The addition of auxiliary work packages, or tooling skids, to ROVs has provided the next step in logical system integration. There is no vehicle that can do all things—contrary to the goal of early ROV developers who failed miserably in trying to produce such beasties. The removable skid allows the primary vehicle to be reconfigurable for various operations, along with being a simpler system when only performing visual inspection or other less complex tasks. Vehicles have been designed to allow the tooling skid to be as simple as an auxiliary hydraulic power supply or as complex as an underwater trencher. The primary consideration is that the new skid must follow the same system integration considerations that the ROV had to follow earlier. The interface between the ROV and the skid must be taken into consideration when the ROV is developed, and the interface between the skid and the system it will work with is just as critical. An example of a removable auxiliary work package is shown in the following figure.

Auxiliary work packages are often the most efficient and sometimes the only method of providing complex and varied intervention services for field operators and installation contractors. The interface requirements for the skid can be specified to ensure the skid can be fitted to and integrated with any work class ROV of opportunity.

With the capability of today’s large and powerful work class ROVs, it was only a matter of time until a system such as Sonsub International’s Diverless Flowline Connection System (DFCS) was developed. The DFCS was developed for the Amoco Liuhau 11-1 field for 13.5-in (34-cm) and 6-in (15-cm) flexible flowline tie-in operations. Some of the DFCS components, which dwarf the ROV, are shown in the photo to the left.

The DFRS is an excellent example of an ROV designed to perform a complex task without repeated trips back to the surface. Some of the key elements include:

• Two specially designed H-frames used to elevate the damaged pipeline from the seabed.
• Two water-inflatable pipeline support trestles inserted under the pipeline using ROV operated winches.
• Two Pipemate general-purpose universal pipeline tools, which can be interfaced to both the Tool Rotation Module and the Spool Docking Module.
• A pipeline replacement spool equipped with subsea buoyancy systems, to allow easy maneuvering of the spool by the ROV without dependence on surface lift.
• A Tool Rotation Module, which interfaces with the Pipemate and can be installed or removed subsea.
• The Pipe-end Preparation Tool (PPT) used to square the pipeline end and prepare it for the X-Loc seal, which was designed to allow installation, activation and seal testing by an ROV.
• A Pipeline Scissor Clamp used to remove debris.

• An ROV-deployed dredging system.

The figure on the right gives a perspective on the magnitude of the overall pipeline repair operation. The section of pipeline about to be inserted can be seen suspended by the underwater buoyancy system.

Subsea acquired tools–equipment or tooling that is placed on the seafloor ahead of time–reduces the number of trips to the surface that an ROV must make. These modules, or tools, which must also be designed with ROV interface in mind, may add several benefits to the ROV design. Without having to carry the tool or skid as part of the ROV system, the overall size, weight and complexity of that system can be reduced. If the tool is put in place while the ROV is operating, then an additional deployment system may be required.

Such examples underscore the complexity of the tasks that can be performed by an ROV offshore when the vehicle and tooling are integrated with the overall system design prior to installation.