Pipeline and flowline lay operations involve a wide variety of water depths, soil conditions and anchor loading. For pipe lay start-up these key variables require careful assessment to ensure a successful anchorage during the lay away.
The simple diverless ROV friendly C-lok Initiation Pile Anchor takes advantage of the unique field proven LRS approved C-lok releasable connector. The C-lok connector allows full adjustment of the anchorage to suit any elevation or heading and is able to generate a wide range of resistance using the same pile.
For initiation piles (impact, vibrohammer or suction) the anchorage capacity is dependent on pile diameter, driven depth and soil strength. The pile resistance estimates are frequently based on incomplete geotechnical data. The key concern is inadequate lateral load capacity during the lay away operation and this leads to selection of a generous pile diameter and driven depth. This conservative approach increases the potential for pile refusal. With the anchorage at a fixed location on the pile a key concern is that pile refusal may occur with the anchorage elevation well above the mudline leading to instability during lay away.
The C-lok solution is fully adaptable and allows the installer to cater for a the widest range of resistances using the same pile and equipment. For the chosen pile diameter the engineer will select a target penetration based on the anticipated soil strength and the resistance required. Should the drive resistance be higher than anticipated and refusal occurs then the C-lok may be released, slipped down the pile and re-set at the mudline using a simple procedure . The pile and C-lok anchor may be used repeatedly for subsequent projects.
In the video a vibrohammer is used rather than the impact hammer as it avoids the need for a piling frame. Further options include incorporate an integral Internal Lifting Tool (ILT) and or swivel to assist upending and overboard the pile.
The C-lok system could equally be used with either impact or suction driving. The same ‘ fly to place’ tool is common for all piles.
Key features and advantages
- Ensures mudline anchorage and heading regardless of pile penetration
- Where pile is successfully driven to target depth no further operations required
- Disengagement and re-engagement , if required, in less than 15 minutes
- Pile is driven with C-lok connector attached
- Allows single pile, connector and tool to be used repeatedly for a wide range of application
- Allows simultaneous attachment of the layaway line
- Operates at any water depth
- C-lok Connector is qualification tested and is afield proven and LRS approved design
- Operated by a standard Workclass ROV (Class III) without specialist ROV tooling
- Uses simple field proven ‘fly to place’ tool (65 kg)
- Caters for full range of API pile sizes and fabrication tolerances
- Allows full 360 degree heading orientation
- Equally suitable for both vibrohammer, impact hammer or suction pile
- Fully caters for pile refusal
- Provides a full strength and fast anchor connection irrespective of water depth or soil type
- Includes dedicated CP anodes
- Allows repetitive use of the single hydraulic tool with a spare tool for redundancy
- All hydraulic equipment is recovered to surface using a simple vertical lift
Outline procedure (vibrohammer)
- Overboard the pile with the C-lok engaged at or near the top of the pile and together with the hold back wire lower to the seabed
- Allow pile to self penetrates.
- Activate the vibrohammer and drive to either full penetration or refusal.
If the pile achieves target penetration and is within heading tolerance then the layaway may commence immediately without any C-lok operation. Should the pile refuse or should the heading be out of tolerance then:
- Deploy the C-lok ‘fly to place’ hydraulic tool and engage in tool receptacle
- Release the C-lok and lower (under selfweight) to the mudline
- Adjust to the correct heading as necessary
- Engage C-lok
- Remove C-lok tool and recover to vessel
- Carry out pipelay operation
- Deploy and reengage vibrohammer to pile top
- Activate the vibrohammer and recover pile together with the attached C-lok back to the surface vessel
- On deck the tool is then used to disengage the C-lok allowing it to be moved to the next planned initiation pile position.