Cathodic Protection Monitoring-Bullwinkle

ABSTRACT The Bullwinkle Platform represents a major advance in the drilling and production of oil and gas, but also in cathodic protection design for deep ocean environments. A unique feature of the cathodic protection design is the cathodic protection monitoring (CPM) system which provides continuous assessment of the effectiveness of the cathodic protection system. In addition, the monitoring system provides information for future cathodic protection designs in deepwater. The CPM system monitors anode operating current and potential, cathode current density, and cathode potential at the -120, -1015 and -1190 ft elevations on the' jacket structure. The design, installation, and testing of the system are discussed as well as some of its performance. INTRODUCTION Cathodic protection (CP) is the principal means of corrosion control for submerged structures. The process typically involves the use of sacrificial anodes distributed throughout the structure to supply protective current to the steel members. Cathodic protection designs for a particular environment require the input of various design criteria. These include the anode operating potential and the required cathode current density for adequate protection. Traditionally, cathodic protection designs use design criteria which have been determined empirically, especially for shallow water systems. However, with the increasing depth of offshore CP systems, the need for optimum design criteria and consideration of the change of environmental parameters with depth is required. The cathodic protection system installed on the Bullwinkle jacket consists of approximately 6300 aluminum-zinc-mercury anodes totaling approximately 2400 net tons of anode material. These anodes are distributed throughout the structure depending on the current requirements for particular depth zones, and are attached by welding. The cathodic protection monitoring (CPM) system was designed and installed on the jacket structure prior to launch in order to provide a continuous assessment of the CP system and to provide information for future CP designs in deepwater. In addition, data obtained from the monitoring system can be used to help validate numerical modelling techniques used for evaluating and optimizing cathodic protection designs. BACKGROUND Fixed monitoring of offshore cathodic protection systems can vary from simply the installation of reference electrodes throughout the structure for potential measurements, to an elaborate array of electronic sensors for measuring anode current and cathode current density. The installation of reference electrodes for potential measurements has had good success, however, the electronic sensors for current and current density measurements have had very limited success, especially after experiencing the forces associated with platform launch and pile driving. In addition, these sensors typically require input power which increases cabling requirements. Data acquisition systems associated with CP monitoring systems have taken several forms. Some systems simply have test points for manually monitoring data while others employ a test panel with data displays installed in the platform control room. Some monitoring systems have been equipped with strip chart recorders or computerized devices for recording data, however, they are typically installed after the platform launch (1).