Learning More about Flexible Risers

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[Posted on August 6th 2014 by Bill Stewart]

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Flexible risers are pipes used to relocate materials from the floor of the sea to the production and drilling structures that are on top of the water surface or from the structures to the sea floor. There are various types of risers, including pull tube risers, attached risers, rise towers, steel catenary risers, flexible riser and drilling risers.  Whether they are helping as export, import or production vehicles, risers are the linking between the production and drilling facilities and the subsea field developments.

Just like flow lines and pipelines, risers carry production materials like gas lift, control fluids and injection fluids as well as hydrocarbons. The risers are generally insulated to tolerate the temperatures at the sea floor. They are also either flexible or rigid.

Types of Risers

Attached riser-they were the first risers to be developed. They are positioned on compliant towers, concrete gravity structures and fixed platforms.

Pull tube risers- they are used on fixed structures. They are flow lines or pipelines that are wound up at the facility’s center. A pull tube with a wide diameter than the riser is preinstalled on the facility. A rope that has a wire is attached to the pipeline on the floor of the sea. The line is pulled through the tube to the top.

Steel catenary risers– they are used to join the sea floor to the production structures above the sea floor. They also join two floating platforms of production.

Top tensioned risers-they are vertical risers that terminate directly below the facility. They can move crossways with the waves and winds. The rigid risers are fixed to the floor of the sea.

Rise towers- they are built to lift the risers to a considerable height to reach the surface of the water. They are designed for extremely deep water environment.

Drilling risers- they transfer mud to the top during activities that constitute drilling. They connect the wellbore temporarily to the surface to avoid fluids from drilling activities from leaking into the water. Flexible risers are connected to the vertical risers and to the structures above.

Flexible risers– they can accommodate various situations. They can withstand both horizontal and vertical movement. This makes them perfect for use with floating structures. The flexible pipe was initially used to join production apparatus onboard floating equipment to export and production risers. They are also found as a primary user. There are various shapes of such risers. Examples are like the steep S and Z, steep wave and lazy wave that use fastened buoyancy modules.

The risers are being seized by metallic systems in several current deep water expansions.  Flexible pipe has been an effective key for both shallow and deep water flow line and water riser systems in the whole world.  In such uses the flexible pipe section can be used along the whole riser length or it can be limited to short dynamic sections such as jumpers. A hydrodynamic analysis is used to solve difficult problems in the marine environment where the risers cannot.

Stewart technology associates has developed and enhanced the risers to answer the challenges posed by steel catenary risers. These improved methods are applied to flexible pipe allowing effective response of the flexible pipes under the most simple and difficult loading conditions.