WO1997014905A1

WO1997014905A1 - Tube coupling

Info

Publication number: WO1997014905A1
Application number: PCT/SE1995/001211
Authority: WO
Inventors: Thomas Arvidsson
Original assignee: Avesta Nords Aktiebolag
Priority date: 1995-10-17
Filing date: 1995-10-17
Publication date: 1997-04-24
Also published as: AU4125596A

Abstract

A pipe coupling comprising a threaded male part (1) having a part which includes an internal conical surface (1a) and an abutment edge (1c) for abutment with a pipe (5) to be connected to the male part, a threaded female part (2), and a bite ring which is located between the male part and the female part and which includes a press-in part which is adapted to be pressed into the conical part of the male part as the male and female parts are screwed together, such that a front edge (3b) of the press-in part will bite into the pipe extending coaxially with the coupling. The press-in part of the bite ring has externally thereon an annular groove (3g) for accommodating a sealing ring (4) which is pressed sealingly against the internal conical surface of the male part as the male and female parts are screwed together.

Description

TUBE COUPLING

FIELD OF INVENTION

The present invention relates to a pipe coupling ofthe kind that includes a threaded male part having a part with an internal conical surface and an abutment edge for abutment with a pipe to be connected to the male part, a threaded female part, and a bite ring which is located between the male part and the female part and which includes a press-in part which is adapted to be pressed into the conical part ofthe male part as the male and female parts are screwed together, such that a front edge ofthe press part will bite into the pipe extending coaxially with the coupling.

DESCRIPTION OF THE BACKGROUND ART

Couplings of this kind have long been used to provide a sealed connection between pipe and other components, without needing to pre- work the pipe. One example of a development of a still older basic principle is disclosed in SE-B-333 851. Couplings of this type are based on the fundamental principle whereby the press-in portion ofthe bite ring is pressed into the conical part ofthe male part as the coupling is tightened, wherewith the outer surface ofthe press-in portion slides against the conical outer surface ofthe male part while generating between the surfaces a pressure of such high magnitude as to cause the front edge ofthe bite ring to bite into the pipe extending coaxially with the coupling. There are created in this way two sealing surfaces, one sealing surface which is located between pipe and bite ring, this seal being extremely tight by virtue ofthe fact that the surfaces in the region ofthe pointed part ofthe bite ring are totally plasticized, and one sealing surface between the bite ring and the conical inner surface ofthe male part. This latter seal, however, is highly sensitive to irregularities in the surface where no true plasticization has taken place but where heavy scratches, scores, and surface irregularities have been caused as a result ofthe surfaces sliding against one another as the coupling is tightened. In addition, the pressure ofthe medium in the pipe generates a reaction force which strives to push out the pipe and therewith reduce the tightening force. While sealing between pipe and bite ring is further enhanced in this way, it can create a serious problem with regard to sealing between bite ring and the conical inner surface ofthe male part at high medium pressures. The use of elastomeric sealing rings, eg rubber sealing rings, normally O-rings, to obtain a good seal is also generally known to the art. US-A-4 258 943 shows some examples of how O-rings can be placed in different couplings. In order for an elastomeric sealing ring to provide an effective seal against high fluid pressure, it is necessary to fulfill a number of basic conditions. One condition is that there must be no clearance between the surfaces where the O-ring is placed. Otherwise the flexible O-ring will be pressed out of its accommodating groove by the pressure ofthe fluid. Another condition is that the surface against which the sealing ring is pressed is very smooth and has not been seriously scratched or scored. The sealing ring itself must also be whole and undamaged. It would therefore appear that the conditions prevailing in the case of a bite ring are unfavourable to the function of an O-ring or to the function of any other elastomeric sealing ring.

SUMMARY OF THE INVENTION

The object ofthe invention is to provide a highly sealing- effective pipe coupling ofthe kind defined in the preamble. More particularly, the object is to provide an effective seal at very high medium pressures and vibrations in pipelines. Another object is to provide a pipe coupling that is comprised essentially of standard components. These and other objects are achieved with a pipe coupling that has the characteristic features set forth in the following claims. Further characteristic features and aspects ofthe invention will be evident from the following description of a preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWING.

The invention will now be described with reference to a preferred embodiment of an inventive pipe coupling and also with reference to the accompanying drawing, in which

Fig. 1 is a cross- sectional view of a coupling-half and a pipe-half, with the centre line indicated; and Fig. 2 is a cross-sectional view ofthe half-coupling and half-pipe after having tightened the thread connection. DESCRIPTION OF A PREFERRED EMBODIMENT

The main parts ofthe coupling comprise a threaded male part 1, a threaded female part 2 in the form of a tightening nut which coacts with the male part, and a bite ring 3, wherein all of said parts are penetrated by the pipe 5 to be coupled in abutment with an abutment edge lc on the male part 1

As will be seen from Fig. 1, the bite ring 3 includes a press-in part 3 a which is intended to be pressed into the male part 1, which has an inner conical mantle surface la, such as to deform the press-in part 3 a The deformed parts have been identified in Fig. 2 with the addition of a prime

The inner conical mantle surface la ofthe male part has a fist slope angle vl . The bite ring 3 has an edge 3 b furthest forward ofthe ring and the region located nearest the edge 3 b is designated the pointed part 3 c. Prior to deformation ofthe bite ring 3, this pointed part will have a mantle surface ofthe same slope angle vl as the inner conical mantle surface 1 a ofthe male part 1. The remainder ofthe press-in part 3 a, which extends from a bend 3d on the bite ring rearwardly to a rear cylindrical part 3g, has a conical mantle surface 3e whose slope angle v2 is smaller than the first slope angle vl This means that a first wedge-shaped (in cross-section) gap 6 will be formed between the conical mantle surface la of the male part and the mantle surface 3e ofthe press-in part 3a rearwardly ofthe front pointed part 3c The mantle surface 3e ofthe press-in part 3 a includes an O-ring groove 3g which accommodates an O-ring 4 The width ofthe groove 3g is greater than the diameter ofthe O- ring 4

The bite ring 3 also typically includes an inner conical part having a rearwardly sloping conical mantle surface 3h such as to form a second wedge-shaped (in cross-section) part 7 between said inner conical surface 3h and the pipe 5 in a known manner The sum ofthe second angle v2 and the wedge angle v3 (or its complementary angle) is typically equal to the first angle vl The wedge-shaped part 7 extends to a plane B which extends peφendicular to the coupling centre line 8 and which forms the base for the region of bite ring deformation By "base for the region of bite ring deformation" is meant that those parts located forwardly ofthe base plane B will be deformed and/or pressed-in against or into the pipe whereas remaining parts, ie those located rearwardly ofthe base plane (to the right ofthe plane B in Fig. 1) will remain intact.

The O-ring groove is placed forwardly ofthe base plane B. More specifically, in the case of the illustrated embodiment the O-ring groove 3g is spaced forwardly ofthe base plane B by a distance which may be smaller than the width ofthe groove 3g, at least in the case of small pipe dimensions (to which the illustrated embodiment relates). When the bite ring 3 has been inserted and its press-in part 3 a located in the male part 1 but still not subjected to deformation forces, the O-ring groove 3g will still lie essentially outside the outer edge lb of the male part 1. The O-ring 4 has no contact with the male part 1 in this initial position.

When tightening the pipe coupling, the coupling nut 2 (the female part) is screwed onto the male part 1 such as to press the rear part 2a ofthe nut 2 forwards against the rear part 3i of the bite ring 3, in a known manner. The forward part 3 c ofthe bite ring will herewith be pressed with great force against the inner conical mantle surface la ofthe male part 1 and slide thereagainst, wherewith the edge 3b ofthe pointed part 3 c will bite into the pipe 5 at the same time as the whole ofthe press-in part 3 a located forwardly ofthe base plane B is successively deformed and/or pressed into the pipe. The inner conical surface 3h ofthe bite ring is thus pressed in against the pipe 5 during bending ofthe bite ring roughly in the base plane B, at the same time as the bite ring advances while the outer conical surface 3e ofthe bite ring and the inner conical surface la ofthe male part slide against one another. In the final moment of this movement, those parts ofthe conical mantle surface 3e that lie immediately forwards of and rearwardly ofthe O-ring groove 3g have still not come into direct contact with the inner conical surface la of the male part 1. This occurs when the rear wall 3j ofthe groove 3g has passed the front edge lb ofthe male part 1. The O-ring 4 will also herewith come into contact with the inner mantle surface ofthe male part, which contact area has not been scored or scratched by sliding between metal surfaces and is therefore undamaged. It is possible that a certain, very slight amount of sliding may take place between the O-ring 4 and the inner conical surface la ofthe male part 1 at the very last moment, although no damage will be caused to the O-ring 4 because said surface is undamaged and free from scratches. In the final stage, as in the ideal case shown in Fig. 2, the mantle surfaces 3e' and 3h' ofthe press-in part 3a¹ will lie essentially against the conical inner surface la ofthe male part 1 and against the pipe 5 respectively, the pointed part 3 c' will be pressed into the pipe 5, and the O- ring 4 will lie sealingly against the inner mantle surface la ofthe male part and against the rear wall 3j ofthe O-ring groove 3g. Complete sealing is achieved with this coupling at pressures of up to at least 1500 bars.

Claims

1. A pipe coupling comprising a threaded male part (1) having a part which includes an intemal conical surface (la) and an abutment edge (lc) for abutment with a pipe (5) to be connected to the male part, a threaded female part (2), and a bite ring (3) which is located between the male part and the female part and which includes a press-in part which is adapted to be pressed into the conical part ofthe male part as the male and female parts are screwed together, such that a front edge (3 b) ofthe press-in part will bite into the pipe extending coaxially with the coupling, characterized in that the press-in part ofthe bite ring has provided extemally thereof an annular groove (3g) for accommodating a sealing ring (4) which is pressed sealingly against the intemal conical surface ofthe male part as the male and female parts are screwed together.

2. A pipe coupling according to Claim 1, wherein the press-in part ofthe bite ring comprises a front part which includes the pointed part having said front edge, and a rear part which extends along half the total axial length ofthe press-in part, characterized in that said annular groove is placed in said rear part.

3. A pipe coupling according to Claim 1 or 2, characterized in that the annular groove (3g) is at least partially visible outside the front edge (lb) ofthe threaded male part prior to the bite ring being pressed thereinto when screwing together the coupling.

4. A pipe coupling according to any one of Claims 1 - 3, characterized in that the bite ring is internally conical in the region between the pointed part, which shall bite into the pipe, and a rear cylindrical part with the imaginary apex ofthe conical surface pointing rearwardly; in that the bite ring has rearwardly ofthe pointed part an external conical mantle surface whose slope angle (v2) is smaller than the slope angle (vl) ofthe intemal conical surface on the threaded male part; and in that the annular groove is placed forwardly ofthe base plane (B) peφendicular to the coupling centre line, where the intemal conical part ofthe bite ring passes into a cylindrical surface.

5. A pipe coupling according to Claim 4, characterized in that the distance between the base plane (B) and the rear edge (3j) ofthe annular groove is smaller than the width ofthe groove.

6. A pipe coupling according to any one of Claims 1 - 5, characterized in that the sealing ring is comprised of an elastomer.

7. A pipe coupling according to Claim 6, characterized in that the sealing ring is an O-ring