This review paper addresses the role of the Remotely Operated Vehicle (ROV) during Installation, Maintenance and Repair of Offshore Structures. Tasks encountered by the ROV are discussed along with problem areas where some research and development is still required.- Two areas specifically discussed are the removal of marine growth for weld inspection and the bulk removal of marine growth in order to reduce structural weight and drag loadings.
The ROV is now well established as a viable tool for supporting drilling operation and conducting route and pipeline surveys. Personnel associated with offshore structure installation, repair and maintenance have been slower to accept the ROV. In many cases this is simply due to the unawareness of an individual as to the capability. It can also rightly be argued that the ROV is still very limited in some roles. It is the intention of this paper to highlight the tasks which an ROV can complete successfully and illustrate areas where the ROV is limited and the reasons why. Further research and development must be encouraged by the oil companies and research groups to overcome these shortcomings if the ROV is to be utilized to cut costs associated with installation, repair and maintenance of offshore structures. With successful research in the areas discussed another hurdle will be overcome in the history of the ROV resulting in significant cost savings to the end users ie the offshore structure owners and operators.
When designing any offshore structure, the designer takes into consideration many factors. These include: method of installation, water depth (beyond diving range?) maintenance routines, repair techniques, expected structural life, etc. Likewise the ROV operator must consider which tasks have to be completed and choose the ROV best suited to the work. He can choose from his armory of:
Eyeball Class ROV's
Inspection Class ROV's
Workhorse Class ROV's
Eyeball Class: A small ROV which has limited capability but can adequately take still and video pictures. Some eyeballs can carry miniature manipulators and tools
Inspection Class: A slightly larger ROV with improved but limited manipulator capability. It also as a limited payload of 50 to 100 lbs.
Workhorse Class: A high powered ROV which can carry a payload in excess of 200 1bs and usually carries two full sized manipulators. It has the capability of interfacing many items of equipment, some of which can be custom designed for the application. This class is able to carry out the majority of the work tasks encountered offshore.
The offshore installation phase starts with the tow-out of the structure to the chosen site. Normal practice is to pre-lay a transponder network to allow accurate positioning of the structure relative to the seabed target area. The barge moves in and at this point the ROV can begin working.