Challenges for Design, Manufacture and Installation of HP/HT Risers for Deep Water
- Richard Lloyd Jones (Subsea 7) | Daniel Karunakaran (Subsea 7) | Gregory Toguyeni (Subsea 7)
- Document ID
- Offshore Technology Conference
- Offshore Technology Conference, 4-7 May, Houston, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2020. Offshore Technology Conference
- HPHT risers, Pipeline materials, Installation, Welding, Design
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With the increasing development of high temperature/high pressure wells, particularly in deep water, riser designs using conventional strength material are utilising increasingly heavier wall thickness pipe, up to 50mm wall thickness in 8" and 10" OD X65 linepipe. Such riser designs are challenging existing seamless linepipe manufacturing and girth welding capabilities. Consequently, Subsea 7 undertook a linepipe material and welding qualification programme in order to provide confidence in the use of heavy wall pipeline and riser designs and installed by R-lay.
Riser designs with heavy wall thickness may impose excessive top tension requirements making them difficult to install cost effectively using R-lay technology. Additionally, such risers may pose excessive payloads on the floating production vessel. Fatigue requirements at the hang off and touch down zones pose further limitations on the use of heavy wall risers. These limitations may impede cost effective development of HP/HT fields.
The application of high strength steel for HT/HP applications as riser material is an attractive alternative. High strength steel reduces the wall thickness and thereby reduces payloads on floating hostfacility and top tension requirements for R-lay installation. Application of high strength steel improves the top end interface design also, due to reduced tension. The qualification status of reelable X80, including CRA lined pipe will be presented.
Another challenge for HP/HT riser application is the top end connection to the floater. Traditional flex-joint solutions may not be feasible, requiring a Stress Joint at the top. For ultra-deep water conditions, special stress joints with titanium may be necessary. The limitation and application of such top end solutions for HP/HT application will be presented in this paper.
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