An Electro-Mechanical Actuator with Hydrostatic Drive for Subsea Trees to Reduce CAPEX and OPEX with Higher Reliability and Safety Levels

Abstract

Although subsea production is already a mature technology, a high engineering effort is currently needed to "industrialize" the applied systems for cost optimization. The drive system applied for the actuation of subsea valves in trees and manifolds reflects exactly this challenge: how to reduce manufacturing costs by increasing safety and availability? The first approach was based on hydraulic cylinders, which were operated by electric-piloted hydraulic subsea valves with topside Hydraulic Power Units. This system is very robust, but leads to very cost-intensive umbilicals to provide the needed fluid power and prevent environmental damages due to leakage of hydraulic fluid into the sea. To reduce environmental pollution, complexity and costs; all-electric solutions were developed. However, hydraulic actuators continue to be used because of important benefits such as high power-density, lower friction and integration of a mechanical override. Is it possible to create a hybrid solution which can combine the benefits of both technologies? In other industries, this dilemma was solved by integrating the hydraulic cylinder into a self-contained electro-hydraulic servo axis, which applies pumps driven by variable-speed motors for accurate positioning. This paper presents the results of the development of an electro-mechanical actuator with hydrostatic drive to operate gate valves of subsea trees and manifolds. The main achievements, demonstrated by simulation and testing using a 2″ valve actuator at 3,000 m water depth, are: Cost-effective modular design using industrial componentsEnvironmentally friendly set upLower power consumptionHigh availability and condition monitoringFunctional safety able to achieve SIL 3Integration of mechanical overrideAdvanced Electric Controls with Industry 4.0 connectivity This system is an important step to close the technology gap to accomplish the all-subsea factory. Especially, it can be applied in cases where the hydraulic actuators are still preferred instead of all-electric actuators.

An All-Electric Gate Valve Actuator for Subsea Production Control Systems, Part A: Prototype and Test

“…The all-electric subsea production control system (AE), a leading-edge and breakthrough technology, was proposed and developed [6], which was driven completely by electric power. The AE system became a development direction due to its advantages in the areas of operation and maintenance costs, control performance, and environmental friendliness [7][8][9][10].…”