Decommissioning of Dolphins assisted by UHP water jet cutting remotely operated tool
Overview
A series of 9 Dolphin structures, located in the North West of Western Australia and adjacent to an iron ore offloading jetty. These Dolphins were no longer fit for purpose and were required to be decommissioned.
These structures were supported by piles laid out in a grid formation, making the interior piles difficult to access. The client was looking to achieve a safe, efficient and innovative solution to deal with the access limitations.
The decommissioning of the Dolphins consisted of removal of the steel platforms and diaphragms, and the supported sub-sea steel piles.
Scope
The project had the following specifications:
| Structure | Dolphin adjacent to wharf |
| Application Type | Decommissioning |
| Operating Environment | Subsea |
| Quantity | 102 Piles on 9 Dolphins |
| Cross Section | Circular hollow steel section |
| Diamter | 0.76m - 1.3m |
| Wall Thickness | 25mm - 32mm |
Solution
- Development of specialised rotating Ultra High Pressure (UHP) abrasive cutting tool producing pressure at 40,000 psi and a water flow of 40 L/m
- Deployment of remotely operated tool (ROT) internally to the pile, designed to self-support by pressing against internal pile walls
- Cutting location below the steel diaphragm structure, close to the water line
- Second cut on each pile at base to remove in a single lift
Benefits
- Deployment of ROT internally overcame access restrictions to interior piles
- Improvement in safety due to removal of divers and rope access personnel from the cutting location
- Reduced contractor footprint
- Improvement in speed and quality of cutting through state-of-the-art monitoring systems
- Internal cutting enabled piles to be cut at the water line, allowing each Dolphin structure to be removed in one lift
- Internal cutting reduced disturbance to marine habitat
