PLC network provides unified control

Silvertech has supplied a unified control system for the Burlington Resources unmanned Calder gas platform, installed in the Irish Sea.

Silvertech has supplied a unified control system for the Burlington Resources unmanned Calder gas platform, installed in the Irish Sea.

The process control system (PCS), emergency shutdown system (ESD) and fire and gas system (F and G), applications each use pairs of GE Fanuc Series 90T-30 PLCs linked on a dual redundant network, enabling full control from one HMI system.

This approach allowed rapid installation and commissioning and reduces running costs.

Silvertech is an approved GE Fanuc integration partner.

With offices in the UK, the Middle East, North and South America, the company specialises in control and safety system solutions for oil and gas extraction and production, the petrochemical and pharmaceutical industries, utility infrastructures and factory automation.

Offshore from NW England, under the eastern sector of the Irish Sea, lie rich gas fields.

A number of these fields are operated by the Centrica subsidiary, Hydrocarbon Resources, on behalf of Burlington Resources (Irish Sea).

The Rivers Fields development is currently underway based around the Calder production platform.

The project includes a new 4550km pipeline to carry the gas for onshore treatment at the new Rivers Terminal next to the existing North Morecambe Terminal at Barrow, in Cumbria.

Steve Elliott, Marketing Manager for Silvertech UK, explained how Silvertech won the contract.

"Burlington was very pleased with the successful operation of our system on the adjacent nearby Millom West platform, and asked us to produce a design using similar principles for the unmanned Calder platform".

Being an unmanned platform, it takes time for maintenance staff to reach the site.

Therefore it is essential that the entire hardware infrastructure is very reliable or productivity will suffer.

It was essential too that the system was designed for high availability, if one element fails then an alternative system element automatically switches in and carries on safely while the fault is repaired.

Redundancy is designed and built in to the system to ensure that no single failure causes production to stop.

Very often, process monitoring and control systems are designed and installed separately from the ESD and fire and gas safety systems.

This tends to make it difficult for the control and safety systems to "talk to" each other.

In this project the three systems were all designed together as a unified control system, using GE Fanuc Series 90-30 PLCs as controllers with a common communications protocol between systems.

The PCS controllers operate in a hot standby configuration, whereas the safety systems controllers operate in a duplex configuration with voting techniques to achieve SIL 2.

The fibre optic communications links to the South Morecambe Field platforms were duplicated.

The controllers are all linked on the same dual redundant network to HMI software running on PCs in the control room on the nearby Morecambe platform and North Morecambe Terminal where the system operators are located.

Thus there is only one "display" system, making it far easier and safer for the operators to cover both process control and safety systems.

Eliott explained some other benefits of the unified approach.

"By using the same hardware from the same supplier the training needed for operators and maintenance personnel is minimised.

The number of spare parts the engineers need to stock is also reduced", he explained.

Silvertech has gained experience with many of the major oil companies in over 200 installations around the world.

The company has developed a standard modular "function block" approach to the programming of the GE Fanuc Series 90-30 PLCs used to control the three main systems - process control (PCS), emergency shutdown (ESD) and fire and gas (F and G) detection.

The process control system uses dual Series 90-30s in "hot standby" mode - if one PLC controlling the system fails, the second automatically switches seamlessly into control.

This is handled by Silvertech developed function blocks.

A local HMI workstation is also attached to the network for occasional engineering use on the platform.

In the ESD and F and G detection systems, duplex Series 90-30 controllers operate independently of each other.

The function block approach has been developed by Silvertech to manage the voting strategies and system diagnostics to meet the requirements of IEC61508 SIL2.

A 1oo2D (2oo2 reverting to 1oo1 on fault detection) voting strategy is used for ESD and a 1oo2 voting strategy is for the F and G.

Adaptive voting ensures that any fault in one controller is automatically taken into account.

Silvertech's independent CASS (Conformity Assessment of Safety-related Systems) certification is as a safety-related system integrator for the provision of electrical/electronic and programmable safety related systems in many hazardous process industries.

The company uses dedicated safety products or standard controller products and adds additional functionality to meet the standard.

The CASS scheme is being introduced in phases and the first phase is for the certification of the organisation's functional safety capability assessment, often referred to as FSCA.

This relates to the methods and processes that the company follows in executing safety related projects, not to individual components, products or systems, or specific operations and maintenance systems.

According to Silvertech, the CASS certification means that there is no need for customers to carry out additional audits on the company's project management, project execution, system design and engineering activities, thus saving them both time and money.

According to a spokesman for the client, engaging Silvertech has brought major benefits in terms of cost, speed of installation and ongoing OPEX expenditure.

The unified control system provides the best engineering solution while minimising the capital expenditure.

It uses proven technical solutions in hardware and software, while relying on a commonality across all systems in terms of hardware platform, software, communications interfaces, HMI and documentation.

It has resulted in reduced operating costs and the lowest life cycle costs.

Elliott concluded: "Being an unmanned platform, high availability of the hardware is paramount to ensure continuity of gas production.

The six-sigma approach to quality adopted by GE Fanuc in its manufacturing and service processes ensures the necessary high quality standards.

This has added to our confidence in choosing GE Fanuc technology".

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