Japan Agency for Marine-Earth Science and Technology (JAMSTEC) is operating a deep sea scientific drilling vessel “CHIKYU” (Figure 1) to promote research on the earth sciences. 21st Century Mohole is one of the most challenging projects among current science proposals for the next decade. In this project it is proposed to penetrate oceanic crust, drill into the uppermost mantle across the Mohorovicic discontinuity and to obtain samples of mantle directly.
In order to accomplish this objective, it is required to drill about 7,000m below deep sea floor which water depth is over 4,000m. One of the elements which have a great influence on the realization of this target is a deep water riser. Generally, the material of a riser is high tensile steel. However, it will be very difficult to apply the steel riser to a drilling operation in the locations of more than 4,000m water depth due to the limitation of the strength. Therefore, JAMSTEC started to study a new material riser. CFRP (Carbon Fiber Reinforced Plastic) was selected as the primary candidate for the new material. It is classified by its raw material to two types, pitch-based carbon fiber (Pitch-CF) and PAN-based carbon fiber (PAN-CF). Pitch-CF has higher modulus of longitudinal elasticity and it will be more favorable for the dynamics of the riser. In this paper, outline on the developments of pitch-based CFRP riser are presented.