GB1516671A - Plug device for closing a pipeline - Google Patents

Abstract

1516671 Pipe-line closing pigs BROWN & ROOT (UK) Ltd 13 June 1975 [26 March 1975] 12633/75 Heading F2P A plug device for closing off a pipe-line comprises a body for insertion into the pipe-line sealing means encircling the body for sealing engagement with the pipe wall, locking means for holding the body at a required position in the pipe-line, means activated by movement of the plug to measure distance travelled along the pipe-line from a starting position and means responsive to the distance measuring means to effect the expansion of the expandable sealing means. The plug device of Fig. 1 is in the form of a pig comprising a chassis 11, front plate 12, rear plate 13, a plurality of cup rubber 16 retained by bolted flanges 14. A compressed air reservoir supplies expandable sealing bags 21 and pneumatic rams 20, the latter actuating spring biased pawls 22 pivotable to contact the inner surface of the pipe wall. The bags 21 are made of a semi-rigid polyurethane outer casing 26 having a high coefficient of friction with a pipe wall and an expandable inner tubing 27. An airtight housing 50 at the rear of the pig communicates with the pipe-line ahead of the pig through conduit 51a and non-return valve 51 to maintain the housing at the same pressure as that of the pipe-line ahead of the pig. In use the pig is inserted front end first into one end of a flooded pipe-line and that end is then closed with a cap through which compressed air is passed to force the pig along the pipe. An odometer 28 measures the distance travelled by the pig and after a preset distance from a starting position has been reached opens a valve in conduit 30 which causes bags 21 to inflate to retard the pig and pawls 22 to pivot into engagement with the pipe wall to prevent reverse movement of the pig. A pressure sensitive switch in housing 50 activates a sonic pinger 34, when the pressure in front of the pig reaches a predetermined level, whose signals are picked up by external microphones causing the compressed air source driving the pig to be switched off. A second pressure sensitive switch mounted on the rear end of the pig may then operate when the pressure of the drained section behind the pig has reached a desired level, to vent the pressure in rams 20 and bags 21 by opening suitably disposed valves and regulator 37 maintains the pressure in conduits 31 and 32 at a predetermined level above the pressure in front of the pig. In an alternative embodiment rams 20 are omitted and the pawls 22 are merely spring loaded.