Hot tapping subsea pipelines plays a critical role in facilitating repair work (scheduled and unexpected), tie-ins, flow assurance, chemical injection and insertion of intelligent tools. But as new pipeline systems are

constructed in increasingly deep waters, carrying out pipeline interventions, such as hot tapping, has become increasingly complex. Deepwater pipelines that lie 3000 m subsea demand interventions that can be carried out without divers, who can only work in depths to 300 m. To provide operators of deepwater developments with a solution that does not rely upon divers or expose them to risk, the Subsea 1200RC Tapping Machine was developed. (See Figure 1). The system is operated by remote control from a laptop onboard a Diving Support Vessel (DSV). By doing so, the hot tapping process is more accurate and diver safety and execution speed are enhanced.

George Lim, T.D. Williamson, the Netherlands,

discusses a new remote-controlled

hot tapping machine that can be used to

facilitate pipeline tie-ins by tapping into

pre and post-installed tees, without diver

assistance.

REMOTE-CONTROLLED HOT TAPPING SUBSEA

Reprinted from OILFIELD TECHNOLOGYAugust 2012

When pre-installed tees are present on the pipeline, the system is operated without divers. If pre-installed tees are not present, divers are required, but only to install the hot tap fitting and the tapping assembly; not to operate the system.

The system makes it possible to access subsea pipelines in any water depth for operational, construction or maintenance purposes, changing the face of offshore pipeline intervention and maintenance.

Subsea hot tapping: how it worksHot tapping involves drilling a hole into a live pipeline without shutting it down or releasing its contents. Today’s subsea hot tap operations are carried out from a DSV that carries the equipment and divers to the hot tap location. Divers enter the water and the hot tap assembly is lowered to the pipeline.

The typical hot tap is as follows: first, the hot tap assembly, which consists of a hot tap machine, permanent isolation valve and hot tap fitting bolted together, is pre-tested on the deck of the DSV. The fittings are two mechanically-bolted clamp-halves. The assembly is lowered with the two clamp-halves in open position over the pipeline, and divers bolt the clamp-halves shut. To ensure integrity, the annulus between pipe and fitting is leak-tested against the tapping machine while the valve is open. To begin the tapping procedure, a pilot drill is positioned in front of the hot tap cutter to make a small hole in the pipeline. This hole helps stabilise the larger hot tap cutter and retain the portion of cut pipe (coupon) after the larger cutter completes the hole. The primary tap is then made into the pipeline with the appropriate size cutter. The valve is closed, and the coupon and tapping machine are recovered. If preparing for a tie-in, the permanent hot tap valve may be connected to a spur line. When the valve is opened, the new connection is ready to be put into service.

Hot tapping challenges subseaThe greatest concern associated with subsea hot tapping is that divers - not experienced tapping professionals - perform the hot tap, which is the most delicate aspect of a subsea tie-in operation: when the pilot drill penetrates the pipeline and the live pipeline is cut. The divers are supervised by a hot tapping professional on the vessel, and this professional communicates via the vessel intercom during the tapping process. Although they are trained in hot tapping during the mock-up testing prior to the operation, the divers are not hot tapping experts. Another concern is the limited number of telltale sensors on today’s subsea machines, with minimal topside visibility. These sensors are used to monitor activity inside the fitting while the line is cut. Without maximum viewing capability, the ability of the diver and hot tapping technician to monitor and control the tapping process may be compromised. Fortunately, new systems can overcome these challenges.

Adapting field-proven technologyThe Subsea 1200RC Tapping Machine is a self-contained tapping machine with a built-in hydraulic and control system powered by a stationary remotely operated vehicle (ROV), and operated by a technician from a laptop that offers a continuous view of all subsea operations. (See Figure 2). The tapping operation is completely controlled by the technician.

Figure 1. Hot tapping is carried out via remote control with the Subsea 1200RC Tapping Machine.

Figure 2. The tapping machine is designed so that technicians control the system, and have a continuous view of subsea operations through a laptop computer onboard the DSV.

Reprinted from OILFIELD TECHNOLOGYAugust 2012

The stationary ROV concept is an improvement over the standard deepwater method that uses ROV arms to operate separate valve functions.

During the hot tapping process, the ROV draws upon its own hydraulic power unit (HPU) to stab into the tapping machine control panel and latch onto the grabber bar. (See Figure 3).

The ROV provides hydraulic power (closed loop) to engage a motor/pump unit placed on the tapping machine frame. The motor/pump unit then sends hydraulics through a valve pack to the appropriate motor/hydraulic function.

The software control program may be operated manually - or automatically - to manipulate all tapping machine functions from a laptop. Its primary functions are to run the feed and drive motors, and engage/disengage the clutch. Sensors transmit data to the laptop on all parameters, including temperature, pressure, cutter position and proximity, rotation speed, and movement of the boring bar and cutter. (See Figure 4).

The camera on the ROV panel is used to monitor some of the key pressures that have a manometer (pressure gauge). The supply and return hydraulic pressures, and motor and drill pressures are monitored by a network of sensors. Two cameras on the tapping machine offer around-the-clock observation of a) the rotation and position of the boring bar, and b) the position of the clutch cylinder.

Should hydraulics, electronics or machine parts fail, several contingencies – including overrides by ROV mechanical interfaces and duplicate monitoring system - are installed on the tapping machine.

Depending on the internal pipeline operating pressures, the tapping machine can operate in depths down to 3000 m.

If tees have not been pre-installed on the pipeline, divers are required to install the tapping assembly and the hot tap fitting. However, no divers are required when a) pre-installed tees are present or b) post-installed tees are incorporated into the hot tap assembly and the integrated assembly can be lowered and connected to the pipeline by remote control.

Figure 3. The remotely operated vehicle stabs into the tapping machine control panel. A technician controls all tapping functions from a laptop computer.

Figure 4. The view of an actual hot tapping operation taking place. Technicians have a clear, continuous view of the entire subsea hot tapping process through the main window of the control program.

Figure 5. Tapping through a pre-installed tee.

Tapping into pre-installed teesOperators often pre-install tees on the pipeline in anticipation of tying in future oil and gas field developments in neighbouring fields. By doing so, output can be routed through the pipeline without going to the expense of laying a new export line that extends to the shore or nearest hydrocarbon collection point.

Pre-installed tees are put in place during the pipe laying process. Working from a laybarge, the tee is placed at the leading end of the new pipe string and welded to the string, while the other end is welded to the next pipe joint placed in the line. The tee is then lowered as part of the pipe string.

A tee is typically an in-line pipe fitting that features a short branch connection, which sports a standard flange used to bolt on a tapping machine in the event that it is located in water depths accessible by divers. In deep water, however, the branch sports a hub designed for subsea mechanical quick connectors (MQC), such as collet connectors, to latch on. Inside the short branch is a tappable steel ‘membrane.’

When the tie-in is required, the hot tap assembly is lowered and connected to the hub in ‘diverless’ mode in order to tap away the membrane, creating access to the pipeline. (See Figure 5). In this case, the hot tap assembly consists of four fixtures: hot tap machine, upper MQC, isolation valve, and lower MQC. The latter is connected to the tee hub, secured and leak-tested to ensure tightness, and the tapping operation commences. After the tap is complete, the coupon is retracted

into the tapping machine, the isolation valve closed. The tapping machine is disconnected at the isolation valve interface, by disengaging the upper MQC, and then returned to the surface. All activities are conducted with built-in remote control systems supported by an ROV.

The hot tap assembly is prepared topside. All connections can be leak-tested and all functions pre-tested before the assembly is deployed subsea. The entire underwater process is conducted in diverless mode and controlled topside from the laptop through the control program.

Tapping into post-installed teesA post-installed hot tap tee is one that is installed after the pipe is laid. (See Figure 6). It typically consists of two clamp-halves. The tee is welded or bolted to the isolation valve, and forms part of the integrated assembly. This assembly is lowered over the pipeline, and the two clamp-halves are hydraulically shut and the bolts are tightened. The sealing elements and mechanical grips are energised by tightening longitudinal bolts. All bolting actions are conducted by hydraulic cylinders actuated by remote control using the ROV, with the tapping machine set in diverless mode.

Remote-controlled subsea fitting installation To install the post-installed tee in ‘diverless mode,’ remote controlled subsea fitting installation methodologies exist in the industry. Such methodologies utilise ROVs during the operation. The ROV activates hydraulic cylinders pre-installed on the fitting halves to close the fitting onto the pipeline. Then a series of bolt spinning and tensioning functions further secure the fitting in place, utilising mechanisms pre-installed on the fitting halves. After pressure testing the installed fitting, the assembly is now ready to tap. After tapping is completed, the tapping machine is disconnected at the valve interface and recovered to the surface.

Separating man from machineBuilding pipeline developments in deepwater environments only makes sense if they can be maintained and operated safely and cost-effectively. With the development of remote-controlled systems and remote fitting installation methodologies, subsea pipeline operators stand to benefit in many ways.

By offering solutions that make it possible to carry out hot tapping operations for repair and intervention, and on lines with pre and post-installed tees, safety and efficiency are enhanced, and costs are reduced. As operators delve into deeper and deeper waters, these innovative remote-controlled systems that ‘separate man from machine’ are poised to revolutionise subsea pipeline maintenance and intervention. O T

Figure 6. Tapping through a post-installed tee.