Deepwater Pipeline Development

To ensure continuity of supply, E&P companies have to consider opportunities in ever increasing water depths. Assisting this are new technological advances, including pipeline manufacture and design that increase the technical feasibility of deepwater developments.To ensure continuity of supply, E&P companies have to consider opportunities in ever increasing water depths. Assisting this are new technological advances, including pipeline manufacture and design that increase the technical feasibility of deepwater developments.


Deepwater pipeline challenges

Conventional pipeline design, although concerned with many factors, is dominated generally by the need to withstand an internal pressure. The higher the pressure that products can be passed down the line, the higher the flow rate and greater the revenue potential. However, factors critical for deepwater pipelines become dominated by the need to resist external pressure, particularly during installation.

Local infield lines, such as subsea umbilicals, risers, and flowlines (SURF) usually are modest challenges as they are small in diameter and inherently resistant to hydrostatic collapse. In smaller sizes, these lines generally are produced as seamless pipe which is readily available and generally economical.

However, deepwater trunklines and long-distance tiebacks present a greater challenge. To increase subsea production these lines tend to be larger in diameter with a thicker pipe wall to withstand the hydrostatic pressure and bending as it is laid to the seabed.

Production from deep-water and ultra-deepwater requires pipelines with high thermal insulation coatings and resistance to aggressive fluids.

X-Stream pipeline for extreme environments

Norwegian independent foundation, DNV says that it has developed a new pipeline concept. It claims its so-called ‘X-Stream’ system can significantly reduce the cost of deep-water and ultra-deepwater pipelines and stay within stringent safety and integrity boundaries. The foundation, which says that 65 per cent of the world’s offshore pipelines are designed to its standards, believes that using X-Stream means a reduction in the pipeline thickness, welding time and installation when compared to current deep-water pipelines.

“Typically, for a gas pipeline in water depths of 2,500m, the wall thickness reduction can be 25 to 30 per cent compared to traditional designs,” according to DNV. Dr. Henrik O. Madsen, DNV’s CEO. Deep-water gas transportation market will “experience massive investments and considerable growth over the coming years,” he said adding: “new safe and cost-efficient solutions are needed.”

X-Stream technology

By constantly controlling the external and internal pressure differential of the pipeline the amount of steel, and therefore the thickness of the pipe wall, can be reduced by up to 30 per cent and perhaps more depending on the product, making manufacturing cheaper installation easier and less expensive, believes DNV. The foundation’s engineers led by DNV in Rio de Janeiro, Brazil utilised and inverted a high pressure protection system (i-HIPPS) and inverted double block and bleed valves (i-DBB) that will immediately isolate the deep-water pressure in the event of a pressure failure so that the internal pipeline pressure can be maintained above the critical level.

During the installation process the pipeline is fully or partially flooded to control the differential pressure, while the i-HIPPS and i-DBB systems ensure that pressure never falls below the collapse pressure, says DNV. Minimum pressure needs to be maintained during pre-commissioning too and DNV says that this is achieved by using produced gas separated from the water by a set of separation pigs and gel; an industry standard practice. X-Stream has just completed the innovation project phase and DNV says that it intends to continue to work with industry on refining and testing.

Subsea tapping machine unveiled

Operating primarily out of Stavanger, Norway the offshore arm of T.D. Williamson Inc., TDW Offshore Services (TDW), has developed and now deployed in the field its Subsea 1200RC tapping machine. The lightweight, remote controlled system means that hot tapping can be carried out from a diving support vessel (DSV) in shallow water and also at depths of up to 3,000 metres.

“The most critical part of the hot tapping process is the point at which the drill penetrates the pipe,” said Mike Benjamin, TDW’s vice president, offshore pipeline solutions for TDW in a statement. “The direct control and visibility from a laptop will revolutionise hot tapping, giving way to a more efficient and safer process.”

Field tested

TDW says that the system has already been successfully tested in relatively shallow water (91m) and aside from the safety benefits the company says the new technology “offers total control and visibility of the tapping operation where there was none before. Built-in sensors allow continuous recording of actual pressures, temperatures, rotation and movement of the pilot drill and cutter.” Operated from a programme on a laptop computer, the end result of the hot tapping operation results in accurate and quality operations, believes TDW.

Other benefits

Other benefits highlighted by TDW for the Subsea 1200RC tapping machine include easier handling because of its weight and no pipeline shutdowns because the system works without disrupting the flow of the pipeline during routine maintenance or in the event of an emergency shutdown. Furthermore, when the system is required for tapping into existing subsea tees the company says there is no requirement for a hot tap fitting as the system can be deployed and hooked up to the isolation valve with a mechanical connector. In particular, TDW considers that its hot tapping system will prove especially useful for the emergency pipeline repair system (EPRS) programmes that it offers to its customers.

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