GB2518844A

GB2518844A - Skid rail gripping apparatus

Info

Publication number: GB2518844A
Application number: GB1317383.6A
Authority: GB
Inventors: Peter Holland
Original assignee: Northern Hydraulic Cylinder Engineers Ltd
Current assignee: Northern Hydraulic Cylinder Engineers Ltd
Priority date: 2013-10-01
Filing date: 2013-10-01
Publication date: 2015-04-08
Also published as: GB201317383D0

Abstract

A skid rail gripping clamp(2) is mountable on a skid rail(1), the clamp(2) having a skid rail(1) gripping state and a skid rail(1) sliding state. The skid rail clamp(2) comprises at least two members(20) configured to grip a skid rail(1) when at least one of the at least two members(20) is subject to an actuating force, at least one fluid powered actuator(41) adapted to exert the actuating force. The at least one hydraulic actuator(41) comprises at least two pistons(34) mounted on a common shaft(3), and each of the pistons(34) is mounted in its own cylinder(50) and wherein adjacent cylinders. Each cylinder includes is port(50) for the passage of pressurised fluid to exert a force on the respective pistons(34) in the same direction.

Description

Skid Rail Gripping Clamp

Field of the Invention

The present invention relates to skid rail gripping clamp and in particular to a skid nil gripping clamp having an integral brake.

Background of the Invention

Skid rail gripping clamps are used where a piece of equipment is mounted on a skid rail and there is a requirement to move that piece of equipment A skid rail gripper is mounted on the skid rail and attached to the piece of equipment by an actuator. The skid rail gripper grips the skid rail so that a force may be applied to the piece of equipment so as to either pull or push the piece of equipment towards or away from the skid rail gripper.

One application where skid rail grippers are used is on drilling rigs in the oil and gas industry where they are used to move the drilling derrick. The present invention is however not limited to use with drilling 1--I--* Moving the dnlling derrick is a lime consuming and dangerous procedure. Where the derrick is provided with its own brakes, those brakes must be released as a prerequisite to moving the drilling dethclc Often this is not easy because the nature of the brakes, which are usually sliding wedges which when pushed together engage the underside of the skid rail. Sometimes these sliding wedges cannot be disengaged using the engagement and disengagement means provided. This is due to the load on the brakes and corrosion of the brake pans.

When the derrick brakes have been released, the next step in moving the derrick from one location to another is to break out the derrick from its current position. The derrick rests on pads, which rest on the skid rail. Corrosion between the pads and the skid rail combine with the weight of the derrick to necessitate very high break out forces to make the initial movement of the deri-ick.

It would be desirable to be able to cxcii a greater break out force with a skid rail gripping damp.

The grippers of the prior art comprise side members which locate to either side of a skid rail, an actuator art-ached to one end of the gripper and a brake 5cr attached to rhe other end of rhe gripper. lbe gripper comprises hydraulic actuators that pull the side members up arainst the underside of the skid rail.

This requires very high hydraulic pressures, which necessitates using very narrow bore hydraulic ppeworlc.

\Vhen the gripper is to he moved, the hydraulic pressure is vented, allowing the hydraulic fluid to return via the narrow bore pipework to the hydraulic reservoir and for sufficient clearance between the skid rail and the gripper to develop. This takes time, up to three minutes For a typical skid rail gripper.

It would be desirable to increase the speed of release.

Another problem associated with skid rail gripping clamps is that failure of hydraulic seals is common. \Vhen a hydraulic seal fails it is usually necessary to st-rip down the gripper in order to replace the seal. This is a rime consuming task in itself, and the reqLdred seal nlay not he to hand. In the case of a drilling derrick at sea, it may be necessary to bring in a part by helicopter.

It would therefhre be desirable to provide a skid rail gripping clamp that may continue to operate after a hydranlic s cal failure.

Summary of the Invention

According to the invention there is provided a skid rail gripping gripping clamp a specified in Claim 1.

Preferred embodiments of the invention are described in the claims dependent on Claim 1, the

drawings and the description.

Brief Description of the Drawings

In the drawings, which illustrate preferred embodilments of the invention, and are by way of example: Figure 1 is a cross-sectional side view of a skid tail gripping device according to the invention: Figure 2 is an end view iii partial cross-section of the device ifiustrated in Figure 1; and Figure 3 is a plan view of the device illustrated in Figures 1 and 2.

Detailed Description of the Preferred Embodiment

Referring now to Figures 1 to 3, there is shown a skid rail upon which is mounted a gripper 2, which together with hydraulic ram 3 form a skid unit 4.

Tilie skid unit shown in Figures 1 to 3 may he used in a well drilling rig for moving the drilling derrick. When so utthsed, typically there woddd he two pairs of sldd units 4, each sldd unit mounted on one of a pair of parallel skid rails.

The gripper 2 comprises a pair of spaced apart side member 20, each of which sits to one side of the rail i.

Each side member 20 is substantially C-shaped in cross-section, and a lower edge of the side member lies helow the skid rail 1 and includes a protruding lip 21, the upper surface 22 of which engages the underside it of the skid rail 1 when the clamping system is engaged. Engagement and disengagement of the clamping systenI will be described in greater detail below.

Mounted between the side members 20 is a clamping system 30. The clamping system 30 comprises a pnnary clamping member 3! and a secotidary clamping member 40.

The primary damping member 31 comprises a housing 32 which housing 32 is attached to the side members 20 by bolts 23, which pass through bores in the side members 2111 and into housing 32 of the primary clamping member 31 Between the lower edge 32a of housing 32 and the upper surface 24 of a horizontally extending portion of i-he side members 20 there is mounted a floating shoe 25. TIbe floating shoe has two spaced apart running strips 25a mounted on rhe underside of shoe 25. The running strips 25a are wearing parts and reqtdrc periodic inspection and replacement or repair.

lTjth a downward force exerted on the floating shoe, friction is generated between: theuppersurface 22 of the protrudinglips 2! of side memher2lll and the underside Ia ofskid rail I; the running strips 25a and the upper surface of the skid rail 1; and between the underside of the floating shoe 24 and the upper surface 24 of the horizontally extending pot-I-i on of side member 20.

A downward force may be exerted on the floating shoe 24 by either or both of the primary and secondard damping members 31, 40.

In the illustrated embodiment, the primary clamping member 31 comprising a plurality (eight in the present example) of pistons 34, each mounted in a piston housing 33. Each pistion 34 comprises a piston head 34a, a piston shaft portion comprising a first shaft portion 34b and a second shaft portion 34c.

Each pistion housing 33 comprises three regions 33a, 33b, and 33c, each of different diarneter.

Extending inward from the lower surface of the housing 32 is the region 33a of largest dimeter, which receives the piston head 34a. The region 33c irns the smallest diameter and receives the pistion shaft portion 34h. TIie diameter oh-he region 33h is intermediate the diameters of the regions 33a and 33c.

A resilient member, in the form of a belleilIe spring 35 in the present example, is mounted about the piston sh>ft 34b and sits in the region 33h of intermediate diameter and butts up >gainst the upper surface of the piston head 34a. The helleville spring 35 exerts a constant force on the piston head 34a, which in turn exerts a force oF the floating head 24 to secure the gripping device onto the skid rail 1 as described above.

TIic housing 32 also includes a plurality of recesses 32a, each associated with a piston housing 33 and configured w receve a gland pack 36. lIhe gland pack provides a hydraulic seal around the first portion 34b of die piston shaft, in both direcfions, that is a seat against egress and ingress of hydraulic fluid across the gland pack.

In addiflon to actuation of the piston 34 by the befleville spring 33, the piston and cylinder are arranged as a i ngle acting hvd raulic mlii. V1ie ii pt-es sun sed hydraulic fluid is in tfl)duced into the space between the piston head 34a and first region of the piston housing 33a, the piston head 34a is pushed towards the floadng shoe 25. When the hydraulic fluid is depressurised, the weight of the components rcacting against the piston 34 force thc hydraulic fluid out of the space between the pistion head 34a1nd the piston housing 33a.

The presence of spthngs that are arranged to force die piston he-Sad 34a into engagement *ith the floating shoe 25 are advantageous for a number ofresons.

1) They pro'ide the skid damp 2 with an integral passive brake. Skid cJainps presenfly in use do not indude a brake. Ihey arc either darnpcd to the skid rail by hydraulic pressurc or they are free to move with respect to the skid rail. The skid rail clamp 2 may be used to brake a derrick after a derrick re-location operation is complete.

2) The springs allow the skid clamp 2 to be mno'ed without waiting for clearance between the side members 20 and the skid rail to develop after de-pressutisarion of the hydraulic fluid actuating the pistons 34. The surface of a skid rail will generally lla'e irregularifies. To allow for these irregularities a skid clamp is typically configured to provmde approximately 12mm of clearance between the underside of the skid rail and the surface of the side member that engages the underside of the skid rail. When the hydraulic fluid pressure on the pistons is remo'ed, it takes typically two to three minutes for sufficient hydraulic fluid to flow out of the space behind the piston such that the aforc-mentioned clearance may develop. As call he seen from Figure 1, the springs 35 hold the housing 32 in a position such that there is clearance between the lower edge 32a and the upper surface of floating shoe 25. The force exerted on the pistons.34 by thc springs 35 may be overcome by the hydraullc ram 3. Hence, the skid clamp 2 nlay be pulled or pushed along the skid rail 1 with the pistions 34 engaged by the springs 35. Looking at Figure 1, if the right most piston head 34a encounters an irregularity in the surface of the skid tail 1, it will move upward against the force of the beileville spring 35 and when the irregularity is passed, the right most piston head 34a will return to its previous position. In this way the piston heads 34a ride oer surface irregtdariries.

3) The force exerted on the piston heads 34a by the springs 35 is additional to the force exerted by hydraullc pressure and therefore the skid clamp can generate a greater break out fbrcc for breaking out a frozen derrick.

Tile secondary clamping member 40 comprises a plurality of actuators 41 arranged to actuate the pistons 34 of the prmlary clamping member 31.

Each actuator 41 comprises a piston head 47 that is attached to the second shaft portion 34c of the piston shaft. In the present example the second shaft portion 34c is externally threaded and the piston head 47 includes a central bore 48, which is internally threaded. The piston head 47 is hence screwed on to the second shaft portion 34c so that the piston head 47 moves with the piston 34. In the present example, the piston head 47 comprises at-ecess 49 extenditig around its outer surface and in which is mounted a bearing ring (not shown).

liie actual-or 4! comprises acyFnder 50 in which the piston head 47 reciprocates.

The actuator 41 ffirther comprises a cylinder head 42 which is removably attached to the cylinder by suitable fastening means, which in the example are bolts 43.

Tn the illsutrated example, thc actuators 4! of the secondary clamping member 40 are double acting, that is the actuator comprises a piston head 47 and cylinder 50 which is configured for pressurisafion to both sides of the piston head 47 so that the actuator may exert a force in two opposing directions.

The actuator includes hydraulic fluid ports situated to provide hydraulic fluid to each side of the piston head 47. Tn the illustrated example, a port 45 is provided in the cylinder head 42 providing for the passage of hydraulic fluid into -and out of the space in the cylinder 50 between the under side of the cyhnder head 42 and the upper surface of the piston head 47.

A second hydraulic fluid port 51 is provided in the wall of cylinder 50. TIlie port SI provides for the passage of hydraulic fluid into and out ofthc space between the underside of piston head 47 and the upper surface of housing 32.

1he second actuator provides a number of different facilities to the skid clamp operator: I) A secondary means for actuafing the pistons 34 is provided. In the event of a failure of a hydraulic seal below the piston head 47, the hydraulic fluid supply may he switched from the hydraulic fluid ports 33d to the ports 45. The ports 33d are connected to atmosphere via a filter and die motive hydraulic force to engage the piston heads 34a is exerted on the uppet surface of the piston heads 47. This in itself is a major advantage, since a breakdown during an operation to ralocate the drilling derrick can be very cosfly. If a part requiring replacement is not to hand there may he a long wait before the skid clamp can be repaired. The skid clamp of the presctit invention allows the operation to be continued, and for maintenance of the skid damp to be carried out when its use is not required.

2) Where the drilling rig has the appropriate number ofpressurised hydraulic lines, the actuators 41 may be used to lift the piston head 34a out of engagement with the floating shoe 25. This is achieved by depressurising the hydraulic fluid line connected to port 33d or 45 and pressut-ising the port 51 to indroduce hydraulle fluid to the underside of the piston head 47, hence llfting the piston 34 away front the floating shoe 25.

3) \Vhen the skid damp 2 is being used to breakout a frozen derrick (the tenn, "frozen derrick" is used to describe a derrick that is very difflcui.t to move as a resui.t of corrosion between the skid rails I and the pads of the derrick which sit on the rails 1) very large forces may be required.

Pressurised hydraulic fluid may be introduced via both the ports 33d and the port 45 so that hydraulic fluid pressure is exerted on on both the piston head 34a and the piston head 47.

The actuators 41 further comprise a mechanical arrangement for kicking the skid rail clamp 2 in its skid rail gi-ipping state. The cylinder head 42 includes an internally threaded bore 42a. A threaded boil 60 engages with the threaded bore 42a. The boll 60 is preferably provided with a domed end 61 which is configured to engage with a corresponding'y domed surface 34d of the piston shnft. By turning the boils 60 so that they engage the pistons a force can be exerted on the floating shoe 25 via the piston heads 34a to lock the skid rail danip 2 in a posithn. This may he to generate an extreme breakout force where a derrick is frozen, to provide a brake for rhe derrick when the derrick relocation operation is complete, or when harsh weather that may cause the derrick to move, such as a hurricane, is forecast.

Claims

1. A skid rail gripping clamp mountable on a skid rail, the clamp having a skid rail gripping state and a skid rail sliding state wherein the skid rail damp comprises at least two members configured to grip a skid rail when at least one of the at least two members is subject to an actuating force, at least one fluid powered actuator adapted to exert the actuating force and wherein the at least one fluid powered actuator comprises at least two pistons mounted on a common shaft, and wherein each of the pistons is mounted in its own cylinder and wherein each cylinder includes is port for the passage of pressurised fluid to exert a force on the respective pistons in the same direction.

2. A skid rail gripping clamp according to Claim 1, wherein each actuator includes a resilient member configured to exert a force on at least one of the pistons to urge said piston into a skid rail gripping state.

3. A skid rail gripping clamp according to Claim 2, wherein the resilient member is a spring.

4. A skid rail gripping damp according to Claim 3, wherein the spring is a compression spring

5. A skid rail gripping clamp according to Claim 3 or 4, wherein the spring is a bclleville spring, a coil spring, a leaf spring or a rubber spring

6. A skid rail gripping clamp according to any preceding claim, ftirther comprising a mechanical lock associated with each fluid powered actuator, the mechanical lock configured to selectively lock the damp in its gripping state.

7. A skid rail gripping damp according to Claim 6, wherein the mechanical lock is configured to exert a force through the common shaft.

8. A skid rail gripping damp according to Claim 7, wherein the mechanical lock is configured to engage thc common shaft.

9. A skid rail gripping damp according to any preceding claim, wherein each piston is provided with a seal, the seal configured to seal between the surface of the piston facing the surface of the cylinder and the said surface of the cylinder.

10. A skid rail gripping cbunp according to any preceding claim, wherein one of the pistons is ptoicled with a second pressurised fluid supply configured to introduce pressurised fluid to the opposing side of the Inston.

II. A skid rail gripping damp according to any preceding daim, finither comprising at east one floating member, wherein the at least one floating member is one of the gripping members and one of the pistons of the at kasr one actuator is arranged to exert an actuating force on the-at least one floating Il1enlbet.

12. A skid unit comprising a skid rail gripping damp according to any preceding daim and an actuator having two ends, one end attached to the skid rail gripping clamp and the other to an object.1:3. A skid rail gripping damp suhstanhally as shown in, and as descrihed with reference to, the drawings.14. A skid unit substantially as shown in, and as described with reference to, the drawings.