Using Offshore Pile Upending Tool to Control the Lifting of Immense Monopiles

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"Using CompactRIO and LabVIEW for the pile upending tool allowed us to rapidly and cost effectively develop a control system that we can easily update and improve for use on future wind farm installations."

- Craig Waddell, Houlder Ltd

The Challenge:
Houlder needed to develop a reliable, fast, and safe system to lift 855 tonne wind turbine steel foundation monopiles from the horizontal position on the deck of the installation vessel to vertical at the target installation position on the seabed in preparation for pile driving.

The Solution:
Designing a wirelessly controlled crane attachment using CompactRIO and LabVIEW that engages with a monopile, upends it, suspends it, and provides precision positioning, and then disconnects remotely and parks once the pile is in position and restrained.

Craig Waddell - Houlder Ltd

About Houlder

Houlder is an independent provider of design, engineering services, and equipment in a wide range of marine markets including offshore renewables, oil and gas, defence, and liquefied natural gas. The company delivers turnkey solutions to relevant problems in these sectors. Our engineers, naval architects, designers, and project managers do more than offer their expertise to the market. They combine forces to bring clarity to industry challenges and present well considered solutions. They also balance intellect, experience, and practical knowledge.

Project Background

Our client required two pile upending tools for operation on board the heavy-lift jack-up installation vessels MPI Discovery and Swire Blue Ocean Pacific Orca. The tool lifts monopiles that will be driven into the seabed to act as the pylon for wind turbine generators. We won the project due to a combination of our experience of innovation in the sector, project success rate, reliability, competitive pricing, and proven ability to find solutions to complex engineering problems.

Project Challenges

  • Our objective was to enable pile upending using a heavy lift crane. We identified a number of engineering challenges to overcome, including:
  • Controlling the upending tool cylinders (a locking cylinder and a pivoting cylinder)
  • Overcoming major safety implications in the event of upending tool failure
  • Powering wireless remote communication between operator and upending tool
  • Monitoring of upending tool parameters
  • Upending tool control system to comply with DNV GL regulation 2.2 “Lifting appliances” and EN ISO 13849-2 “Safety of machinery -- Safety-related parts of control systems”

Addressing these issues would result in a faster, cost effective, safer, and more reliable monopile installation process.

Project General Solution

We developed an upending tool that is self-powered during operation. We achieved this by using Absorbent Glass Mat (AGM) batteries for the control system and hydraulic accumulators and a charging pump to provide hydraulic power for the upending tool actuators. The tool includes two hydraulic actuators, a pivot cylinder, and a locking cylinder. The pivot cylinder facilitates the tool rotation and locking mechanism. This allows it to engage the monopile whilst being positioned horizontally on the vessel deck. The locking cylinder links mechanically to two locking latches. We can use it to lock the upending tool in place on the monopile upper flange.

Figure 2. Rotated Tool, Ready for Locking Cylinder to Extend and Secure Pile

Figure 3. Upending Tool Parts: a) Crane Attachment, b) Flange Hook, c) Control Cabin, d) Hydraulic Accumulators, e) Rotating Cylinder, f) Hydraulic Reservoir, g) Hydraulic Pump, h) Locking Cylinder  

During pile upending, the pivot cylinder goes into float mode so the tool can pivot freely and the pile can reach the vertical (Figure 4ii–iii). Once the pile is vertical, we lift it to the installation position and restrain it using Houlder’s gripper arm (Figure 4v). We can then lower the monopile to the seabed, ready to be hammered. As the pile upending tool links wirelessly to a controller, the operator can remotely retract the latching cylinder and disengage the tool from the pile (Figure 4vii).

Figure 4. Upending Tool Operational Procedure: i) Upending Tool Engages Pile, ii) Rotating Cylinder in Float Mode,  Crane Lifts the Pile, iii) Pile Upended, iv) Pile Moved to Desired Location, v) Pile Positioned With Gripper Arm, vi) When Pile Hits Seabed, Upending Tool Disengages, vii) Upending Tool Removed, Ready for Pile Hammering

LabVIEW and CompactRIO

We used the CompactRIO platform to overcome many of the engineering challenges we faced. The CompactRIO system controls the hydraulic valves and the hydraulic power supply. It also monitors the position of the cylinders, accumulator pressure, angle of the tool, reservoir level, and battery level. Additionally, the system controls the warning signals and relays the information to the operator through a radio transmitter/receiver module. It also helps implement safety standards. For instance, when there is a communication error in the radio signal, the CompactRIO system ensures all the outputs fail safely. Similarly, the system sends a watchdog signal to a safety relay. The tool fails safely in the case of a power outage. The following diagram shows how the CompactRIO interfaces with the other elements of the upending tool design.

Figure 5. Control System Diagram for the Upending Tool

Early in the design process, we considered several alternative solutions to the CompactRIO. The first solution we considered was using relay logic. However, this had limited functionality and scope for future development. Alternatively, we reviewed using a PLC controller or embedded hardware, but they lacked significant advantages compared to developing a solution with LabVIEW and CompactRIO. The LabVIEW development environment significantly improves the design process due to:

  • Modular software design leads to seamless integration between software written by multiple developers.
  • Intuitive debugging makes it is easier and faster to pinpoint errors when writing the software.
  • Easy to reuse code by leveraging subVIs and libraries across multiple different projects, reducing the engineering time for future projects.
  • Numerous libraries allow fast and efficient programming by using pre-existing functions.
  • Faster programming with the drag-and-drop interface.
  • Easy to make a GUI.
  • Compatibility with other programming languages empowers developers to programme in specialised languages and use LabVIEW to interface them all together.
  • Native CompactRIO compatibility using prebuilt drivers
  • Standard service programme help us complete online training and reduce training costs. NI also has specialised support engineers to help resolve any technical issues with hardware or software.
  • Ideal for simulating hardware.

In addition to improving the design process, using CompactRIO alongside LabVIEW helped us add important features to the project that we could otherwise not implement:

  • We used the CompactRIO FPGA as a watchdog to monitor the safety relay.
  • We also used the FPGA to generate pulse width modulation (PWM) signals for the locking latch and pivot cylinder hydraulic control valves to provide smoother system operation.
  • We could remotely monitor certain parameters by using shared variables.
  • We created bespoke interfaces for different clearance levels, for example, operator, service engineer, software engineer, and diagnostics checks.

We used the following easily configurable and interchangeable modules with the CompactRIO chassis (cRIO-9075), increasing the scope for improvement:

  • NI-9425 digital input module
  • NI-9476 digital output modul
  • NI-9203 analogue input module
  • NI-9263 analogue output module

An Independent Solution

The main advantage of our upending tool compared to previous solutions is its independence from external power sources during operation. This drastically reduces upending time as we do not need to manage, connect, or disconnect services for every monopile. This decreases the downtime of the heavy lift crane. Instead the tool is parked and plugged into the deck’s power supply to charge the hydraulic accumulators and battery while the crane carries out other operations (hammering, for instance). This solution is simpler to operate and more independent thanks to the radio control unit replacing signal lines. Using wireless data transfer, however, is less robust than physically connected cables. The CompactRIO ensures that in the event of a communication error there are no unexpected failures.

Figure 6. Handheld Controller

Project Updates

We have installed all 116 monopiles in the wind farm, proving the reliability and robustness of both upending tools. We have also fitted the transition pieces and expect the wind farm to be fully operational in 2018. The upending tools can be used in future wind farm installations.

Author Information:
Craig Waddell
Houlder Ltd
22 Witney Way, Boldon Business Park,Tyne & Wear

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