Transport processes in steam generator crevices - III. Experimental results

Corrosion within the tube/support plate crevices of pressurized water react or steam generators (SGs) has proven to be an important operating problem i n the nuclear power industry. In order to explore the electrochemical natur e of SG crevice corrosion, and to evaluate our previously published theoret ical models (Parts I and II), a SG simulator was developed to perform selec ted experiments. These experiments involved three different bulk solution e nvironments (acidic, neutral, and alkaline), a bulk water temperature of 20 0 degreesC at a pressure of 21 kg cm(-2), and experimental times of up to 1 5 days. The crevice was divided into four different components: an alloy 60 0 tube within the crevice, an alloy 600 tube external to the crevice, an AI SI 4140 steel support plate within the crevice, and an AISI 4140 steel exte rnal surface., with each component being electrically isolated from the oth ers. The coupling currents flowing between the components were measured usi ng zero resistance ammeters and maps of galvanic activity have been derived . Under heat transfer conditions, it was found that the crevice is inverted , with positive current flowing from the external environment into the crev ice. This inversion was predicted theoretically in Part I of this series. F inally, the general corrosion rate of each component has been estimated. an d the inversion of the crevice has been explained in terms of the effect of thermohydraulic processes on the crevice chemistry. (C) 2001 Elsevier Scie nce Ltd. All rights reserved.