Highly Sensitive Undersea Corrosion Monitoring System

Corrosion monitoring of undersea metallic structures has become one of the major challenges for the energy industry in the last two decades. Reliability, autonomy and high grade of accuracy is expected from a network of sensors distributed along subsea distribution grids and maintenance equipment. Despite the many techniques proposed by the scientific literature, the most extended techniques rely on the corrosion of low and ultra-low resistive elements with degradation rates similar to the metallic structures under monitoring, more commonly known as corrosion probes. However, the sensitivity of resistive sensors is limited to 25 mu m/yr in a time frame of 10 days which reduces the time response of the sensor to fast corrosion process. The most extended solution is to decrease the thickness of the resistive element. This solution increases the resolution by increasing the resistance of the resistive element and the influence of any material reduction due to corrosion. However, a decrease in thickness leads to shorter lifetimes and a higher influence of thermal variations. In this work, a highly sensitive resistive corrosion sensor and its performance are presented. The functionality of a highly sensitive mu Ohm-meter as a corrosion sensor and its uncertainty in corrosion rate are analyzed. Different sensor prototypes for laboratory and field deployment are described thoroughly and tested for calibration purposes in corrosive environments. The final prototype is connected to an autonomous platform and deployed in an offshore platform located at the Cantabrian Sea resulting in a corrosion rate sensitivity of similar to 1.1 mu m/yr in 4 hours time frame.