GB2202022A

GB2202022A - Flanged joint

Info

Publication number: GB2202022A
Application number: GB08802979A
Authority: GB
Inventors: Kalle Lampela
Original assignee: GS Hydro Oy
Current assignee: GS Hydro Oy
Priority date: 1987-03-05
Filing date: 1988-02-10
Publication date: 1988-09-14
Anticipated expiration: 2008-02-10
Also published as: IT1219475B; FR2611853B1; GB2202022B; CN88101004A; ES2006840A6; GB8802979D0; SE8800742D0; IT8847680A0; FR2611853A1; JPS63231087A; NO880889D0; YU39388A; KR880011519A; SE8800742L; FI870983A0; DE3806162A1; NO880889L; CN1007751B; FI870983A

Description

- 1 FLANGED JOINT k The present invention relates to a flanged joint

consisting of the pipe ends to be joined, each of which is provided with a collar with a flat front surface essentially perpendicular to the longitudinal axis of the pipe, and flanges provided with central holes for the pipes, the flanges being placed behind the collars and tightened together in the axial direction of the pipe with suitable securing means, such as bolts and nuts, the thickness of the collar increasing from the collar periphery towards the centre of the pipe, so that the form of the back face of the collar is different from that of the front face.

To produce this type of a flanged joint, the pipe ends to be joined are generally first provided with collars essentially perpendicular to the longitudinal axis of the pipe. There are several alternatives for making such collars. One is presented in the Finnish patent application 791695. Another method for producing such a collar at the pipe end is proposed in the Finnish patent application 870799, whereby the collaring operation is performed in two stages, the pipe end being first expanded into an angle of approx. 35-40' and then, using an auxiliary expanding head, into an angle of 90. Another commonly used method for producing a 90 collar is to weld a separate short piece provided with a ready-made collar onto the pipe end.

Once the collars have been produced, the flanges placed behind the collars on the opposite pipes are tightened together with suitable securing means, such as bolts and nuts. A gasket is usually placed in the joint between the pipe ends.

At present, this type of flanged joints are made using flanges in which the surface pressed against the collar is e 2'12'J 2 0 25-1 2 straight and essentially rerpendicular to the longitudinal axis of the pipe. A collar with a straight back can be produced e.g. by using a straight backing plate in the collaring machine. Although it rs possible to produce a collar with a straight and flat back face with a minimum of shaping work, a larger amount of material will be accumulated on the front side near the central region of the collar, so that the front face does not have a straight form. However, in flanged joints it is important that the collars of the pipes to be joined are brought as tightly together as possible. In other words, if the front face of the collar is not of a flat form, it must be worked so as to make it flat.

When the pipe end is expanded to produce a collar at right angles to the longitudinal axis of the pipe, the thickness of the collar is reduced as the diameter increases. If the front face of a 90' collar on a pipe with a large diameter is further worked to make it flat, this means that the thickness of the collar, which is a critical factor, is reduced and the quality of the collar lowered.

US patent 3,533,449 proposes a collaring machine for making a 900 collar at the end of a pipe. The collar is produced using a backing plate in which the surface facing the back side of the collar differs from the perpendicular plane. It is obvious that when a straight flange is mounted on a collar like this, the resulting joint is not the best possible because the flange and collar surfaces pressed together do not match exactly in shape.

The object.of the present invention is to achieve a flanged joint which is free of the disadvantages mentioned. The flanged joint of the invention is characterized in that that surface of the flange which is pressed against the collar differs from the plane perpendicular to the longitudinal axis of the pipe in such manner that that part of the flange f v th 4 3 which is pressed against 'he peripheral part of the collar lies closer to the front end of the pipe than the part of the flange which is pressed against the central part of the collar, so that the opposite surfaces of the collar and the flange are substantially alike in shape and thus fit together.

An advantageous embodiment of the flanged joint of the invention is characterized in that the flange surface pressed against the collar is of a curved form in vertical section.

Another advantageous embodiment of the flanged joint of the invention is characterized in that the flange surface pressed against the collar is of a flat form in vertical section and forms a slight angle relative to the longitudinal axis of the pipe.

The flanged joint of the invention offers many advantages over the solutions previously known in the art. Using modern equipment, it is easy to produce the perpendicular collar required for the joint. The collar needs no further working, so that its thickness is not excessively reduced. The collar is thicker in its central part than in its peripheral part, with the result that it has greater resistance to axial shearing forces, which cause a strain on the bend between the collar and the pipe.

Another advantage offered by the invention is that the angle between the collar and the pipe at the back of the collar can be made quite straight, which makes it possible to reduce the distance between the inner sphere of the flange and the outer surface of the pipe. This increases the joint's resistance to pressure, since the torque arm bending the collar is reduced. 'Torque arm' refers to the distance 01 4 between the mid-line of the pipe wall and the innermost point of contact between the flange and the collar.

In the following, the invention is described in detail with reference to the drawings attached, wherein:

Fig. 1 shows part of the vertical section of the pipe end immediately after a perpendicular collar has been formed.

Fig. 2 shows the same pipe end after further working.

Fig. 3 shows part of the vertical section of a pipe end according to an embodiment of the invention.

Fig. 4 shows part of the vertical section of a pipe end according to another embodiment of the invention.

Fig. 5 shows the flanged joint of the invention in sectional view.

Figure 1 shows a section of a pipe end 1 which has been expanded so as to produce a collar 2 essentially perpendicular to the pipe's longitudinal axis. The back face 3 of the collar has been given a straight and even form in order that it should fit tightly against the flange in a flanged joint. A straight back face can be produced e.g. by using a straight backing plate in the collaring machine. The collaring machine will not be described in this context. A machine like e.g. the one proposed in the Finnish patent application 870799 may be used. It is not necessary to use a collaring machine at all if a short extension provided with a perpendicular collar is welded onto the pipe end.

As is obvious from figure 1, the front face of the collar 2 is not straight in form. During the expansion operation, the thickness of t.he pipe material has been reduced in the d 1 peripheral part of the collar and increases towards the central part. However, the front face of the collar should be straight and flat in form, because in a flanged joint it will be pressed against the collar of the other pipe, generally with a gasket placed between the two collars. Therefore, the collar has to be worked further to make it straight and flat (see fig. 2). Figure 2 shows that after such additional treatment the whole collar is thinner than the original pipe wall.

Figure 3 shows a collar 2 as provided by the invention. Its back face 3 is not straight but, in this embodiment, preferably slightly curved, whereas the front face 4 is straight and flat. This is explained by the fact that when the pipe end is expanded to form a collar, the peripheral part of the collar becomes thinner than the central part. As the collaring methods commonly used employ straight-faced backing plates, the presence of a larger amount of material in the central region of the collar becomes obvious in that the front face can only be straightened through additional rolling.

The basic idea of the invention is to provide the collaring machine with a backing plate having a backing surface that differs from the perpendicular plane so as to allow the material congested in the central region of the collar during the expansion operation to be spread out on the back face 3 of the collar. In this way, the front face of the collar will be given a flat form and needs no further treatment.

ip Neither does the back face of the collar need any additional treatment, because the flange used in the joint is so designed that the surface pressed against the collar 2 has the same form as the back face 3 of the collar 3.

01 6 k Figure 4 shows another variant of the collar, with a back face 3 that is flat in vertical section but, unlike the front face 4, not exactly perpendicular to the pipe 1. The angle between the front and back faces is relatively small, perferably 5-100 depending on the diameter of the pipe and the thickness of the pipe wall, yet always larger than 1. In this embodiment as well, the collar is thicker in its central region than in the peripheral part.

zR Figure 5 shows a flanged joint as provided by the invention, in which two pipes 1 are joined together end to end. The pipe ends are provided with collars 2 as described above and flanges 5, which are so designed that the surfaces pressed against the collars are of the same form as the back faces 3 of the collars 2. The flanges 5 are provided with holes 9 to accommodate the bolts 7, which are tightened with nuts 8. The joint is sealed with a circular gasket 6 placed between the two collars.

It is obvious to a person skilled in the art that the invention is not restricted to the examples of its embodiments described above, but that it may instead be varied in the scope of the following claims.

1 IF 7

Claims

CLAIMS k 1. Flanged joint, consisting of the pipe ends to be joined, each

of which is provided with a collar (2) with a flat front surface (4) essentially perpendicular to the longitudinal axis of the pipe (1), and flanges (5) provided with central holes for the pipes (1), the flanges being placed behind the collars and tightened together in the axial direction of the pipe with suitable securing means, such as bolts (7) and nuts (8), the thickness of the collar (2) increasing from the collar periphery towards the centre of the pipe so that the form of the back face (3) of the collar (2) is different from that of the front face (4), c h a r a c t e r i z e d in that that surface of the flange (5) which is pressed against the collar (2) differs from the plane perpendicular to the longitudinal axis of the pipe (1) in such manner that that part of the flange (5) which is pressed against the peripheral part of the collar (2) lies closer to the front end (4) of the pipe than the part of the flange whi. ch is pressed against the central part of the collar (2), so that the opposite surfaces of the collar (2) and the flange (3) are substantially alike in shape and thus fit together.
2. Flanged joint according to claim 1, c h a r a c t e r i z e d in that that surface of the flange (5) which is pressed against the collar (2) has a curved form in vertical section.
3. Flanged joint. according to claim 1, c h a r a c t e r i z e d in that that surface of the flange (5) which is pressed against the collar (2) has a flat form in vertical section and forms a slight angle relative to the longitudinal axis of the pipe (1).

1 8
4. Flanged joint substantially as described with reference to Figure 3, Figure 4 or Figure 5 of the accompanying drawings.

i 1 11 published 1988 at The Patent 0Mce, State House, 66171 High Holborn, London WC1R 4TP. Further copies may be obtained from Mie Patent Mce,