GB2145491A - Pipe coupling - Google Patents

Abstract

A pipe coupling comprises a coupling body 1, a ferrule 5, and a clamping member 4. The ferrule is in the form of a collet and the clamping member has a corresponding internal surface. The collet has means for engaging with corresponding means e.g. a groove 7 on the pipe to be coupled. A shoulder 2 in the coupling body is adapted to engage with the end of the pipe to form a seal. The coupling is less susceptible to incorrect assembly. <IMAGE>

Description

SPECIFICATION Couplings for pipes and tubes The present invention relates to improved couplings for pipes and tubes.

Couplings, especially compression couplings are devices used with pipes or tubes to make leak-proof connections in a fluid system. Such couplings usually comprise a ferrule for mounting externally and a clamping nut slideably mounted on the pipe, a fitting body having external screw threads adapted to receive the nut such that upon tightening the nut on the body, a leak-proof seal is formed between the clamping nut, the ferrule, the fitting body, and the pipe.

Conventional compression couplings of this type have several drawbacks and unless properly installed may be unsafe. For instance, such couplings, because of their apparent ease of assembly, are assembled by relatively unskilled operatives. However, if they are assembled incorrectly, external inspection usually will not reveal the error in assembly. The only means of checking the correctness of the installation is to dismantle the coupling. This is time consuming because the coupling has to be reassembled and has to be pressuretested. Some of the reasons for the faults which may occur during installation are: (i) a ferrule may be used with a coupling for which it is intended; (ii) the ferrule might be used back to front.

(iii) one portion of a two-ferrule coupling may be accidentially omitted or wrongly assembled; (iv) the clamping nut might not have been tightened properly thereby causing the pipe to blow out; (v) the clamping nut may have been overtightened and so cut too deeply into the pipe which may break off; (vi) the pipe may not have been fully inserted into the coupling and may therefore blow out; and (vii) the pipe end may have been prepared badly, eg a hacksaw used to cut the pipe may have slipped, or the external surface of the pipe where the ferrule must bite may have been damaged.

In short, the problems and faults may be due to the lack of operative skills or the inadequacy of visual inspection methods or both.

It has now been found that by using a novel design of the coupling the problems and faults experienced hitherto can be mitigated.

Accordingly, the present invention is a pipe coupling comprising a coupling body, a ferrule and a clamping member, said ferrule and clamping member adapted to be slideably mounted on a length of pipe to be joined to the coupling member, and the clamping member being adapted to be brought into screwed engagement with the coupling body so as to retain the ferrule on the pipe and to cause sealing of the coupling characterised in that (a) the ferrule is in the form of a collet adapted to mate with a corresponding internal surface on the clamping member, (b) the collet has pipe engaging means on its internal surface adapted to engage with corresponding collet engaging means on the external surface of the pipe to be coupled, (c) there is a shoulder within the coupling body adapted to engage with the end of the pipe to be coupled so as to form a seal when the clamping member is fully tightened on the coupling body.

In this specification the term pipe is meant to embrace both pipes and tubes i.e.

both large thick bore and small bore tubing.

The clamping member is conveniently a nut with an internal screw thread adapted to engage with a corresponding external screw thread provided on the coupling body.

The collet preferably has two segments which are preferably semicircular, although the collet may be split into more than two segments. On assembly, the segments combine to form the ferrule when placed in position around the pipe. The pipe engaging means on the collet is preferably an internal lip. The lip may be integral with the interior of the collet or may take the form of a replaceable clip inserted into an internal recess in the collet to form the lip. The internal lip may extend either around the entire internal circumference of the collet or around only a part thereof to enable the stress, if any, on the collet to be distributed evenly. The external surface on the split collet is preferably a bevelled area at one end thereof mating with a corresponding internal surface on the clamping member.The length of the collet is preferably such that one end of the split collet extends and protrudes from the nut away from the pipe end thereby enabling visual inspection to ensure that during assembly a collet has been used and that it has been properly assembled. Upon assembly the part of the collet protruding from the clamping member has the appearance of a sleeve on the pipe.

The end of the collet of smallest diameter may be provided with an external circular clip to facilitate retention thereof on the pipe during assembly.

The collet engaging means is preferably an external annular groove on the pipe which is formed to mate with a lip on the collet, and is appropriately spaced from the end of the pipe to be connected to ensure that the abutment between the pipe end and the internal shoulder of the coupling body is adequate to form a metal to metal seal. The distance of the groove from the pipe end may be predetermined and cut as required.

Further, to maximise the sealing effect the internal shoulder of the fitting body is preferably of reactangular shape and the pipe end abutting against it is preferably externally chamfered such that upon assembly the chamfer of the pipe abuts against the rectangular edge of the shoulder. The seal may also be formed by a rectangular pipe end abutting with a chamfered shoulder in the fitting body.

Typically, a hand tool of conventional design may be used to prepare the pipe for connection to the fitting body. Thus the tool should be able to cut for instance the external sealable surface on the pipe end and the external annular groove on the pipe at a predetermined distance from the pipe end.

The fitting body to which the pipe is connected may be for instance an elbow fitting, a T-fitting, a stud coupling or any of the typical straight pipe coupling.

The present invention in one of its embodiments is described with reference to the accompanying drawing.

The Figure shows a view, partly in section, of an assembled coupling.

In the Figure a fitting body (1) is provided with an internal rectangular shoulder (2) and an external fine pitch screw thread (3). A clamping nut (4) has a matching screw threads and is shaped internally (9) to receive a collet (5) which has an external surface (11) at one end and an internal lip (6) at the same end adapted to mate and engage with an external annular groove (7) on a pipe (8). The pipe (8) has a chamfered end (10) and the groove (7) is at a predetermined distance from the chamfered end (10).

The end of the collet (5) furthest from the flange (11) protrudes from the clamping nut (4).

The dimensions of the collet (5), clamping nut (4) and the fitting body are so chosen that a small space (12) is provided between the collet and the fitting body to allow for expansion.

Upon assembly, the nut (4) is placed on the pipe first and then collet (5) is placed on the pipe (8) so that the collet lip (6) engages with the pipe groove (7) and the clamping nut (4) is slid thereon to retain the split collet (5) on the pipe. Upon tightening the clamping nut (4) on the fitting body (1), the clamping nut (4) via the collet (5) forces the chamfered pipe end (10) to abut against the rectangular internal shoulder (2) of the body (1) thereby forming a metal to metal seal.

At the same time, the internal surface (9) of the nut (4) bears on the external surface (11) of the collet (5) causing the collet to grip the pipe (8) and form a mechanical support for the pipe (8).

The collect is held in position on the pipe by the lip (6) engaging with the groove (7).

As the nut (4) is tightened the collet is compressed by the tapered recess in the nut, so compressing the collet. However because the collet is held in position on the pipe it then resists further tigthening of the nut because of the interaction of the external surface of the collet and the internal surface (9) of the nut.

It can be seen that the coupling cannot be assembled unless the proper collet is used.

The coupling cannot be wrongly assembled with the collet or with a wrong collet. The coupling cannot be overtightened. Even if it is marginally loose, the coupling may leak slightly but the pipe cannot fly out. A relatively unskilled person can assemble the components and most importantly the assembled coupling can be readily inspected visually and externally without dismantling to check whether it has been correctly installed.

The couplings of the present invention have the following additional advantages.

1. The couplings have been designed such that they can be examined for stresses and strains by accepted mechanical engineering codes and methods.

2. The couplings can be used in corrosive environments without undue safety risks.

3. The couplings can be easily fitted with existing and conventional designs of pipes and tubes of nominal bore (eg 1/8 inch to 2 inches) used in the petrochemical industry.

Claims (7)

1. A pipe coupling comprising a coupling body, a ferrule and a clamping member, said ferrule and clamping member adapted to be slideably mounted on a length of pipe to be joined to the coupling member, and the clamping member being adapted to be brought into screwed engagement with the coupling body so as to retain the ferrule on the pipe and to cause sealing of the coupling is characterised in that (a) the ferrule is in the form of a collet adapted to mate with a corresponding internal surface on the clamping member, (b) the collet has pipe engaging means Oi.

its internal surface adapted to engage with corresponding collet engaging means on the external surface of the pipe to be coupled.

(c) a shoulder within the coupling body adapted to engage with the end of the pipe to be coupled so as to form a seal when the clamping member is fully tightened on the coupling body.

2. A pipe coupling according to either one of claims 1 to 2 wherein the clamping member is provided with the tapered internal surface and has an internal screw thread to engage with an external screw thread on the coupling member.

3. A pipe coupling according to any one of the preceding claims wherein the pipe engaging means is a lip on the collet and the collet retaining means is an annular groove on the pipe adapted to mate with the lip.

4. A pipe coupling according to claims 1 to 3 wherein the pipe engaging means is a groove on the internal surface of the collet carrying a circular clip which engages with a corresponding groove on the pipe.

5. A coupling according to claim 1 coupled to a pipe.

6. A coupling according to claim 5 wherein the position of the pipe engaging means on the collet and the collet engaging means on the pipe and the dimensions of the coupling member and the clamping member are so selected that the collet allows the coupling members to be brought into sufficiently close screw threaded engagement to cause a sealing abutment of the shoulder with the pipe but prevents excessive tightening of the coupling.

7. A coupling according to either one of claims 5 to 6 wherein the dimensions of the collet are such that the collet projects beyond the clamping member to provide a visual indication of its presence.