Fundamental Research on a development of CFRP Riser Pipe for 4000 m Deep Sea Scientific Drilling

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A deep sea scientific riser drilling vessel "Chikyu" was constructed in Japan and it is planned to drill the sea floor at the water depth of 4000 m to obtain the mantle in the near future. However, it is almost impossible to use the steel riser pipe at the water depth of 4000 m and the development of CFRP riser pipe is desired. The key element of the CFRP riser pipe is its mechanical structure where the CFRP pipe is connected at the pipe ends to the steel connectors through several pairs of mutually contacting threads. This research is concerned with the development of this type of CFRP riser pipe.In the research of 2005, the configuration and dimension of the mechanical structure were parametrically changed and their influence on the strength of the mechanical structure was made clear using FEM analysis and the optimization of the mechanical structure of the CFRP riser pipe was performed. The characteristic of the axial vibration of the optimized CFRP riser pipe was also studied and it was confirmed that the riser pipe had no resonance with the heaving of the drill ship.In the research of 2007, a tensile test model, which had the optimized dimension, was fabricated and tested and its tensile strength, elongations and strains were obtained. The fracture process of the mechanical structure was made clear from the correlation between the experimental strains and the calculated strains which were obtained from FEM analysis with assuming crack propagation passes based on the damage observation of the CFRP pipe section.Based on the results stated above, the thinking concerning the design of the CFRP riser pipe for 4000 m deep sea has been summarized.