A 5,000-m-long, 15-in (38-cm) outer-diameter, full-scale pipe was deployed from the large Moon Pool of the Hughes Glomar Explorer while a deep-ocean mining system operated from the ship in the North Pacific Ocean in 1976 and 1979. From the standpoint of design as well as operation, one of the most critical parameters in deepocean mining and deep-ocean drilling is the behavior of the pipe along its length, with its bottom free. The at-sea test includes the first-ever measurements of the full-scale pipe responses coupled with the Explorer's motion in the deep ocean. The measurements showed that the pipe bottom undergoes dynamic stretching at axial resonance in addition to its static stretch. In addition, this occurrence of axial resonance was predicted by the calculations and it agreed with them. The axial resonance period is in the range of the commonly encountered ocean-wave periods. Further, this study in 1976-80 changed the industry's common perception of bending stress as design stress: The axial stress can be an order of magnitude larger than the bending stress for such a long pipe, and the bending is less of an issue. This paper presents the axial stress amplitudes, including amplification at the pipe's resonance, which are coupled with the Explorer's motions. This design and operation issue applies to deep-ocean drilling as well.
At the outset of development of the commercial deep-ocean mining project in the 1970s, one of the critical technical issues for the safe atsea operation of a very long (from 4,000 to 6,000 m) pipe was the 3-D static as well as dynamic pipe motions along the pipe's length and the positioning control of its bottom. And this issue remains one of critical concern, not only for pipe design, but also for its deployment and the positioning control operation of the pipe bottom and the equipment at its bottom.
