GB2263951A

GB2263951A - Sealing arrangement for joint

Info

Publication number: GB2263951A
Application number: GB9202174A
Authority: GB
Inventors: John Nicholas Booth; David Stephen Robinson; David Lockhart Vidler
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1992-02-01
Filing date: 1992-02-01
Publication date: 1993-08-11
Anticipated expiration: 2012-02-01
Also published as: GB2263951B; GB9202174D0

Abstract

A joint between components (10) having corrosion resistant coatings (16) includes a sealing gasket (22) between the components, which takes up any movement of the joint caused by extrusion of the coating (16) under the compressive forces in the joint. A spacer member (26) of harder material than the gasket (22) is interposed in an aperture (24) in the gasket (22) to make contact with both components (10) to prevent compression of the gasket (22) beyond its elastic limit. The coating (16) of the components is absent from the areas (18) of the components (10) that are in contact with the spacer (26). In the arrangement shown, the spacer (26) is formed integrally with a bolt (32) passing through the flanges (12) of pipes (10) to be secured together, but it may be integral with a flange (12) or formed separately. <IMAGE>

Description

Sealing Arrangement for Joints This invention is concerned with sealing arrangements for surfaces having malleable coatings. It is suited for such coated surfaces which are to carry loads within joints, such as the engaging surfaces of components secured together by bolts or other fasteners applying compressive forces to the components. It is particularly suited to, but not limited to, flange joints between pipe or ducting sections.

Components such as pipe sections are often provided with coatings to protect them from corrosive attack. These coatings are often of a plastics material such as PVC which is chemically inert but softer than the underlying material, which is typically a metal.

The coatings are applied by dipping the components in the coating material in its molten state, and thus the coating extends over the entire component including any faces which come into engagement in a joint. On these faces the coatings are subject to creep under the compressive forces in the joint, resulting in destressing of the joint and the consequent necessity to retighten it. In extreme cases the coatings can be completely squeezed out of the joint, resulting in the loss of the sealing capability of the joint and exposing the surfaces to corrosive attack.

According to the invention, the problem of coating creep is solved by the provision of one or more gaskets of resilient material between the engaging surfaces, provision on at least one of the surfaces that are to come into engagement of an exposed area in which the coating is absent such that the underlying materials of the components are exposed, and the provision, in the areas where the coating is absent, of at least one spacing member of relatively hard material sized so that the gasket or gaskets cannot be compressed beyond their elastic limit.

The invention also comprises a sealing arrangement for a joint comprising a gasket and a spacing means associated with the gasket and dimensioned such that the gasket cannot be compressed beyond its elastic limit. In this way it can be ensured that the seal is maintained and that the joint remains fully tightened, since any movement in the joint or extrusion of the coatings can be taken up by expansion or contraction of the gasket.

The invention also comprises a joint between two components, the components both having coatings of relatively soft material, the coatings being absent from areas of the engaging surfaces of the components such that the underlying material of the section is exposed, comprising one or more gaskets of resilient material positioned between the engaging surfaces, fastening means for securing the joint in compression, and one or more spacing members of relatively hard material positioned between the engaging surfaces such that it engages the exposed underlying materials of the components, the size of the spacing member being such that when positioned between the components the gasket cannot be compressed beyond its elastic limit.

The process by which the component is coated may use masking to create the exposed areas, but where the component is supplied already coated, the exposed areas may be created by removal of the coating where required The fastening means are preferably bolts or similar fasteners passing through holes in the components, although an externally clamped arrangement is also within the scope of the invention.

Advantageously, to minimise the number of components in the joint and to ensure that the spacing members are inserted, they can be formed integrally with the bolt shanks. Alternatively they can be formed as exposed bosses on the surface of one of the components, projecting beyond the surface of the coating.

An embodiment of the invention will now be described by way of example only with reference to the accompanying diagrammatic drawings, of which - Figure 1 shows in partial section the flanges of two pipes coupled together according to the invention, and - Figure 2 shows an elevation of the flange of one pipe with the gasket, spacer and stud removed.

Two metal pipes (10) each terminate in a flange (12) through which is provided a number of holes (14). The pipes (10) are provided with a PVC coating (16) by a hot dipping process. Adjacent to the holes (14) the coating (16) is removed to leave areas (18,20) where the underlying metal of the pipes (10) is exposed. When joining the two pipes together, an expanded silicone gasket (22) of complementary shape to the flanges (12) is arranged in between the flanges. The gasket has apertures (24) which come into registration with the holes (14). A carbon steel spacing member (26) is arranged in each aperture. The spacing members (26) are formed integrally with a threaded stud (32) which extends through holes (14). On the external ends of the stud (32) nuts (28) are threaded, which engage washers (30) co-operating with the exposed areas (20) in order to secure the joint.The spacing members (26) make metal to metal contact with the exposed areas (18) of the pipe, and are of such a size that the gasket (22) cannot be compressed beyond its elastic limit which is typically reached at about 40% compression. Any movement of the joint due to thermal expansion or contraction, or from extrusion of the coating (16) under the compressive forces in the joint, can be accomodated by the resilience of the gasket (22), which provides a seal. The metal to metal contact between the washers (30) and exposed areas (20) prevents loosening of the joint due to extrusion of the coating material (16). The spacing members (14) prevent the gasket (22) being compressed beyond its elastic limit, at which point it would lose its resilience and cease to form an effective seal.

By this construction the compressive forces in the joint are not carried by the PVC coating material (16), and an effective seal is ensured by the resilience of the expanded silicone gasket (22). The material of the gasket (22) is selected to be resistant to corrosion from the material intended to be carried by the pipe, and the external environment in which the pipe is to be used, and to have the required degree of resilience to accomodate movement of the joint. The spacing member need not be integral with the fastening means. In one alternative arrangement, the spacing members take the form of bosses formed integrally with one of the flange surfaces, and have exposed metal surfaces which come into engagement with exposed areas of the other flange.

Although the invention has been described in relation to a joint between flanges in a pipe coupling, the invention is not limited to connections between such components.

Claims

1. A method of fastening together two components having coatings of relatively soft material , comprising the provision of fastening means to hold the components together in compression, the provision of one or more gaskets of resilient material between the facing surfaces, provision on at least one of the surfaces that face each other of an exposed area in which the coating is absent such that the underlying materials of the components are exposed, and the provision, in the areas where the coating is absent , of at least one spacing member of relatively hard material sized so that the gasket or gaskets cannot be compressed beyond their elastic limit.

2. A method according to claim 1, where the coatings on the components initially cover the entire surface, the exposed areas being formed by removal of the coating.

3. A method as claimed in either preceding claim , in which the gasket or gaskets are formed of expanded silicone

4. A method as claimed in any preceding claim in which the fasteners pass through holes in the components.

5. A method according to claim 4 in which the areas of the engaging surfaces in which the coating is absent are provided adjacent to the holes.

6. A method as claimed in claim 5 wherein the fastener is integral with the spacing member

7. A method as claimed in any of claim 4 to 6, wherein the fastener has a screw thread

8. A method as claimed in any preceding claim, wherein the coating is made of a PVC material

9. A method as claimed in any preceding claim, wherein there is a single gasket having a plurality of openings, and a plurality of spacing members occupying some or all of the openings

10. A method as claimed in any preceding claim, wherein the components are flanges of pipes

11 A method as claimed in any preceding claim, wherein the spacing member is an exposed boss integral with one of the components and the exposed area is on the other component

12. A joint formed by the method of any preceding claim

13.A sealing arrangement for a joint comprising a gasket and a spacing means associated with the gasket and dimensioned such that the gasket cannot be compressed beyond its elastic limit

14. A joint between two components, the components both having coatings of relatively soft material, the coatings being absent from areas of the facing surfaces of the components such that the underlying material of the section is exposed, comprising one or more gaskets of resilient material positioned between the engaging surfaces, fastening means for securing the joint in compression, and one or more spacing members of relatively hard material positioned between the engaging surfaces such that it engages the exposed underlying materials of the components , the size of the spacing member being such that when positioned between the components the gasket cannot be compressed beyond its elastic limit.

15. A joint as claimed in claim 14, in which the gasket or gaskets are formed of expanded silicone

16. A joint as claimed in either of claims 14 or 15 in which the fastening means pass through holes in the components.

17. A joint as claimed in claim 16 in which the areas of the engaging surfaces in which the coating is absent are adjacent to the holes.

18. A joint as claimed in claim 16 wherein the fastening means is integral with the spacing member

19. A joint as claimed in any of claims 16 to 18, wherein the fastener has a screw thread

20. A joint as claimed in any of claims 14 to 19, wherein the coating is made of a PVC material

21. A joint as claimed in any of claims 14 to 20, wherein there is a single gasket having a plurality of openings, and a plurality of spacing members occupying some or all of the openings

22. A joint as claimed in any of claims 14 to 21, wherein the components are flanges of pipes

23. A joint as claimed in any of claims 14 to 22, wherein the spacing member is an exposed boss integral with one of the components and the exposed area is on the other component 24 A sealing arrangement substantially as described with reference to the accompanying drawings 25. A joint substantially as described with reference to the accompanying drawings 26. A method of joining coated components substantially as described with reference to the accompanying drawings