Patent GB-1259130-A (GB)
IPC: B63B35/03
Filed: 1969-11-24
Abstract: 1,259,130. Laying underwater pipe-lines. SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ N.V. 24 Nov., 1969 [25 Nov., 1968], No. 57300/69. Heading F2P. A method for laying a pipe-line on the floor of a body of-water from a vessel containing at least one trolley mounted for substantially horizontal movement along said vessel comprises holding said pipe-line stationary relative to said trolley whilst sections of said pipe-line are assembled, applying a constant restraining force on said trolley to thereby apply a constant tension on said pipe-line during vessel surge caused by wave motion etc., movement of the vessel relative to the pipe-line being allowed for by movement of the trolley, and maintaining a constant tension on the pipe-line when it is released relative to the trolley as the vessel is moved to effect paying out of the pipe-line. The apparatus may comprise trolley 15, Fig. 1, or a series of linked trolleys (18, Fig. 2, not shown) running on rails 14 on the deck of vessel 11. Pipe-line 13 is supported on rollers 21 and held relative to the trolley by gripper 30, thus facilitating the welding of a new section 27 to the end 29 of the pipe. Trolley 15 is connected by wire 31 and an arrangement of pulleys, Fig. 5, to the pistons of hydraulic cylinders 41 and 42 and to winch 49. The pulleys are arranged so that a given displacement of trolley 15 results in pistons 43, 44 of hydraulic cylinders 41, 42 being displaced half that amount. The hydraulic cylinders exert a constant tension on trolley 15 and thus on pipe-line 13, whilst allowing the pipe-line to be paid out or drawn in by movement of the trolley when vessel 11 is lifted relative to the pipe-line by a wave-crest or lowered by a wave-trough respectively. When pipe section 27 has been welded to pipe-line 13 the pipe-line is paid out the length of one pipe section by releasing the grip of gripper 30 on the pipe-line and moving vessel 11 forwards whilst maintaining a constant tension in the pipe-line. The constant tension may be maintained by gripping the pipe with gripper 64, which is fastened to the piston-rods 61 and 62 of hydraulic cylinders 58 and 59 respectively through cross-bar 63, so that as the vessel 11 and trolley 15 move forwards together the pipe-line is slowly paid out against the constant tension exerted by the hydraulic pressure in cylinders 58 and 59. Alternatively the constant tension may be exerted by winch 22 through cable 23 and tool 24. Various embodiments of the gripper 30 which spread the tension over a large area of the pipe surface and thus avoid damage to the protective coating preferably given to pipes, include a pair of endless belt tracks (66, 67, Fig. 6, not shown), a soft-lined basket weave wire sleeve gripper (70, Fig. 7, not shown) and a series of inflatable bag closing grippers (72, Figs. 8, 9, not shown). All but the last inflatable gripper (72c) are free to slide on rail (76) and are connected to the pistons (81a, 82a) of hydraulic cylinders (79, 80) which provide the tension applied to pipe-line 13, and to the proceeding cylinder. The tension applied by any one gripper is therefore limited to that provided by an individual hydraulic cylinder, and is set low enough to avoid damage to the pipe-line coating. If the tension required exceeds that provided by the first gripper (72a), it slides with the pipe-line until its associated piston (81) reaches the end of hydraulic cylinder (79), causing movement of cylinder (79) and activation of the second gripper (72b). Additional work stations may be carried on trolleys (85, Figs. 10, 11, not shown) which clamp themselves to the pipe in order to maintain their relative position. Additional pipe supports may be mounted on movable trolleys (94, Figs. 12, 13, not shown).