Building blocks for an electric subsea future

John Bradbury

May 1, 2015

Electronic subsea control modules are being designed to go deeper – and be smaller and lighter. John Bradbury takes a look.

Aker Vectus control system pulled from Larssen MCE DD 20154 presentation; NB low resolution.  Image from Aker Solutions.

New generation subsea control systems being rolled out to the offshore industry could one day become the key building blocks for both new and brownfield developments.

That is the proud assertion of a senior engineering research manager who suggests his company’s new subsea electronic control modules and actuators could be capable of managing most deepwater subsea field scenarios.

But, these are not super-heavyweight, giant pieces of hardware. Rather, they are modular, small – modest even – and configurable.

Einar Winther Larssen, a research and design manager within Aker Solutions’ corporate technology organization, describes these new units as “Next generation subsea electronics and actuation platforms,” which will have wide-ranging applications. “I think these types of systems will be suitable for all [subsea] systems in the future,” Larssen says.

Aker Solutions’s offering is based on its Vectus 6.0 subsea control unit released in September 2014, and its El-drive actuator system.

Vectus comes with an electronics module, auxiliary and power supply modules, while the electronic actuator is also offered in a small, modular package. Both are designed for deepwater.

Larssen foresees deployment of these new units in a variety of subsea scenarios: in production and workover systems, in subsea pumping and compression applications, and within the “subsea factory” concept Aker Solutions has been promoting across the industry.

The hardware can be used without performing too many mechanical changes Larssen says, using configurable software that is available in stackable parts, describing the technology at the Marine Construction Europe - Deepwater Development conference in London in March.

Explaining the virtues of Vectus controls, Larssen said they represent a next-generation subsea control system, offering a number of benefits: Less deployment effort and risk, through planning and configuration tools, and modular architecture.

Enhanced operational features include subsea electronics module (SEM) and maintenance, and advanced condition monitoring systems. Improved performance is provided, Larssen says, through better processing power, interface capacity, and networking capabilities.

Aker’s new electronic drive unit is 85cm-high, and can be mounted either horizontally or vertically. The unit has an API class 4 standard interface, modular design, and it can be installed in up to 4000m (13,120ft) water depth, with up to 2700 Nm (Newton metres of torque) maximum torque available. A subsea gearbox on the unit has an API rating from class 7 to class 4, suitable for ball valves, from 2-20in; in a 7in and 3/8in latched configuration for use on Xmas trees; in HIPPS (high integrity pressure protection systems) applications, and it can be deployed as a linear process actuator.

Other potential applications are suggested for electronic manifolds in double expanding branch valves, and in electronic chokes.

Single side low-voltage and dual redundant high-voltage actuators have been developed. Both feature communications and motor control processors, and motor drivers.

Fitted with dual motor and gear oil systems, the drivers are made using a high-volume production method – to ensure component standardisation. They feature thermal management through direct convection to sea water.

Gearboxes have been tested at up to 1800 Nm with continuous operations, and feature a tailor-made motor unit with life time testing successfully completed. The drive unit is designed for predictable fabrication and qualification units have been built on a production line with fully traceable components. A contract manufacturer has been used for electro-mechanical component production to secure knowledge retention in a cyclic market.

Turning to the economics of the units, a study looking at the performance of a medium-sized subsea production system using electric branch valves and chokes indicated potential lifetime savings of US$25 million through less hydraulic fluid consumption, less power consumption, and faster start up times — meaning less lost production time from a well.

Also the electrical system offers the potential for faster failure detection through enhanced monitoring, Larssen explains.

During 2012, Larssen said Aker Solutions undertook a subsea equipment mapping exercise and determined that valves and drivers were among the most important components in any system. He noted: “Leakage rates for new subsea valves are quite high.”

To prove these new systems, Aker Solutions carried out shock and vibration testing of the electronics, with three stages used before a qualification build. Finite element analysis (FEA) was also used to examine and modify the design.

Test results

Sub-module qualification tests have been conducted for the gearbox and motor unit, systems testing has been undertaken, and a system pre-qualification test. Formal system qualification testing has also been performed, providing increased confidence in reliability and reduced risk for the unit.

Future applications for these units are foreseen in HIPPS and Xmas tree actuators: So far, a proof of concept system has been built and tested on a 7in and 3/8in valve. Aker Solutions already has its I-Con subsea control system, and SubseaWeb — its subsea architecture concept offering a means of monitoring and controlling subsea systems, using OPC (open process control) connectivity, and transmission control protocol and internet protocol systems.

With the new hardware, however, the company believes it has the enablers for a fully electronic subsea system.