GB2200179A

GB2200179A - Flanged joint

Info

Publication number: GB2200179A
Application number: GB08701450A
Authority: GB
Inventors: Barry Porter
Original assignee: DESTEC ENG Ltd
Current assignee: DESTEC ENG Ltd
Priority date: 1987-01-23
Filing date: 1987-01-23
Publication date: 1988-07-27
Anticipated expiration: 2007-01-23
Also published as: GB8701450D0; GB2200179B

Abstract

A flanged joint for e.g. a connection between pipes carrying high-pressure fluid, in which there are two pairs of mating joint faces 13 and 18 at radially inner and outer positions respectively on opposing flange faces. Fastening means 16 pass through a clearance 15. There is a small axial difference between a radial plane including the inner mating faces and a radial plane including the outer mating faces, so that when the joint is initially assembled as in Figure 1, a small gap remains at 18. This gap is closed when the fastening means are correctly tightened. The improved joint is resistant to a) overstressing during tightening; b) axial tension; and c) external bending stress. <IMAGE>

Description

F#LANGED JOINT This invention relates to a flanged joint, particularly in a pipe coupling, e.g. for a pipe carrying high-pressure fluid.

Conventional designs have weaknesses which can be categorised in terms of the location of the joint in relation to the pitch circle diameter (PCD) of the fastening-means, e.g. bolts and nuts, and the type of stress to which the joint is subjected. The object of the invention is an improved flanged joint with advantages which will appear from the detailed description. In this specification, the word joint is used only to refer to the actual contact area of flanges, where tightening takes place between opposing flange faces, with or without the interposition of a seal ring or gasket therebetween.

Figure 1 is half of an axial section of a flanged joint according to the invention.

Figures 2 and 3 are similar sections of different types of flanged joints, illustrating their weaknesses, in order to explain the invention.

In Figure 1, opposed flanges 11 and 12 are rigidly secured by means (not shown) to opposing pipe ends (not shown). On initial make-up, the initial joint 13 is made between substantially flat faces formed on opposing flange ends, substantially normal to the pipe axis. Material contact is made, e.g. metal-to-metal.

A sealing ring 14, preferably of the cone type shown, is inserted to contain the pressure and protect joint 13 against the temperature or other properties of the fluid being carried. At a larger diameter than joint 13, a clearance 15 is formed, bridged by the fastening-means 16 which may comprise bolts and nuts, preferably with part-spherical seats 17. A second and smaller clearance 18 is formed at the periphery of the flanges, outside the radius of the fastening-means. The pipe axis is indicated at 19 and the PCD of the fastening-means at 21. PCD 20 at the radially outer edge of joint 13 is of significance in relation to Figure 2.

Figures 2 and 3 are more briefly described to illustrate certain weaknesses of known flanged joints. Different reference numbers are used.

In Figure 2, a joint 22, with gasket 23, or other sealing means, has a radially outer edge at PCD 24, radially inside fastening-means PCD 25 and similar in this respect to the Figure 1 PCD 20 and PCD 21. Clearance 26, starting inside (i.e. at a smaller diameter than) the PCD 25 extends radially to the periphery of the flanges. Upon assembly, the fastening-means draw the peripheries of- the flanges toward each other, as shown by arrows 27, thus pre-stressing the flanges and storing energy that assists the joint during normal conditions of use, i.e. the opposing forces that tend to pull axially away from joint 22 as the pipe carries pressurised fluids, indicated by arrows 35. The location of joint 22 inboard of the fastening-means is the best placement to resist these opposing forces.However, overstressing of the flanges may occur during assembly, and this type of joint is unsatisfactory when external forces place a bending stress upon the joint, in a manner to force one or both pipes away from the nominal pipe axis 28. Bending stress tends to act to 'try' to cause differential movement of one flange in relation to the other about PCD 24, and may cause the joint to fail.

In Figure 3, joint 29, with gasket 30, is a 'full-face' type, making contact from bore to periphery, both inside and outside fastening-means PCD 31. In this type, tightening of the fastening-means cannot pre-stress or bend the flanges, but when the pipe is pressurised there is an axial pull in both directions away from the joint, as shown by arrows 32, and the flanges may part at the inner face 33. External bending stress may tend to cause differential movement of one flange in relation to the other about the joint perip#hery 34, but because of the larger diameter at 34 as against PCD 24 in Figure 2, the full-face joint is more resistant to pipe bending forces.

The improved design of Figure 1 is resistant to all the stresses mentioned above in relation to the prior art, and may thus be made smaller and lighter for given pipe sizes and pressures to be contained. The said stresses are: (a) Pre-stressing by tightening of the fastening-means, which may lead to overstressing; (b) Axial tension, pulling in both directions away from the joint, when the pipe is carrying high-pressure fluid; and (c) External bending stress.

The invention meets (a) above with small clearance 18 at a larger diameter than clearance 15, which is in turn at a larger diameter than joint 13. Clearance 18 is dimensioned in relation to flange size, material, pipe pressure and other relevant parameters, so as to close when correct pre-stressing and fastening tightness are achieved. Any displacement of one flange relative to the other during assembly is accommodated by the part-spherical seating 17 without inducing off-axis forces in the fastening-means. Thus, overstressing is impossible, and correct fastening tightness facilitated.

The invention meets (b) above with initial joint 13 at a location radially inside the fastening-means PCD 21, which is ideal for this type of stress as metioned in relation to Figure 2.

The invention meets (c) above by virtue of the closed clearance 18. The feature of the closing of clearance 18 upon correct assembly provides a further and final joint, in addition to initial joint 13. This, being at the periphery, confers optimum resistance to external pipe-bending forces, and, in effect, converts the joint into the equivalent of a full-face type with its advantages but without its attendant disadvantages, as described in relation to Figure 3.

Claims

1. A flanged joint between two members in which the opposing flange faces have first and second concentric mating joint faces which are formed at differing radii and in differing radial planes in relation to the axis of said members, the first or radially inner mating joint faces meeting upon initial assembly and the second or radially outer mating joint faces meeting to complete the joint only after correct tightening of fastening means positioned radially between said first and second mating joint faces.

2. S flanged joint between b#o members in which substantially flat mating faces are formed on opposing flange faces which are adapted to be drawn together and tightened by releasable fastening means, characterised in that the following features are situated at successively larger diameters in relation to the axis of said members: a) a flat mating joint made directly, without the interposition of a gasket, between said members; b) a clearance between said members at a time when said joint is initially assembled, said clearance being dimensioned to remain when said joint is tightened, and said clearance being bridged by c) fastening means; and d) a second and smaller clearance at a time when said joint is initially assembled, adapted to close and provide a second mating joint at a time when said fastening means are correctly thightened

3. A flanged joint between components adapted to be drawn together and the joint tightened by releasable fastening means, comprising in relation to the axis of said components:a) pairs of radially inner and outer plane mating faces formed on opposing flange faces; b) said pairs being separated radially; c) with an axial clearance bridged by fastening means positioned radially between said pairs; and d) said pairs also being separated axially; e) so that the inner pair makes the joint first upon initial assembly, leaving the radially outer pair with a second and smaller clearance therebetween, adapted to complete the joint after correct tightening of the fastening means.

4. A flanged joint according to any of the preceding claims, in which the fastening means are tightened in part-spherical seatings.

5. A flanged joint according to any of the preceding claims, in which a sealing ring of cone type is inserted into complementary recesses formed in said members or components in a manner to protect the radially inner mating faces against conditions within the flanged members or components.

6. A flanged joint substantially as described and/or as illustrated in Figure 1 of the drawings.