Developing a Subsea Flow Line Connection Tool Controlled by CompactRIO

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"CompactRIO hardware and the LabVIEW Real-Time and LabVIEW FPGA modules helped us create a versatile system. The CompactRIO and LabVIEW platform is well-suited for critical applications, and the FPGA functionality is unique."

- Bjørn Endressen, SubC Solutions

The Challenge:
Developing a universal connection tool (UCT) control system that connects flow lines to subsea oil field structures and deploying it on the ocean floor within two months.

The Solution:
Using NI CompactRIO hardware and NI LabVIEW system design software to quickly develop and test a control system that operates at depths of up to 300 m and is remotely controlled from an offshore vessel

Author(s):
Bjørn Endressen - SubC Solutions

SubC Solutions, an engineering company established in 2007, specializes in subsea oil and gas industry projects. A creative, multidiscipline group of engineers located in Bergen, Drammen, Oslo, and Trondheim, Norway, we offer engineering, consulting, and subsea task control system development. Recently, we received a request from Statoil to build a qualified control system to connect and disconnect pipelines at the bottom of the North Sea, at depths of up to 300 m.

Oil Well Control and Maintenance

A UCT is a dedicated structure to connect and disconnect an Xmas tree (XMT) valve to flow lines. An XMT is an ocean-floor system connected between the well and flow lines that carry chemicals and product (oil and gas). XMT functions include providing a safety barrier, injecting chemicals into the well, controlling downhole valves, and regulating pressure. Multiple flow lines are connected to the XMT. The UCT is an expensive tool developed to disconnect and connect the flow lines so that the XMT can be recuperated for maintenance. A UCT typically weighs around 20 metric tons.

A UCT uses electrohydraulic actuators to lock and unlock bolts from the flow lines to the XMT. In this particular situation, the system needed maintenance, but the operator discovered that the control system was not working properly and parts were obsolete. In order to keep using the UCT, Statoil planned to develop a new subsea cutting tool to cut the flow lines to the XMT; however, existing cutting tools did not meet qualifications. The only option was to quickly develop a new control system to lock and unlock the bolts.

UCT Upgrade

The UCT upgrade process presented specific challenges, including a short delivery time of two months. The UCT, which contains 16 directional control valves with high electric power demands, connects to the control platform with a 1 km umbilical cable with a limited cross section. The control system had to handle harsh shocks and vibrations and remain easy for offshore vessel personnel to operate.

We developed an upgrade solution based on several qualified components we had used in previous projects. The subsea hardware installation included a subsea rack containing power supplies and filters with which to pass power to and from the UTC; a CPS power line modem for a serial communication system that uses the power line for data transmission; and CompactRIO. This was the first time we used CompactRIO for a subsea project.

CompactRIO is the heart of the rugged system that operates reliably in harsh environments. We selected it for many reasons, including the following:

  • High temperature range, vibration, and shock specifications
  • Small size to fit in the existing tubing
  • Flexible I/O module range

We selected an NI cRIO-9012 real-time controller, a 4-slot NI cRIO-9111 reconfigurable chassis, an NI 9478 digital output module, and an NI 9208 analog input module. Analog inputs read the valve pressure and proximity switches, and the digital outputs control valve position, which actuates the latches, positions the jackscrew motor, and engages the motor to unlock the flow lines.

Because most of the CompactRIO application functionality happens in the field-programmable gate array (FPGA), it ensures deterministic performance and the highest safety level. The FPGA also controls the valves. For the processor, we developed a typical two-loop CompactRIO application with a critical and noncritical loop. The critical loop ensures and guards safety interlocks and communicates with the FPGA. The noncritical loop uses a Modbus server to communicate with the topside (offshore vessel) application. LabVIEW and a powerful VxWorks real-time OS make it easy to configure critical and noncritical loop priorities. For UTC communication, the Modbus protocol uses CPS modems.

On the topside (at the offshore vessel), we used an in-house-developed SubC Solutions control rack with CPS modems and power supplies, and a laptop running the LabVIEW application. Developing the operator interface with LabVIEW gave us a pleasing, easy-to-read interface compared to those developed with standard programming languages. With LabVIEW, it was very fast and easy to implement and test our system.

On-Time, On-Budget Solution

NI products helped us deliver a solution on time and on budget. Offshore operators have indicated that the system is user-friendly and quite easy to operate.

Designing electronics and control hardware can be expensive, but SubC Solutions controls costs by using the latest off-the-shelf hardware from companies such as NI. Large companies typically have more R&D resources, which frees us up to focus on our specific design needs.

CompactRIO hardware and the LabVIEW Real-Time and LabVIEW FPGA modules helped us create a versatile system. The CompactRIO and LabVIEW platform is well-suited for critical applications, and the FPGA functionality is unique.

Author Information:
Bjørn Endressen
SubC Solutions
Norway
Tel: (+47) 47 90 22 00
mail@subc.no

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