Combined grip control of elevator and spider slips

Apparatus for gripping and releasing a tubular and comprising an elevator (13) having slips (15) for gripping and releasing a tubular (39,40). A spider (12) has slips (14) for gripping and releasing the tubular (33). A mechanically operated valve (18) is provided for controlling the supply of pressurised fluid to move the spider slips (14) between a gripping position and a release position, with sensor means (28) detecting when the elevator slips (15) are in the gripping position. Means (31) mechanically inhibits movement of the valve (18) to a position in which the spider slips (14) release the tubular (40) when said sensor means (28) detects that the elevator slips (15) are not in a correctly gripping position. A second valve (20) controls movement of the elevator slips (15) and a guide plate (24) links control of both valves (18, 20).

The present invention relates to a method and apparatus for gripping tubulars, for example drill pipe. More particularly, the present invention relates to the provision in such a method and apparatus of a mechanism for avoiding the accidental release of tubulars during a handling operation.

During the construction and maintenance of oil wells it is necessary to construct extremely long strings of tubulars. For example, in order to drill a well a drill string is used, whilst after a well has been drilled a casing string must be constructed in order to line the well. Subsequently, a tubing for conveying oil to the surface is inserted inside the casing. Due to the great weight of such tubular strings, possibly several hundred tons, extreme care is required when constructing, raising, and lowering the strings.

FIG. 1illustrates in schematic form a typical tubular handling system which is mounted on the surface of an oil drilling platform1. Mounted in the platform itself is a spider2for gripping a tubular3extending beneath the platform1into a well. The spider2may be mounted within a rotary table, for example where the string3is a drill string. Suspended above the platform1is an elevator4which is arranged to grasp individual lengths of tubular5which are to be attached to the string3, or alternatively which have just been removed from the string3. The elevator5must also take the full weight of the string3during the raising or lowering of the string3through the spider2(and immediately following the addition or removal of a length of tubular from the string). Both the spider2and the elevator5must be able to take the full weight of the string3.

A typical sequence of events during the making up of a string is as follows:the spider grips the existing string;a new length of tubular is removed from a storage rack and is gripped in a vertical orientation by the elevator;the elevator is moved to position the lower pin7of the new length above the upper box6of the string projecting from the spider—and the opposed pin and box are engaged;the grip of the elevator is released, and the new length is engaged by a power tong and spinner and the joint tightened;the elevator again grips the string and is raised slightly to take the weight of the string, and the spider releases the string;the string is lowered by the elevator through the spider by the height of one length of tubular;the string is once again gripped by the spider, and the elevator released to collect a further length of tubular.

The basic construction of the spider2and the elevator5is the same and is illustrated in a cross-section inFIG. 2. A hollow cylindrical structure8has an inner wall which slopes outwardly towards its upper opening. A member9supports a set of slips (for example three)10which are shaped to slide into the upper opening of the structure8and at to engage the sloping inner sidewalls of the structure8. The slips10are free to move radially to a limited extend. Each slip10can be raised and lowered relative to the structure8by a pneumatically or hydraulically driven piston11which engages a cylinder extending into the structure8. It will be understood that when the slips10are in the lowered position, they will engage the outer surface of a tubular passing through the centre of the apparatus. The weight of the tubular and the friction between the tubular and the slips10will force the slips10downward and inward (as a result of the reaction force between the slips10and the inner surface of the structure8). Thus the grip tightens on the tubular5.

The hydraulic or pneumatic power which can be applied to the pistons which move the slips is limited. The resulting force is not sufficient to raise the slips of an elevator or spider when that elevator or spider is taking the weight of any significant length of tubular. In theory at least it is not possible for an operator to release the slips of the elevator and the spider at the same time, an action which would result in the dropping of the tubular into the well.

A potential problem with the slip design described however is that it is possible, when the new length of casing has been attached to the string and the elevator regrips the tubular, for the elevator to grip the tubular at too high a point such that the slips contact the tubular at the junction between the outstanding box and the main body of the tubular. Thus, the only contact between the slips and the tubular may be over a small part of the length of the slips. This situation is illustrated inFIG. 3. The elevator may be able temporarily to hold a sufficient proportion of the full tubing string weight to allow the spider slips to be released. However, following the raising of the spider slips, the elevator may not be able to take the full weight of the string with the string being dropped into the well.

A possible solution to the problem has been disclosed in U.S. Pat. No. 4,676,312. This document describes an interlock circuit in which the supply of pressurised air to the valve which controls the movement of the spider slips is prevented by an interlock valve if the elevator slips are not correctly engaged with the tubing.

According to a first aspect of the present invention there is provided apparatus for gripping and releasing a tubular, the apparatus comprising:an elevator having slips for gripping and releasing the tubular;a spider having slips for gripping and releasing the tubular;a valve for directly controlling a supply of pressurised fluid to move the spider slips between a gripping position and a release position; andmeans for mechanically inhibiting movement of said valve to a position in which the spider slips release the tubular when the elevator slips are not in a gripping position.

As used here, the term “elevator” means apparatus which is arranged to grip and hold a tubular for the purpose of raising and lowering the tubular. The term “spider” means an apparatus arranged to grip and hold a tubular whilst remaining substantially stationary.

Embodiments of the present invention may significantly reduce the risk of a tubular being dropped into the well as a result of the elevator slips not properly engaging the uppermost length of a tubing string. The movement of the valve controlling the opening of the spider slips is mechanically inhibited if the elevator slips are not correctly engaging the tubular.

Preferably, said valve for directly controlling the supply of pressurised fluid to move the spider slips is a mechanically operated valve which is operated manually. Alternatively however, the valve may be operated by an electrical motor, solenoid, etc, and/or may be remote controlled (e.g. using radio, infra-red, or ultrasonic signals).

In certain embodiments of the present invention, the valve for controlling the supply of pressurised fluid to the spider slips is operated by a lever. The means for mechanically inhibiting movement of the valve comprises a guide plate through which the lever projects. The guide plate is moveable between first and second positions. In a first position the guide plate prevents movement of the lever to open the valve and in a second position allows movement of the lever to open the valve. Movement of the guide from the first position to the second position is prevented if the elevator slips are not correctly closed.

In certain embodiments of the present invention, the apparatus comprises sensor means for detecting when the elevator slips are in the correct gripping position. The sensor means is coupled to said means for mechanically inhibiting movement of the spider control valve.

In certain embodiments of the invention, the sensor means comprises a piston and cylinder arrangement coupled between the main body and the slips of the elevator. The piston and cylinder arrangement is coupled hydraulically to said means for mechanically inhibiting movement of the spider control valve.

In other embodiments of the present invention, said sensor means comprises a switch which is moved from a first position to a second position when the elevator slips are moved to the correct closed position. When the switch is in the first position, movement of the guide plate from its first to its second position is prevented. When the switch is in the second position, movement of the guide plate from its first to its second position is possible. More preferably, the switch controls the supply of pressurised fluid to a piston and cylinder arrangement, the piston of which locks the guide plate in its first position when the supply of pressurised fluid to the cylinder is prevented, and releases the guide plate when the supply of pressurised fluid to the cylinder is allowed. Preferably, said switch is arranged to directly open and close a hydraulic or pneumatic circuit. Alternatively, the switch may form part of an electrical circuit which is arranged to open and close a hydraulic or pneumatic circuit.

The means for mechanically inhibiting movement of the spider control valve may comprise a piston and cylinder arrangement of a hydraulic or pneumatic circuit coupling an elevator control valve to a piston and cylinder arrangement for opening and closing the elevator slips. The first mentioned piston and cylinder arrangement is located between the piston and cylinder arrangement for moving the slips and the elevator control valve. A rod of the first mentioned piston and cylinder arrangement is displaced by the flow of fluid in the circuit to inhibit or allow movement of the spider control valve.

Other arrangements for locking and unlocking the guide plate are envisaged. The sensor may be an optical or electrical switch which detects closure of the elevator slips. The switch may control the supply of pressurised fluid (pneumatic or hydraulic) to a guide plate locking means.

The apparatus may comprise a mechanical link coupling the elevator slips to the means for mechanically inhibiting movement of the spider control valve. For example, the link may be a Bowden cable where movement of the elevator slips causes a corresponding movement of the core of the cable which is connected to the means for inhibiting movement of the spider control valve.

It will be appreciated that the apparatus may also comprise a mechanically operated valve for controlling the supply of pressurised fluid to move the elevator slips between a gripping position and a release position. This valve may be operated by a lever which also projects through said guide plate. Preferably, when the guide plate is in its first position, the lever may be moved to open the elevator slips, whilst when the guide plate is in its second position, movement of the lever to open the slips is prevented.

In alternative embodiments of the invention, the mechanically operated valve for controlling the supply of pressurised fluid to move the spider slips between a gripping position and a release position may be operated by a switch, knob, or the like, with movement of the knob, switch, etc being inhibited to prevent the valve being operated to open the spider slips when the elevator slips are not correctly closed.

An additional user operable locking means may be provided for preventing accidental movement of the guide plate between the first and second positions.

In alternative embodiments of the invention, the apparatus comprises a second valve for directly controlling a supply of pressurised fluid to move the elevator slips between a gripping position and a release position, wherein said means for mechanically inhibiting movement of the first mentioned valve comprises a mechanism for meshing said first and second valves together.

Preferably, the first and second valves are capable of controlling the flow of pressurised air and hydraulic fluid. More preferably, the first and second valves are ball valves.

Preferably, the first and second valves may each be rotated between a first position in which the associated set of slips is caused to be closed and a second position in which the associated set of slips is caused to be open. More preferably, the meshing of the valves results in the locking of the first valve in the first position, when the second valve is in the second position, and the release of the first valve when the second valve is rotated from the second to the first position. The meshing of the valves may also result in the locking of the second valve in the first position, when the first valve is in the second position, and the release of the second valve when the first valve is rotated from the second to the first position.

The first and second valves may each comprise a substantially cylindrical body member rotatable around its longitudinal axis. Each cylindrical body has an arcuate section cut away, and the cylindrical bodies are arranged co-axially so that when the first valve is located in the first position, and the second valve is located in the second position, part of the second valve is located in the cut away of the valve, and vice versa when the first valve is located in the second position and the second valve is located in the first position.

Preferably, the means for mechanically inhibiting movement of the spider slips control valve further comprises sensor means for detecting when the elevator slips are in the correct gripping position. The sensor means is coupled to a mechanism for locking said first valve in the first position when the elevator slips are detected to be open, thus preventing rotation of the first valve from the first to the second position, and the release of the second valve.

Preferably, second sensor means is provided for detecting when the spider slips are in the correct gripping position. The second sensor means is coupled to a mechanism for mechanically locking the second valve in the first position when the spider slips are detected to be open, thus preventing rotation of the second valve from the first to the second position, and the release of the first valve.

The first and second detector means and the respective valve locking mechanisms ensure that a valve cannot be moved from the first to the second position to open the associated slips, unless the other set of slips are detected to be closed.

In certain embodiments of the invention, the first and second sensor means comprise respective piston and cylinder arrangements arranged beneath the slips of the elevator and spider. Each piston and cylinder arrangement is coupled hydraulically or pneumatically to the corresponding locking mechanism. Each locking mechanism may comprise a hydraulically or pneumatically operate locking rod which is moveable between a position in which the rod engages the corresponding valve and a position in which the rod is disengaged from that valve.

The apparatus may comprise a mechanical link coupling the elevator slips to the means for mechanically inhibiting movement of the spider control valve. For example, the link may be a Bowden cable where movement of the elevator slips causes a corresponding movement of the core of the cable which is connected to the means for mechanically inhibiting movement of the first valve.

Preferably, said valves for directly controlling the supply of pressurised fluid to move the spider and spider slips are mechanically operated valves which are operated manually. Alternatively however, the valves may be operated by electrical motors, solenoids, etc, and/or may be remote controlled (e.g. using radio, infra-red, or ultrasonic signals).

In one embodiment of the invention, said means for mechanically inhibiting movement of said valve comprises a sensor coupled to the elevator slips and arranged to sense movement of the elevator slips between an open and a closed position, the sensor being coupled to an electronic controller arranged to control a means for mechanically inhibiting movement of said valve.

According to a second aspect of the present invention there is provided a method of controlling the gripping and releasing of a tubular and comprising mechanically inhibiting movement of control means for directly controlling a flow of fluid to raise and lower a set of spider slips, when a set of slips of an elevator are not correctly gripping the tubular, such that the spider slips cannot be moved from a gripping to a release position.

Preferably said control means is a valve. However, the control means may be any other suitable apparatus such as a pump.

According to a third aspect of the present invention there is provided a method of gripping and releasing a tubular, the method comprising the steps of:gripping the tubular with a spider;actuating a set of slips of an elevator in order to move the slips from a position in which the tubular is not gripped by the elevator slips to a position in which the tubular is gripped by the elevator slips;in the event that actuation of the elevator slips does not cause the slips to move into the gripping position, mechanically inhibiting movement of a valve directly controlling the movement of a set of spider slips such that the spider slips cannot be moved from a gripping to a release position; andin the event that the elevator slips achieve the correct gripping position, allowing said valve to be operated to move the spider slips from the gripping to the release position.

According to another aspect of the present invention there is provided apparatus for gripping and releasing a tubular, the apparatus comprising:an elevator having slips for gripping and releasing the tubular;a spider having slips for gripping and releasing the tubular;a first valve for directly controlling a supply of pressurised fluid to move the spider slips between a gripping position and a release position;a second valve for directly controlling a supply of pressurised fluid to move the elevator slips between a gripping position and a release position, andsaid first and second valves being meshed together in order to mechanically inhibit movement of said first valve to a position in which the spider slips release the tubular when the elevator slips are not in a gripping position.

According to another aspect of the present invention there is provided apparatus for gripping and releasing a tubular, the apparatus comprising:an elevator having slips for gripping and releasing the tubular;a spider having slips for gripping and releasing the tubular;a first valve for directly controlling a supply of pressurised fluid to move the spider slips between a gripping position and a release position;a second valve for directly controlling a supply of pressurised fluid to move the elevator slips between a gripping position and a release position;sensor means coupled to the elevator and the spider for detecting opening and closure of the respective slip sets; andmeans coupled to the sensor means and arranged to lock or release the first and second valves in dependence of the outputs of the sensor means.

According to another aspect of the invention there is provided apparatus for gripping and releasing a tubular, the apparatus comprising:an elevator having slips for gripping and releasing the tubular;a spider having slips for gripping and releasing the tubular;a first valve for directly controlling a supply of pressurised fluid to move the spider slips between a gripping position and a release position;a second valve for directly controlling a supply of pressurised fluid to move the elevator slips between a gripping position and a release position; andsensor means coupled to the elevator and the spider for detecting movement of the elevator and/or spider slips when taking over the load of a tubular.

A conventional system for handling tubulars using an elevator and spider arrangement has been described above with reference toFIGS. 1 to 3. There will now be described a control system for controlling the operation of such a spider and elevator arrangement in order to reduce the risk of a tubular being dropped down a well. The following discussion concerns the making or breaking of a drill pipe string although the apparatus and control system can equally be used with a well casing or tubing.

With reference toFIG. 4, there is illustrated a spider12having a set of slips14, and an elevator13having a set of slips15. The spider and elevator each have a construction which is similar to that illustrated inFIG. 2. More particularly, the slips14,15of the spider12and elevator13are raised and lowered by respective hydraulically operated piston and cylinder arrangements16,17(only one piston cylinder arrangement is shown inFIG. 4for each of the elevator and spider). Pressurised fluid is supplied to the piston arrangement16of the spider12via a spider control valve18and supply lines19. Similarly, Pressurised fluid is supplied to the piston and cylinder arrangement17of the elevator13via an elevator control valve20and supply lines21.

Both the spider control valve18and the elevator control valve20are operated by respective levers22,23. In order to close a set of slips14,15which are currently in the release position, the lever of the corresponding control valve is moved for a short time (e.g. a few seconds) to a “close” position. After the slips have been moved, the lever is returned to a central “neutral” position. Similarly, in order to open a set of slips14,15currently in a closed position, the corresponding lever is moved for a short time to an “open” position before being returned to the central neutral position. Each lever22,23therefore has three positions; open, close, neutral. In the arrangement shown inFIG. 4, the close position for the control valves18,20is the uppermost position of the respective levers22,23, whilst the open position is the lowermost position of the levers. The neutral position lies in the centre.

In order to control the operation of the levers22,23, the control valves18,20are mounted directly beneath a guide plate24(in the schematic illustration ofFIG. 4, the control valves18,20and levers22,23are shown displaced from the guide plate24for the sake of clarity). The guide plate24has a series of slots25machined into it. The slots25define the various positions to which a lever22,23can be moved during certain stages of a pipe handling process. The guide plate24is slidably mounted within a box26which contains the spider and elevator control valves18,20. The guide plate24can be slid between a first rightmost position to a second leftmost position, providing that both levers22,23are in the close positions (and that the guide plate24is not otherwise locked—see below).

In the first operational position, the elevator control valve lever23can be moved from the neutral position to both the open and close positions, whilst the spider control valve lever22may be moved between the neutral and the close position. In the second operational position of the guide plate24, the elevator control valve lever23must remain in the close position, whilst the spider control valve lever22may be moved from the neutral position to both the open and close positions.FIG. 5illustrates the guide plate arrangement in more detail.

With reference again toFIG. 4, an auxiliary hydraulically operated piston and cylinder arrangement28is shown coupled to the annular ring29on which the elevator slips15are mounted. The arrangement28does not play an active part in raising and lowering the slips15, but rather acts as a passive slip position sensor. The position of the piston within the cylinder tracks the position of the elevator slips15. The arrangement15is coupled via hydraulic fluid supply lines30to a guide plate locking mechanism31. This mechanism comprises a further piston and cylinder arrangement. A rod32coupled to the piston35of the mechanism31is arranged to engage the guide plate24when the piston35is fully extended, locking the guide plate24in its rightmost position. However, when the piston35is withdrawn, the rod32disengages the guide plate24allowing the guide plate to move freely between its leftmost and rightmost positions (subject to the position of the levers22,23).

FIG. 5illustrates a lock27which blocks a slot which, when unblocked, allows the movement of the spider control valve lever22to the open position—in exceptional circumstances, when it is required to open the spider slips14and the elevator slips15at the same time, this lock27may be manually removed.

The operation of the control system ofFIG. 4will now be described, assuming that the system has previously been operated such that the slips of the spider12are gripping a lower portion of a drill string33whilst the slips15of the elevator13are in the raised or open position relative to an upper length of drill pipe34. Assume now that the upper length34has been attached to the lower drill pipe string33and that the joint has been sufficiently tightened. In order to allow the drill string33to be lowered through the spider12such that a further length of drill pipe may be attached to the top of the string33, the slips14of the elevator13must be closed to allow the elevator13to take the full weight of the drill string39when the spider slips14are raised. The guide plate24is currently in the rightmost position such that the lever23of the elevator control valve20can be moved from the neutral position to either the open or close position. The lever23is moved by the operator to the close position and the control valve20opened to supply pressurised fluid to the top of the piston cylinder arrangement17. The application of pressurised fluid results in the slips being lowered into the elevator13.

The position of the piston within the arrangement28tracks the position of the elevator slips15relative to the elevator body. Movement of the piston within the cylinder causes fluid to be expelled from the cylinder, through the supply lines30into the top of the cylinder of the arrangement31. This causes the piston35to be withdrawn into the cylinder, moving the locking rod32away from the guide plate24. When the elevator slips15have been lowered to the correct position in which they engage the body of the pipe length34, the rod32is disengaged from the guide plate24. In this position, the guide plate24can be moved by the operator to the left providing that both levers22,23are held in the close position. The lever22can then be operated to open the spider slips14. This configuration is illustrated inFIG. 6.

In the event that the operator moves the elevator control valve lever23to the close position whilst the elevator13is located at too high a position with respect to the upper length of drill pipe length34, it is possible that the elevator slips15may close around the junction between the upper box of the pipe and the main body of the pipe (the situation illustrated inFIG. 3). If this happens, then the grip achieved by the elevator13on the pipe length34is not necessarily sufficient to take the full weight of the drill pipe string33. The grip achieved might be sufficient to take enough of the weight to allow the spider slips14to be raised. As has already been described, this situation can result in the subsequent dropping of the string into the well. However, it will be appreciated that if the elevator slips15close about the box of the pipe length34, then the slips15will not be able to move to their correct lower position relative to the elevator body. Rather, the slips15will become “jammed” at some intermediate position.

If this situation arises, the piston of the sensor arrangement28will not be sufficiently withdrawn into the cylinder. The volume of fluid transferred to the arrangement31will not be sufficient to fully disengage the rod32from the guide plate24. It will not therefore be possible for an operator to move the guide plate24to the left, and to open the spider slips14. This embodiment of the present invention therefore provides a mechanical “sequencer” for the spider and elevator control valves18,20.

FIG. 7illustrates an alternative control system for ensuring that the spider slips14cannot be opened when the elevator slips15are not correctly gripping the drill string. Components common to the system ofFIG. 4have been identified using the same reference numerals. A piston and cylinder arrangement40has a rod41coupled to its piston42. This rod41provides the locking mechanism for the guide plate24. The arrangement40is located within the fluid circuit44,45coupling the control valve20to the arrangement17which raises and lowers the elevator slips15. A one way valve43is connected in parallel with the arrangement40. When the elevator slips15are lowered, fluid is expelled from the cylinder(s) of the arrangement17. This fluid drives the piston41into its cylinder (no fluid can flow through the valve43), causing the rod41to disengage from the guide plate24. Assuming that the elevator slips15are lowered to the correct position, the guide plate24is free to move to the left. Of course if the slips are not lowered correctly, then the guide plate24is prevented from moving by the rod41.

When the valve20is subsequently operated to raise the elevator slips15(following the opening and closing of the spider slips14), pressurised fluid drives the piston42out of its chamber. The pressurised fluid expelled from the chamber is in turn forced into the chamber(s) of the elevator slip drive arrangements17, causing the elevator slips15to be raised. The valve43is provided to compensate for leaks, and ensures that sufficient fluid is available to fully open the elevator slips15when required.

FIG. 8illustrates another control system according to the present invention. Again, reference numerals used inFIG. 4have been reused to identify common parts. It is noted that the embodiment ofFIG. 8uses a guide plate24having a different arrangement of guide slots50. This arrangement allows the guide plate24to be shifted only when both levers22,23are in the neutral position (and movement is not prevented by the locking rod32). The guide plate24is shown in more detail inFIG. 9.

With reference toFIG. 8, a mechanically operated valve switch51is rigidly attached to the main body52of the elevator13. The valve switch51forms part of a pneumatic control circuit. A contact member53is attached to the upper annular ring29which supports the slips15. When the spider slips15are in the raised position, i.e. the spider is in the release position, the contact member53is not in contact with the valve switch51. In this position, the valve switch51remains closed and does not pass compressed air from its input to an output. However, when the spider slips15are in the correct lowered position, and the spider13is in the gripping position, the contact member53contacts the valve switch51, causing the switch to open and compressed air to be supplied from the input of the valve switch51to its output.

Pressurised fluid is supplied to the input of the valve switch51via a supply line54(which is coupled to a pressurised source of fluid which is not shown in the drawing). The output of the valve switch51is provided to the input of a delay circuit. This circuit comprises a one way flow regulator55which allows the compressed air from the output of the valve switch51to be fed to the input of an accumulator56. The output of the accumulator56is provided to a control input of a second valve switch57. The main input of the second valve switch57is coupled to the supply line54. The output of the second valve switch57is provided to an input of the piston and cylinder arrangement31, which input is situated in front of the head of the piston35.

In the event that the elevator slips15close about the main body of the drill pipe34, the slips15will be lowered relative to the elevator13to the required extent. The contact member53will contact the valve switch51, causing the switch to open. Compressed air will flow from the supply line54, through the flow regulator55to the input of the accumulator56. Pressure builds up in the accumulator56until the pressure at the output of the accumulator56causes the second valve switch57to open. The time taken for the accumulator56to charge to a sufficient pressure to activate the second valve switch provides a short time delay between the closure of the elevator slips15and the possible release of the guide plate24. As long as the second valve switch57remains closed, no pressure is present at the head of the piston35and the piston remains in its fully extended position in which the guide plate24is locked in its rightmost position. However, when the second valve switch57is opened, compressed air from the supply line54is conducted to the head of the piston35causing the piston to be retracted within its cylinder. The retraction of the piston35causes the guide plate24to be released. Assuming therefore that the operation of the lever23has resulted in the elevator slips15being moved to their correct lowered or closed position, the operator can slide the guide plate24to its leftmost position. The operator can then operate the lever22of the spider control valve18to move the spider slips14to their raised or open position. The elevator13then takes the full weight of the drill pipe string33. This configuration is illustrated inFIG. 10.

In the event that the elevator slips15grip around the box of the drill pipe34, the contact member53attached to the slip support ring29will not contact and open the valve switch51. Thus, no pressure will be applied to the head of the piston35and the guide plate24will remain locked in its rightmost position. In this position, the lever22operating the spider control valve18cannot be moved from its neutral position to open the spider slips.

FIG. 9illustrates a manually operable locking mechanism58which is mounted in the box26supporting the guide plate24. The locking mechanism58is of a type which when pulled out allows movement of the guide plate24from the left to the right and vice versa whilst when pushed in prevents such movement of the guide plate24. In order to move the guide plate24from the right to the left position, in addition to the piston35being fully withdrawn into the cylinder29, the operator must pull out the locking mechanism58(against a spring force) and at the same time slide the guide plate24from the right to the left. When the operator releases the mechanism58, the guide plate cannot be shifted to the right unless the operator again pulls out the mechanism58. The locking mechanism58therefore provides an obstacle to an operator moving the guide plate24to the left, opening the spider slips, and then sliding the guide plate to the right and opening the elevator slips (this could of course only happen in the case that a small length of drill pipe is being held by the spider elevator arrangement).

FIG. 11illustrates a further control system for controlling an elevator and spider arrangement such as has been described with reference toFIGS. 1 to 3. In this arrangement, the contact member53, coupled to the elevator slips15, is arranged to open and close an electrical switch60. The electrical switch60forms part of a circuit comprising a battery61and an electrically controlled valve62. When the elevator slips15are in the raised position, the contact member53is out of contact with the switch60, and the switch60is in the open position. The electrical circuit comprising the switch60therefore remains open and no electric power is supplied to the control input of the valve62. However, when the elevator slips15are correctly lowered, the contact member53closes the switch60such that the battery61is coupled to the control input of the valve62. This supply of power to the valve input causes the valve to close, connecting the supply line54to the input of a delay circuit having at its input a one way flow regulator63. As with the embodiment described with reference toFIG. 8, the output from the flow regulator63is provided to the input of an accumulator64.

When the pressure in the accumulator64reaches a predefined level, the pressure causes a valve switch65to move from a closed position in which no compressed air is passed from the supply line54to the piston head of the piston35, to an open position in which compressed air is provided to the piston head. Therefore, when the elevator slips15are raised (or are jammed at an intermediate position), the piston35remains in its fully extended position, locking the guide plate24in its rightmost position. However, when the elevator slips15are correctly lowered, the piston30is withdrawn within the cylinder29and movement of the guide plate24is allowed.

With reference toFIG. 12a,there is illustrated a spider102having a set of slips104, and an elevator103having a set of slips105, with the slips104,105of the spider102and elevator103being raised and lowered by respective hydraulically operated piston and cylinder arrangements106,107. As with the embodiment ofFIG. 4, pressurised fluid is supplied to the piston arrangement106of the spider102via a spider control valve108and supply line109, with pressurised fluid being supplied to the piston and cylinder arrangement107of the elevator103via an elevator control valve120and supply lines121.

Each of the control valves108,120comprises a cylindrical top plate122,123and a cylindrical body member124,125depending from the top plate. Both the top plate and the cylindrical body are rotatable together about their longitudinal axes, within the valve housing126. As can be seen inFIG. 12, each of the top plates122,123has an arcuate cut out section for receiving a part of the other cylindrical plate when both plates are in a given orientation. Levers127,128extend from the plates and project through the housing126to facilitate rotation of the valves.

Each of the valve cylinders124,125is arranged to rotate a ball member within a spherical socket formed in the valve housing. Each ball member has two bores extending through it in a transverse plane. The bores are arranged to couple fluid flow lines (leading to the piston and cylinder arrangements106,107and slip closure sensors to be described below) to a source of pressurised hydraulic fluid P and to a tank for draining fluid. The advantage of the particular valve arrangement described here is that it can handle both air (pneumatic) and hydraulic fluid without leakage, although only the use of hydraulic fluid is described here.

The spider102and elevator103are provided with respective slip closure sensors129,130. Considering the spider slip closure sensor129, this comprises a piston and cylinder arrangement, with a rod131extending from the piston head132being in contact with associated slips104. When the spider slips104are open, the piston is extended whilst when the slips are fully closed the piston is compressed within the cylinder. Hydraulic fluid flow lines133,134are coupled to the cylinder in front of and behind the piston head. The hydraulic lines133,134are coupled to a piston driven locking mechanism135, in front of and behind the piston head of that mechanism. When the spider slips104are moved from the open to the fully closed position, fluid is expelled from the bottom of the cylinder of sensor129, through the line134, causing a rod136of the locking mechanism135to be retracted into the cylinder. Fluid expelled from the cylinder of the mechanism135flows through line133into the top of the cylinder of the sensor129. The elevator slip closure sensor130operates in a similar manner to control a locking rod137of a locking mechanism138. It will be understood fromFIG. 4that the locking rods136and137are effective to prevent or allow rotation of the elevator and spider control valves respectively.

The operation of the system ofFIG. 12awill now be described. In the configuration illustrated in the Figure, the control valves108,120are oriented such that the elevator slips105are closed and the spider slips104are open. This results in the locking rod137locking the spider control valve108in place, with the locking rod136being disengaged from the elevator control valve120. Because of the position of the meshing of the valves108,120, the elevator control valve120can be rotated to a position in which pressurised fluid can be conducted to the piston and cylinder arrangement107to lower the elevator slips.

When the elevator slips are fully lowered, the piston of the sensor130is fully depressed. This in turn results in the locking rod137of the locking mechanism138being fully retracted, releasing the spider control valve108. Because of the new location of the cut out in the cylindrical plate123of the elevator control valve120, the spider control valve can now be rotated to conduct fluid to the piston and cylinder arrangement106to raise the spider slips104. The raising of the spider slips104is detected by the sensor129, and when the slips104are fully raised, the result is that the locking rod136is fully extended. This prevents rotation of the elevator control valve120to open the elevator slips105.

At this stage, all of the weight of the tubular is taken by the elevator102, whilst the accidental opening of the elevator slips105is prevented. The tubular may now be lowered through the spider102. When the tubular is at the correct height, the spider control valve108can be rotated (the locking rod137is at this stage retracted and the valves are meshed to allow rotation of the spider control valve) to engage the spider slips104. Both the spider and the elevator are now holding the tubular. The sensor129detects closure of the spider, and causes the locking rod136to retract, releasing the elevator control valve120. The elevator control valve120can then be rotated to raise the elevator slips105. This completes one cycle of operation.

The system ofFIG. 1has been described as using hydraulic power to raise and lower the slips, and to drive the control valve locking mechanisms. However, pneumatic power could be used for one or both of these purposes. In particular, it is envisaged that the elevator slips may be hydraulically operated, with the spider slips being pneumatically operated. With the ball valve arrangement described above, the same valve hardware may be used for both circuits.

FIG. 12billustrates a control system for the apparatus ofFIG. 1, and which comprises a pair of locking rods for locking respective intermeshing spider and elevator control valves. The locking rods are operated by respective single acting sensing cylinders associated with the spider and the elevator.

There is illustrated inFIG. 12ca further embodiment of the present invention. According to this embodiment, sensor cylinders501,502of the spider and elevator are connected via respective hydraulic circuits to locking rods503,504. The locking rods are moved into and out of engagement with the guide plate (seeFIG. 13) to restrict movement of the guide plate. It will be appreciated that in such an arrangement, temperature changes may adversely affect operation, i.e. temperature changes may result in the expansion and compression of fluid in the circuit (similar changes may result from changes in the operating altitude of the apparatus). To mitigate this problem, both hydraulic circuits are coupled to pressure compensation circuits505,506.

Each pressure compensation circuit comprises a valve which is opened or closed when the corresponding slip set is opened or closed, with the valve being coupled to a reservoir (or accumulator)507. When a valve is open and the apparatus is heating up, expanding fluid may flow through the valve from the hydraulic circuit and expands into the accumulator. In the same way, when the apparatus is cooling, fluid is sucked from the accumulator, through the valve, into the hydraulic circuit.

With reference toFIG. 13, there is illustrated a spider201having a set of slips202, and an elevator203having a set of slips204. The spider and elevator each have a construction which is similar to that illustrated inFIGS. 2 and 3. More particularly, the slips of the spider and elevator are raised and lowered by respective pneumatically operated piston and cylinder arrangements205,206. Pressurised air is supplied to the piston arrangement of the spider via a spider control valve207and supply lines. Similarly, Pressurised fluid is supplied to the piston and cylinder arrangement of the elevator via an elevator control valve208and supply lines.

Both the spider control valve and the elevator control valve are operated by respective levers209,210. In order to close a set of slips which are currently in the release position, the lever of the corresponding control valve is moved to a “close” position. Similarly, in order to open a set of slips currently in a closed position, the corresponding lever is moved to an “open” position. In the arrangement shown inFIG. 13, the close position for the control valves is the uppermost position of the respective levers, whilst the open position is the lowermost position of the levers.

In order to control the operation of the levers209,210, the control valves are mounted directly beneath a guide plate211(in the schematic illustration ofFIG. 13, the control valves and levers are shown displaced from the guide plate for the sake of clarity). The guide plate211has a series of slots212machined into it. The slots define the various positions to which a lever can be moved during certain stages of a pipe handling process. The guide plate is slidably mounted within a box (not shown) which contains the spider and elevator control valves. The guide plate can be slid between a first rightmost position to a second leftmost position, providing that both levers are in the close positions (and that the guide plate is not otherwise locked—see below).

In the first operational position, the elevator control valve lever210can be moved between both the open and close positions, whilst the spider control valve lever209is held in the closed position. In the second operational position of the guide plate211, the elevator control valve lever must remain in the close position, whilst the spider control valve lever may be moved between the open and close positions.

Sensor arrangements213,214are coupled to each of the spider and the elevator. These may be electrical, optical sensors, etc, and are arranged to detect when the slips of the spider and elevator are in the open and the closed positions. Both sensor arrangements are electrically coupled to a PLC215. The PLC contains logic for analysing the outputs of the sensors and controlling a pair of locking rods216,217accordingly. The locking rods may be driven by solenoids in response to control signals generated by the PLC, and are arranged to lock the guide plate in either its leftmost or rightmost position. When the PLC detects that the slips of the spider are closed, the rightmost locking rod is withdrawn, allowing the guide plate to be slid to the right, thus releasing the lever controlling the elevator slips (in this position, the left most locking rod snaps back into a locking position). This lever can then be moved to open the elevator slips. Similarly, when the elevator slips are subsequently closed (after for example the connection of a further tubular to a string), the left most locking rod is withdrawn, allowing the guide plate to be slid to the left, releasing the spider slip control lever which can be moved to open the spider slips. The right most locking rod has by this time snapped back to the locking position.

FIG. 14illustrates a modification to the system ofFIG. 13. In this modified arrangement, the electrical/optical sensors for sensing opening and closing of the slips are replaced by stroke sensors300,301located in the slip cylinders302,303. Yet another modified design is illustrated inFIG. 15. In this arrangement, a locking rod400,401is associated with each of the spider and elevator slip control valves. Each locking valve is driven by a solenoid electrically coupled to the PLC402. The PLC monitors the open/closed (and/or correct gripping) status of the slips and shifts the locking rods accordingly.

The stroke measurement can be used to monitor slip movement while taking over the string load to analyse the performance of the actual grip, i.e. as a quality control measurement.

It will be appreciated by the person of skill in the art that various modifications may be made to the above described embodiment without departing from the scope of the present invention.