Sensor Implementation For Saltwater Ingress Detection In Deep Sea Actuators

Subsea oil and gas Xmas trees are critical components of offshore drilling and production systems. These structures are installed on the seabed and serve as connectors between subsea wells and production facilities on the surface. Xmas trees control the flow of oil and gas from the well, allowing operators to regulate production and implement safety measures. They typically consist of actuators, valves, chokes, sensors and other equipment to manage pressure and ensure the efficient extraction of hydrocarbons from beneath the ocean floor. These actuators can be either hydraulic, electro-mechanic or all- electric. A reliable design of the actuators is mandatory as in the event of an emergency a safety-relevant function needs to be performed to prevent major environmental damage. All these actuators are permanently exposed to the surrounding sea water and are therefore at risk of saltwater intrusion, which can result in accelerated degradation. Hence the detection of saltwater ingress enables better diagnostics, providing for increased safety and higher availability due to predictive maintenance. Within this paper an innovative sensor design for the in-situ detection of saltwater ingress in a subsea all-electric actuator is proposed. In these actuators, the motor and gearbox are installed into an oil-filled chamber, which adapts to the ambient pressure. This saltwater ingress leads to the formation of saltwater in oil emulsion. Throughout the research two sensor geometries have been tested with different excitation methods to detect saltwater within such an emulsion. The testing was performed using a Design of Experiments. With respect to the relevant environmental parameters in the deep sea, measurements from 0 °C up to 80°C were included in the experimental design and depths of ~3000 m have been simulated by testing with pressures of up to 330 bar. In addition, the vulnerability of the measurement principle to electromagnetic interference was tested. The information obtained by this sensor can be used for advanced diagnosis of the health state of the entire system. Therefore, through knowledge gathered by degradation tests of e.g., the motor windings in electric actuators, the measurement of saltwater concentration can be used for the determination of the remaining useful lifetime or as an indicator for optimal maintenance. The proposed sensor design provides, in manufacturing and implementation, a low-cost and easy-to-use detection method for saltwater ingress in subsea actuators.