IE922428A1

IE922428A1 - Locked pipe fitting with composite seal assembly

Info

Publication number: IE922428A1
Application number: IE242892A
Authority: IE
Inventors: Alain Andre Pierre Percebois; Jean-Paul Ory; Claude Bucher
Original assignee: Pont A Mousson
Priority date: 1991-07-26
Filing date: 1992-07-24
Publication date: 1993-01-27
Also published as: IE78622B1; FI923381A0; MX9204356A; ATE135096T1; DK0526373T3; NO922917D0; BR9202827A; RU2076259C1; FR2679622B1; FI98951B; GR3019242T3; FI98951C; FR2679622A1; EP0526373A1; NO922917L; SA92130231B1; FI923381A; EP0526373B1; TR27220A; ES2077543T3

Abstract

The head (24) of each insert (18) for locking the seal has, on the body side, a sharp-edged snout (30) delimited by two disengaged surfaces (29, 31), the arrangement being such that when the seal is in place in the housing (socket) (3) and the male end (1) is forcefully inserted into the latter, thereby radially compressing the body of the seal, the two disengaged surfaces (29,31) form between them, in the vicinity of the sharp edge (30), an angle projecting towards the bottom of the housing (socket), and this is the case at least for large diameters of the male end. Application to locking pressurised pipelines made of spheroidal graphite cast iron. <IMAGE>

Description

The present invention relates to locked joints between a spigot of one pipe and a socket of another pipe. It concerns first and foremost a composite packing for a locked joint of pipes with spigot and socket, of the type comprising a body and an anchor lug made of resilient material, and several locking inserts made of rigid material embedded in the lug and arranged in general along generatrices of a cone having the same axis as the packing and converging in the direction of the body, each insert projecting out of the packing towards the axis thereof.

In joints between pipes using such packings, each locking insert made of hard material is braced along a certain inclination between the socket and the spigot. Such locking prevents axial movements of one pipe relative to the other which might compromise proper sealing of the joint and even completely sever the pipes initially joined, under the action of the axial forces of separation produced by pressure of the fluid contained in the pipes.

This type of locking advantageously replaces a costly system for fixing a pipe line to foundations anchored in the ground, as well as devices with bolted clamp and counter-clamp.

However, such locking is fully efficient only if it can guarantee a maximum distance of backward movement of the spigot when the fluid pressure is established. For this it is necessary to be sure that force fitting the spigot in the socket will not extrude the inserts or the whole packing towards the back of the socket in the annular space between the latter and the spigot.

It is the object of the invention to provide a simple solution to this problem, adaptable directly to existing pipes.

For this purpose, the invention relates to a packing of the type mentioned hereinbefore, characterised in that the head or radially outer portion of each insert comprises, on the side of the body, a projection for retaining the insert during insertion of the spigot in the socket, this projection having a sharp edge and being bounded by two free surfaces, the arrangement being such that when the packing is in place in the socket and the spigot is force fitted in the latter, radially compressing the body of the packing, the two free surfaces form between them, in the vicinity of the sharp edge, an angle projecting towards the back of the socket, this being at least for large diameters of the spigot.

According to other characteristics: - the two free surfaces form an angle projecting towards the back of the socket for any diameter of the spigot within its range of tolerance and for any position of introducing the spigot into the socket; - said angle is distinctly smaller than 90°; - said angle is slightly greater than 90°; - each insert comprises several teeth for locking on the spigot, offset from each other axially and radially; - the head of each insert comprises, on the side opposite the projection, a surface inclined radially towards the interior and axially towards the exterior of the socket, this surface preferably ending in rounded portions; - the packing comprises, on the input side of the socket, a substantially radial inner sealing lip.

The invention also relates to a locked joint with spigot and socket comprising a packing as defined above, the body of the packing being compressed radially between the socket and the spigot, its lug being accommodated in an anchor groove of the socket bounded by a bottom flanked by two stop walls, one of which is a more or less radial front wall, the radially inner portion of each insert is adapted to lock onto the periphery of the spigot with its head abutting against the bottom of the groove and, if occasion arises, against its stop wall situated on the input side of the socket.

In the event that, as already indicated, the head of each insert comprises, on the side opposite the projection, a surface inclined radially towards the interior and axially towards the exterior of the socket, this surface preferably ending in rounded portions, advantageously the stop wall of the socket situated on its input side comprises a radially outer frustoconical portion, so that the head of the inserts bears approximately on the junction between this portion and the bottom of the groove for large diameters of the spigot, whereas it bears both on this bottom and on the same inclined portion for small diameters of the spigot.

According to another characteristic of the joint, the angle formed by the outer free surface with said front wall is smaller than the angle formed with the latter by the other free surface.

An embodiment of the invention will now be described with reference to the attached drawings, in which: - Figure 1 is a half-view in axial section of a socket provided with a packing according to the invention and a spigot ready to be introduced into this socket; - Figure 2 is a similar view showing the resulting locked joint; - Figures 3 and 4 illustrate on a larger scale, also in an axial half-section, the behaviour of the inserts of the packing during introduction of the spigot, for a maximum diameter and for a minimum diameter of this spigot respectively, the resilient portion of the packing having been omitted for clarity of the drawing; and - Figures 5 to 8 illustrate in a similar way locking of the joint for decreasing diameters of the spigot.

In Figure 1 is shown the spigot 1 of a first pipe 2 and the socket 3 of a second pipe 4, this socket being provided with a packing 5. The three components 1, 3 and 5 are substantially bodies of revolution about the same axis X-X which is assumed to be horizontal. The two pipes are made of nodular graphite iron, for example.

The spigot 1 comprises a cylindrical outer surface, chamfered externally at 6 at its end.

The socket 3 comprises an input collar 7, then successively from the rear to the front, that is, from this collar to the back of the socket: a relatively deep anchor groove 8, a shallower sealing cavity 9, an inner protuberance 10 axially limiting this cavity 9, and a front cavity 11 shallower than the cavity 9 and freely receiving the end of the spigot 1. For a given input diameter of the socket, the result of manufacturing tolerances of the spigot and faults in its positioning (offset and angular deviation) is that, in each half-plane of axial section, the outer generatrix of the spigot may be located within a whole range of positions, between a position corresponding to practically zero radial play relative to the collar 7 and maximum radial play relative to this same collar. This is equivalent to a range of outside diameters of the spigot between a maximum value and a minimum value with a perfectly centred position of the spigot, and hereinafter reference will be made only to such a range of diameters.

As can be seen better in Figure 3, the groove 8 of the socket is bounded at the rear by a radially inner wall 12 slightly inclined to the vertical, and by a radially outer wall 13 which is distinctly more inclined, at approximately 45° in the example shown. The wall 13 is connected to the cylindrical bottom 14 of the groove 8, which is in turn connected to an approximately radial front wall 15 of this groove. In respect of the cavity 9, this comprises a cylindrical bottom 16 connected to the wall 15, and an approximately radial front end shoulder 17.

The packing 5 (Figure 1) is a moulded piece of flexible or resilient material, for example an elastomer, in which are embedded a series of locking inserts 18. It comprises at the front a solid body 19, and at the rear an anchor lug 20 projecting radially outwards and a lip 21 projecting radially inwards.

At rest, the rear and radially outer profiles of the packing are substantially the same as the profiles of the surfaces 12 to 16 of the socket 3. To be more precise, the packing is accommodated without notable deformation in the socket, and then a clearance exists between it and the surfaces 12 to 14 of the socket, while it is applied to the surfaces 15 and 16. A free space then exists between the front end 22, of concave shape, of the body 19 and the surface 17.

Furthermore: - the inner surface 23 of the body 19 converges towards the front in a substantially conical manner from a diameter close to the inside diameter of the collar 7 to a diameter smaller than the smallest possible outside diameter of the spigot 1, in the sense indicated above; - the lip 21 is oriented substantially radially and extends approximately between the same diameters as the inner surface 23, extending the rear end surface of the body 19.

Each insert 18 (Figures 1, 3 and 4) is contained in a radial plane, is generally L-shaped and comprises a radially outer head 24 embedded in the lug 20 and a radially inner tail 25 which converges towards the front until it projects slightly on the surface 23 of the body of the packing, approximately halfway along the latter.

The head 24 (Figures 3 and 4) has a basic rectangular shape, with: - at the rear, a side 26 which, at rest, is approximately parallel to the surface 13 of the socket; - radially on the outside, a side 27 approximately perpendicular to the one above and connected thereto by a rounded portion 28; and - at the front, a beak-shaped side in two portions: a radially outer portion 29 forming an obtuse angle, of the order of 135° in this example, with the side 27, and extending as far as a sharp edge 30; and a radially inner portion 31, rounded and concave widthways having an angle of about 90° at the centre. The tangent to this rounded portion at the level of the edge 30 forms with the beak portion 29 an angle slightly greater than 90°. In a variant this angle could also be distinctly smaller than 90°.

The tail 25 is bounded laterally by two approximately parallel sides: a rear side 32 connected to the side 26 by a rounded portion 33, and a front side 34 connected tangentially to the rounded portion 31. The tail 25 ends in four protuberances 35 offset from each other axially and radially. As will be explained in detail below, the three protuberances 35 situated towards the rear form teeth for locking onto the spigot, while the fourth protuberance 35 situated towards the front, that is, towards the back of the socket, forms an anti-penetration lug, limiting penetration of the teeth into the spigot.

When the spigot 1 is introduced into the socket 3, it bends back the lip 21, then pushes the body 19 forwards, compressing it radially. The whole packing then has a tendency to be displaced forwards. This brings the sharp edge 30 of the inserts 18 into contact with the surface 15 of the socket (Figures 3 and 4), and the arrangement is such that whatever the outside diameter of the spigot, during introduction of the latter, this edge 30 always projects forwards onto the head of the inserts and is always located opposite the surface 15.

This free stop 30-15 prevents the inserts from sliding radially towards the interior of the socket, out of the chamber, and hence from being extruded. As Figures 3 and 4 indicate, this mode of operation could continue as far as the fictitious position, that is, beyond the normal range of operation, indicated in dot-and-dash lines, thus offering a wide safety margin.

Moreover, for normal ranges of operation, that is, for the range of spigot diameters and for the interlocking positions provided, and even beyond, the pair 30-15 behaves like a unidirectional system, further increasing the reliability of the whole assembly. In fact, the angle of incidence a between the surfaces 29 and 15 remains smaller than the angle β between the surfaces 31 and 15 (Figures 3 and 4), so that the insert can easily enter the chamber 8 (towards the surface 14 of the socket) when it is subjected to radial forces in this direction, whereas it is blocked if the direction of the radial forces is reversed.

It should be noted that the width of the tail 25 is smaller than the radial clearance between the surface 16 and the spigot, to avoid any risk of the joint jamming. Furthermore, it will be realised that the stop 30-15 is important mainly for large outside diameters of the spigot, for which the risk of entraining the packing is high (Figure 3).

When introduction of the spigot is over and the pipe line is pressurised, the spigots are in general biassed rearwards. The inserts 18 limit this backward movement in the following manner, illustrated in Figures 5 to 8.

When the outside diameter of the spigot is maximal (zero radial clearance between the spigot and the collar 7 of the socket), its backward movement brings the rounded portion 28 of each insert approximately into the angle formed by the surfaces 13 and 14 of the socket, and the second tooth 3 5 from the rear engages with the spigot. This defines a bracing force 36 and a centre of rotation 37 of the insert. The arrangement is such that the inclination in the radial direction of the force 36 is between a lower limit at which the tooth risks perforating the spigot, and an upper limit at which there would be a risk of the tooth sliding on the spigot.

For outside diameters of the spigot decreasing from the maximum diameter (Figure 6), bearing of the head of the inserts on the socket is the same as above, but the two intermediate teeth 35, and then only the third tooth, engage with the spigot, which has the effect of keeping the inclination of the bracing force 36 within the above limits in spite of the greater inclination of the tail of the inserts.

The outside diameter of the spigot continuing to decrease, tilting of the inserts continues until the side 26 is applied to the surface 13 of the socket (Figure 7). The centre of rotation of the inserts then passes from the point 37 to another point 38 situated closer to the axis XX and further to the rear, allowing the bracing force to remain within the desired limits, whereas it would depart from them for the same spigot diameter without this principle.

Finally, within the lower range of outside diameters of the spigot (Figure 8) , the third tooth 35 is always engaged with the spigot, and the head of the inserts is supported at two points in the groove 8: by the rounded portion 28 on the bottom 14, and by the rounded portion 33 on the surface 13. Again, the centre of rotation 38 is situated so as to guarantee a suitable inclination of the force 36.

This maintenance of the inclination of the force 36 owing to double support of the head of the inserts has the advantageous consequence of increasing the internal pressure admissible in the pipe line, this pressure being substantially proportional to the angle formed by the bracing force with the radial direction. It should be noted that this is obtained without involving any extra tooth of the inserts, which makes it possible to make savings of material, overall dimensions and manufacture of the inserts.

In all cases, support of the edge 30 on the surface 15 during interlocking limits the maximum possible backward movement of the spigot when the pipe line is put into operation.

The smallest end protuberance 35, situated on the input side of the socket, is a safety device for cases of poor positioning of the inserts relative to their normal position. The end protuberance 35 situated towards the back of the socket is an anti-penetration lug which makes it possible to limit the contact pressure of the adjacent intermediate tooth on spigots comprising the smallest diameters, and thus makes it possible to increase the maximum permitted pressure threshold.

The lip 21 ensures sealing in relation to external elements, that is, makes it possible to avoid the introduction of aggressive or corrosion external elements into the locked zone. Owing to its radial orientation, it does not risk being positioned under the inserts during interlocking.

If desired, the inserts may be coated with an electrically insulating material, for example a ceramic material.

Claims

1. Composite packing for a locked joint of pipes with spigot (1) and socket (3), of the type comprising a body (19) and an anchor lug (20) made of resilient material, and several locking inserts (18) made of rigid material embedded in the lug and arranged in general along generatrices of a cone having the same axis (X-X) as the packing and converging in the direction of the body (19), each insert projecting out of the packing (5) towards the axis thereof, characterised in that the head (24) or radially outer portion of each insert (18) comprises, on the side of the body, a projection for retaining the insert during insertion of the spigot in the socket, this projection having a sharp edge (30) and being bounded by two free surfaces (29, 31), the arrangement being such that when the packing is in place in the socket and the spigot is force fitted in the latter, radially compressing the body of the packing, the two free surfaces (29, 31) form between them, in the vicinity of the sharp edge (30) , an angle projecting towards the back of the socket, this being at least for large diameters of the spigot.

2. Packing according to claim 1, characterised in that the two free surfaces (29, 31) form an angle projecting towards the back of the socket for any diameter of the spigot (1) within its range of tolerance and for any position of introducing the spigot into the socket.

3. Packing according to claim 1 or 2, characterised in that said angle is distinctly smaller than 90°.

4. Packing according to claim 1 or 2, characterised in that said angle is slightly greater than 90°.

5. Packing according to any of claims 1 to 4, characterised in that each insert (18) comprises several teeth (35) for locking on the spigot (1), offset from each other axially and radially.

6. Packing according to any of claims 1 to 5, characterised in that the head (24) of each insert (18) comprises, on the side opposite the projection (29 to 31) , a surface (26) inclined radially towards the interior and axially towards the exterior of the socket, this surface preferably ending in rounded portions (28, 33).

7. Packing according to any of claims 1 to 6, characterised in that the packing (5) comprises, on the input side of the socket (3), a substantially radial inner sealing lip (21) .

8. Locked joint with spigot (1) and socket (3) comprising a packing (5) according to any of claims 1 to 7, the body (19) of the packing being compressed radially between the socket and the spigot, its lug (20) being accommodated in an anchor groove (8) of the socket bounded by a bottom (14) flanked by two stop walls (12-13, 15), one of which is a more or less radial front wall (15), the radially inner portion (25) of each insert (18) is adapted to lock onto the periphery of the spigot with its head (24) abutting against the bottom (14) of the groove (8) and, if occasion arises, against its stop wall (12-13) situated on the input side of the socket.

9. Joint according to claim 8, characterised in that the packing (5) is in accordance with claim 6 and the stop wall (12-13) of the socket (3) situated on its input side comprises a radially outer frustoconical portion (13), so that the head (24) of the inserts (18) bears approximately on the junction between this portion (13) and the bottom (14) of the groove (8) for large diameters of the spigot (1), whereas it bears on this bottom (14) and on the same inclined portion (13) for small diameters of the spigot.

10. Joint according to claim 8 or 9, characterised in that, for any diameter of the spigot (1) within its range of tolerance and for any position of introduction of the spigot into the socket, the angle (a) formed by the outer free surface (29) with said front wall (15) is smaller than the angle (β) formed with the latter by the other free surface (31).

11. Packing according to any preceding claim substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

12. A locked joint according to any preceding claim substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.