Abrasive Water-Jet and Diamond Wire-Cutting Technologies Used in the Removal of Marine Structures
Authors: Brandon John W. , Ramsey Bob , Macfarlane James W. , Dearman David 
Published: October 2008

The paper provides information describing the current state of abrasive water-jet and diamond wire cutting technologies presently in use for platform decommissioning and general marine construction activities, in conjunction with industry usage of these cutting technologies and future development requirements.

Introduction

The use of Abrasive Water-Jet Cutting in the removal of marine structures has achieved significant advancements in the past decade, with continuing advancements required as the demands and challenges of increased decommissioning activities present themselves.

Abrasive Water-Jet Cutting, with the introduction of Diamond Wire Cutting Systems, provide the marine contractor with reliable, safe, ecologically sound and economical methods to detach marine structures from their foundations for decommissioning and salvage operations.

The increasing number of deepwater structures reaching the end of their production lives, often in environmentally sensitive areas of the world, will require the use of such cutting systems on an even larger scale than at present today.

The majority of structures removed in recent years have been in water depths of less than 150 feet, but two or more structures in water depths exceeding 300 feet were abrasively cut and removed in the Gulf of Mexico in 1999. The number of such deeper water structures scheduled for removal is increasing.

This paper reviews the advantages of incorporating Abrasive Water-Jet and Diamond Wire cutting system techniques into the decommissioning plan so as to provide reliable and efficient removal methods for the contractor and operator.

The selection of a particular cutting system is often based upon accessibility to the foundation piles. Internal cutting by abrasive water-jet is the preferred method if below mudline access to the foundation pile is achievable with external cutting via abrasive water-jet or diamond wire as secondary alternatives. Large structures may require reduction into smaller sections of manageable lift weight, where both internal and external cuts of legs and bracing is performed to reduce the physical size of the structure for on site reefing. An important aspect in using abrasive water-jet or diamond wire cutting is the neat clean cut, allowing ease of pile removal from the platform leg, thereby reducing lift weight and assisting in re-installation and refurbishment activities.

Irrespective of the method selected, diligent planning and execution by the cutting service supplier and the contractor are essential to successful operations.

The equipment and operational methods involved with abrasive water-jet cutting operations and diamond wire cutting operations are addressed by this paper.

Abrasive Water-Jet Cutting System

The Abrasive Water-Jet Cutting technology, long used in industrial and manufacturing processes, has been adapted to meet the challenges of the subsea marine working environment. The Abrasive Water-Jet Systems consists of a the cutting tool or manipulator to control the positioning and movement of the nozzle, the abrasive mixing or dispensing unit, high pressure water pump(s) and supporting hydraulic power unit, control panels and cut monitoring systems.

The Abrasive Water-Jet Cutting process can be used on vertical or batted jacket legs and piles, whether below mudline, nid-water, or above the mudlinee.