Effects of Potential on the Electrical Conductivity of a Solution within a Crevice of Stainless Steel in High-Temperature Water

Abstract

This study investigates the effects of potential [electrochemical corrosion potential (ECP)] on the water chemistry within a crevice of stainless steel in 288°C water containing Cl− major anionic impurities. In situ measurements of the electrical conductivity of a solution within a 15-μm-gap crevice (σcrev) were conducted using small sensors installed at different crevice depths. The ECP at the external surface of the crevice specimen (Eext) was controlled by the dissolved oxygen concentration in the bulk water. An increase in Eext from approximately −0.49 VSHE (vs. a standard hydrogen electrode at 288°C) to −0.12 V resulted in an increase in σcrev from 12 μS/cm to 160.3 μS/cm at 21 mm from the crevice mouth. Finite element model analysis taking into account the electrochemical reaction quantitatively reproduced this behavior. Cl− was considered to be the major anionic species transported into the crevice in this potential range. A further increase in Eext up to 0.3 V led to a decline in σcrev. An increase in the flux of oxidizing (O2 and and alkalizing species (OH−) into the crevice was considered the cause of this behavior.