GB2175355A

GB2175355A - Seal assembly

Info

Publication number: GB2175355A
Application number: GB08508529A
Authority: GB
Inventors: Richard Alvin Armell
Original assignee: Nowsco Well Service Ltd; Nowsco Well Service Inc; Drexel OilField Services Inc
Current assignee: Nowsco Well Service Ltd; Nowsco Well Service Inc; Drexel OilField Services Inc
Priority date: 1985-04-02
Filing date: 1985-04-02
Publication date: 1986-11-26
Also published as: GB8508529D0

Abstract

A seal assembly comprises two annular end portions (10,14) with substantially plane end surfaces (20) considering the assembly as a whole and surfaces facing each other (24,24') of dished form. An intermediate portion (12) lies between the end and has respective end faces complementary to the dished faces of the end portions and the intermediate portion has a Shore hardness less than that of the end members and has recesses accommodating respective annular metal members (16,18) of a interrupt the overall complementary configuration such that they do not form of the engaging faces of the end portions and the intermediate portions. <IMAGE>

Description

SPECIFICATION High-pressure seal assemblies This invention relates to high pressure seal assemblies used, for example, in test tools such as that disclosed in UK-B2056091.

To effect a temporary seal in a pipe or pipe coupling to be tested, one form of seal which has been found broadly to be operable effectively, involves applying an axial pressure to an annular resilient sealing member which then expands laterally (Poisson effect) in order to produce the required sealing action. It has been known for many years that under such conditions natural or synthetic rubbers are liable to take on the characteristics of a viscous liquid and thus flow into any available space such as a clearance between an axial pressure applying member and the wall of the tubing, piping or coupling being tested. This extrusion effect does not necessarily adversely affect the quality of the seal, and indeed may improve it. However, the extrustion effect is wholly unacceptable in practice because the seal assembly cannot be re-used for obvious reasons.

In our co-pending application 83.03109, a seal assembly is described which has proved to be adequate under many conditions of pressure, temperature, humidity and so on, is not, however, always satisfactory under very high pressures of the order of 560-850 Kg/sq.cm. This applies, the more so, when it is desired that the seal assembly should have a long life of efficient operation without deterioration. The objective is that in the specific testing tool referred to in the first mentioned co-pending application, as many as 500 cycles should be withstood without giving rise to danger or the risk of unsatisfactory test results.The basic reason why the seals must be reliable over a long period is that the related test method can be carried out both quickly and reliably and the need for frequent seal replacement will certainly adversely affect the average time for each test to be carried out.

According to the present invention there is provided a seal assembly comprising two annular end portions with substantially plane end surfaces considering the assembly as a whole and surfaces facing each other of dished form, an intermediate portion lying between the end portions and having respective end faces complementary to the dished faces of the end portions and the intermediate portion having a Shore hardness less than that of the end members and having recesses accommodating respective annular metal members of a configuration such that they do not interrupt the overall complementary form of the engaging faces of the end portions and the intermediate portions.

A seal assembly embodying the invention will now be described, by way of example only, with reference to the accompany diagrammatic drawing in which: Figure 1 is an external elevation of a seal assembly in accordance with the invention; and Figure 2 is a longitudinal section of the seal assembly of Fig. 1.

The seal assembly embodying the invention includes three main portions 10,12,14 each of annular section, and two auxiliary portions 16, 18 nested within the assembly and not visible in the external view of Fig. 1. The portions 16, 18 are identical in the preferred embodiment.

In more detail, the upper end portion 10 as illustrated in Figs. 1 and 2 has a plane upper face 20 with a 45" chamfer 22 and as apparent from Fig. 2 the lower face 24 is dished, more specifically, frusto-conical. The inner edge of this frusto-conical face 24 is sharp in relation to the central bore 26 whereas the outer edge is rounded in relation to the outer cylindrical surface. In the preferred embodiment the cone angle of the frusto-conical face 24 is 30".

The lower portion 14 is generally similar to the upper portion but has a larger axial dimension and like the upper portion has a frustoconical inner face directed towards the upper portion. Corresponding parts have been given the same reference numerals with the addition of a prime. Both the upper and lower portions are of polyurethane having a Shore hardness of 95.

The intermediate main portion 12 is of rubber, is generally annular and has dished upper and lower faces 28, 30 complementary to the internal faces 24, 24', of the upper and lower end portions 10, 14. However, these frustoconical faces are interrupted adjacent the central annular passage by recesses, each of which accommodates one of the auxiliary portions of the assembly in the form of a brass ring, the central bores 32 matching the central bores of the main portions and with end faces of frusto-conical shape with a cone angle identical to the cone angles of the main end portions 10, 14 and the intermediate portion 12. It will be appreciated that the rings 16, 18 do not interrupt the overall dished form of the engaging faces of the end portions and the intermediate portion.

The intermediate portion 12 is preferably of natural or synthetic rubber having a Shore hardness of 70. Alternatively, it may be of nitrile with the same hardness index. The intermediate portion 12 is primarily responsible for effecting the required sealing.

The configuration of the seal assembly has been found to provide the required sealing effect at pressures up to 850 Kg/cm2 and tests have shown that seal assemblies in accordance with the invention are satisfactory for at least 500 cycles. The provision satisfactory for at least 500 cycles. The provision of the metal rings ensures that there is no extrusion internally and the end portions ensure that the rubber of the central portion cannot extrude because the polyurethane itself undergoes radial expansion thus matching precisely the internal bore of the tubing, piping or coupling.

Claims

1. A seal assembly comprising two annular end portions with substantially plane end faces considering the assembly as a whole and surfaces facing each other of dished form, an intermediate portion lying between the end portions and having respective end faces complementary to the dished faces of the end portions and the intermediate portion having a Shore hardness less than that of the end portions and having annular recesses accommodating respective annular metal members of a configuration such that they do not interrupt the overall complementary form of the engaging faces of the end portions and the intermediate portion.

2. An assembly according to claim 1, wherein the dished faces are frusto-conical.

3. An assembly according to claim 1 or claim 2, wherein each annular metal member is accommodated in an annular recess of the corresponding complementary surface of the intermediate member.

4. An assembly according to any one of claims 1 to 3, wherein each annular metal member is of triangular section in a radial plane passing through the longitudinal axis of the seal assembly.

5. An assembly according to any one of the preceding claims, wherein each end portion is of polyurethane and the intermediate portion is of natural or synthetic rubber.

6. An assembly according to any one of the preceding claims, wherein the Shore hardness of the intermediate portion is 70.

7. An assembly according to any one of the preceding claims, wherein the end surface of each end portion is chamfered at its outer periphery.

8. An assembly according to any one of the preceding claims, wherein the cone angle of each frusto-conical surface is 60 .

9. An assembly according to any one of the preceding claims, wherein the end portions are of different axial lengths.

10. A high pressure annular seal assembly comprising a first annular end portion having a plane end surface and a concave dished surface, a portion annular end portion having a plane end surface and a concave dished surface, the end surfaces of the end portions facing outwardly of the seal assembly as a whole and the dished surfaces being directed towards one another, an intermediate annular portion lying between the end portions and having two end surfaces of complementary form to the concave dished surfaces of the end portions, respective surfaces of the end portions and the intermediate portions engaging one another, and two metal annular members each having an inner diameter substantially equal to the inner diameter of the end and intermediate portions, each metal member being accommodated between one of the dished surfaces and the corresponding one of the complementary surfaces of the intermediate portion, the intermediate portion having a Shore hardness less than that of the end portions.

11. A high pressure annular seal assembly comprising a first annular end portion of polyurethane with a Shore hardness of 95 having a plane end surface and a frusto-conical surface, a second annular end portion of polyurethane with a Shore hardness of 95 having a plane end surface and a frusto-conical surface, the end surfaces of the end portions facing outwardly of the seal assembly as a whole and the frusto-conical surfaces being directed towards one another, an intermediate annular portion of natural or synthetic rubber with a Shore hardness of 70 lying between the end portions and having end surfaces of complementary form to the frusto-conical surfaces of the end portions, respective surfaces of the end portions and the intermediate portions engaging one another, and two brass annular members each having an inner diameter substantially equal to the inner diameter of the end and the intermediate portions, each brass member being accommodated between one of the frusto-conical surfaces and the corresponding one of the complementary surfaces of the the intermediate portion, the annular brass members each being of triangular section considered in a radial plane of the assembly containing the longitudinal axis of the assembly and being accommodated in a respective recess of intermediate portion in the surface thereof directed towards the corresponding frusto-conical surface of the adjacent end portion.

12. A seal assembly substantially as hereinbefore described with reference to the accompanying drawing.