Katana VentraIP

Submarine pipeline

A submarine pipeline (also known as marine, subsea or offshore pipeline) is a pipeline that is laid on the seabed or below it inside a trench.[1][2] In some cases, the pipeline is mostly on-land but in places it crosses water expanses, such as small seas, straits and rivers.[3] Submarine pipelines are used primarily to carry oil or gas, but transportation of water is also important.[3] A distinction is sometimes made between a flowline and a pipeline.[1][3][4] The former is an intrafield pipeline, in the sense that it is used to connect subsea wellheads, manifolds and the platform within a particular development field. The latter, sometimes referred to as an export pipeline, is used to bring the resource to shore.[1] Sizeable pipeline construction projects need to take into account many factors, such as the offshore ecology, geohazards and environmental loading – they are often undertaken by multidisciplinary, international teams.[1]

Seabed mobility: and megaripples are features that move with time, such that a pipeline that was supported by the crest of one such feature during construction may find itself in a trough later during the pipeline's operational lifespan. The evolution of these features is difficult to predict so it is preferable to avoid the areas where they are known to exist.

Sand waves

: They result from high sedimentation rates and occur on steeper slopes. They can be triggered by earthquakes. When the soil around the pipe is subjected to a slide, especially if the resulting displacement is at high angle to the line, the pipe within it can incur severe bending and consequent tensile failure.

Submarine landslides

: High currents are objectionable in that they hinder pipe laying operations. For instance, in shallow seas tidal currents may be quite strong in a strait between two islands. Under these circumstances, it may be preferable to bring the pipe elsewhere, even if this alternative route ends up being longer.

Currents

: In shallow waters, waves can also be problematic for pipeline laying operations (in severe wave regimes) and, subsequently, to its stability, because of the water's scouring action. This is one of a number of reasons why landfalls (where the pipeline reaches the shoreline) are particularly delicate areas to plan.

Waves

Ice-related issues: In freezing waters, floating ice features often drift into shallower waters, and their keel comes into contact with the seabed. As they continue to drift, they and can hit the pipeline.[12] Stamukhi can also damage this structure, either by exerting high local stresses on it or by causing to soil around it to fail, thereby inducing excessive bending. Strudel are another pipeline hazard in cold waters – water gushing through them can remove the soil from below the structure, making it vulnerable to overstress (due to self-weight) or vortex-induced oscillations. Pipeline route planning for areas where these risks are known to exist has to consider laying the pipeline in a back-filled trench.

gouge the seabed

Submarine pipeline characteristics[edit]

Submarine pipelines generally vary in diameter from 3 inches (76 mm) for gas lines, to 72 inches (1,800 mm) for high capacity lines.[1][2] Wall thicknesses typically range from 10 millimetres (0.39 in) to 75 millimetres (3.0 in). The pipe can be designed for fluids at high temperature and pressure. The walls are made from high-yield strength steel, 350-500 MPa (50,000-70,000 psi), weldability being one of the main selection criteria.[2] The structure is often shielded against external corrosion by coatings such as bitumastic or epoxy, supplemented by cathodic protection with sacrificial anodes.[2][14] Concrete or fiberglass wrapping provides further protection against abrasion. The addition of a concrete coating is also useful to compensate for the pipeline's positive buoyancy when it carries lower density substances.[2][15]


The pipeline's inside wall is not coated for petroleum service. But when it carries seawater or corrosive substances, it can be coated with epoxy, polyurethane or polyethylene; it can also be cement-lined.[2][14] In the petroleum industry, where leaks are unacceptable and the pipelines are subject to internal pressures typically in the order of 10 MPa (1500 psi), the segments are joined by full penetration welds.[2][14] Mechanical joints are also used. A pig is a standard device in pipeline transport, be it on-land or offshore. It is used to test for hydrostatic pressure, to check for dents and crimps on the sidewalls inside the pipe, and to conduct periodic cleaning and minor repairs.[1][2]

Surface tow: In this configuration, the pipeline remains at the surface of the water during tow, and is then sunk into position at lay site. The line has to be buoyant – this can be done with individual buoyancy units attached to it. Surface tows are not appropriate for rough seas and are vulnerable to lateral currents.

[20]

Near-surface tow: The pipeline remains below the water surface but close to it – this mitigates wave action. But the used to maintain the line at that level are affected by rough seas, which in itself may represent a challenge for the towing operation.

spar buoys

Mid-depth tow: The pipeline is not buoyant – either because it is heavy or it is weighted down by hanging chains. In this configuration, the line is suspended in a between two towing vessels. The shape of that catenary (the sag) is a balance between the line's weight, the tension applied to it by the vessels and hydrodynamic lift on the chains.[23] The amount of allowable sag is limited by how far down the seabed is.

catenary

Off-bottom tow: This configuration is similar to the mid-depth tow, but here the line is maintained within 1 to 2 m (several feet) away from the bottom, using chains dragging on the seabed.

Bottom tow: In this case, the pipeline is dragged onto the bottom – the line is not affected by waves and currents, and if the sea gets too rough for the tow vessel, the line can simply be abandoned and recovered later. Challenges with this type of system include: requirement for an abrasion-resistant coating, interaction with other submarine pipelines and potential obstructions (reef, boulders, etc.). Bottom tow is commonly used for river crossings and crossings between shores.

[24]

Jetting: This is a post-lay trenching procedure whereby the soil is removed from beneath the pipeline by using powerful pumps to blow water on each side of it.[39]

[38]

Mechanical cutting: This system uses chains or cutter disks to dig through and remove harder soils, including ,[40] from below the pipeline.

boulders

Plowing: The principle, which was initially used for pre-lay trenching, has evolved into sophisticated systems that are lighter in size for faster and safer operation.

plowing

Dredging/excavation: In shallower water, the soil can be removed with a or an excavator prior to laying the pipeline. This can be done in a number of ways, notably with a ′′cutter-suction′′ system, with the use of buckets or with a backhoe.[36]

dredger

Environmental and legal issues[edit]

The Espoo Convention created certain requirements for notification and consultation where a project is likely to have transboundary environmental effects. Scholars are divided on how effective Espoo is at mitigating environmental harm. Law of the Sea concepts involved in the construction of transboundary pipelines concern territorial waters, continental shelves, exclusive economic zones, freedom of the high seas and protection of the environment. Under international law the high seas are open to all states to lay underwater pipelines and for various other types of construction.[43]


Underwater pipelines pose environmental risk because pipelines themselves may become damaged by ship's anchors, corrosion, tectonic activity, or as a result of defective construction and materials. Stanislav Patin has said that study on the effects of natural gas on underwater ecosystems, fish and other marine organisms has been limited. Researchers found a cause-effect relationship between mass fish mortality and natural gas leaks after drilling accidents in the Sea of Azov in 1982 and 1985.[43]


Concerns about the environmental risks of underwater pipelines have been raised on numerous occasions. There have been at least two serious incidents involving oil pipelines on the UK's continental shelf. There have also been several "minor spills and gas leaks" involving other North Sea pipelines. In 1980 a pipeline was damaged by a ship's anchor and in 1986 a pipeline valve failed due to pressure changed. Both incidents resulted in oil spills. Several Baltic countries expressed concerns about the Nord Stream pipeline. The route of the 1,200 km underwater pipeline would travel through fishing areas of the Baltic Sea, as well as area where chemical weapons from World War II had been discarded.[43]

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Barrette, P (2011). . Cold Regions Science and Technology. 69: 3–20. doi:10.1016/j.coldregions.2011.06.007.

"Offshore pipeline protection against seabed gouging by ice: An overview"

Brown R.J. (2006) Past, present, and future towing of pipelines and risers. In: Proceedings of the 38th Offshore Technology Conference (OTC). Houston, U.S.A.

Croasdale K., Been K., Crocker G., Peek R. & Verlaan P. (2013) Stamukha loading cases for pipelines in the Caspian Sea. Proceedings of the 22nd International Conference on Port and Ocean Engineering under Arctic Conditions (POAC), Espoo, Finland.

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Gerwick B.C. (2007) Construction of marine and offshore structures. CRC Press, New York, 795 p.

& Been K. (2011) Pipeline geohazards for Arctic conditions. In: W.O. McCarron (Editor), Deepwater Foundations and Pipeline Geomechanics, J. Ross Publishing, Fort Lauderdale, Florida, pp. 171–188.

Palmer, A.C.

& King R. A. (2008). Subsea Pipeline Engineering (2nd ed.). Tulsa, USA: Pennwell, 624 p.

Palmer, A. C.

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