![]()
ABSTRACT Constant extension rate tensile (CERT) tests are traditionally used to understand the influence of material composition, heat treatment, temperature and environmental variables on stress corrosion crack (SCC) initiation. However, fluid flow rate has not been investigated as a parameter that could affect SCC initiation until recently. These studies have exhibited longer time to failure under high flow conditions indicating delayed crack initiation. Because these experiments have been performed in highly oxygenated water, no correlation has been established between the influence of flow velocity on the electrochemical corrosion potential (ECP) and the time to failure of tensile test specimens. The interrelationship between the fluid flow velocity, ECP and the time to failure is of great interest to the Boiling Water Reactor (BWR) applications primarily because of the previous observations that the ECP of Type 304 stainless steel increases with fluid flow velocity.
This paper describes an attempt that has been made to understand the interrelationship between fluid flow velocity, ECP and the time for crack initiation in high temperature high purity water simulating both the BWR chemistry and the component flow velocity conditions. The range of flow velocities employed in the present study was 0.002 to 2 II/s. The studies indicate that while high flow velocities can increase ECP there is a delayed effect on crack initiation.
INTRODUCTION Constant extension rate tensile (CERT) tests are traditionally used to understand the influence of material composition, heat treatment, temperature and environmental variables on stress corrosion crack (SCC) initiation. However, fluid flow rate has not been investigated as a parameter that could affect SCC initiation until recently. The earliest published work on the influence of flow rate on the corrosion rates of stainless steel and low alloy steel in oxygenated high temperature water has been reported by Nesmeyanova et al [1]. However, the influence of flow velocity on crack initiation has not been a subject of this latter study. More recently, a limited number of studies have been performed to explore the influence of fluid flow velocity on crack initiation [2-4]. These studies [2] have been performed with both low alloy steels and sensitized Type 304 stainless steel in high temperature water in the presence of 8 ppm oxygen. The fluid flow rates used were relatively low at 0.0086 to 11.4 crnfs. Nevertheless, these authors [2] report longer time to failure under high flow conditions indicating delayed initiation of the stress corrosion cracks. Because these experiments have been performed in highly oxygenated water, no correlation has been established between the influence of flow velocity on the electrochemical corrosion potential (ECP) and the time to failure of the tensile test specimens. The interrelationship between the fluid flow velocity, ECP and the time to failure is of great interest to the Boiling Water Reactor (BWR) applications primarily because of the previous observations that the ECP of Type 304 stainless steel increases with fluid flow velocity which consequently could increase its propensity to result in higher stress corrosion crack growth rates. Because of this latter supposition, which no longer is considered to be true [5,6], a question has been raised over the years, whether crack initiation is also affected by the local hydrodynamic conditions generated by varying fluid flow conditions.
This paper describes the work performed to understand the interrelationship between fluid flow velocity, ECP and the time for crack initiation in high temperature high purity water simulating both the BWR chemistry and the componen
Site News