by
Nai Kuang Liang, K. F. Lin, Y. J. Lee and L. W. Chen
National Taiwan University
R.O.C.
While a soft pipe is under negative pressure, the axial stress is more pronounced than the circumferential stress and its maximum axial stress is at somewhere close to the pipe ends. The negative pressure due to pumping seawater could inhibit the lateral force induced by pipeline's curvature and has a function to restraining pipeline's vibration. Furthermore, initial tension of the pipe, interior material damping and external seawater damping have the same effect as the negative pressure. Hence, there is no problem of vibration, although single line mooring are employed. After testing one founds that the fiber-reinforced rubber pipe could not endure 5m water pressure head. However, increasing annular steel has solved this problem.
The production cost of a 2.5m in diameter and 6m long pipe is about 1.3 million NT. A 4kw long, deepwater flexible pipeline and its installation cost is approximately 1.1 billion NT. The proposed installation way is still bottom pull method. If 50 MW is an appropriate size for OTEC plant, the eastern Taiwan would have a potential of 150 to 200 shelf-mounted OTEC plants. We suggest that the shelf-mounted OTEC plant is the first priority goal in the domestic OTEC development. We could at first build an 1MW pilot plant in the vicinity of Hua-lien Port. In the long run, grazing floating OTEC plant is more promising, and a detached CWP is suggested.
The flexible underwater pipeline can also be used for other purposes such as ocean outfall, pumping power plant's cooling water, etc.. The installation method is naturally single-length-floating. the installation time should be very short. Although pipe production cost is higher, but the project may be cheaper on the whole.