfaces in aqueous environments. In BWR, one approach to lowering the ECP is to decrease the dissolved oxidant levels by adding hydrogen in the feedwater, a process known as hydrogen water chemistry (HWC).1 The goal of the HWC process is to lower the ECP of exposed structural materials to a value below the critical potential required for the IGSCC mitigation. For some time, it has been generally recognized that simple monitoring of dissolved hydrogen and/or oxygen concentrations in HWC water is unsatisfactory for process control. It has been similarly recognized that measurement of the redox potential of the water with a platinum probe is also unrewarding bec