Diverless hot taps available at 10,000 ft

March 1, 2001
Oceaneering has teamed up with Oil States, TD Williamson, and Williams to develop a system for tying in new lines to existing deepwater carrier pipelines without interrupting flow.

Oceaneering has teamed up with Oil States, TD Williamson, and Williams to develop a system for tying in new lines to existing deepwater carrier pipelines without interrupting flow. The Deep Tap system is designed to tap carrier pipelines between 6 in. and 20 in. in diameter. The system requires a 250 ft or greater ROV support vessel with a light crane and an A-frame, as well as a 100 hp ROV or greater.

The process begins with an ROV survey of the section of pipeline and seabed under consideration. The survey uses a metrology tool to determine the bow, sag, or ovality of the carrier pipe. This ensures it is compatible with the Deep Tap system. Then a pipeline lift frame is lowered over the carrier pipe and onto the seabed. The frame has retractable mud mats that are deployed to support it in soft seabed conditions.

Once the frame is in place, it latches onto the pipe and lifts it off the seabed. A 20-in. pipe can be lifted as much as 60-in. off the seabed. The same process is repeated further down the line so that a section of pipe is raised between the two frames. The length of this section is calculated and controlled to remain within API 5L guidelines for bow, sag, and ovality. Raising the section of pipe eliminates the need for dredging and puts the pipe in clearer water where there is less chance of mud or silt interfering with the tapping project.

Once the pipe is raised, the fitting orientation frame is lowered over it. The frame is guided onto preinstalled mud mats and landed on its four leveling legs. With the frame in place and the pipeline raised into position, the tool control module (TCM) is mated to the frame. The TCM provides many of the functions of an ROV including hydraulic power, control functions, and feedback to the surface. The TCM is capable of 40 hydraulic and 48 electric connections and allows technicians on the surface to perform the hot tap operations by remote control.

With the TCM engaged, the pipeline is grabbed and lifted into the open fitting on the frame. The frame is used to transport the deep tap fitting (DTF) to the sea floor, align the fitting to the pipeline, and rotate the fitting to the vertical position. The frame also supports the tapping tool and will support the weight of the fitting left on the pipeline after the project is completed.

Working from the surface via the TCM, a technician closes the fitting around the pipe. The studs are run, the lock plate engaged, and the studs tensioned. Once the fitting is engaged and rotated, grips and seals are set. With a seal made, the TCM is disengaged from its junction plate and returned to the surface. Topside, the TCM is connected to the hot tap machine running frame.

Then the frame and TCM are launched from the vessel and soft-landed on the tap fittings at the top of the frame. A collet connector is used to make a connection with the tap fitting, which has been rotated to vertical. Once the connection is made, the fitting and tap machine are lowered back onto the seabed. This prevents the weight of the machine, frame, and fitting from damaging the pipeline.

With the pipeline lowered and the seal made a Cameron all-weld ball valve is rotated open and the inside of the fitting flushed of seawater. Then the tap tool drills into the carrier pipe. Once the tap is completed, the tool and coupon are retracted, the ball valve is closed, and the collet connection is released. The hot tap machine, running frame, and TMC are retrieved to the surface and the tap is completed with the installation of a rigid jumper spool.

Concept for cost-effective subsea intervention

On remote locations, providing a full-time remotely operated vehicle (ROV) support vessel can be expensive. Many companies are working toward the development of a hybrid system that would eliminate the need for such a vessel. Mentor Subsea, a subsidiary of J. Ray McDermott has taken an unusual approach.

The company has teamed with International Submarine Engineering Ltd. (ISE), to develop an unmanned semisubmersible system for deploying ROVs. This means a field could use conventional ROV systems, deployed from a remotely controlled semisubmersible vessel. The vessel could be stored and launched from a platform such as a floating production, storage, and offloading vessel (FPSO), a tension leg platform (TLP), or Spar producer in the same manner as a lifeboat. The system draws power from diesel generators and can transport the ROV system as much as 15 miles from the host platform.

The system is called SAILARStrademark, an acronym for semi-autonomous intervention, launch, and recovery system. It can transmit high bandwidth data back to the platform and is guided by remote control.

Once on station, the system will remain dynamically positioned as the ROV is deployed on an umbilical from below the vessel. The system is designed to work with a variety of ROV tether management systems and workclass ROVs. Once deployed, the ROV system functions as it would if launched from a surface vessel. The ROV draws power from one of two diesel generators fitted in the floating unit, so it can perform a full set of workclass functions. Once the activities are complete, the ROV would return to its cage, the umbilical would be spooled up, and the unit would return to the host platform for recovery and refueling.

The hybrid autonomous underwater vehicle/remote operated vehicle (AUV/ROV) can operate and provide power for 50-150 hp workclass ROVs. The unit is designed to operate in significant wave height (Sea State 6). Its communications equipment and the exhaust for the generators are located on a mast, which extends from the rear of the vessel to above the surface.

Compared to a fully submersible AUV in the hybrid role, the semisubmersible unit can provide much higher levels of endurance and power to the ROV. Because it is communicating through electromagnetic waves, the unit can transmit high-bandwidth ROV data to the controlling platform and maintain more accurate positioning. Additionally, the unit does not require any infrastructure support from a platform. This means the system can be run from any of the thousands of existing offshore platforms rather than just those platforms specially equipped for hybrid AUV/ROVs.

Lee Taylor, division manager for technology products for J. Ray McDermott, said advances in information technology, increased capacity of solid state electronics, and reliability of remote controls have helped to create a new generation of ROVs. These same advances make remote deployment practical and safe for offshore oil and gas operations and a range of other applications.

The unit can be used to inspect, repair, and maintain communications cable, subsea pipelines, wellheads, manifolds, and other seabed infrastructure in the oil and gas, communications, and power industries, he said. Other uses for the unit include:

  • Touchdown monitoring
  • Trenching support for communications cable
  • Subsea pipeline and umbilical installation
  • Search and recovery operations
  • Oceanographic research where active sensing and sampling data are required.

Development of the unit began in 1999, when Mentor contracted with ISE to conduct an initial feasibility study. ISE designs and integrates autonomous and remotely operated vehicles and terrestrial robotic systems. A cost-effective design was subsequently identified and a model constructed for testing. Taylor said all the key technologies are in place and a working unit could be produced within two years of the first contract.