GB2101257A

GB2101257A - Joining tubular members

Info

Publication number: GB2101257A
Application number: GB08118951A
Authority: GB
Inventors: Barry Wootton Staynes
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-06-19
Filing date: 1981-06-19
Publication date: 1983-01-12
Also published as: GB2101257B

Abstract

A joint between two tubular members 1 and 2 is shown. The member 1 may for example be the end of a damaged underwater tie of an oil rig, the damaged part of which has been cut away, and the member 2 may be a replacement section. The members 1 and 2 are positioned in telescoped relation with an annular space 3 therebetween. The outer surface of the existing member 1 is formed adjacent its end with an annular groove 4 which forms a radial enlargement of the annular space 3. The replacement member 2 is provided with an annular projection 5 forming a restriction of the annular space. The annular space 3 is filled with a cured epoxide which is placed under triaxial compression when the members 1 and 2 are placed in tension and thus resists separation of the joint. Other joints are described which are adapted to resist both tension and compression forces, and which join members which are not coaxial. <IMAGE>

Description

SPECIFICATION Jointing system This invention relates to a method of making a joint between tubular members and to a jointed structure formed by the method.

Many structures are formed of or are reinforced with tubular members which are joined together, for example steel tubes which are welded together. Important examples of such structures are marine structures such as oil rigs. Such structures may occasionally become damaged due to the impact of ships, accidentally dropped equipment or in other ways and it is then necessary to repair the damaged part in such a way that the strength of the structure is maintained.

If an underwater tubular steel tie or strut becomes damaged it is possible to cut out the damaged portion and weld in a replacement. The welding of large structural members requires the provision of a dry environment and this can be very difficult and costly to provide. An underwater repair of an oil rig may typically cost of the order of one million pounds. In order to avoid the difficulties associated with underwater welding, a number of attempts have been made to form a bonded joint between a replacement part and an existing structural member. However, structural members existing under water are often corroded and it is difficult to bond to the corroded surface or to prepare the surface for bonding adequately under water.

According to the invention there is provided a structure including two cylindrical or tubular members joined together, the members being disposed in telescoped relation over part of their length with an annular space therebetween, one of said members being provided adjacent its end with an annular groove to form a radial enlargement of said space, and the other of said members being provided adjacent its end with an annular projection to form a radial restriction of said annular space, the space between said groove and projection being filled with a rigid cured resin.

The two members may be assembled and the resin injected in the uncured state. The resin may be a filled or unfilled epoxide or other resin. After it has cured, the resin is held firmly in position by the groove and projection and any attempt to draw the two members apart places the epoxide under triaxial compression, in which condition it strongly resists the longitudinal separation of the members.

When the resin is compressed longitudinally it tends to expand radially and this is of course resisted by the joined members. It should be noted that under these conditions the resin presses on the cylindrical surfaces of the members rather than suffering shear forces at the surfaces, and so the strength of the bond with the surfaces does not substantially affect the integrity of the joint.

Such a joint is particularly suitable for joining two members in tension.

The annular projection may be formed integrally with said other member or it may be a separately-formed ring fixed thereto.

Preferably the groove is cylindrical over a certain length at its deepest part and is chamfered at its axial limits, i.e. in longitudinal cross-section the groove has a flat base and radially and axially outwardly sloping sides. This shape of groove has been found to give good results compared to many other configurations which have been tested. If desired, more than one groove may be formed to increase the strength of the key between the resin and the grooved member.

Where the joint is to join a new member to an existing member where access is difficult, e.g.

under water, the groove is preferably formed in the existing member. For example, where a damaged part of a tubular tie of an oil rig is to be replaced, the damaged part may be cut out and the groove formed in the outer surface of the remaining part of the tie. The groove may be made by automated machinery, for example a cutting machine which clamps to the outside of the tube and rotates around the tube cutting a groove. A suitable blanking plug is then positioned in the machined end of the tube and the replacement portion having the projection at its end and carrying an injector nozzle is slid telescopingly thereover.

Uncured resin is injected until the annular space between the two members to be joined is full and when it cures a strong joint results.

Thus according to the invention there is provided a method of joining two tubular members comprising forming an annular groove in the surface of one member and an annular projection from the surface of the other, sliding the two members towards one another axially so that they are positioned in telescoped relation with an annular space therebetween, the groove and projection being axially spaced apart and forming respectively an enlargement and restriction of the annular space, and injecting into the annular space a curable resin which on curing rigidly resists axial separation of the members.

In a preferred embodiment of the invention, one of the members is provided with two cylindrical portions and the end of the other member fits between these cylindrical portions defining two annular spaces. The two cylindrical portions each carry adjacent their ends an annular projection projecting radially into the respective annular space and the other member carries adjacent its end two annular grooves each forming an enlargement of the respective annular space. Thus two coaxial joints are effectively formed one within the other thereby substantially increasing the strength of the joint. Preferably the two grooves in the end of the other member are axially spaced apart so as not to excessively weaken the material. This form of the joint is very strong and compact and is easily adapted to joining two tubular members of the same diameter.

Again, where the joint is to be made under water, the grooves are preferably formed in the end of the existing member and the two cylindrical portions are mounted on the replacement member which of course may be prefabricated. The replacement member preferably carries a circular end plate carrying the two cylindrical portions. In use, cured resin completely fills the annular space between the two cylindrical portions (which is divided into two annular spaces by the end of the existing tubular member) and such a joint is also adapted to withstand axial compression forces.

Viewed from another aspect, the invention provides a structure including two cylindrical or tubular members joined together, the members being disposed in telescoped relation over part of their length with an annular space therebetween, said annular space being filled with a rigid cured resin, and each of said members being provided with means for forming a key between the cured resin and the respective member, the key forming means being axially spaced apart along the annular space whereby longitudinal forces between the members causes compression of the resin via the keys. The means for forming the keys preferably comprise an annular groove formed in one member and facing the annular space and an annular projection formed on the other member and projecting radially towards the annular space.

One of the members may be provided with two key forming means and the other member provided with key forming means positioned axially therebetween. Such an arrangement is able to resist both tensile and compressive longitudinal forces between the members.

In addition to joining two coaxial members, the joint of the invention can be employed in a variety of situations, for example to join or repair the intersection between cylindrical members. A strong jacket may be made to fit around the intersection and the various cylindrical members may be joined to the jacket by means of joints according to the invention.

If the joint is to be made under water, the resin used must of course be capable of displacing water and of curing in a space originally filled with water. Some epoxide or other resins are suitable.

Some embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through a joint according to the invention between two tubular members of different diameters; Figure 2 is a longitudinal cross-section through another joint according to the invention, which joins two tubular members of the same diameter: and Figure 3 is a cross-section on the line Ill-Ill of Figure 2; and Figure 4 is a longitudinal cross-section through a joint according to the invention between two intersecting cylindrical members.

Referring to the drawings, Figure 1 shows a joint between two tubular members 1 and 2. The member 1 may for example be the end of a damaged underwater tie of an oil rig, the damaged part of which has been cut away, and the member 2 2 may be a replacement section. The members 1 and 2 are positioned in telescoped relation with an annular space 3 therebetween. The outer surface of the existing member 1 is formed adjacent its end with an annular groove 4 which forms a radial enlargement of the annular space 3. The replacement member 2 is provided with an annular projection 5 forming a restriction of the annular space. The annular space 3 is filled with a cured epoxide resin as will be described below.

As may be seen in the drawing, the groove 4 has a cylindrical base 6 over a certain length at its deepest point and is provided with chamfered edges 7 at its axial limits, i.e. in longitudinal crosssection the base of the groove is straight and the axial ends of the groove slope radially and axially outwardly. This shape of groove has been found suitable for positively transmitting forces from the tubular member 1 to the cured epoxide. If desired, two or more grooves may be formed in the region of the groove 4. The projection 5 comprises a ring welded within the end of the replacement member 2. If desired, a ring may be welded on the axial end face of the member 2 or a radially inwardly extending projection may be formed integrally with the member 2.

In order to repair a damaged tie under water, the damaged section is first cut away. The cut does not need to be accurately perpendicular to the axis of the tube. The groove 4 is then formed, for example by means of an automated cutting machine which clamps to the outside of the end of the existing tubular member 1 and rotates therearound cutting the groove. The replacement member 2 may be preformed with the projection 5 in a workshop on land, for example. The member 2 is provided with a blanking plug 8 in which is mounted an injection port 9. The port 9 is fitted with a tube 10 for supplying uncured epoxide resin. The cut end of the existing member 1 is provided with a blanking plug 11 and the member 2 is slid into the position shown in Figure 1.

Uncured epoxide resin is then forced through the injection port 9 to fill the circular space 12 and the annular space 3. The resin displaces the water in these spaces and eventually exudes out of the annular space 3 past the projection 5. Clearly the resin must be suitable for displacing water in this way and capable of curing in the presence of water. A commercially available standard structural adhesive has been found to be suitable.

When the joint is full the injection is terminated and the resin cures. If the joint is now placed in tension, the cured resin in the space 3 from the groove 4 to the projection 5 is compressed and tends to expand radially against the adjacent cylindrical surfaces of the members 1 and 2. The cured resin is thus placed under triaxial compression under which conditions it strongly resists the longitudinal separation of the members 1 and 2. Tests with joints made under sea water have shown that the joint of the invention may be stronger than the tubular members 1 and 2.

If it is necessary to slide the member 2 further to the right in Figure 1 over the member 1 so as to allow the other end of the replacement member 2 to be fitted over another cut end of an existing member, the axial extent of the circular space 12 may be increased as necessary without significantly affecting the strength of the joint, although a greater quantity of resin will of course be required to fill the joint.

Figures 2 and 3 show another, more complex, example of a joint according to the invention. In this case the existing member 1 and the replacement member 2 are of the same diameter.

The replacement member 2 carries on its end a circular plate 20 which itself carries two tubular portions 21 and 22 thereby defining two annular spaces 3 and 23 in conjunction with end of the existing member 1. The end of the existing member 1 is formed with two annular grooves 4 and 24 forming radial enlargements of the respective annular spaces. The grooves 4 and 24 are spaced apart axially so as not to excessively weaken the end of the member 1. The cylindrical portion 21 is formed with an integral annular projection 25 extending radially inwardly to form a restriction in the space 3. The cylindrical portion 22 carries a circular plate 26 of slightly larger diameter which thus forms a restriction in the annular space 23. An injection nozzle 9 is mounted in plate 26 and the supply tube 10 passes through the plate 20 and the wall of the replacement member 2.

In use, the end of the existing member is cut and grooves 4 and 24 formed, preferably with an automated machine. A blanking plug 11, e.g. an inflatable bag, is inserted in the end of the member 1. The replacement member 2 is prefabricated and preferably all of the parts are joined together by welding. The two parts are slid together in telescoping relation as shown in Figure 2. Guides 27 may be provided to assist assembly and to maintain the parts at the proper spacing. Uncured epoxide resin is injected through the portion 9 and into the annular spaces 23 and 3 until it exudes past the projection 25. If desired, the projection 25 may be provided with a flexible seal engaging the outer surface of the member 1 and provided with holes to allow venting during resin injection. This may result in a more even filling of the joint with resin.It is possible, however, to position a seal 28 on an extension of the tubular portion 21 as shown in Figure 2. This has the advantage that a reservoir 29 of resin is available to return past the projection 25 in case of shrinkage on curing.

After curing, if the joint is placed in tension the epoxide in the annular space 3 from the groove 4 to the projection 25 and the epoxide in the annular space 23 from the groove 24 to the projection 26 is placed under compression whereby longitudinal separation of the members is strongly resisted.

This form of joint also resists compression under which condition the cured epoxide in the space between the plate 20 and the cut end face of the member 1 is compressed. If it is desired to increase the resistance to compression, a further groove may be formed in the inner surface of the outer tubular portion 21 spaced apart in the axial direction towards the plate 20 from the groove 4.

The cured resin between the groove 4 and the further groove will be placed into compression if the members 1 and 2 are urged towards one another, thereby strongly resisting axial compression forces.

Referring to Figure 4, the use of joints according to the invention in joining two intersecting cylindrical members at a T-joint is illustrated. In this example the member 31 is an existing underwater member and the member 32 is a replacement member. The only preparation which need be carried out under water is the forming of two annular grooves 34 in the existing member 1; the remaining parts shown in Figure 4 may be prefabricated and brought to the member 31 for assembly.

The replacement member 32 is cut to size and formed with an annular groove 35. A jacket 36 which is separable in a plane parallel to the paper is formed to fit around the assembled joint and is provided with integral annular projections 37. The members 31 and 32 are positioned and the jacket 36 is assembled therearound, e.g. by bolting or riveting. When the joint is assembled, annular spaces 38 are defined and these are filled with an epoxide resin which may be injected through the wall of the jacket 36. Alternatively, an end cap 39 carrying an injection port 40 may be fixed to the member 32 and sealingly engage the jacket 36.

When cured the resin strongly resists the axial separation of the jacket and the cylindrical members. Clearly by the use of a suitably shaped jacket many other joint configurations can be made; a jacket may be used to repair a damaged weld.

It may be seen that the invention allows the joining of two tubular members under water in a manner which is substantially cheaper than methods employed heretofore. The bulk of the preparatory work can be carried out in a steel fabrication shop on shore and no unusual or expensive skills are required in this fabrication; specialised surface preparation of the steel work under water is unnecessary as the joint does not rely on structural bonding between the resin and the steel; and divers are not required to use unrealistic skills as the preparation of the damaged section and the injection can be automated. A diver will be required primarily only to locate the automated equipment and the fabricated joint.

Claims

1. A structure including two cylindrical or tubular members joined together, the members being disposed in telescoped relation over part of their length with an annular space therebetween, one of said members being provided adjacent its end with an annular groove to form a radial enlargement of said space, and the other of said members being provided adjacent its end with an annular projection to form a radial restriction of said annular space, the space between said groove and projection being filled with a rigid cured resin.

2. A structure as claimed in claim 1 wherein the resin is an epoxide resin.

3. A structure as claimed in claim 1 or 2 wherein the annular projection is formed integrally with said other member.

4. A structure as claimed in claim 1 or 2 wherein the annular projection is a separately formed ring fixed to said other member.

5. A structure as claimed in any preceding claim wherein the groove is cylindrical over a certain length at its deepest part and is chamfered at its axial limits.

6. A structure as claimed in any preceding claim wherein more than one groove is formed in said one member.

7. A structure as claimed in any preceding claim wherein one of the members is provided with two cylindrical portions and the end of the other member fits between these cylindrical portions defining two annular spaces, each cylindrical portion carrying adjacent its end an annular projection projecting radially into the respective annular space and the other member carrying adjacent its end two annular grooves each forming an enlargement of the respective annular space.

8. A structure as claimed in claim 7 wherein said two grooves are axially spaced apart.

9. A method of joining two tubular members, comprising forming an annular groove in the surface of one member and an annular projection from the surface of the other, sliding the two members towards one another axially so that they are positioned in telescoped relation with an annular space therebetween, the groove and projection being axially spaced apart and forming respectively an enlargement and restriction of the annular space, and injecting into the annular space a a curable resin which on curing rigidly resists axial separation of the members.

10. A method as claimed in claim 9 wherein one of the members is provided with two cylindrical portions and the end of the other member fits between these cylindrical portions defining two annular spaces, each cylindrical portion carrying adjacent its end an annular projection projecting radially into the respective annular space and the other member carrying adjacent its end two annular grooves each forming an enlargement of the respective annular space.

11. A method as claimed in claim 10 wherein said one member carries a circular end plate carrying the two cylindrical portions.

12. A structure including two cylindrical or tubular members joined together, the members being disposed in telescoped relation over part of their length with an annular space therebetween, said annular space being filled with a rigid cured resin, and each of said members being provided with means for forming a key between the cured resin and the respective member, the key forming means being axially spaced apart along the annular space whereby longitudinal forces between the members causes compression of the resin via the keys.

13. A structure as claimed in claim 12 wherein the means for forming the keys comprise an annular groove formed in one member and facing the annular space and an annular projection formed on the other member and projecting radially towards the annular space.

14. A structure as claimed in claim 12 or 13 wherein one of the members is provided with two key forming means and the other member is provided with key forming means positioned axially therebetween.

15. A method of joining two tubular members, substantially as herein described with reference to the accompanying drawings.

16. Structures including joined tubular members, substantially as herein described with reference to the accompanying drawings.