US3711000A

US3711000A - Surface apparatus for handling an elastic column

Info

Publication number: US3711000A
Application number: US00178924A
Authority: US
Inventors: R Reynard; R Tindy; E Daniel
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 1968-09-04
Filing date: 1971-09-09
Publication date: 1973-01-16
Anticipated expiration: 1990-01-16
Also published as: GB1265420A; NL162711B; FR1595580A; NL162711C; ES371176A1; SE356786B; JPS49642B1; NL6913451A; DE1944920A1; DE1944920C3; SU639467A3; DE1944920B2

Abstract

This apparatus is provided with at least two devices for gripping an elastic column, including a lower and an upper gripping device, one at least of these devices being displaceable along the axis of the column in a released position. In this apparatus each of said devices is constituted by a plurality of separate gripping elements arranged in series, these gripping elements being interconnected through elastic means.

Description

United States Patent 1 1 Reynard et al.

[111 3,711,000 1 Jan. 16, 1973 [54] SURFACE APPARATUS FOR HANDLING AN ELASTIC COLUMN [75] Inventors: Remi Reynard, Montessori; Roger Tindy, Bougival; Edmond Daniel, Saulx-Les-Chartreux, all of France [73] Assignee: Institut Francais du Petrole des Carburants et Lubrifiants, Paris, France 22 Filed: Sept. 9, 1971 211 App]. No.: 178,924

Related US. Application Data [63] Continuation-in-part of Ser. No. 854,983, Sept. 3,

[30] Foreign Application Priority Data Sept. 4, 1968 France ..68l65l09 [52] US. Cl. ..226/8, 226/112, 226/115, 226/162 [51] Int. Cl. .J ..B65h 17/36 [58] Field of Search ..226/8, 158, 162, 163, 164,

[56] References Cited UNITED STATES PATENTS 1,028,523 6/1912 Anderson ..226/l64 X 3,330,459 7/1967 Cullen ..226/l73 Primary ExaminerRichard A. Schacher Attorney-Craig, Antonelli & Hill ABSTRACT This apparatus is provided with at least two devices for gripping an elastic column, including a lower and an upper gripping device, one at least of these devices being displaceable along the axis of the column in a released position.

ln this apparatus each of said devices is constituted by a plurality of separate gripping elements arranged in series, these gripping elements being interconnected through elastic means.

11 Claims, 7 Drawing Figures PATENTEUJM 16 I975 3.711.000

sum 1 or 4 INVENTORS ROGER TINDY REMI REYNARDI wma game/v0 DA I L PATENTEDJAN 16 Ian SHEET 2 [IF 4 I INVENTORS REM! REYNARD ROGER TINDY EDMOND DANIEL ATTORNEYS PATENTEDJAH 16 I973 SHEET 3 BF 4 INVENTORS REMI REYNARD ROGER TINDY EDMOND DANIEL BY r (JUN?) ATTORNEYS PATENil-ID AN 1 m 3.71 1. 000 SHEET u 0F 4 I INVENTORS REMI REYNARD ROGER TINDY EDMDND DANIEL BY 01%, RANQQ; r M110 ATTORNEYS SURFACE APPARATUS FOR HANDLING AN ELASTIC COLUMN This is a continuation-in-part application of copending US. patent application Ser. No. 854,983, filed on Sept. 3, 1969.

The present invention relates to a surface apparatus enabling an elastic column, particularly a column introduced into a borehole in the ground, to be handled, i.e., lowered into the borehole and raised back to the ground surface.

This column may, for example, be a flexible drill pipe used in the drilling process wherein there is substituted for the usual string of rigid stems a continuous flexible pipe at the lower end of which a bottom motor ,is directly connected to a drill bit for actuation thereof.

It is however also possible to use the apparatus according to the invention for handling a column or any elongated member of solid cross-section lowered in a borehole, such as a cable, liable to undergo some elongation under its working conditions.

The handling apparatus according to the invention is of a type provided with devices for gripping the elastic column, some of these gripping devices being movable along the column.

A first object of the invention is to provide an apparatus which may be associated with conventional equipment used in conventional drilling methods, such as derricks, hoisting devices using winches, cables and pulley blocks, without requiring any substantial change in these equipments.

The main object of the invention is to provide an apparatus for handling an elastic column capable of supporting loads which may reach many hundred tons, without imparting any sliding to this column relative to the gripping devices, under the action of the load, which sliding results in deteriorations of the wall of the column which are in contact with these gripping devices, or to creeping phenomena of this column, relative to the gripping devices applied thereto.

The apparatus according to the invention, whereby are achieved these objects, includes at least two devices for gripping the elastic column, comprising a lower and an upper gripping device, each of said devices being associated with means for displacing at least one of said devices parallelly to the column axis, means for sequentially controlling said displacing means and for causing a gripping action on said column through either of said gripping devices, so that there is always at least one of said gripping devices in its gripping position, the displacement of said gripping devices being effected in a first direction in the gripping position of the device and in the opposite direction in the released position of this device.

According to the invention, each of said devices for gripping the column is constituted by a plurality of separate gripping elements surrounding the column, arranged in series and interconnected through elastic means.

According to one particular embodiment of the invention, the elastic connection between the gripping elements of a gripping device is constituted of plates of elastic material, each gripping element being provided with a tubular housing engaged in a sleeve member integral with the tubular housing of an adjacent gripping element, thereby forming a telescopic mounting and the plates of elastic material being secured both to the external wall of each tubular housing and to the internal wall of the sleeve member wherein this housing is inserted.

The suspension of each gripping element from the adjacent upper gripping element might also be achieved by any other elastic means, using for example spring means or jack means connected to a source of fluid under pressure.

The so-constituted telescopic mounting exhibits the essential advantage of enabling the gripping jaws equipping each gripping element to follow a substantial elongation of the elastic column within the lower and the upper gripping devices.

An embodiment of the invention will be described hereinunder, with reference to the attached drawings, wherein FIG. 1 diagrammatically illustrates an overall view of the device;

, FIG. 2 illustrates a gripping element;

FIGS. 3, 3A, 3B and 3C represent schematically particular embodiments for the arrangement of the gripping elements each consisting of lower and'upper gripping members;

FIG. 4 illustrates an embodiment of the means for synchronously controlling the hoisting winch of the upper gripping device and for controlling reversible jacks adapted to move the jaws into and out of gripping position.

In FIG. 1 which diagrammatically shows an overall view of a drilling equipment for a flexible drill pipe, including an apparatus according to the invention for handling this pipe, the reference numeral 1 designates the drill pipe and 2 a derrick at the top of which the pipe passes over a pulley 3.

The pipe 1 is stored on a winch 4 associated with means for supplying the pipe with drilling fluid through a rotary coupling and passes between this winch and pulley 3 through a tension regulating device diagrammatically represented at 5, the winch 5 and the tension regulating device 5 forming however no part of the present invention.

The apparatus according to the invention, used for handling the flexible pipe 1, comprises a lower device 6 for gripping this pipe, this lower gripping device consisting of a series of gripping elements surrounding the flexible pipe, each of which is provided with gripping jaws and with a device for moving these jaws into and out of gripping position, adapted to reversibly displace them between a gripping position of the pipe 1 and a released position wherein the pipe can freely slide between the jaws and giving passage to the rigid metallic elements connected to the lower part of the flexible pipe, these elements comprising the drill bit and the driving motor for this bit.

This lower gripping device 6 is stationary, being integral with the substructure 7 of the derrick.

In combination with this stationary lower gripping device, the apparatus according to the invention includes an upper device 8 for the pipe 1, this device also consisting of a series of gripping elements, each of which is provided with jaws associated with a reversible device for displacing these jaws in a direction transverse to the pipe. This upper device is movable vertically over a stroke L along the pipe, in the released position of its jaws.

In the embodiment illustrated by FIG. 1, the means providing for the displacement of the upper gripping device 8 along the pipe 1 is constituted by a hoisting device of the type used in the rotary drilling method for handling the drill string and its elements.

This device includes cables 9 passing over a stationary pulley block 10 located at the top of the derrick (this stationary pulley block includes forexample two pulleys located on both sides of pulley 3) and over a travelling block 11 from which is suspended the upper gripping device 8, by means of a hook 12. The vertical displacements of the travelling block 11 are achieved by means of a winch 13 on which is wound a free end 9a of cables 9;

The adaptation of this conventional hoisting device to the embodiment illustrated by FIG. 1 of the apparatus according to the invention, for handling a flexible pipe, is achieved by providing an axial passage such as 14 through the travelling block 11 and axial bores through the hook 12, this passage and these bores being of a sufficient diameter for providing a free passage to the flexible drill pipe.

In combination with the above-indicated elements, the device according to the invention includes means for synchronously controlling on the one hand the means for displacing the upper gripping device 8 (winch 13 in the illustrated embodiment) and'on the other hand the means for moving the jaws of the two

gripping devices

6 and 8 into and out of gripping position.

These control means, which are not shown on FIG. 1 will be described hereinunder, with reference to FIG. 4.

These means are adapted to repeatably provide for either of the two following series of operations:

I. RAISING OF THE PIPE l. Simultaneous gripping of the pipe by the jaws of the. two

gripping devices

6 and 8, when the upper gripping device is in its lower position, substantially in contact with the device 6.

2. Releasing of the jaws of the lower gripping device 6, the upper gripping device remaining in its gripping position.

3.'Actuating the hoisting winch 13 so as to raise the upper gripping device 6.

4. Stopping this upper gripping device in its uppermost position at the end of its stroke L.

5. Moving the jaws of the lower gripping device into gripping position, then releasing the jaws of the upper gripping device 8, while the jaws of the device 6 remain in their gripping position.

6. Lowering of the empty device 8 over the stroke L, back to its lowermost position and stopping it in this position.

7. Moving the jaws of the device 8 into gripping position, in the lower position of this gripping device.

II. LOWERING OF THE PIPE l. Simultaneous gripping of the pipe by the jaws of the two

devices

6 and 8, while the upper gripping device is in its upper position at the top of the derrick.

2. Releasing of the jaws of the lower gripping device 6, the upper gripping device'8 remaining in its gripping position.

3. Downwardly moving the device 8 under the load of the flexible pipe with braking of this movement, for example through winch 13.

4. Stopping of the device 8 in its lowermost position.

5. Moving the jaws of the device 6 into gripping position, then releasing the jaws of the device 8, while the jaws of the device 6 remain in their gripping position.

6. Raising back the device 8 without load up to its uppermost position and stopping it in this position.

7. Moving the jaws of the device 8 into gripping position, in the upper position of this device.

FIG. 2 diagrammatically illustrates the structure of an element or gripping element constituting each of the

gripping devices

6 and 8.

This element includes at least two gripping jaws for the pipe 1 (jaws 15 and 16) which may grip the pipe 1 by means of reversible hydraulic jacks 17a, 17b which bear against a tubular-housing 18 whereon these jacks are articulated.

The

jaws

15 and 16 roll on rollers along inclined guide paths integral with this tubular housing.

These jaws and their guide paths constitute an automatic gripping system so designed as to exert on the pipe a gripping action always proportional to the downwardly directed vertical force (indicated by the arrow in FIG. 2) to which it is subjected as a result of friction between the jaws and the pipe, this arrangement being a safety factor.

In the examplative embodiment of FIG. 2, each of the

jaws

15 and 16 is constituted by two superimposed wedges integral with each other.

The reference numerals 37, 38, 39 and 40 designate rollers the axes of which are carried by

jaws

15 and 16, these rollers rolling along inclined guide paths carried by the tubular housing 18.

Each gripping element may obviously be provided with more than two gripping jaws, distributed along the periphery of the flexible pipe 1.

Inside each gripping element, such as the one shown by FIG. 2, the relative elongation. of the pipe 1 withrespect to the gripping jaws will be reduced since each gripping element only supports a fraction of the overall load supported by each of the

gripping devices

6 and 8 and because moreover the length of the pipe 1 passing through this element is only a fraction of the overall length of the pipe 1 passing through each of the

gripping devices

6 and 8.

In order to permit some relative displacement without any creeping of the pipe 1 inside each gripping jaw, it will be advantageous to provide each gripping I jaw, such as jaw 15 or jaw 16, with an internal coating or shoe made. of an elastomer on the internal wall of this jaw which comes into contact with pipe 1, or to fix the shoe to a pad made of an elastic material, such as an elastomer.

This shoe may moreover be divided into several super-imposed elements, optionally with some clearance left between the elements constituting the shoe.

FIG. 3 diagrammatically shoes a telescopic arrange-v ment, according to the invention, of the gripping ele-' ments constituting each of the

gripping devices

6 and 8.

In the illustrated embodiment the elements mounted in series are four in number, but this number is by no way limitative.

The number n of gripping elements constituting each gripping device will be selected sutficiently high so that, taking into account the coefficient of elongation of the column or pipe and the maximum load T to be supported by the lower and upper gripping devices, the maximum load T/n to be supported by each gripping element will correspond to a tolerable elongation ofthe portion of column or pipe passing through this gripping element.

The tubular housings of three of the four gripping elements (housings 18a, 18b and 180) is at one of its ends, for example at its lower end, extended through a sleeve member (

sleeve members

19a, 19b, 190) which is integral with this tubing and is adapted to receive the housing of an adjacent gripping element, thereby constituting a telescopic mounting in which the tubular housing 18 of an element and the sleeve member 19 surrounding this housing are interconnected through an elastic connection, for example by inserting one or more plates of elastomer, particularly an annular coating or sleeve of elastomer (coatings 20a, 20b and 200).

The fixation of the plates of elastomer onto the external wall of the housing 18 and to the internal wall of the sleeve member 19 may for example by achieved by vulcanization.

When the assembly of the gripping elements shown in FIG. 3 constitutes the movable upper element (FIG. 1), the housing 18a of the upper belt will be suspended from the hook 132.

FIG. 3A represents schematically another embodiment of the arrangement of the elements 18 to 18d constituting one gripping member.

Each gripping element is rendered integral with two crowns, a lower crown 100 and upper crown 101, the

end elements being equipped with only a single crown. These crowns have been identified with the reference numerals 101a, 101b, and 1010, and 100b, 1001: and 100d in FIG. 3A. Each upper crown carries a plurality of rods (102b, 1026 and 102d) being adapted to glide through orifices (103a, 103b and 1030) provided in the lower crown corresponding to the adjacent element positioned directly above.

An elastic spring (104b, 1040 and 104d) operating at the compression is placed between the lower crown of an element in a stopping plate made integral with the rods (102b, 1020 and 102d). The springs thus allow, because of the action of the charge supported by the column, for a relative displacement of the consecutive gripping elements constituting the gripping member.

FIG. 3B is a modified embodiment as to compare to FIG. 3A in which the springs have been replaced by jacks (105a, 105b, 1050), for example, pneumatic jacks connected by means of ducts (106a, 106b and 106a) to a storage or reservoir (not shown) containing a gas whose pressure makes it possible to regulate the stiffness of the elastic means thus provided.

FIG. 3C is another embodiment regarding these elastic means. In this example, the castings and jackets of the successive elements glide within each other, delimiting volumes supplied with gas under pressure by means of ducts (106a, 106b and 1066).

An embodiment of the means for synchronously controlling the hoisting winch 13 and the jacks which provides for moving the jaws into and out of gripping position is described hereinunder with reference to FIG. 4.

The reversible jacks 21a to 28a controlling the jaws 21b to 28b of the upper gripping device 8 and the jacks 29a to 36a of the jaws 29b to 3612 of the lower gripping device 6 are supplied with hydraulic-fluid from a tank 45, by means of a motonpump unit W, through two slide-

valves

46 and 47 which are mechanically interconnected, so as to be displaced synchronously.

This connection is diagrammatically indicated by a rod 48 in FIG. 4.

An arm 49 providing for electrical contact and forming a T with the connecting rod 48 integral with this arm provides for synchronous control of the actuation of the winch 13 and of that of the jaws, by closing electrical contacts A, O and B connected respectively to elements 59, 60 and 61 adapted to achieve the control of the motor driving the winch 13 in the direction corresponding to the operation to be affected on the column. These elements may comprise, for example, reversing means of the mechanical type with two positions in such a manner that for the operation of raising the pipe, the contact A assures the engagement of the winch in the direction for raising the movable upper gripping member, and the contact B assures the disconnection of the which 13, allowing for lowering the member 8 due to the effect of the charge with braking of the winch;

for operation of lowering the pipe, the contact A assures the disconnection of the winch 13, allowing for the lowering of the member 8 due to the effect of the charge with braking of the winch, then the contact B assures the engagement of the winch in the direction of raising the upper movable gripping member, the contact O assuring in each of these operations the stopping of the which.

The movements of the assembly of the slide-

valves

46 and 47 are controlled through an electrovalve 50, which, by admission of hydraulic fluid onto either of the end faces 51 and 52 of this assembly of slide-valves, through the ducts shown in dotted lines in FIG. 4, causes the displacement of this assembly of slide-valves either to the right or to the left of the drawing.

In the hydraulic circuit of FIG. 4, F designates a filter, the devices such as 53 and 54 are non-return valves, 55 a pipe supplying make-up hydraulic fluid so as to compensate for the losses in hydraulic circuit (this make-up supply of fluid is for example achieved from gauged oleopneumatic accumulators) and 56 designates a safety valve.

The devices such as 57 and 58 are devices for regulating the flow rate of the hydraulic fluid supplied to the jacks during gripping or releasing movement of the jaws respectively.

The position shown in FIG. 4 of the assembly of the control slide-

valves

46 and 47 corresponds to the gripping position of the jaws of the two

gripping devices

6 and 8, the winch 13 being stopped (arm 49 on contact 0), which corresponds to the stopping of the mova ble upper gripping element 8.

The elements 59, 60 and 61 having been brought, for example, into the position corresponding to the operation of lowering the pipe, by moving to the right of FIG. 4 the assembly of the two distributing slide-valves 46 and 47 (which is achieved by controlling the electrovalve 50 so as to move its slide to the left) the jaws of the lower gripping device 6 are moved away from each other, while the jaws of the upper gripping device 8 remain in gripping position.

The arm 49 for electric contact comes unto the contact M, which so actuates the winch 13 as to raise the gripping device 8.

A not-illustrated device, such as an electric retarding device, may be used so that the actuation of winch 13 be effected only after opening the jaws of the device 6.

By movingto the left of FIG. 4 the assembly of the distributing slide-

valves

46 and 47 by electrically controlling the electrovalve 50 displacing the slide of this electrovalve toward the left of the drawing, the jaws of the upper gripping element 8 are moved away from each other, while those of the lower element 6 remain in their gripping position.

By electrically controlling the electrovalve 50, it is thus possible to perform the different operations, the succession of which, following a predetermined order, enables the lowering or raising of the flexible drill pipe after having selected the position of the elements 59, 60 and 61.

This control may either be manual, by actuating an electrical switch (not shown) or made fully automatic by using a programming device which may be of any suitable known type, for example a drum driven in rotation at a constant speed and provided around its periphery with electrical contacts having the shape of annular sectors which will successively actuate at predetermined instants which are functions of their respective positions on the drum, a switch located in the immediate vicinity of this drum and controlling the electrovalve 50. This programming may also be achieved by automatic control based on the displacements of the upper gripping device, for example by means of photoelectric cells placed at convenient levels, at the upper and lower ends of the stroke of this upper gripping device.

It has been assumed in the foregoing that the gripping action by each of the

gripping devices

6 and 8 is performed by moving simultaneously the different jaws of these devices into gripping position.

It will also be possible to so constitute the gripping means of the jaws that the weight of the flexible line 1 which is supported by each of the

gripping devices

6 and 8 alternatively (this weight varying moreover as a function of the unreeled length of the flexible pipe) is taken up by successively moving into gripping position the different belts which constitute each .of these devices (dephased gripping), by first moving into gripping position in each gripping element the element whose displacement, under the action of the load is the smallest, the elements being moved out of gripping position by following the reverse order.

This will make it possible for the flexible pipe to expand below each gripping element, under the action of the fraction of the weight W which is supported by this element and by the elements which are already in their gripping position, thereby reducing the relative displacementresulting from a sliding motion or creeping or from a deterioration of the wall of the flexible pipe within this element.

In practice, since the gripping action by each element becomes effective only after some time from the instant of actuation of the jacks such as 17a, 17b (automatic clamping action of the flexible pipe by the

jaws

15 and 16, FIG. 1), there will be some overlapping of the periods for successively movinginto gripping position the elements of each

device

6 and 8, so as to not overload any gripping element.

Assuming for example that the overall load W is 200 tons and each of the

devices

6 and 8 includes four gripping elements, i.e.', the maximum load which is to be supported by each element is 50 tons; the gripping of the flexible pipe 1 by the upper gripping element 8 in the lowermost position of the latter may be achieved by first moving into gripping position the jaws 21b and 22b (FIG. 4) of the upper element of this gripping device and by'increasing through actuation of the winch the load supported by this element up to about 40 tons, after the automatic clamping action has been initiated while the lower gripping element 6 is at the same time progressively unloaded.

The jaws 23b, 24b of the nearest lower element are then moved into gripping position without waiting that the jaws 21b, 22b have reached their maximum load of 50 tons.

Similarly, as soon as the fraction of the weight W supported by the assembly of the jaws 21b, 22b and 23b, 24b reaches about 50 40 90'tons, the jaws 25b, 26b are moved into gripping position etc.

This method of gripping, wherein an element is placed into its gripping position without waiting that the previously actuated element has reached its maximum load, results in an elongation of the pipe between these two elements, with respect to its position at the beginning of the gripping action by the lower element,

' such an elongation occurring duringthe above-defined overlapping period (for example when the load of the upper element of the gripping device continues to increase from the value 40 tons, corresponding to the beginning of the gripping action of the next element, up to its maximum value 50 tons).

The arrangement, according to the invention, of the gripping elements inside each of the

gripping devices

6 and 8, such as illustrated in FIG. 3, permits a relative displacement of the elements, corresponding to the elongation of the flexible pipe between these elements in their gripping position.

Various modifications may be made without departing from the scope of the invention.

For example, both gripping devices may be movable along the axis of the pipe over a stroke C, so that the displacement of one of the gripping devices in its released position is effected during the displacement of the elastic column or pipe carried by the other gripping device.

It will also be possible, for example, to use three gripping devices arranged in series, the intermediate gripping device being stationary with respect to the drilling rig, while the upper lower gripping devices are movable along the axis of the column or the flexible pipe.

We claim:

l. A surface apparatus for handling an elastic column, provided with at least two devices for gripping the elastic column, including a lower gripping device and an upper gripping device, each of said gripping devicesbeing associated with means for placing said devices into and out of gripping position, means for displacing at least one of said gripping devices along the axis of the column, means for actuating said displacing means, adapted to always keep at least one of said gripping devices in its gripping position and to perform the displacement of said gripping device successively in a first direction corresponding to the gripping position of this device and in the oppositedirection corresponding to the released position of said gripping device, each of said gripping devices being constituted by a plurality of separate gripping elements located in series and interconnected through elastic means.

2. An apparatus according to claim 1, wherein said elastic means is constituted by spring means.

3. An apparatus according to claim 1, wherein said elastic means is constituted by jack means connected to a source of compressible fluid under pressure.

4. An apparatus according to claim 1, wherein said elastic means is constituted by connecting means made of elastomer.

5. An apparatus according to claim 1, wherein each of said gripping elements includes a housing extended by a sleeve member adapted to receive the housing of an adjacent gripping element so as to constitute therewith a telescopic mounting and wherein said elastic connecting means is constituted by a sleeve of elastic material secured both to the internal wall of said housing and to the external wall of said housing inserted in said sleeve member.

6. An apparatus according to claim 1, wherein said gripping element includes a housing provided with means for gripping the elastic column, said gripping means including at least two gripping jaws having a gripping surface substantially parallel to the axis of the column, each of said jaws being slidable along a guide path integral with said housing and inclined with respect to the column axis so as to downwardly come closer to this axis, thereby being adapted to perform an automatic clamping action on the elastic column, when the latter is subjected to a vertical downwardly directed tension, each of said jaws being actuated by jack means articulated to said housing and to said jaw, said jack means being adapted to move the jaw closer to the axis of the elastic column in its gripping position and to move the jaw away from this axis in its released position. 7 Y

7. An apparatus according to claim 6, wherein each of said jaws is provided with at least one roller which can roll along said inclined guide path.

8. An apparatus according to claim 5, wherein said gripping surface of each jaw is adapted to partly cover the external surface of said elastic column, said gripping surface being coated with an elastomer lining.

9. An apparatus according to claim 6, wherein said jack means is adapted to move said jaw away from the axis of the elastic column against the action of an elastic device adapted to automatically move said jaw toward this axis in the absence of any action of said jack means on said jaw.

10. A method for operating a device according to claim 1, wherein in each gripping device is successively actuated a first of said elements for gripping the elastic column, said first element being the one for which the displacement relative to its initial position, as a result of the applied load, is the smallest, then is actuated the gripping element adjacent to said first gripping element, when said first element is substantially in its gripping position, and so on for the different grlppmg elements of said gripping device.

11. A method according to claim 10, wherein gripping of the elastic column by said adjacent gripping element is performed before said gripping element has fully reached its gripping position, when the load supported by said first gripping element has reached a predetermined fraction of its final load in its position of full'gripping.

Claims

1. A surface apparatus for handling an elastic column, provided with at least two devices for gripping the elastic column, including a lower gripping device and an upper gripping device, each of said gripping devices being associated with means for placing said devices into and out of gripping position, means for displacing at least one of said gripping devices along the axis of the column, means for actuating said displacing means, adapted to always keep at least one of said gripping devices in its gripping position and to perform the displacement of said gripping device successively in a first direction corresponding to the gripping position of this device and in the opposite direction corresponding to the released position of said gripping device, each of said gripping devices being constituted by a plurality of separate gripping elements located in series and interconnected through elastic means.

6. An apparatus according to claim 1, wherein said gripping element includes a housing provided with means for gripping the elastic column, said gripping means including at least two gripping jaws having a gripping surface substantially parallel to the axis of the column, each of said jaws being slidable along a guide path integral with said housing and inclined with respect to the column axis so as to downwardly come closer to this axis, thereby being adapted to perform an automatic clamping action on the elastic column, when the latter is subjected to a vertical downwardly directed tension, each of said jaws being actuated by jack means articulated to said housing and to said jaw, said jack means being adapted to move the jaw closer to the axis of the elastic column in its gripping position and to move the jaw away from this axis in its released position.

10. A method for operating a device according to claim 1, wherein in each gripping device is successively actuated a first of said elements for gripping the elastic column, said first element being the one for which the displacement relative to its initial position, as a result of the applied load, is the smallest, then is actuated the gripping element adjacent to said first gripping element, when said first element is substantially in its gripping position, and so on for the different gripping elements of said gripping device.

11. A method according to claim 10, wherein gripping of the elastic column by said adjacent gripping element is performed before said gripping element has fully reached its gripping position, when the load supported by said first gripping element has reached a predetermined fraction of its final load in its position of full gripping.