A deep-sea riser drilling vessel is now under construction in Japan for the purpose of scientific drilling. The target water depth of the vessel is 2500m for the time being and will be extended to 4000m in future. In the field of offshore oil drilling, the riser drilling has been practiced for many years and in recent years it is confirmed that the target water depth of 3000m with using steel riser pipes will be possible. However, the drilling up to the water depth of 4000m has not been experienced at all and will have a lot of technical issues. One of the most important issues is to make the weight of the riser pipe lighter and its axial rigidity higher. The purpose of this research is to make clear the design concept of the CFRP riser pipe that has multiple traplock structure and develop a CFRP riser pipe capable of drilling in 4000m deep waters. Here, referring to a series of research results on the leg fixing device for jackup rigs where similar fitting structure is adopted, a prototype of CFRP riser pipe which has multiple traplock structure is designed and five experimental models are fabricated and tested. Resulting from the comparison of the experimental results with those of finite element analysis, the findings have been obtained and it has been confirmed that it will be possible to develop an actual CFRP riser pipe that has enough strength for 4000 m water depth.
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