GB1420400A - Device for applying a predetermined force to an elongate member connected to an installation subjected to alternating movements - Google Patents

Abstract

1420400 Maintaining constant tension in lifting element INSTITUT FRANCAIS DU PETROLE 6 Sept 1973 [15 Sept 1972] 41997/73 Heading B8B [Also in Division E1] A device for maintaining a predetermined force in a jack 8 from which a drill string 1 is suspended through block and tackle 4, 5, 6, when the jack cylinder 9 which is secured to a floating installation 2, moves relative to the drill string 1, comprises interconnected passive and fine arrangements 10 and 17 for compensation of these alternating relative movements. The load supporting block 5 is secured to the rod 7 of the piston in jack 8, and relative movement between the jack piston and cylinder supplies or withdraws fluid to or from a jack 13 of the passive compensation arrangement 10. The jack 13 is pivotally mounted at 15 and is pivotally connected at its other end to a block 16 slidable along a path T, the block 16 also being pivotally coupled to one end of a further jack 12 of the arrangement 10, the other end of which is secured to a pivot point 14. The jack 12 is in fluid communication with oleopneumatic accumulators 11, which through the two jacks 12 and 13 and their sliding interconnection 16, supplies or absorbs energy in response to variation in fluid pressure in the jack 8 upon movement of the floating installation 2, to maintain a fairly constant force in the jack 8. The sliding block 16, however, is also influenced in its travel by a double-acting jack 18 of the fine compensation arrangement 17, which is supplied at both ends from a pump 22 through a device 21 controlling the pressure difference between the two chambers of the jack 18 independently of the displacement thereof. The arrangement 17 adjusts and improves the action of the passive compensation, in response to the actual measured value of a parameter which is a function of the vertical displacement of the installation 2, and this parameter, e.g. the tension in the depending drill string, is measured by a sensor 23 which supplies a signal to a comparator circuit 26 which is also supplied with a predetermined reference tension signal. After comparing the actual and reference signals, the comparator 26 sends a control signal to the device 21 for adjusting the jack 18 and influencing the passive compensation arrangement 10 until the actual and reference signals balance. In the embodiment of Fig. 2 (not shown), the system is used in laying a blow-out preventor on to an underwater well head and the actual parameter measured, is the distance between well head and blow-out preventor, this being measured by a sonar detector.