WO2016145485A1

WO2016145485A1 - Butt fusion welding of pipes in situ

Info

Publication number: WO2016145485A1
Application number: PCT/AU2016/050181
Authority: WO
Inventors: Wayne Gregory Mitchell; Ross William BENNETT; Darren John POYNTON
Original assignee: Wayne Gregory Mitchell
Priority date: 2015-03-16
Filing date: 2016-03-15
Publication date: 2016-09-22

Abstract

Apparatus for use in butt fusion welding of pipe segments in situ includes a frame (12) having ground engageable members (16) configured to stably support the frame adjacent a first of the pipe segments. A first clamp assembly (25) is mounted on the frame and is configurable to receive and be closed onto the first pipe segment adjacent an open pipe end thereof, the first clamp assembly defining a centre axis (101) of the first pipe segment. A second clamp assembly (35) is configurable to receive and be closed onto the second of the pipe segments adjacent an open pipe end thereof. One or more guide tracks (50, 51) are provided on the frame to support the second clamp assembly for movement in a direction oblique to the axis. First actuator means (60)10 effects the movement of the second clamp assembly, whereby to open and close a space between opposed rims of the open pipe ends that extends generally normal to the aforesaid direction. Also discussed are a method of butt fusion welding pipe segments in situ, and a method of inserting a junction in a fusion weldable pipe in situ.

Description

Butt Fusion welding of pipes in situ

Field of the invention

This invention relates to the joining of fusion weldable pipe segments in situ. In an application of particular interest, the invention relates to the insertion of a junction in a fusion weldable pipe in situ. By 'in situ' in this context is meant that the pipe or pipe segments are already in the ground or otherwise in position in a trench, excavation or other installed location. The in situ pipe or pipe segments may already have been employed for fluid conveyance or may not yet be operational.

Background of the invention Fusion weldable thermoplastic pipes, most commonly high density polyethylene

(HDPE) pipes, are widely employed as conduits in water or gas networks, or as a protective sheath for cabling. The pipes typically come in diameters up to 2 metres. From time to time, it is desirable to insert a junction in a pipe already in place, whether as part of an operating network or in a new installation yet to be deployed. There are two conventional methods of inserting a T junction using butt fusion welding, in a fusion weldable thermoplastic pipe. In one, sometimes called the "S" method, a preformed T piece, or an assembly of a cut out and T junction, is inserted between spaced cut ends of the main pipe, and the insert is joined to the cut ends by butt fusion welding. To effect one of these welds, one cut pipe end is pulled aside and a rig brought into place to complete the weld at the other end in a normal manner. At the pulled aside end, the slack pipe is now typically deformed into a hump to allow it to be pulled back to create the necessary free movement for performing the normal butt fusion process. The difficulty with this approach is the ongoing presence of a deviated pipe section after weld completion, which can accumulate gas at its peak in a water pipeline or water at its bottom in a gas line, in both cases reducing the volume transported. In a typical underground installation, there is also the hazard of the hump or bulge being thereafter closer to the ground surface.

Butt fusion welding entails insertion of a facing plate, usually a rotary planer, between the two ends, which are thereafter pushed against the plate. Rotation of the plate effects smooth precision matched polishing of the ends exactly at 90° to the axis of the pipe. The plate is then withdrawn and a heater plate inserted. The gap is again closed and the rims or ends of the pipe heated, typically for a time in seconds approximating the outside diameter of the pipe in millimetres for an average thickness (SDR1 1 ) pipe, to around 220°C. The thicker the pipe the longer this heat soak time is. The heater plate is rapidly withdrawn and the two semi-molten pipe ends are pressed together under pressure. The two pipe rims merge and polymerise to form a joint, and the material subsequently exhibits substantial continuity.

The other method of inserting a T junction in an in situ pipe is by electro-fusion welding. This method employs special sleeves with built-in electrical coils that are fusion welded about the respective pairs of opposed ends of the insert and the pipe. Electro- fusion coupling is more widely employed than butt fusion welding for this purpose because it is somewhat easier to practice, but the problem of this method is the relatively high failure rate of the join, in some cases around 3% with everything going well, but in some cases as high as 30% when external factors such as pipe ovality issues or dimensional issues coupled with poor installation techniques, cleanliness, clamping, scraping and the like come into play

An improved method or apparatus for inserting junctions in an in situ pipe would be expected to have wider application to the joining of pipe segments in situ. A simple example is the pipe segment installed in a special operation, e.g. under a road or rail or tramline, that must then be joined to the next segment in an adjacent trench.

It is an object of the present invention to provide a new method and apparatus for in situ butt joining of fusion weldable pipe segments that is at least an alternative to and preferably an improvement of the afore-described conventional methods, and that preferably has particular application to the insertion of a junction in a fusion weldable pipe or to join two pipes together in situ in ground.

Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and/or combined with other pieces of prior art by a skilled person in the art. Summary of the invention

Various aspects of this invention entail a concept of butt fusion welding at an oblique angle to the axis of the pipe, most typically at 45°. This approach allows one pipe segment to be moved aside normal to an obliquely oriented pipe end to provide the space needed to carry out the steps of butt fusion welding.

In a first aspect, the invention provides apparatus for use in butt fusion welding of pipe segments in situ, comprising: a frame having ground engageable members configured to stably support the frame adjacent a first of said pipe segments; a first clamp assembly mounted on the frame configurable to receive and be closed onto the first pipe segment adjacent an open pipe end thereof, said first clamp assembly defining a centre axis of the first pipe segment; a second clamp assembly configurable to receive and be closed onto the second of said pipe segments adjacent an open pipe end thereof; one or more guide tracks on the frame supporting said second clamp assembly for movement in a direction oblique to said axis; and first actuator means for effecting said movement of the second clamp assembly, whereby to open and close a space between opposed rims of said open pipe ends that extends generally normal to said direction axis. The frame preferably further includes a sub-frame for housing a heater plate at a location aligned with said space between opposed rims of the open pipe ends, and second actuator means for moving the heater plate into said space for heating and softening the rims, and for withdrawing the plate to said location, whereupon the first actuator means is configured to move the second clamp assembly to close the space and butt fusion weld the softened rims.

The apparatus preferably includes mounts for selectively locating, as a detachable fitting to the frame, a rotary planer or finishing plate and/or a cutter for cutting through the pipe, in both cases at a position aligned with said space between opposed rims and oblique to said axis.

In an advantageous embodiment, the one or more guide tracks are pivotally adjustable to vary the angle to said axis of the direction of movement of the second clamp assembly. This variable angle of travel may include 90° to said axis of the pipe or pipe segment.

In a second aspect, the invention provides a method of butt fusion welding pipe segments in situ, comprising: providing said pipe segments at respective open ends thereof with corresponding respective rims that are oblique to the axis of the respective pipe segment; clamping a frame that is stably ground supported to a first of the pipe segments, adjacent to the open pipe end thereof, utilising a first clamp assembly; clamping a second clamp assembly to a second of the pipe segments, adjacent the open pipe end thereof; moving the second clamp assembly in a direction substantially normal to the oblique rim of the first pipe segment whereby to open and close a space between the opposed rims that extends generally oblique to said axis; and temporarily inserting a heater plate into said space, and closing said space to butt fusion weld said rims and therefore the pipe segments. Optionally, the method includes inserting a finishing plate or a rotary planer into said space for finishing the rims of the open pipe ends.

Optionally, the method includes inserting a saw cutting device into the frame for performing an oblique cut through the pipe with which to obtain matching ends.

In a third aspect, the invention provides a method of inserting a junction in a fusion weldable pipe in situ, comprising: cutting the pipe at at least two axially spaced locations and removing the resultant separated length of pipe, resulting in two spaced open pipe ends; and inserting between said spaced open pipe ends a substitute pipe segment that includes a junction with a lateral pipe portion, including forming joins between the substitute pipe segment and the respective open pipe ends by butt fusion welding; wherein at least one of the joins to the spaced open pipe ends and/or a join within the substitute pipe segment is a butt fusion welded joint between rims oblique to the axis of the pipe.

In one embodiment of the third aspect of the invention, the substitute pipe segment is formed by butt fusion welding together a first pipe section that includes the junction and the lateral pipe portion and a shortened retained section of the separated length of pipe.

Where the pipe in which the junction is to be inserted is underground, the method includes a preliminary step of forming an excavation or trench in the ground of sufficient length along the pipe to encompass the subsequent separated length of the pipe and where required a sufficient portion of the pipe on one or both sides thereof to allow the pipe to flex back as the respective open pipe end is moved substantially normal to the rims oblique to the axis of the pipe.

As used herein, except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additives, components, integers or steps.

Brief description of the drawings

The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a somewhat diagrammatic plan view of a work site at which a junction is to be inserted in a pipe in situ;

Figures 2A to 2E are a series of diagrams that illustrate steps in the process of inserting a junction in the pipe according to an embodiment of the third aspect of the invention, and entailing as one of the steps an embodiment of the second aspect of the invention; Figure 3 is a front perspective view of apparatus according to an embodiment of the invention at the point at which it has been positioned at the location of a proposed junction, with its clamp assemblies open to allow the apparatus to be moved about the pipe; Figure 4 is an end elevation of the apparatus of Figure 3;

Figure 5 is a view similar to Figure 3 but shown after closure of the clamp assemblies about the pipe;

Figure 6 is an end elevation of the apparatus of Figure 5;

Figure 7 is a view from above of the apparatus of Figures 3 to 6 but now shown clamped to two pipe segments that are to be joined;

Figure 8 is a front view of the situation shown in Figure 7 in which a rotary planer or finisher has been inserted in the oblique space between the pipe end rims;

Figures 9 and 10 are a front elevation and a plan view of the apparatus of Figure

8; Figures 1 1A to 1 1 F illustrate the sequence of steps required for the joining of two existing in-ground pipe ends in an existing buried pipeline, utilising the apparatus of Figures 3 to 10; and

Figures 12A to 12E diagrammatically depict steps in a process for inserting a junction in a pipe according to an alternative embodiment of the third aspect of the invention.

Detailed description of the embodiments

It is proposed to first describe a preferred embodiment of the third aspect of the invention, i.e. a method of inserting a junction in a fusion weldable pipe 100 in situ. The pipe in question has a centre axis 101 and is a thermoplastic pipe comprising a HDPE or fuseable PVC water or gas main already buried a substantial distance underground. With reference to Figure 1 , the first step is to excavate the ground at the work site of the proposed junction to form an excavation or trench 102 extending an appropriate distance along the pipe that will become apparent from subsequent discussion. Typically, a new trench 103 for the branch pipe 101 will extend away from excavation 102. The HDPE pipe 100 will typically be of a diameter in the range 200-1 , 000mm but may be smaller or larger.

With reference to Figures 2A to 2E, a series of cutting and butt fusion welding steps is carried out according to a preferred embodiment of the third aspect of the invention. These steps will preferably be carried out utilising apparatus 10 of the form illustrated in Figures 3-10 and an embodiment of the first aspect of the invention but for initial purposes the steps will be described without reference to this apparatus.

In this embodiment of the method, the first step (Figure 2A) is to cut through the pipe at two spaced locations, 1 10, 1 12, whereby to form a separated length of pipe 1 14. One of the cuts, 1 10 is normal to the centre axis 101 of the pipe while the other 1 12 is substantially oblique to the axis of the pipe, preferably and typically at 45°. The separated length of pipe 1 14 is then shortened by further cutting at an intermediate position 1 13, normal to the axis (Figure 2B). The resultant portion 1 14a with a normal end is discarded and replaced with a pre-fabricated T piece 120 which includes the desired junction 122 to a lateral pipe portion 124. The T piece 120 and reduced residual portion 1 14b of the original separated length of pipe are 90° fusion butt welded at joint 125 (Figure 2C): this can be effected either on equipment external to excavation 102, or in the excavation by the apparatus of Figures 3-10. The substitute pipe segment 140 thus formed is now inserted between the two spaced open pipe ends 142, 144 formed at the original cuts 1 10, 1 12. The end 142, which is normal to the axis 101 , is butt fusion welded at 90° according to conventional practice, while the end 144 at 45° to the axis is butt fusion welded using the apparatus of Figures 3-10 and designed for this purpose. As depicted in Figure 2D, the apparatus deflects the pipe segment 140 aside to separate the opposed oblique 45° ends 144, 154 in a direction substantially normal to the planes of their rims. The deflection forms the necessary space 145 between the pipe end rims to accommodate the rotary planer or finisher and the heater plate utilised in the butt fusion welding process. Once the rims have been heated and softened, indeed substantially melted, the pipe ends 144, 154 are pressed back together again under pressure to form the join (Figure 2E). The reliance on at least one 45° butt fusion weld obviates the need to hump or bulge the pipe - an unavoidable part of the traditional 90° butt fusion welding approach performed in situ, as earlier described.

Turning now to Figure 3, apparatus 10 has a frame 12 with a generally rectangular base or floor 14 that mounts ground engaging members 16 at or near its respective corners. Each ground engaging member 16 has an underlying vertically adjustable skid 17 and the engagement to base 14 is also vertically adjustable. These arrangements allow the frame to be stably ground supported on an underlying surface with an allowance for the surface to be uneven. An upper post structure 20 at a corner of base 14 mounts a series of spaced parallel vertically extending plates 22 joined by a rear web structure. Plates 22 are of general C-shape (Figure 4) to define a semicircular seat 24 for a horizontally extending pipe segment 100. Plates 22 are interchangeable to suit different pipe diameters and form a stationary sub-assembly 23 of a first or fixed clamp assembly 25. The other major part of the clamp assembly 25 is a clamp gate 26 that is pivoted to the stationary sub-assembly 23 above the pipe seat 24 on an axis 27. Gate 26 is opened and closed by a pair of overhead pivotally mounted hydraulic actuators 28. The gate defines a part cylindrical seat 29 complementary to seat 24, and the assembly includes a releasable locking mechanism on the underside to hold the gate 26 closed to sub-assembly 23. A second or moveable clamp assembly 35 of similar construction, including fixed plates 32 defining a pipe seat 34 and a pivoted gate 36 (with releasable locking mechanism) operated by actuators 38, is movably supported guide tracks provided by top 50 and bottom 51 rails via sub-frame 52. For reasons which will become apparent shortly, guide rails 50, 51 extend horizontally in respective vertical planes at 45° to the axis 101 of the pipe and are themselves fixed in an upright frame 54 ultimately fixed to base 14. At its outer end, sub-frame 54 includes a double post 55 positioned beyond a back corner of base 14, while the other end of sub-frame 54 lies above and below the clamp assemblies and pipe clamping location and is thus cantilevered from the top of upright post 20 by projecting plate and spar structure 59. Sub-frame 52 has top and bottom plates 58 with upstanding or depending blocks

57 that are slideable on rails 50, 51 . Top rail 50 is part of a hydraulic actuator 60 by which sub-frame 52 and therefore clamp assembly 35 is linearly moved backwards and forwards in a direction at 45° to the pipe axis 101 .

Figures 3 and 4 show apparatus 10 being readied for use in the first step of the operation depicted in Figure 2, the cutting of the pipe 100. The apparatus has been lowered into the excavation 102 and moved about the exposed pipe with both clamp gates 26, 36 fully open. Figures 5 and 6 depict the arrangement when the clamp gates 26, 36 are both closed and also illustrates a particular feature of the apparatus: the respective clamp assemblies 25, 35 have, in their closed state, opposed but slightly spaced end rims 70, 72 aligned in vertical planes at 45° to the pipe axis 101 . In turn aligned with the gap 145' between these pipe rims 70, 72 and located at the rear of the apparatus is a relatively narrow sub-frame 80 of substantially rectangular form for detachably mounting a butt fusion heating plate, shown in position at 82 (Figures 6 and 10). This plate 82, of conventional form, has internal heating coils that are actuable via an electrical interface 83. Sub-frame 80 can alternatively house a cutter (not shown) deployable to cut through pipe 100 in the space between rims 70, 72, i.e. to form open pipe ends with rims at 45° to the pipe axis.

Figures 7 to 10 depict the operation of the illustrated apparatus to carry out a butt fusion weld at 45° to the axis of the pipe segments 100a, 100b being joined. Apparatus 10 is first brought into place in the excavation and clamped to pipe segment 100a, being either the protruding section of the original pipe left in place after the earlier removal of the separated length of pipe 1 14, or the substitute pipe segment 140. The movable clamp assembly 35 is then opened, brought about and clamped to the other pipe segment 100b to be joined. Actuator 60 is then activated to withdraw one pipe segment from the other - at 90° to their oblique rims. This is the position shown in Figure 7. The heater plate now in position in sub-frame 80 is activated to pre-heat, and a rotary planer or finisher plate 90 is introduced into the space 85 between the separated pipe end rims (Figure 8). This component may be introduced from the front and may be fitted to mounts on the apparatus, or alternatively it may be lowered into position with a crane for attachment to a top support arm while resting on a lower support (not shown). Actuator 60 is activated to close the pipe segment rims onto the rotary finisher or planer plate 90, whose motor 92 is then started to plane and finish the rims of the pipe segments. Actuator 60 again opens the space between the rims, the rotary planer 90 is withdrawn/dismounted and the heater plate 82 slid into position between the pipe end rims. The pipe end rims are closed onto the plate for 1 -5 minutes during which the rims are softened and partially melted, actuator 60 re-opens the gap, the heater plate 82 is rapidly withdrawn and actuator 60 fully closes the gap to merge the softened pipe rims onto each other under pressure for a prescribed time. This completes the butt fusion weld.

It will be appreciated that, before the pipe rims are closed onto the rotary finisher or planer plate, the moving halves of the clamp assembly will need to be adjusted to allow the correct offset of the pipe ends. This offset is to accommodate for the material removal in the following facing and melting processes, so as to ensure that, after welding, the pipes are concentric. To do this, the moving half (i.e. the gate) of the clamps is released and the rams activated so that the clamps shift to the required position. The clamps are then closed and locked. The rams should thereafter be activated to bring the pipes together until touching, to check the required offset has been achieved.

In a modified embodiment, the subframes 54 and 80 are mounted to the main frame 12 for angular adjustment of their angles of inclination to the axis 101 . To enhance the versatility of the apparatus, the adjustment includes respective positions (0°, 90° to axis 101 ) at which the apparatus is configured to form a conventional 90° butt fusion weld.

Figures 1 1 A to 1 1 F illustrate the sequence of steps required for the joining of two existing in-ground pipe ends in an existing buried pipeline, utilising the apparatus of Figures 3 to 10. This arrangement often occurs on newly laid pipe systems where it is required to use this location for system testing. After completion of system testing the pipe ends must be joined together. In large diameter lines this often requires much additional excavation to enable the 'S' method to be used. The apparatus of Figures 3 to 10 reduces excavation work involved and simplifies the process.

After required excavation of a bell hole at the location (Figure 1 1 A), the pipes are cut aback within the trench as such (Figure 1 1 B). Both a traditional welder 200 and an apparatus 10 are introduced into the trench (Figure 1 1 C). The pipe is cut at 45° with the aid of apparatus 10. The rams or actuators 60 are activated to separate the pipes, and then the clamps of the fixed side are released so that the pipe therein is free to slide (Figure 1 1 D). The traditional welder is used to perform a weld at the 90° interface of the original pipe ends (Figure 1 1 E), and apparatus 10 is employed to complete the process at weld 2 at the 45° interface (Figure 1 1 F).

In an alternative sequence to that described above with reference to Figures 2A to 2E, the two cuts 1 10, 1 12 are both effected at 90° to the pipe axis 101 and the 45° fusion weld is within the substitute pipe segment 140. In this approach, the respective portions of the substitute pipe segment are butt fusion welded to the respective open ends of the pipe 100 and the 45° weld is formed in the excavation by the apparatus 10. An example of this alternative sequence is illustrated diagrammatically in Figures 12A to 12E. A pipe segment 240 is pre-prepared for a Tee 120 by adding "pups" 214a, 214b, i.e. added lengths of straight pipe each side of the Tee (Figure 12A). After required excavation of the bell-hole, a pipe section is cut out to allow for inserting of the pupped Tee 240. Using a crane, one end of the existing pipe is flexed to allow for insertion of the pupped Tee, which is aligned with the other exposed end of existing pipe (Figure 12B). Using a traditional square end butt weld machine in the ditch, one pup end of the tee insert is welded to one of the existing pipe ends (weld 1 in Figure 12C). The apparatus 10 may be put in place to hold the other side of the Tee while the traditional welder performs its duty. The deflected end of the in situ pipe is now released and lined up with the long end of tee insert 240. Apparatus 10 is positioned at the long side of the pup and clamped. A traditional welder is also clamped onto both the long end of pup and the end of the in situ pipe. The pup is cut at 45° within the jaws of apparatus 10 and the pipes separated with actuators 60. The clamps on the fixed side are released so that the pipe therein is free to slide. Using the traditional butt welder, the in situ end of pipe is welded to the now separate (and free to move) end of pup (weld 2 - Figure 12D). Using the apparatus 10 as earlier described, the 45° weld is now performed to complete the process (weld 3 - Figure 12E).

Claims

1 . An apparatus for use in butt fusion welding of pipe segments in situ,

comprising: a frame having ground engageable members configured to stably support the frame adjacent a first of said pipe segments; a first clamp assembly mounted on the frame configurable to receive and be closed onto the first pipe segment adjacent an open pipe end thereof, said first clamp assembly defining a centre axis of the first pipe segment; a second clamp assembly configurable to receive and be closed onto the second of said pipe segments adjacent an open pipe end thereof; one or more guide tracks on the frame supporting said second clamp assembly for movement in a direction oblique to said axis; and first actuator means for effecting said movement of the second clamp assembly, whereby to open and close a space between opposed rims of said open pipe ends that extends generally normal to said direction.

2. Apparatus according to claim 1 wherein the frame further includes a sub-frame for housing a heater plate at a location aligned with said space between opposed rims of the open pipe ends, and second actuator means for moving the heater plate into said space for heating and softening the rims, and for withdrawing the plate to said location, whereupon the first actuator means is configured to move the second clamp assembly to close the space and butt fusion weld the softened rims.

3. Apparatus according to claim 1 or 2 further including mounts for selectively locating, as a detachable fitting to the frame, a rotary planer or finishing plate and/or a cutter for cutting through the pipe, in both cases at a position aligned with said space between opposed rims and oblique to said axis.

4. Apparatus according to claim 1 , 2 or 3 wherein the one or more guide tracks are pivotally adjustable to vary the angle to said axis of the direction of movement of the second clamp assembly.

5. Apparatus according to claim 4 wherein the variable angle includes 90° to said axis.

6. A method of butt fusion welding pipe segments in situ, comprising: providing said pipe segments at respective open ends thereof with corresponding respective rims that are oblique to the axis of the respective pipe segment; clamping a frame that is stably ground supported to a first of the pipe segments, adjacent to the open pipe end thereof, utilising a first clamp assembly; clamping a second clamp assembly to a second of the pipe segments, adjacent the open pipe end thereof; with the rims at the open ends of the pipe segments generally opposed, moving the second clamp assembly in a direction substantially normal to the oblique rim of the first pipe segment whereby to open and close a space between the opposed rims that extends generally oblique to said axes; and temporarily inserting a heater plate into said space, and closing said space to butt fusion weld the rims and therefore the pipe segments.

7. A method according to claim 6 including inserting a finishing plate or a rotary planer into said space for finishing the rims of the open pipe ends.

8. A method of inserting a junction in a fusion weldable pipe in situ, comprising: cutting the pipe at at least two axially spaced locations and removing the resultant separated length of pipe, resulting in two spaced open pipe ends; and inserting between said spaced open pipe ends a substitute pipe segment that includes a junction with a lateral pipe portion, including forming joins between the substitute pipe segment and the respective open pipe ends by butt fusion welding; wherein at least one of the joins to the spaced open pipe ends and/or a join within the substitute pipe segment is a butt fusion welded joint between rims oblique to the axis of the pipe.

9. A method according to claim 8 wherein the inserted substitute pipe segment includes a shortened retained section of the separated length of pipe and a pipe section that includes the junction with the lateral pipe portion, which sections are butt fusion welded together.

10. A method according to claim 9 where said cutting of the pipe includes cutting the pipe obliquely at one of said axially spaced locations whereby one end of the separated length of pipe includes an oblique rim, and the retained end portion includes this oblique rim, which is then one of the oblique rims butt fusion welded to form said joins.

1 1. A method according to any one of claims 8 to 10 where the fusion weldable pipe in which the junction is to be inserted is underground, the method further including a preliminary step of forming an excavation or trench in the ground of sufficient length along the pipe to encompass the separated length of the pipe and where required a sufficient portion of the pipe on one or both sides thereof to allow the pipe to flex back as the respective open pipe end is moved substantially normal to the rims oblique to the axis of the pipe.