Patent GB-1513581-A (GB)
Title: Constructions for deep water installations
IPC: E21B43/017
Filed: 1975-07-17
Abstract: 1513581 Mooring systems TAYLOR WOODROW CONSTRUCTION LTD 16 July 1976 [17 July 1975 18 July 1975] 30124/75 and 30310/75 Heading B7V Two hollow structural members of a deep water installation (which in the preferred embodiments are a foundation base and column of a platform) are connected together by articulated joint which comprises a plurality of tendons. In a first embodiment the base 6 of the column and the foundation 1 are joined together by a shaft 8 which affords access for men and equipment between the two and comprises one or more concentric walls (two as shown in Fig. 2) each formed by a plurality of oil filled annular members 22 and plates 21. In a second embodiment (Fig. 3), a rigid shaft 8<SP>1</SP> is mounted at its two ends in the base of a column and a foundation base respectively by way of a spherical bearing surface 14 against which bears a primary watertight seal 11, a secondary watertight seal 12 which is provided in case of failure of the seal 11 and an inflatable seal 13 which is inflated for maintenance operations on either of the seals 11 or 12. Access to these seals is provided by hatches 17. The upper end of the shaft 8<SP>1</SP> slides on similar seals (11), (12), (13) within the associated spherical bearing surface 14 to permit leave of the column and access to these seals is via a hatch 19. Alternatively the upper end of the shaft 8<SP>1</SP> may be connected to the spherical bearing surface 14 by a tube constructed in the same manner as one of the walls of the shaft 8 described above. To renew a tendon various methods are disclosed. In a first (Fig. 7) both ends of a tendon are accessible and have cylindrical steel mem- 123, 124 carrying seals 127 and mounted within sleeves 215 of anchorages 126 provided in the base 1 and column 6. One end of the member 123 is threaded and carries a tendon tensioning nut 129 whilst the opposing end of the member 124 has an abutment shoulder 124A. Normally sealing domes surround these ends to ensure watertightness in case the seals 127 fail. When the tendon 4 is to be replaced a shear key housing 134, a-piston head 135 and a pressure bottle 136 are fitted at one end and a cylindrical extension member 132 and a sealing cap 133 at the other after the nut 129 has been removed with the bottle 136 pressurized via an inlet 137 to the actual hydraulic pressure. The cap 133 is pressurized and bottle 136 is depressurized via an outlet 139 so as to move the parts 135, 124, 4 and 123 into the bottle 136 and the extension member 132 into the sleeve 125 in the column. Seals 128 are inflated and the shear keys in the housing 134 are engaged in a notch 143 in the member 132 to lock it in position. Thereafter the bottle 136 is removed with the old tendon 4 and its parts 123, 124 and the part 123 of a new tendon is attached to the member 132. This process is then reversed to move the parts 123, 4 and 124 of the new tendon into position and bolt them in place with the bolt 129. A guide may be provided to guide the parts as they move between the column 6 and the base 1. Other similar but alternative methods are disclosed where only one end of a tendon is accessible.