ABSTRACT:

A conventional lifting pipe for deep sea mining is usually very long and consist of many short pipe pieces. In order to connect these pipes, each piece must have a special connecting mechanism and this part is vulnerable to fatigue damage during local operation period. To improve these structural and operational drawbacks, the pipe tow method may be applied. Among many tow methods, the most feasible method is selected and its applicability is confirmed using analytical solutions for static tow conditions. Together with the well established tow procedure, an efficient procedure for installing and operating a lifting pipe and a miner is studied to reduce down-time.

INTRODUCTION

The tow method has been widely applied to install offshore pipelines. The basic concept of the tow method is to tow and lay the pipe at an off-shore location after joining and testing the system at an on-shore fabrication site. This method, therefore, assures improved production quality of pipelines and reduces offshore work significantly and can be applied economically and easily to all kinds of pipe. There has been many studies and reports on the towing of pipelines (Costello et al, 1983, Nedergaard et al, 1989, den Boer et al, 1990, and Jang, 1996), tension leg platform (TLP) tethers (Ishikawa et al, 1992), and pipes for ocean thermal energy conversion (OTEC, Nihous, 1995) and these showed that with careful design the tow method can be applied successfully to all kinds of pipe regardless of pipe size, pipe type and water depth. In case of a conventional lifting pipe for deep sea mining, it is usually very long and consists of many short pipes. In order to connect these pieces, each piece must have a special connecting mechanism and this part is vulnerable to fatigue damage during long operation period.

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