JPH0420704B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to insulated conduits for use in wells, and more particularly to concentrically spaced insulated tubular conduits having an annular cavity between the tube walls for enclosing insulation material. .

During production of the well, steam is injected into the injection well to increase hydrocarbon recovery by reducing high viscosity or heavy crude oil. By lowering the viscosity, the oil becomes easier to pump out. One technique for doing this is to pump large amounts of steam into the production zone containing the crude oil, about 3
It is a long-term injection, such as from a week to about 5 weeks. In this way, the viscosity of the heated crude oil is reduced and it can be easily pumped through the production well leading to the production zone. Injection wells are also used for production. A steam stream is provided in accordance with known techniques to convey steam and produced hydrocarbons to nearby production wells.

One of the problems with injecting steam into an underground production zone via conventional well conduit is that it damages the wellbore casing and surrounding formations as it is transported toward the production zone. This means that a lot of heat is lost. Attempts have been made to reduce the heat loss absorbed by the geological formations. One such method is disclosed in US Pat. No. 3,511,282, issued May 12, 1970.
This patent discloses a double-walled tube construction with insulation enclosed between the inner and outer walls by bushings welded at each end between the walls. The inner wall is preloaded with tensile stress prior to welding. The cavity formed between the inner and outer walls is filled with a conventional insulation material such as calcium silicate. Although this technique is satisfactory for certain types of oil field equipment, it is not satisfactory for oil field equipment where there is a large temperature difference between the inner and outer walls. In this case, although the inner wall is preloaded with tensile stress, the heated inner wall stretches relative to the outer wall, changing the inner wall from tension to compression, creating the risk of twisting. The large forces induced are localized to the weld and cause cracking that exposes the device to well fluids, eventually causing damage or degradation of the insulation structure. Centralizers have been incorporated to reduce torsion, but the typical durability of such devices also introduces heat loss.

Another known technique for dealing with the above-mentioned temperature difference and the resulting elongation between the inner and outer walls of the insulated pipe is as follows:
Thin bellows are placed between the two walls at each end of the assembly, with one end of each bellows being secured to the inner wall and the other end of the bellows being secured to the outer wall. By this technique, the strain applied to the welded portion and joint structure between the inner and outer walls is naturally relieved by the relative movement between the inner and outer walls.
However, other problems arise with bellows. That is, because bellows are generally made from heat resistant, resilient materials, they are relatively thin and delicate and cannot withstand the rough handling commonly encountered in the oil industry.

SUMMARY OF THE INVENTION The object of the present invention is to provide a concentrically spaced insulated tubular conduit that overcomes the above-mentioned problems.

The configuration of the present invention is as follows. A concentrically spaced insulated tubular conduit for forming a tubular string in a well has an inner tube member flared at its end. The flared end, which has a thickness greater than the intermediate nominal wall thickness of the inner tube member, is welded to the outer tube member. Only two welds are required for each conduit. The expanded end portion is manufactured by forging the end of the offset expanded diameter tube member. Although the thickness of this end is reduced by forging, it still remains appreciably thick and facilitates the integrity of the weld. The inner tube part is preferably prestressed in tension relative to the outer tube part.

An outer coupling joins adjacent outer tubular members, and an inner coupling extends between the flared portions of the inner tubular member ends. Thermal insulation is provided in the annular cavity between the inner and outer couplings as well as between the inner and outer tube members. Bracket insulation, load-bearing solid insulation, and a low heat emitting thermal barrier are provided within the axially extending cavity.

Preferably, one of the tubular members, more preferably the inner tubular member, is corrugated along substantially its entire length, so that when one is relatively hot and the other is relatively cool, the concentric tubes Excessive force is prevented from acting on the members and connecting members.

The concentrically spaced conduits are preferably manufactured using standard tubing commonly used in the oil and gas field, with the inner tubing initially having an upset flared end. Ru. By manufacturing with standard tubing in this manner, only two welds are required for each conduit to join the flared end, which is thicker than the intermediate nominal wall thickness, to the outer tubing. Concentrically spaced tubular conduits are obtained.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram illustrating the use of parts of a tubular string formed by concentrically spaced insulated tubular conduits according to the present invention. The tubular string T shown in FIG. 1 allows steam to be injected from the surface of the well through a conduit into the formation below. The insulated tubular string is intended to prevent large heat losses between the tube surface and the formation so as not to impair the action of the injected steam. A tube string T consisting of a plurality of individual insulated tubular conduits 2 is arranged within the well and within the well casing C in much the same manner as conventional tubular strings.

FIG. 2 shows the components of each conduit and the interconnections between adjacent tubular conduits. The opposing ends of each conduit are generally of the same shape as shown in FIG.
Each concentric heat insulating member 2 consists of an outer tube 4 and an inner tube 6. The outer tube 4 consists of a straight cylindrical member having a conventional thread 10 at each end. A conventional outer coupling 8, which engages the threaded portion 10, is used to join adjacent concentric members. To reduce the number of welds required to hold the inner tube 6 to the outer tube 4, the ends of the inner tube 6 are flared outwardly, as shown in FIG. A single circular weld 30 can then be made between the inner tube 6 and the outer tube 4. The inner tube 6 is formed in such a way that the end has essentially three sections. First, the outermost flared end 32 generally consists of a radius of an effective radius of curvature that is approximately equal to or on the order of the separation between the inner and outer tubes. Although the radius of curvature is not limited to this distance, a desired structure can be obtained by adopting a radius of curvature of this order. As shown in FIG. 2, the thickness of this radius is approximately equal to the value _D3 . Adjacent to the diverging end 32 at each end of the inner tube 6 is a first tapered section 34 . The degree of taper in this region need not be large, and in the embodiment of the present invention a 1 degree taper is provided in the radial direction. In embodiments of the invention, a second, more significant, tapered section 36 is employed to form a transition between the first tapered section 34 and the central portion of the inner tube. This second tapered portion 36 has a taper of approximately 5 degrees in this embodiment.

In the assembled configuration of a single insulated conduit, the second
As shown in the figure, an annular cavity 13 is formed between the outer tube 4 and the inner tube 6. This annular cavity 13 is filled with a heat insulating material. In an embodiment of the invention, the insulation consists of a combination of blanket insulation 12 with ceramic fibers, at least one solid insulation 14 and reflective insulation 13. At least one solid cylindrical insulation member 14 is arranged within the annular cavity 13 between the welded ends joining the outer tube 4 and the inner tube 6. In an embodiment of the invention, the solid insulation member is a refractory pipe block insulation formed from hydrated calcium silicate. This shaped calcium silicate member 14 provides structural support between the inner tube 6 and the outer tube 4 between the ends of the annular cavity 13. In the embodiment of the present invention, the heat insulating member 1
4 is a conventional pipe block insulation member available on the market. One of the molded calcium silicate insulation members used in this invention is under the trademark "Thermo 1".
2" by Johns-Manville. These pipe block insulation members are available as halves that are placed around the inner tube 6. The metal band 16 is then made into a single piece. Fitted around the two halves to form an annular member, this insulating member structurally supports the outer tube 4 relative to the inner tube 6.

The remainder of the annular cavity 13 is filled with blanket insulation 12, which is also commercially available. Insulating blankets are commercially available, constructed from long mechanically bonded heat resistant fibers that provide strength, flexibility and heat resistance. In an embodiment of the present invention, John's is manufactured under the trademark "Thermomat" or "Ceramics".
Blanket insulation of the type manufactured by Manville is employed to provide insulation within the annular cavity 13. The insulation blanket is held in the inner tube between the calcium silicate insulation member 14 and the end of the annular space 13. This insulation blanket 1
2 is retained in the inner tube 6 by wrapping conventional fiberglass tape around the outside of the insulation blanket 12. Used in combination, the blanket insulation 12 and solid calcium silicate insulation member 14 can substantially fill the annular cavity between the inner and outer tubes. In embodiments of the invention, at least a partial vacuum is provided within the annular cavity 13 to prevent deterioration of the insulation performance from moisture.

In addition to the convective insulation protection provided by blanket insulation 12 and solid insulation 14, radiant insulation 18 is provided. In the embodiment of the invention, this radiant insulation is incorporated into the outer surface of the inner tube 6 and is made of a material with a relatively low thermal emissivity. In this embodiment, aluminum foil is used around the inner tube 6. The aluminum foil comprises a reflective surface that further reduces heat transfer in the tube assembly.

The annular cavity 13 provides sufficient space to accommodate insulation to maintain adequate heat transfer properties over substantially the entire length of the conduit. However, a space is left between the internally diffused ends of adjacent conduit members. An inner coupling or cylindrical spacer 20 is used to completely seal the outer coupling 8 with the area otherwise bound by the enlarged inner tube end of the adjacent conduit. The inner coupling 20 has outer portions 24 and 2 having a thickness less than the thickness of the central portion 28 of the coupling.
It consists of a cylindrical member having a diameter of 6. As shown in FIG. 2, ends 24 and 26 are press-fitted into tapered portion 34 of each inner tube 6. As shown in FIG. A heat insulating material is placed around the inner coupling 20 to reduce heat loss in the coupling portion. In an embodiment of the invention, a blanket insulation of the same type as the blanket insulation 12 used in the annular cavity is installed around the inner coupling central portion 28 in a donut shape. Bracket insulation fills the space between the flared ends of adjacent inner tubes and the inner and outer couplings. The assembled tube string or conduit consisting of a plurality of individual insulated conduits 2 will have insulation disposed within the annular cavity between the inner tube 6 and the outer tube 4 along substantially its entire length. Finally, a second protective material or radiation insulating material with a low thermal emissivity is provided on the outside of the outer tube. The outer tube is painted along its entire length to form this protection. The two low thermal emissivity protectors act to reduce heat transfer throughout most of the conduit.

The flared end of the inner tube 6 not only provides an effective means of improving welding performance by reducing the number of welds and increasing the weld area, but also reduces heat loss due to conduction from the weld joint. It is something. The only heat transfer path at the junction of the inner coupling 20 and the tapered portion 34 of the inner tube 6 will exist along the relatively long and thin expanded conduit itself. Relatively wide bushes with large heat transfers are not required. Additionally, the flared end of the conduit is of sufficient thickness to provide an integral weld.

Another embodiment, shown in FIG. 6, employs a corrugated inner tube 72 with a wall thickness on the same order of magnitude as a conventional well conduit of the same diameter, and which is structurally strong and axially resilient. It provides certain elements. The ends of the inner tube 72 have tapered or straight portions 74 and 74' and flared ends 76 and 76', respectively, with the ends of each flared end 76, 76' being joined by welds 78, 78'. Each is shown retained on the inner surface of the outer tube. Additionally, flared ends 76 and 76' are for receiving insulation 86.
In this embodiment of the invention, an annular cavity 84 is formed. In this case, the straight parts 74 and 7
4' will comprise a transition surface between the flared end and the corrugated portion. The flared ends 76 and 76' are radially spaced from the corrugations of the inner tube 72.
To prevent heat loss, it is essential that the corrugations, whether sinusoidal or helical, do not touch the outer tube. As in other embodiments, inner tube 72
Flared ends 76 and 76' located at the ends of the tube are formed to reduce the number of welds and at the same time contact the outer tube.

One of the very important features of the present invention is that it can be manufactured using only conventional commercially available materials. Although concentric conduit 2 can be manufactured using a variety of cylindrical members, the preferred embodiment of the present invention is manufactured using standard American Vetroleum Institute conduit. For certain sizes, the present invention uses a standard 2-3/8 tube with an upset or flared end to produce an inner tube 6 with a flared end.
APIJ-55 conduit with an inch outside diameter is used.
For the same shape, 4-1/2 inch APIJ-55
A conduit without an absorptive or bulged end is used for the outer tube 4. 2-3/ shown in Figure 3
A standard conduit, such as an 8 inch outside diameter J-55 conduit, has a nominal wall thickness D ₁ along most of its length. This thickness D ₁ is smaller than the thickness D ₂ of the upset end. The ends of standard J-55 conduits are expanded to their final shape by forging with a swage 42 as shown in FIG. One end of the swage is a chamfered portion 44. Adjacent to this chamfer 44 is a cylindrical guide portion 46 which serves to align the conduit during forging. A radially tapered transition portion 48 extends from the lower end of the guide portion 46. This transition shape is a mirror image of the transition portion 36 of the manufactured inner tube. In embodiments of the invention, the taper in this section is on the order of 5 degrees. Adjacent to the transition section 48 is a tapered section 50 corresponding to the first tapered section 34 of the content 6 manufactured. Tapered portion 50 is less than the taper of transition portion 48, which in embodiments of the present invention is approximately 1 degree, consistent with the taper of first tapered portion 34. The lower end of the swage is a radiused portion 52. Shape part 4
8 and 50, the radially shaped portion 52 is intended to coincide with the cooperating portion of the final inner tube 6. The divergent end 32 of the inner tube 6 is formed when a standard upset J-55 conduit is forged with a modified profile section 52. Although the shaped portion 52 is referred to herein as a radial shape, it should be understood that this need not necessarily be created by a constant curvature. The term "radial shape" refers to the outward extent of the second tapered portion 36 created by the shape portion 52 at the flared end 32 of the inner tube 6.
This is merely used to indicate that the width of the first tapered portion 34 is considerably larger than the width of the first tapered portion 34. However, since the actual shape is almost close to a curved surface with a constant curvature, it is called a “radial shape”.
The word seems appropriate. Since the basic purpose of this radius is to provide a radial transverse separation between the inner tube 6 and the outer tube 4, the magnitude of the separation between the outer tube 4 and the inner tube 6 is An effective curvature of the order of magnitude is effective in forming this shape. As shown in FIG. 3, the final shape of the inner tube 6 is such that the swage 42 has a swollen or upset end 4.
0 into a standard conduit 38. Prior to this forging process, the area adjacent the upset end 40 will be heated. When the swage is advanced into the conduit end, the conduit extends radially to form the flared end shape predetermined in embodiments of the present invention. During this forging process, standard conduit 3
The ends of 8 will not only widen radially, but will also be elongated in the forging process. The thickness of each conduit decreases as the ends are stretched. The expanded inner tube 6 has an expanded end 32 with a thickness D ₃ , a first tapered portion 34 with a thickness D ₄ , and a second tapered portion 36 with a thickness D ₅ .
has. If the spread and elongation of the standard conduit material is limited to the upset ends, the thickness
D ₃ , D ₄ , D ₅ are greater than or at least equal to the nominal wall thickness D ₁ of a standard conduit. The final thickness of these sections will be the nominal thickness of the conduit.Using a conduit with an initially upset or flared end may facilitate structural integration of the flared end of the conduit. However, due to elongation, the thickness D ₃ , which is less than the original thickness D ₂ of the upset conduit end 40,
This reduces D ₄ and D ₅ . By forming the inner tube 6 from a standard tube member with an upset end, the thickness of the flared end 32, D ₃ , is reduced while the thickness of the standard upset end is reduced.
It is an important advantage that D ₁ is greater than the nominal wall thickness dimension D 1 in the middle of the inner tube member. Since the wall thickness is increased in this way, the outer tube 4 along the expanded end 32
Structural integration of the parts 30A and 30B welded to each other is promoted. The weld extends over a large surface area and
The thickness of the inner tube adjacent the weld, including the flared end 32, the first tapered section 34, and the second tapered section 36, will not be less than the nominal wall thickness intermediate the inner tube member. This improved weld integrity increases weld reliability and allows the number of welds at each end to be reduced.

After both ends of the inner tube 6 are expanded by the forging process shown in FIG. 3, it takes on the final shape shown in FIG. 4. At this point, a reflective thermal barrier or a low heat dissipation protective wall is applied to the outer surface of the inner tube.
In an embodiment, aluminum foil is wrapped around the inner tube. Solid insulation is then installed at appropriate locations along the outside of the inner tube by placing the two halves around the inner tube and holding these calcium silicate insulation members with metal bands. It is carried out by. Blanket insulation is then installed along the remaining portion of the inner tube 6.

The next step in manufacturing the insulated conduit 2 is to insert the inner tube assembly with the insulation attached to the outer tube 4. Upon insertion, a continuous circumferential surface formed at each free end of the expanded inner tube is located inside the outer tube along its inner circumference, which is welded along the outer tube. It's the location. The flared end of the inner tube 6 is welded to the outer tube 4 along one end of the concentric tube assembly. This first weld 30A extends completely along the connection point between the inner tube expanded end 32 and the outer tube 4. Multiple passes are used to make this weld structurally strong and to provide a complete seal between the inner and outer tube joints.

In the embodiment of the present invention, it is desirable to apply a tensile stress to the inner tube 6 and a compressive stress to the outer tube 4 in advance. The preloading is important because of the loads placed on the conduit during high temperature operation. The outer tube under compressive stress acts to maintain the inner tube in a substantially pre-stressed or pre-stretched configuration. Therefore, the lengths of the concentric tube assemblies are substantially equal in their cold and heated configurations. After one end of the inner tube is held to the outer tube by welding, the desired pre-tensile stress loading is applied by pulling the inner tube at the other end of the concentric tube assembly. This stretching process is performed by mechanically pulling the inner tube while holding the outer tube fixedly, or alternatively by heating the inner tube relative to the outer tube. In an embodiment of the invention, the inner tube 6 is not initially preloaded with tensile stress to the extent that it exceeds the drop point. After a predetermined pre-tensile stress load has been applied to the inner tube, a second weld 30B is made that extends completely around the joint between the inner tube and the outer tube. Again, this weld consists of multiple passes to enhance weld integrity.

The welds 30A and 30B not only hold the inner tube 6 to the outer tube 4, but also seal the annular heat-insulating cavity 13 between the outer tube and the inner tube. In embodiments of the present invention, it may be desirable to increase the insulation capacity of the insulation within the annular cavity 13 by venting the annular cavity 13 to create a vacuum. This vacuum is created by drilling the outer tube 4 and providing an opening in the annular cavity 13.

As shown in FIG. 5, a fixation device 54 is used to puncture the outer tube 6 and vent gas from the annular cavity. This fixation device consists of a clamp 56 extending around the outer circumference of the outer tube. A passageway 68 extends radially through the fixation device to the surface of the outer tube 6. A not shown drill pusher is inserted into the passageway 68 and an aperture or hole 60 is drilled in the outer tube along the passageway 68.
This same fixation device is used to create at least a partial vacuum inside the annular cavity 13 while maintaining its alignment with the drilled hole 60. The drill pusher is removed and a plug, such as a tapered pin surrounded by an annular seal 62, is inserted into the passageway 68, as shown in FIG. A vacuum hose 50 is attached between the fixture 54 and a vacuum pump (not shown). Vacuum hose 58 communicates with annular cavity 13 via passage 68 . O-ring seal 66 between fixation device 54 and the outer surface of insulated conduit 2
This prevents leakage during venting of the annular cavity 13. Leakage from the passageway 68 at the location of the taper pin 64 is eliminated by the taper pin 64 extending into the passageway 68 and the annular seal 62 extending around the taper pin 64.
This is prevented by After a predetermined vacuum is achieved within the annular cavity 13, the tapered pin 64 is inserted into the hole 60.
is pushed into the hole to close it. The outside of the taper pin 64 protruding from the surface of the outer tube 4 is removed,
If necessary, welding is used to seal this pin.

Once each conduit is manufactured, the multiple conduits are connected to form a single insulated conduit by first inserting an inner coupling 20 into one end of each conduit. The inner coupling ring is press-fitted into the enlarged end of the inner tube 6. Preferably, each inner coupling 20 is deeply inserted into one conduit rather than an adjacent conduit. When the inner coupling ring is pressed deeper into the tapered portion 34 of one conduit than the other,
The inner coupling remains attached to the designated conduit during disassembly. This simplifies outdoor disassembly.

A preferred embodiment of the invention comprises concentric prestressed tubular members having insulation along substantially their entire length.

Convective insulation is provided along with radiant insulation, and venting of the annular cavity between two concentric tubular members removes moisture therein and reduces heat transfer between the insulation materials. Furthermore, preferred embodiments have two
This is for welding the parts. The integration of welds carried out in the present invention is achieved by reducing the number of welds, as well as by employing an inner tube with a flared end, the thickness of which does not become less than the nominal wall thickness dimension of the middle part of the inner tube. Improved. Furthermore, the individual concentric insulated conduits 2 are manufactured using conventional tubing material.

Although the present invention has been described in detail with reference to specific embodiments, this is for illustrative purposes only, and the present invention is not limited to this embodiment, and modifications and variations will be apparent to those skilled in the art from this disclosure. The technology will be revealed. Many such variations may be made without departing from the spirit of the invention.

[Brief explanation of drawings]

1 is a schematic diagram showing the injection of steam through a tubular string formed of conduits according to the invention; FIG. 2 is a cross-sectional view showing two conduits joined at their ends; FIG. Fig. 3 is a schematic diagram showing the forging process of expanding conventional upset pipe material using a swage to manufacture the inner tube, and Fig. 4 shows the inner tube with the end expanded. Fig. 5 is a sectional view for explaining how the annular cavity between the inner and outer tubes is evacuated;
The figure is a sectional view showing a second embodiment of the present invention. 2...Concentric tubular conduit, G...Outer tube, H...Inner tube, 8
... Outer coupling, 12... Blanket insulation, 13... Annular cavity, 14... Solid insulation, 18...
Reflective insulation material, 20...Inner coupling, 30...
Welded part, 32... Expanded end part, 34... Tapered part, 3
8... Upset pipe member, 72... Corrugated inner pipe.

Claims (1)

[Scope of Claims] 1. A concentrically spaced insulated tubular conduit for forming a tubular string in a well, comprising an outer tube member and a concentric inner tube member, the inner tube member comprising: an outer tube member; is an original tube end upset tube member whose tube end has the same inner diameter as the intermediate inner diameter of the inner tube member and a larger wall thickness, and has at least one outwardly open expansion welded to the outer tube member. has an open end portion, the wall thickness of the expanded end portion is greater than the thickness of the intermediate portion of the inner tube member, and a position where the expanded end portion is welded and fixed to the outer tube is near the tube end of the outer tube, and A concentrically spaced insulated tubular conduit characterized in that a heat insulating material is inserted into an annular cavity formed between an inner and an outer tube. 2. The insulated tubular conduit according to claim 1, wherein the expanded end portion is formed at the tip of a tapered portion that is continuously provided in the intermediate portion of the inner tube member. 3. The insulated tubular conduit according to claim 1 or 2, wherein the expanded end portion has a curved surface whose curvature is approximately equal to the distance between the inner tube member and the outer tube member. 4. An insulated tubular conduit according to any one of claims 1 to 3, wherein the outer tube member and/or the inner tube member is a corrugated tube along its entire length. 5. The insulated tubular conduit according to any one of claims 1 to 4, wherein at least the inner tubular member is welded and fixed to the outer tubular member under tensile stress. 6. A concentrically spaced insulated tubular conduit capable of connecting a number of them to form a tubular string in a well, the concentrically spaced insulated tubular conduit comprising an outer tube member, a concentric inner tube member, and the inner tube member. The pipe end is an original pipe end upset pipe member whose inner diameter is the same as the inside of the intermediate part of the inner pipe member and has a large wall thickness, and it has an expanded end that opens outward and is welded to the outer pipe member. an outer coupling means for coupling adjacent tubular conduits and adapted to engage the inner tube member adjacent one of said flared ends and to engage an adjacent flared end of an adjacent tubular conduit; a concentrically spaced insulated tubular conduit comprising an inner coupling means extending between the inner and outer tubes, the annular cavity between the inner and outer tubes having an insulating material inserted therein. 7. The insulated tubular conduit according to claim 6, wherein the expanded end portion is formed at the tip of a tapered portion that is continuously provided in the middle portion of the inner tube member. 8. The insulated tubular conduit according to claim 6 or 7, wherein the expanded end has a curved surface whose curvature is approximately equal to the distance between the inner tube member and the outer tube member. 9. An insulated tubular conduit according to any of claims 6 to 8, wherein the outer tube member and/or the inner tube member is a corrugated tube along its entire length. 10. The insulated tubular conduit according to any one of claims 6 to 9, wherein at least the inner tubular member is welded and fixed to the outer tubular member with tensile stress applied thereto. . 11 A method for manufacturing a concentrically spaced tubular conduit used in a well, wherein the inner tube member is made from an original tube end upset tube whose inner diameter is the same as the inner diameter of the intermediate portion of the inner tube member and whose wall thickness is large. the tube end upset tube member being expanded outwardly at the upset tube end, the inner tube member being inserted into the outer tube member, and the flared end portion being welded to the outer tube member. 1. A method of manufacturing a tubular conduit comprising the steps of: fixing the tubular members to form a concentrically spaced tubular conduit having an annular cavity between the tubular members; and inserting a heat insulating material into the annular cavity. 12. The method of manufacturing an insulated tubular conduit according to claim 11, wherein the expanded end portion is formed at the tip of a tapered portion that is continuously provided in the intermediate portion of the inner tube member. 13. The method of manufacturing a heat-insulating tubular conduit according to claim 11 or 12, wherein the expanded end portion is formed into a curved surface whose curvature is approximately equal to the separation distance between the inner tube member and the outer tube member. . 14 forming first and second expanded ends at both tube ends of the inner tube member, and after welding the first expanded end to the outer tube member and before welding the second expanded end, 14. The method of manufacturing a heat-insulated tubular conduit according to any one of claims 11 to 13, wherein a tensile stress is applied to the pipe member. 15. Claims 11 to 14, wherein the upset tube end of the tube member is expanded outward by forging using a swage having the same shape.
A method for manufacturing an insulated tubular conduit according to any of paragraphs.