Stolt Comex Seaway, with financial assistance from the EC, has undertaken a project to demonstrate the value of titanium alloy pipes as a practical alternative to current flexible pipe technology for dynamic risers in floating production systems for the recovery of oil and gas reserves. As field developments move into ever-deeper waters and involve the handling of high pressure, high temperature and highly corrosive products, there is concern that current flexible pipe technology will be a limiting factor. The benefits of titanium alloy pipes include strength, low weight, low elastic modulus and exceptional corrosion resistance.
Example field development projects were identified and used to evaluate riser design and installation concepts for various configurations. This ranged from simple catenary risers to more complex configurations such as the âsteep waveâ?. This included several types of floating production (FPSO, semi-submersible, SPA and TLP), environmental conditions applicable to different geographic locations and water depths to 1500m.
The available titanium alloys were assessed in relation to the intended application with the objective of selecting candidate material for the main test programme. Ti-6Al-4V, the most readily commercially available titanium alloy, was fully validated for the application. The results demonstrated that excellent quality and properties could be achieved for the pipe and welding process (Gas Tungsten Arc and Radial Friction).
The project concentrated on two main installation techniques, the Tow Out Method and the Vertical Laying Method. Both of the installation options are reliant on cost-effective fabrication and joining methods. Extensive testing was therefore carried out to demonstrate the suitability of the selected processes for titanium together with the development of equipment and procedures. Finally, a full-scale offshore trial was performed with 6â? diameter titanium pipe that was entered into the pipe handling and deployment system of the Seaway Falcon. The trials confirmed that controlled deployment could be achieved using equipment and procedures similar to those used for conventional pipe-laying.
