This invention relates to an apparatus for and method of bending pipes. The invention is primarily but not exclusively intended for bending large diameter pipes such as sewer, sweet water and especially hydrocarbon pipes. These pipes may typically have a diameter of around 0.66m and section lengths around 6 to 12m. Other lengths and diameters may be bent.

Hitherto such pipes have been difficult to bend accurately. Furthermore it has not hitherto been possible easily to bend pipes having a plastics insulating coating without damaging the coating. Conversely it can be difficult evenly to apply inεulant to a bent pipe.

A known method of bending such pipes comprises a process of supporting the pipe and moving an end of the pipe relative to the pipe to deform it. If smaller radius bends are required the pipe is deformed at a number of locations. Such a process is inaccurate and leads to a pipe having an irregular segmented bend somewhat like the shape of the lobster's back.

The invention provides a form retainer functioning in a manner broadly similar to a plumber's spring. The form

retainer comprises an articulated string of bobbins each provided with gripping means for gripping a pipe bore. The gripping means are preferably actuated by hydraulic cylinders. The gripping means may comprise arcuate shields having elastomeric gripping surfaces for gripping the pipe bore. Preferably there are four gripping means per bobbin. One or more runners may be provided to facilitate introduction of the retainer into the bore when the gripping means are retracted.

This form retainer is uεuable in a wide range of apparatus and methods of bending pipes and serves to reduce the possibility of uncontrolled deformation.

The invention further provides a method of bending a pipe in which a form retainer preferably but not exclusive of the type hereinbefore described is inserted into the pipe bore.

According to the invention there is provided a method of bending a pipe comprising the steps of: i. inserting a form retainer into the pipe bore so as to occupy a central portion of the pipe bore but not the ends thereof; ii. inserting a bending arm into each unoccupied end portion of the pipe bore, and iii. relatively moving the bending arms so as to bend the Dioe.

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The invention further provides apparatus for bending a pipe the apparatus comprising: a. a form retainer for insertion into a pipe such that in use the form retainer occupies a central portion of the pipe bore but not the ends thereof, and b. relatively movable bending arms for insertion into the unoccupied portions of the pipe bore and capable of relative rotation so as to bend the pipe permanently.

The various aspects of the invention will be illustrated by reference to embodiments shown in the accompanying drawings of which:-

Figure 1 is a plan view of a string of bobbins in rectilinear and curved configurations;

Figure 2 is a plan view of a bobbin assembly of a bending mechanism in a retracted position.

Figure 3 is a plan view of the bobbin assembly of the bending mechanism in an expanded position.

Figure 4 is a side view of the bending mechanism.

Figure 5 is a side view of a pair of bending mechanisms.

Figure 6 is a plan view of a pipe, cradles, bending mechanisms and sensors in an operative position.

Figure 7 is a cross-section of a bobbin with two actuable shields.

Figure 8 is a cross-section of a bobbin with one

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actuable shield.

F igure 9 is s crap view of an engagor in a f irst configuration .

Figure 10 is a scrap view of the engagor of Figure 9 in a second configuration.

Figure 11 is a perspective view of a further bending mechanism.

Figure 12 is a cross-section of a bobbin with four actuable shields.

One aspect of the invention provides a form retainer. The form retainer comprises a string 1 of bobbins 2, 2a. Each bobbin 2 is fully articulated with its neighbour 2a allowing free but limited movement. Each bobbin 2 may behollow and made of reεiliently expandable material. The interior of the bobbins 2, 2a is charged with pressure fluid capable of causing the bobbins 2 , 2a to expand. The bobbins 2 , 2a can take a variety of shapes and rollers or wheels 4 at the edges of the bobbins 2 , 2a enable the string 1 to be located within a pipe. Figures 2 and 3 show similar bobbins 2 , 2a as an assembly 100 on a bending mechanism 101.

As may be seen each bobbin has a central core 10 for articulation with an adjacent bobbin 2. Each bobbin further comprises a plurality of hydraulic cylinders 11, 11a carrying shields 12, 12a of substantially similar

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radius of curvature to the inside of the pipe. Actuation of the cylinders 11 with pressure fluid forces the associated shield 12, 12a outwards. Where the bobbins are provided with a plurality of runners which can be in the form of hard composition wheels or rollers, these runners extend beyond the retracted shields but not beyond the extended shields. The function of the runners is to minimise damage during positioning in the pipe.

The outer surfaces of the shields 12, 12a are preferably convex and provided with a hard rubber or elastomer coating to allow a degree of movement between the pipe and shields in use with little or no damage to any relatively delicate surface coating.

In use a string of bobbins each with retracted shields is inserted into a length of pipe. A typical pipe length and hence string length is about 6 to 12m. The cylinders are actuated so that the shields grip and engage the pipe wall but without occasioning significant damage; the pipe may then be bent in any convenient manner with a reduced probability of kinking of damage to an outer layer such as insulating syntactic material.

It is by no means essential for each bobbin to have four shie :1s. In general little extra benefit is obtained using more than four shields. Those skilled can readily devise embodiments with few thai

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shields. For example Figure 7 shows a bobbin having a central core 10 and two opposed shields 12. Similarly Figure 8 shows a bobbin with a core 10 and a single actuable shield 12. In this case at least part of the core (at 13) abuts the pipe bore in use.

A further aspect of the invention provides for apparatus for bending a pipe which may contain a string of bobbins as hereinbefore described with reference to Figure 2 to 6.

Pipe 100 is carried on cradles 101. The cradles are εlidable and rotatable to take up any movement of the pipe. Cradles 101 are preferably padded to minimise damage to an outer coating. Preferably the central section of the pipe contains a form retainer such as the hereinbefore described string 1. Regions of the pipe adjacent the ends do not have a form retainer.

The apparatus is further provided with bending mechanisms 1000 having bending arms 1200 carried on capstans 1201 or pivots. Preferably either or both bending arm 1200 is telescopic with rams 1204.

The bending arms are provided with engagors 1210 for contact with the pipe bore. The engagors can be provided with grippers as described hereinbefore. Alternatively the engagor can simply be a length of material, preferably resilient material such as rubber,

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slightly less in diameter than the pipe bore. In use as will be described in more detail hereinafter the bending arms 1200 are rotated relative to each other and this causes the engagors 1210 to engage the pipe wall. In a third embodiment the engagor 1210 comprises a cylindrical piece of resilient material. By causing plates 1220 and 1230 to move together the outer surface of the engagor 1210 is caused to move outwards and engage the pipe bore. This is shown in Figures 9 & 10. The form retainer may work in this fashion too.

The bending arms 1200 with the associated engagors are introduced into the unoccupied end bore portions. For example this can be done by untelescoping the bending arms but other methods will suggest themselves to those skilled in the art.

When the form retainer and bending arms are situated inside the pipe bore any actuators are actuated so as to support the pipe bore.

It is not mandatory to use the form retainer hereinbefore described. Acceptable results are obtainable by using a length or lengths of resilient material such as natural or synthetic rubber into the bore. The length may be of uniform cross-section or may comprise a series of barrel shaped pieces. Insertion of the bending arms 1200 and engagors 1210 into the pipe

bore compresses the length in a lengthwise direction and hence causes it to expand in diameter. This expansion results in gripping of the pipe bore. Removal of the bending arms enables the length to 'relax' to its rest position and hence be removed readily.

A capstan 201 is rotated, for example, clockwise eg., by drive 1280 and optionally simultaneously the other capstan is rotated counterclockwise thereby bending the pipe. Typically bends of three to nine degrees especially about six degrees will be required and are obtainable.

When the desired bend has been obtained the form retainer and bending arms are removed, if necessary after collapsing the engagors and gripping means. The invention allows large pipes to be precisely bent without damage to surface coatings.

In a preferred embodiment of this aspect of the invention distance sensors are provided. Preferably three or more sensors 300 are provided.

The precise nature of the sensors is not of the essence of the invention. Conveniently they may be of the type used in camera auto focusing. For example they may rely on ultrasonics, electromagnetic radiation (especially infra-red) or on contrast detection. In conjunction with associated control means (not shown) the sensors can

monitor the bending process and if necessary adjust the rate of rotation of the capstans. After bending, the pipe has linear sections at each end and a central section with a smooth curve. The bending conditions are so mild that a coated pipe, coated for example by the method described in our co-pending application PCT/GB91/01 214 (the disclosure of which is incorporated herein by reference) filed 19 July 1991 may be bent without significant damage to the coating.

In order to facilitate loading the string or snake-like form retainer into the pipe bore a snake holder 2000 may be provided (see Figure 11). The snake holder 2000 comprises an inclined plane and is provided with a winch 2010. In use the form retainer is mounted on the snake holder. Cables attached to the form retainer pass over the winch 2010 and hold it in position. When it is desired to load the form retainer the pipe 100 and holder 2000 are aligned and the form retainer allowed to slide under the action of gravity into the bore. Alternatively or additionally winch 2020 may be used to draw the form retainer into position. Under these circumstances the snake holder need not be an inclined plane. Pipe support trolley 2030 may be powered for example by hydraulic power pack 2040 controlled from control panel 2050 to facilitate alignment. Rotational movement of the

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pipe ends is not mandatory. Linear movement* provided for example by hydraulic rams 2060 is suitable. Movable for example pivoted end bungs 2070 may be provided.

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