The electrification of subsea control and production systems is essential to achieve the low carbon emission and high productivity targets that the offshore industry is facing now. But how to electrify these controls without compromising safety? This paper provides a comparison of the design strategies using mechanical springs or electric batteries to implement safety functions in control systems, considering as a case study the development of the new subsea electric actuator for small-bore valves SVA R2 from Bosch Rexroth. Traditionally, to control process valves with safety functions, hydraulic actuators have been applied with field-proven springs to bring the valve to a specific position (open or closed, depending on the application) in case of a safety-related failure such as a loss of power supply. However, the first electric subsea actuators developed with fail-safe springs turned out to be too large, heavy, inefficient, and costly due to their complex electro-mechanic system for broad adoption by the subsea industry. Thus, new electric subsea actuators [2] were developed using electric batteries to reduce overall size, but this added new risks: now the safety control has to detect a dangerous situation by itself and actively drive the system to the safe position. But, at the OTC 2021, a new electric subsea actuator for small bore valves was presented which achieves Safety Integrity Level SIL 3 using field-proven springs as compact as a hydraulic actuator (OTC-31083-MS) [17]. Following the functional safety methodology acc. to the IEC 61508, IEC 61511 and ISO 13849, this work provides a comparison between a control architecture with mechanical springs and another with electric batteries, considering the whole product life cycle (design, manufacture, installation, commissioning, and operation). An evaluation of the failure modes and failure mechanisms of existing subsea equipment, from field data available in the OREDA@Cloud, gives a proper assessment of the risks associated with implementing the new functional safety architecture. Costs of engineering, production and operation are taken into account to find out the most technical and economically feasible solution. This case study is a reference for the design and qualification of new subsea electric actuators with functional safety requirements using mechanical springs or electric batteries. It provides technical guidelines and risk assessment for designers and users of subsea control systems such as machine builders, EPCI companies, operators, service providers or certification bodies. If electrification is a prerequisite for a low carbon future, safety is a prerequisite for the adoption of all-electric control systems. This paper shows how to electrify subsea production and process systems by using mechanical springs or electric batteries without compromising safety.
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.
This paper presents the development and qualification of a novel Subsea Electric Actuator, especially designed for rotary small-bore valves. One of the main challenges was to design an electric actuator which is as compact as the existing hydraulic actuators, but able to provide a fail-safe mechanism by field-proven springs and full integration of all necessary components, including the electric drive and controls, inside of a compact enclosure. Furthermore, the design team had to considerably reduce its power consumption and weight in comparison to existing solutions. Finally, the system was designed for lean manufacturing, allowing considerable cost-saving benefits for all the partners due to extensive standardization work. The paper shows the engineering requirements obtained by interviewing different users, the design methodology applied and the qualification of the new system up to TRL 3 with Digital Twin and Rapid Prototyping. Finally, an outlook is presented with the planned TRL 4 and TRL 5 qualification tests and a summary of the technical and economic benefits for the users of this novel Subsea Valve Actuator.
The offshore energy industry relies on heavy-duty equipment to execute complex operations in harsh environments over a long time with remote control and limited maintenance. But how is this equipment powered and controlled to enable reliable and safe operation? Hydraulics have been often used because of the high robustness and safety; but hydraulics also include complex installation, low energy-efficiency and potential environmental risks. On the flipside, subsea electrification seems cost-intensive due to its high power and large batteries needed. This paper explains how a novel subsea electric actuator technology enables a sustainable energy transition combining the ability to move high forces while being cost effective. For CO2 storage, it enables an all-electric subsea tree, comparable in price to a traditional hydraulic tree, but without demanding expensive umbilicals or topside hydraulic power units. In applications requiring long control distances, such as oil & gas fields with long subsea tiebacks or deepsea mining, it allows safe and reliable operation with minimal electric power consumption, capable of precisely handling even high loads.
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