Top Tensioned Riser Systems

TTRs are used as conduits between dynamic floating production units (FPUs) and subsea systems on the seafloor, for dry tree production facilities such as spars and TLPs. TTRs are individual risers that rely on a top tension in excess of their apparent weight for stability. TTRs are commonly used on TLPs and spar dry tree production platforms. TTRs are generally designed to give direct access to the well, with the wellhead on the platform. This type of riser has to be capable of resisting the tubing pressure in case of a tubing leak or failure. The four types of TTRs are drilling risers, completion/workover risers, production/injection risers, and export risers. Tensioned Riser Applications Specifications:


  • MODU drilling risers
  • Surface wellhead platform drilling risers
  • API RP16Q
  • API RP 2RD


  • MODU completion/workover risers
  • Surface wellhead platform completion/workover risers
  • API RP 17G
  • API RP 2RD


  • Surface wellhead platform production risers
  • Subsea tie-backs
  • API RP 2RD
  • API RP 1111


  • Surface wellhead export risers
  • API RP 2RD
  • API RP 1111
  • ASME B31.4
  • ASME B31.8
  • 30 CFR
  • 49 CFR

Top Tensioned Riser Configurations

TTRs consist of long, flexible circular cylinders used to link the seabed where the wellheads are located to a floating platform. TTRs are provided with tension at the top to maintain the angles at the top and bottom under environmental loading
File:Typical TTR System Configurations.png
Typical TTR System Configurations
conditions. TTRs often appear in a group arranged in a rectangular or circular array. The following major design considerations are important when designing a TTR to prevent failure:
  • Allowable floater motions;
  • Allowable stroke of tensioning system;
  • Maximum riser top tension;
  • Size of stress joints and flexjoints;
  • Keel joints;
  • Increasing length of riser joints;
  • Design criteria for the safety philosophy of liquid barriers, valve, and seals;
  • Current, interface with array, and VIV;
  • Impact between buoyancy cans and hull guides.

Top Tensioned Riser Components

The TTR configuration depends on the riser function and the number of barriers selected (single or dual).

Riser System

In general, the riser configuration comprises the following components:

  • The main body is made up of rigid segments known as joints. These joints may be made of steel, titanium, aluminum, or composites, although steel is predominantly used.
  • Successive joints are linked by connectors such as threaded, flanged, dogged, clip type, box, and pin connectors.
  • The riser is supported by a tensioning system, such as traditional hydraulic tensioners, air cans,RAMtensioners, tensioner decks, and counterweights.

Buoyancy System

File:TLP Tensioned Riser System.png
TLP Tensioned Riser System

For water depths exceeding 2000 ft, buoyancy systems are required to provide lift, which reduces the top tension requirements, prevents excessive stresses in the riser, and reduces the hook load during deployment/retrieval of the BOP. Both synthetic foam and air-can buoyancy systems have been used for deepwater riser systems, either individually or in combination.Buoyancy cans decouple the vertical riser movement from the vessel, and can be built by the fabrication yard. However, either a heavy lift vessel or a specially designed rig is required for offshore installation. It has large relative vertical motion in storm conditions and may generate lateral loads between the buoyancy cans and the spar center wall.

Design Phase Analysis

File:Spar Tensioned Riser System.png
Spar Tensioned Riser System

Before designing the TTR, several analyses need to be conducted to ensure that the riser design is up to specifications. To design a TTR system, these analyses must be performed:

  • Top tension factor analysis;
  • Pipe sizing analysis;
  • Tensioning system sizing analysis;
  • Stroke analysis;
  • Riser VIV fatigue analysis [27,28];
  • Interference analysis;
  • Strength analysis;
  • Fatigue analysis.


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