Background of the Invention

1. Field of the Invention

This invention relates to a method of joining tubing with a gas tight seal- In the oil and gas exploration industry it is known to have a requirement for the creation of a metal-to-metal sealed joint between tubing of similar or dissimilar diameters, or the connection of tubing to equipment such as logging instruments, downhole pumps, milling, reaming or other tools requiring to be attached to the tubing, where the joint is required to be made or operated in hazardous areas.

2. Description of the Related Art

There are a number of existing methods of joining tubes such as, for example, welding, brazing, etc., using an open flame, but such methods cannot be safely undertaken in the presence of volatile fuel or gas, as would be experienced on a well head. Jointing by cutting threads, recessing or tube belling, lower the pressure resistance of the tube, since the wall of the tube is weakened. Joints which use compression of dissimilar metals, as in the compress of copper or brass sealing rings between tapered threaded connectors cannot always guarantee a seal around a tube and the addition of an elastomer or similar type of "0" ring may temporarily improve the seal, but in time acidity can destroy the "0" ring.

It is known from GB-A-771026 to provide a connection for drill rods for deep drilling in which the working life of the drill rod is increased by mounting parts to be connected together on the base of a press and then a body

connector element is heated to a moderate temperature and a tube end is frozen, for example by the use of liquid air or carbon dioxide or liquid nitrogen, and introduced into the heated connector element. After cooling to room temperature, a rigid connection of the individual parts is achieved. However, such a joint is not capable of supporting a great hanging weight, since the structure of the G.B. patent is intended to enable forward and rotating pressure. For example, when coiled tubing is used, 8.9cm (3.5 inch) outside diameter pipe for use in a 4,572 metre (15,000 feet) deep well will use coiled tube in 1,219 metre (4,000 feet) coils, and so would require four joints. The tubing weight on a tubing 3.8mm (0.156 inch) wall is 8.29Kg/m (5.5711b/ft) so the joints require, at worst, to take a hanging weight of 38,102Kg (84,0001bs) to include a safety margin, and the joints must also equal the tubing pressure capacity of at least 41,640kPa (6,040 psi) . The tubing joints are also required to be able to take a torque equal to the tubing torque yield of 10,847Nm (8,000lb/ft) and such torque strength cannot be achieved by the jointing method disclosed in the G.B. patent.

The present invention seeks to overcome the foregoing difficulties and, in a preferred embodiment, to use a jointing method which can be applied with minimal danger in a Zone 0 condition, that is where highly volatile gas or liquid is present. It is also desirable that the joint, when made, produces no restriction within the tube, thereby eliminating vortex or conditions conducive to wax or calciate accumulation.

SUMMARY OF THE INVENTION

According to this invention there is provided a method of joining tubing with a gas tight seal including the steps of providing two lengths of tubing having ends to be joined, said ends having male and female portions

respectively, said male portion having a larger diameter at ambient temperature than the female portion, cooling said male portion to contract said male portion outside diameter, heating said female portion to expand the internal diameter thereof, mounting the male portion into the female portion and bringing the male and female portions to ambient temperatures so that the male and female portions are sealed together, characterized by forming grooving on at least one of the outside diameter of said male portion or the inside diameter of the female portion to increase both surface area and friction between said male and female portions.

The provision of grooving increases contact area between the male and female portions and, in this respect, the grooving preferably has an increased hardness with respect to the portion with which it is to be joined, whereby the grooving bites into the portion of a mating member.

Advantageously, the grooving has a Rockwell C scale hardness which is at least twenty points higher than the portion with which the grooving is to be mated.

Preferably, the grooving has a flank angle in the range 30° - 45° and a depth of no more than 10% of the tubing wall thickness. In one preferred embodiment, said male portion has an externally enlarged portion to act as a stop when said male portion is inserted into said female portion, and at a location remote from said male portion that is inserted into said female portion, said tubing end is provided with an external screw thread for attaching a connection means, and there is provided a tubular shroud member having an end for passing over said external screw thread but which has a smaller diameter than the enlarged portion on said male portion, said male and female portions, once joined together, are shrunk by cooling with liquid nitrogen, said shroud member is expanded by heating, and said shroud

member is pushed over said external screw thread to abut said enlarged portion so as to provide a joint of increased strength.

In another embodiment of the invention, a female sealing ring is provided about the tube male portion, said tube male portion having a larger diameter at ambient temperature than the female sealing ring, said tube male portion is cooled in liquid nitrogen to contract the outside diameter of said male portion, said sealing ring is heated to expand the inside diameter thereof, said sealing ring is mounted over said tube male portion and the sealing ring and tube male portion are brought to ambient temperature, whereby at least one of the external diameter of the male tube portion or the internal diameter of the female sealing ring have grooving thereon of greater hardness than the sealing ring or male portion respectively.

Preferably, said sealing ring has oppositely tapered surfaces in an axial direction of said sealing ring, a female connector is located over the tubing remote from said male portion, said female connector having an internal screw thread and an internal taper for cooperating with one of said tapers on said sealing ring, said sealing ring is located inside a tubular male connector having an external screw thread for mating with said internal screw thread on said female connector, said male connector has an internal taper for cooperating with the other of said tapers on said sealing ring, and said male and female connectors are threadably engaged together to sealingly secure said sealing ring inside said male connector and with said female connector, whereby said taper sealingly connect the tube with said male connector.

Advantageously, an end of said male portion is relieved and a corresponding, mating relieved portion is provided inside said tubular male connector, whereby the tube male portion is prevented from turning inside said

-D- male connector.

Conveniently, a lock means is mounted about said male connector for preventing said male and female connectors rotating with respect to one another after assembly together.

Preferably, said lock means comprises an indentation in said female connector and a lock ring for fixation on said male connector, said lock ring having a tang for engagement in an indentation in said female connector, and securing means are provided for securing said lock ring to said male connector. Conveniently, said securing means are set screws.

Preferably, said male connector, at a position remote from said female connector, has a connecting portion of any desired form, for example an externally threaded portion for threadable securement with a cooperating internally threaded portion.

In yet another embodiment, two tubes are joined together, each having sealing rings connected thereto, said tubes and sealing rings being sealingly connected in a common, double-ended male connector, and held in location therewith by respective female connectors.

In yet a further embodiment, the female portion has an external screw thread formed thereon and a tapered end surface for mating with a complementary taper in a shroud located on a tube to be joined therewith, said tube to be joined also having a compression cap mounted thereabout, said compression cap having an internal screw thread for mating with the external screw thread on said female portion, whereby threading engagement between said screw threads draws the complementary tapers together to thereby join the tubes.

Advantageously, compressed air is used to bring said male and female portions to ambient temperature. Advantageously, the liquid nitrogen is at a temperature of approximately -207°C (-340°F) .

The present invention is extremely useful for use at oil and gas well heads, since nitrogen gas is commonly available when using coiled tubing. The nitrogen gas is stored in liquid form at approximately -207°C. The amount of contraction of the male portion is dependent on tube wall thickness, diameter and timing contact with the liquid nitrogen.

A safe method of expanding the female portion was found to be immersion in boiling water. Thus, expansion and contraction is achieved by means which are safe in a Zone 0 condition.

The provision of grooving results in increased contact area in friction due to the tubing contacting the sides of the grooves and the bite of the groove crowns increases the strength of the joint by several thousand Kg.

For a 3.8cm (1.5 inch) diameter tubing joint it is preferred to shrink the male portion by 0.15mm (0.006 inches) and to expand the female portion by 0.05mm (0.002 inches) so that there is provided an 0.2mm (0.008 inch) interference fit.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure l shows an exploded view of tubing to be joined in a first embodiment in accordance with the method of this invention,

Figure 2 shows an exploded view of tubing to be joined in a second embodiment in accordance with the method of this invention,

Figure 3 shows the joint formed with the second embodiment,

Figure 4 shows a further version of the joint formed using the second embodiment in accordance with this

invention,

Figure 5 shows an exploded view of tubing to be joined in a third embodiment in accordance with the method of this invention, Figure 6 shows the tubing joined together using the third embodiment, and

Figure 7 shows an exploded view of tubing to be joined in a fourth embodiment in accordance with this invention.

In the Figures like reference numerals denote like parts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The tubing shown in Figure 1 to be joined has a female tube l within which is to be securely fastened by an interference fit at ambient temperature, a male tube 2 having an external portion 3 upon which is formed grooving 4 which may extend along the whole axial length of the portion 3, as shown, or along only a part thereof. The grooving that is formed is a fine groove of, for example, helical form. The grooving on the portion 3 is arranged to have a hardness of Rockwell C scale at least twenty points higher than the internal surface of the female tube 1. The grooves have a depth no more than 10% the thickness of the female tube 1 wall and the grooves have a 30° - 45° flank angle. The portion 3 terminates in an enlarged diameter collar 5, the diameter of which is arranged to be approximately the same as the external diameter of the female tube 1. The male tube 2 has an externally threaded portion 6 on the side of the collar 5 remote from portion 3, the external threaded portion 6 being for securement to an attachment means which may be, for example, a milling tool. A cylindrical shroud 7 has an open end 8 corresponding to the internal diameter of the cylindrical shroud and a reduced internal diameter end formed by a flange 9. The internal diameter of the shroud 7 is

arranged to fit over the collar 5 and female tube 1 and the flange 9 is arranged to pass over the external screw threaded portion 6 to abut the collar 5. The collar 5 may have a tapered portion 10 which engages a corresponding taper on an internal surface of the flange 9.

For easy assembly, a clearance of not less than ⁰ . ⁰ 25mm is desired for smaller male members from ₂ 5mm diameter to 150mm and 0.05mm is desired for male members of above 150mm diameter for cold insertion of the male member into the heated female member.

If ambient temperature is 15°C, and the temperature for liquid nitrogen is -196°C, then the coefficients of expansion and contraction for common metals over this range an ^d the maximum shrinkages available with liquid nitrogen cooling are given in the following table:

Maximum shrinkage in metals cooled by L

Cooling assumed to be 15°C to -196°C

In operation of the method, the female tube 1 is expanded by heating in boiling water or steam and the male tube 2 is shrunk by cooling in liquid nitrogen at a temperature of approximately -207°C. If the female tube 1 is a 3.8cm (1.5 inch) diameter tube, so the female tube l is shrunk by approximately 0.15mm (0.006 inches) and the portion 3 is expanded by 0.05mm (0.002 inches). With the female tube 1 expanded and the portion 3 contracted, the male tube 2 is inserted into the female tube 1, preferably using a locking jig. An air blast may then be used to return the female tube l and male tube 2 to ambient temperature. Because the grooving 3 is harder than the internal surface of the female tube 1, so the grooving bites into the internal surface of the female tube 1 upon contraction and the internal wall of the female tube l tends to flow down the grooving so that the surface area contact between the internal surface of the female tube l and the male tube 2 is increased, as is friction therebetween. Such a joint has a bond which is almost 100% stronger than the tube torque acceptance capability.

The joint thus formed is shrunk with liquid nitrogen and the shroud is expanded by heating and pushed over the previously formed joint so that the flange 9 abuts collar 5. The combination is then brought to ambient temperature and an interference fit formed between the shroud 9 and collar 5 and female tube 1.

The joint thus formed has the strength thereof improved by the provision of the shroud 7.

The connector shown in Figure 2, which is suitable for high torque, has a tube 20 to be connected to a like- dimensioned tube 21. An end of the tubes 20, 21 has a relieved portion 22, 23 respectively extending approximately about a semi-circular part of the tube. A connector body 24 has a planar portion 25 and externally screw threaded ends 26, 27 respectively. Internally provided at respective end of the connector body are

relieved portions 28 which permit mating acceptance of the relieved tube portions 22, 23, such that the tubes 20, 21 cannot be rotated with respect to the body 24. The planar portion 25 of the body has circumferentially disposed dimples 29 for reasons that will be described hereinafter. Located to be freely mounted over the tubes 20, 21 is an internally threaded cap 30 (the cap 30 about tube 20 only being shown) . The internally threaded cap 30 has an end 31 which is an easy running fit on the tube and an enlarged diameter portion 32 within which is located the internal screw thread. A notch 33 is provided in the portion 32. A sealing ring 34 having opposed tapered surfaces 35, 36 has internal grooving similar to the grooving 4. It is, therefore, to be appreciated that the grooving 4 of this invention may be applied to the internal surface of a female member or the external surface of a male member, or both surfaces.

The tapered surfaces 35, 36 on the sealing ring have corresponding mating surfaces inside the cap 30 and body 24, which corresponding surfaces are not shown for clarity. In operation, the cap 30 is placed over the end of the tube 20 and the tube end 20 is shrunk using, for example, liquid nitrogen, although other cooling means may be employed if available. The sealing ring is expanded by heating and pushed over the tube end.

The connector body is brought into mating engagement with the end of the tube 20, by virtue of the "dog" type connection between the relieved mating portions, and the cap is threadably connecting to the connector body 24 which, thus, pushes the sealing ring into tight engagement between the cap and the connector body so that a seal is formed by the mating surfaces contacting with tapered surfaces 35, 36. The joint thus formed is then brought to ambient temperature using, for example, compressed air. So as to prevent the cap from threadably disengaging from the connector body, so a lock ring 38 having a tang 39

which locates in the notch 33 is mounted over the planar portion 25 of the body 24. The lock ring is provided with circumferentially spaced, radially directed, internally threaded holes 39 which align with the dimples 29. Set or grub screws are used to secure the lock ring to the connector body, the tapered end of the set screw locating within a respective dimple 29.

The tube 21 is then secured to the body 24 in a similar manner using a sealing ring 44, a cap (not shown) similar to the cap 30 and a lock ring 48, which is similar to the lock ring 38.

The completed joint is shown in Figure 3. To assist in threadably engaging the members flattened portions 51 on diametrically opposed surfaces of the body 24, and caps 30 are provided for tightening with a spanner or wrench. The tube 21 is shown connected to a utilization means which, in Figure 3, is an expanding bladder 52.

In the version shown in Figure 4 a joint is formed, as described hereinabove, with reference to Figure 2 , but instead of the connector body 24 having like opposing ends, one end is provided with a tapered "Acme" type thread 55, but the end of the connector body 24 remote from the tube 20 may be machined to any required shape or configuration. By such an expedient, two different types of tube connector can be provided.

The embodiment shown in Figures 5 and 6 demonstrates a method of jointing where there is no increase in outer diameter from the original tubing external diameter, but it is to be emphasized that only tubing with heavy wall thickness is suitable for such a type of jointing.

Tubing 61 and 62 to be joined together are formed so that an end 63 of the tubing 61 is reduced in diameter to have a tapered surface which increases in diameter toward the end of the tubing 61 and the surface 63 is provided with grooving 64. The tubing 62 is internally bored to have a tapered surface 65 which mates with the taper on the

surface 64, the respective diameters of the portions 64, 65 being such as to provide an interference fit. The end of the tube 62 is heated so that it is expanded and the end of the tube 61 is shrunk by cooling and the two ends are pushed together and brought to ambient temperature. An interference fit between the tubes 61, 62 is thus formed. The tube 62 may have a projection 66 and the tube 61 a notch 67 for receiving the projection 66 so that relative rotation between the tubes 61, 62 is prevented. The joint shown in Figure 7 is for connecting a tube 70 to a tube 71. A male shroud 72 is formed to have an internal diameter which is an interference fit on the tube 70, either or both the tube 70 and internal diameter of the shroud 72 being provided with grooving of the type discussed above for increasing surface area contact and friction between the male and female joining members, i.e. tube 70 and shroud 72. The shroud has an external screw thread 73 and a tapered end portion 74, an opposing end of the shroud from the portion 74 having a pair of diametrically opposed flat surfaces 75 for engagement with a spanner or wrench.

The tube 71 has a compression cap 76 disposed thereabout which is a rotatable and slidable fit on the tube 71. The cap 76 has indents 77 for securement of a spanner (not shown) , and a plurality of circumferentially and radially directed internally threaded holes 78, through which lock screws may be inserted.

An end of the tube 71 is provided with a female shroud 80 which is an interference fit on the tube 71 and grooving is provided between the contacting surfaces of the shroud

80 and tube 71.

An internal portion of the female shroud 80 is provided with a tapered surface corresponding to the tapered portion 74 for mating with the tapered portion 74. The external diameter of the female shroud 80 is less than the internal diameter of the compression cap 76.

In making the joint between the tubes 70, 71, the end of the tube 70 is shrunk by cooling and the male shroud 72 is expanded by heating and then pushed over the tube 70. Similarly, the female shroud 80 is heated and the end of the tube 71 shrunk and the female shroud fitted over the tube 71. When the parts have reached ambient temperature, so the male and female shrouds 72, 80 are an interference fit on the respective tubes 70, 71. The male shroud is then pushed into the female shroud so that the tapered portion 74 abuts the corresponding tapered surface inside the female shroud and the compression cap 76 is slid axially along the tube 71 and rotated so as to be threadably engaged with the external screw thread 73. Tightening of the compression cap onto the male shroud 71 urges the male and female shrouds together to form a gas tight seal.

The provision of male and female members which are respectively contracted and expanded prior to fitting together and the provision of grooving between the male and female members, whereby an interference fit is formed between the members, facilitates a gas tight seal of extreme strength caused by increased surface area contact between the male and female members. It is to be understood that the grooving may be applied either to the external surface of the male member or to the internal surface of the female member or both said surfaces may be grooved.

The joint of this invention has the following advantages: l. Metal-to-metal tubes may be joined with a gas tight seal.

2. The joint can be safely made in hazardous areas, since the use of liquid nitrogen and boiling water provide no explosive risk. 3. The online connection of Figures 1 - 4 and 7 does not damage or weaken the tubing and the inline connection

of Figures 5 and 6, although machining does take place, is considered stronger than other machining methods.

4. The amount of tension load on the online connection is limited only by the coil tubing yield strength. The joint is particularly advantageous when used in conjunction with larger diameter coiled tubing run as syphon string tail pipes.

5. The connection of multiple lengths of large diameter coiled tubing for completion or syphon drill strings is facilitated.

6. The joint also has particular advantage in smaller diameter coiled tubing used for acidizing and nitrogen lifting without fear of seal and joint deterioration. 7. There are no internal diameter restrictions in the tubing in the embodiments of Figures 2 - 7.