Engineering Task Plan for Fourth Generation Hanford Corrosion Monitoring System

Abstract

This Engineering Task Plan (ETP) describes the activities associated with the installation of cabinets containing corrosion monitoring equipment on tanks 241-AN-102 and 241-AN-107. The new cabinets (one per tank) will be installed adjacent to existing corrosion probes already installed in riser WST-RISER-016 on both tanks. The corrosion monitoring equipment to be installed utilizes the technique of electrochemical noise (EN) for monitoring waste tank corrosion. Typically, EN consists of low frequency (4 Hz) and small amplitude signals that are spontaneously generated by electrochemical reactions occurring at corroding or other surfaces. EN analysis is well suited for monitoring and identifying the onset of localized corrosion, and for measuring uniform corrosion rates. A typical EN based corrosion-monitoring system measures instantaneous fluctuations in corrosion current and potential between three nominally identical electrodes of the material of interest immersed in the environment of interest. Time-dependent fluctuations in corrosion current are described by electrochemical current noise, and time-dependent fluctuations of corrosion potential are described by electrochemical noise. The corrosion monitoring systems are designed to detect the onset of localized corrosion phenomena if tank conditions should change to allow these phenomena to occur. In addition to the EN technique, the systems also facilitate the use of the Linear Polarization Resistance (LPR) technique to collect uniform corrosion rate information. LPR measures the linearity at the origin of the polarization curve for overvoltages up to a few millivolts away from the rest potential or natural corrosion potential. The slope of the current vs. voltage plot gives information on uniform corrosion rates.