METHOD OF PRODUCING MULTIPLE-WALL, COMPOSITE TUBULAR STRUCTURES

Abstract: In the method of producing a double-wall composite tube by the steps of 1) applying heat to an outer tube (2), and 2) applying expanding pressure to an inner tube (3) inserted into the outer tube (2) so that the inner tube (3) expands in diameter into tight contact with the outer tube, at least one of the steps 1) and 2) is carried out with respect to a local zone of the tubes (2 and 3) which travels progressively from one end to the other of the tubes thereby to cause the outer tube (3) to successively expand locally in the traveling local zone and the inner tube (2) to undergo plastic deformation in expansion to fit tightly against the outer tube (2), and the expanding pressure acting on the inner tube (3) is thereafter removed, the two tubes being left to attain the ambient temperature, whereby a tight interference fit is obtained therebetween. The heating may be carried out by means of high-frequency induction heating means (11). The expanding pressure may be applied either hydraulically or mechanic­ ally.

Description: METHOD OF PRODUCING MULTIPLE WALL, COMPOSITE TUBULAR STRUCTURES This invention relates generally to the production of composite metal tubes having laminated multiple walls and used for piping in chemical and other plants, as oil and gas well tubings, for oil and gas pipelines, and like pipes. Among the multiple-wall composite tubes of the character referred to above and known heretofore for transporting fluids such as those containing corrosive substances, there are double-wall pipes in each of which the inner pipe or liner tube is made of a corrosionresistant material for effective conducting of corrosive fluid, while the outer pipe is designed to provide strength to withstand internal pressures and external forces. For example, there is a double-wall pipe comprising a stainless-steel inner pipe and a carbon-steel outer pipe in which the inner pipe is fitted. Among the known methods of producing such composite pipes, the shrink-fit method and other tube heating and expanding methods have been developed. In these methods, in general, the inner pipe is inserted into the outer pipe and expanded while the outer pipe is heated, the outer pipe thereafter being cooled and shrunk thereby to obtain a tight or interference fit between the two pipes. In a known tube heating and expanding method, however, a considerably large-scale heating device comprising a large number of heating elements or the like must be provided on the outer side of the outer tube, whereby the required equipment becomes disadvantageously large and expensive. Another difficulty arises in the case of tubes of long length in that the weight of the apparatus and equipment becomes great, whereby the operation and maintenance thereof become troublesome. Still another problem encountered in the prior art is the possibility of cracking, implosion, and the like occurring in multiple-wall composite tubes during use because of insufficient degree of interference fit between the constituent tubes. Furthermore, there has been a lack in the prior art of an efficient, accurate, and economical apparatus for producing multiple-wall composite walls of excellent characteristics as are afforded by the method of this invention. It is an object of this invention to provide a method of producing multiple-wall, composite tubular structures in which method the above described difficulties encountered in the practice of ths prior art are overcome. According to this invention, briefly summarised, there is provided a method of producing multiple-wall composite tubes comprising the step of applying heat to an outer tube and the step of applying pressure to the inner surface of an inner tube inserted into the outer tube thereby to cause the inner tube to plastically expand in diameter into tight contact with the outer tube, the heat and pressure being removed thereafter, characterized in that at least one of the above steps is carried out with respect to a traveling local zone of the tubes extending fully transversely across the tubes substantially perpendicularly to the axis thereof, the local zone being caused to travel progressively from one end to the other end of the tubes thereby to cause the outer tube to successively expand locally in diameter in the traveling local zone and the inner tube to undergo plastic deformation in expansion to fit tightly against the outer tube. The nature, utility, and further features of this invention will be more clearly apparent from the following detailed description with respect to preferred embodiments of the invention when read in conjunction with the accompanying drawings, in which: FIG. 1 is a fragmentary perspective view, with a part cut away, showing an example of a multiple-wall composite tube produced by the method of this invention; FIG. 2 is a side view, in longitudinal section, showing the essential parts of one example of apparatus for practicing the method of the invention; FIG. 3 is a relatively enlarged, fragmentary side view indicating a state of heating to establish a heated zone; FIG. 4 is a graph indicating stress-strain relationships for a description of the changes occurring in inner and outer tubes in the method of the invention; ; FIGS. 5 and 6 are side views, similar to FIG. 2, respectively indicating other modes of practice of the method of the invention, in each of which expanding pressure is applied to the inner tube by a mandrel; FIGS. 7 and 8 are also side views, similar to FIG. 2, respectively indicating further modes of practice of the method of the invention, in each of which a die is used in conjunction with a mandrel; and FIGS. 9, 10 and 11 are further side views, in longitudinal section, respectively showing still further modes of practice of the method according to the invention for producing multiple-wall composite tubes, FIG. 10 being a fragmentary enlarged view of the part E in FIG. 9. In one embodiment of this invention which will first be described with reference to FIG. 2, the method of this invention is applied to a unit double-wall tube 1, as also shown in FIG. 1, to be used as an oil well tubing. This double-wall tube 1 comprises an outer tube 2 of carbon steel, for example, and an inner tube 3 of a corrosion-resistant material, such as stainless steel,placed by a suitable procedure in the outer tube 2. The tube 1 is suitably supported in fixed state by means not shown. The opposite ends of this double-wall tube 1 are tightly closed by closing plugs 4 respectively coupled to hydraulic-pressure jacks (not shown) for applying closing force to the plugs. One of these plugs is provided with a liquid passage 6 through which a liquid for tube expanding such as, for example, cold water 5 at a temperature of approximately zero degrees Centigrade is fed by a positive-displacement pumping means (e.g., a plunger pump, not shown) to fill the interior of the inner tube 3. Then, after the interior of the inner tube 3 has become full of water, pressure F is applied to this water by means of the plunger pump thereby to impart a tube-expanding pressure p to the entire inner wall surface of the inner tube 3. Thereafter, the applied liquid pressure is maintained at value of an order to impart plastic deformation to the inner tube 3. The inner tube 3 is therefore pressed into tight contact with the inner surface of the outer tube 2. With the double-wall tube 1 in this state, the outer tube 2 is heated locally in an annular heated zone thereof around its cylindrical wall to a specific temperature, the annular heated zone being caused tor travel at constant speed from one end A to the other end B of the outer tube 2. This mode of heating of the outer tube 2 is accomplished by a suitable high-frequency induction heating device 11 annularly encircling the outer tube 2 and riding on rollers 10 rolling along a plurality of rails 7 supported on the outer side of the double-wall tube 1 parallelly to the axis thereof. The heating device 11 is driven along the rails 7 from the end A to the end B by a locomotive truck or carriage 9 driven by a driving motor 8 thereby to cause the annular heated zone to travel as described above. The outer tube 2 is thus heated in the annular heated zone by the heating device 11 to a depth which is made as near the inner side of the outer tube 2 without any appreciable heat transmission to the inner tube 3 as indicated in FIG. 3, in which the heated zone is represented in a simplified manner in longitudinal section as the area 12 of raised temperature of the order of 3000C, for exmaple. Depending on the design, the outer tube 2 may be heated on only its outer portion. It is to be noted that the use of a high-frequency induction heating device in this invention is advantageous in that the high-frequency induction heating can be controlled easily as to the depth of the portion of material to be heated thereby. This means that the heating device 11 can be so controlled as to apply heat only to the outer tube 2 and not to the7 inner tube 3. Therefore, establishment of substantial temperature difference between the outer and inner tubes can be made possible even in the state where the inner tube 3 is pressed against the inner surface of the outer tube 2 and there is no clearance between the two tubes. Thus, as the high-frequency heating device 11 travels in the longitudinal direction of the doublewall tube 1, the heated portion 12 travels from the end A to the end B. As a consequence, in the traveling heated zone, the tube-expanding force due to the hydraulic pressure applied to the interior of the inner tube 3 causes the inner tube to expand plastically in diameter so as to conform to the thermally increased diameter of the outer tube 2. After the heated zone has passed by each portion of the tube 1, the inner and outer tubes in that portion shrink in diameter. These changes in diameter can be described more clearly by means of the graphical representation of FIG. 4 indicating local stress-strain relationships. The stress-strain (hoop tension versus variation in diameter) relationship of the inner tube 3 is indicated by curve Pi. The inner tube 3 has an initial, natural outer diameter as at a but, when it is filled with the cold tubeexpanding liquid 5, is cooled and contracts to the state indicated at b. Then, when the liquid pressure is increased, the tube expanding force (hoop tension) acting on the inner tube 3 increases, whereby its diameter expands until it yields and can undergo plastic deformation. On the other hand, the inner diameter of the outer tube 2 as indicated by curve Po increases slightly from diameter d to diameter e as a consequence of the effect of heat of the heated area 12 as the high-frequency heating device 11 travels over each portion of the outer tube 2 as indicated in FIG. 3. When the outer tube 2 assumes this state at e, the outer tube 2 expands and reaches a point f. At the same time, since the inner tube 3 is in a plastically deformable state, it follows the expansion of the outer tube 2 and reaches the state c. The heated region 12 of the outer tube 2 does not reach the inner tube 3 as stated hereinbefore. When the above described state at each portion of the tube 1 comes to an end, that is, when the highfrequency heating device 11 has passed by that portion, the heated region 12 no longer exists, and a cooling state commences. As a consequence, the outer tube 2 is cooled and shrinks; the hoop stress begins to disappear; and inner tube 3 also shrinks in a similar manner. Then, when the high-frequency heating device 11 reaches the terminal end B, the plugs 4 are removed to discharge the tube-expanding water 5 and release the tube-expanding pressure, whereby both the inner tube 3 and the outer tube 2 are no longer subjected to tubeexpanding force and thereby respectively shrink to unstressed states at g and h as indicated in FIG. 4. At the same time, the temperature of the inner tube 3 rises from the previous cooled value to the natural ambient temperature, whereby the diameter of the inner tube tends to increase from g to i, while the outer tube 2 is cooled and tends to shrink from h to i. As a result, an interference fit corresponding to AD is obtained between the two tubes. In the above described process, since the heated region 12 does not reach the inner tube 3, the temperature of the tube-expanding water 5 does not rise, whereby the water retains its cooling effect. The modes of practicing this invention are not limited, of course, to those of the above described embodiments of the invention. In one example of specific experimental practice of this invention, an inner tube of stainless steel (AISI 316L) of l-mm wall thickness was inserted in a carbon-steel outer tube of an inner diameter of 90 mm and 9-mm wall thickness, and a hydraulic pressure of 800 Rg/mm2 was applied to the interior of the inner tube. The composite tube thus formed was heated, while the internal pressure was being applied to the inner tube, according to the method of this invention by a high-frequency induction heating device comprising essentially an induction coil adapted to encircle the outer tube and having a width of 120 mm in the longitudinal or axial direction of the tubes. Electric current at a frequency of 3 KHz was passed through this induction coil as it was caused to travel in the axial direction at a speed of 300 mm/minute, whereby each point or cross section of the outer tube was heated for a period of approximately 25 seconds. As a result, it was found that the outer tube temperature was 3500C (average) and that of the inner tube was 500C (average). The modes of practicing this invention are not limited, of course, to those of the above described embodiments of the invention, various other modes being possible. For example, a high-frequency induction heating device of a shape corresponding to a convolution of a helix can be used in the heating device to heat the outer tube 2 along a helical heating path. Furthermore, the method of producing composite tubes according to this invention is not limited to producing tubes for oil and gas well tubings but is also advantageously applicable to the production of pipes for fluidconveying pipelines, pipes for piping in plants, and other pipes and tubular and cylindrical structures. The annular heating device used in this method is advantageous in that it is basically applicable to composite tubes of any length because the heating device is of a locally-heating traveling type and is not required to cover the entire length of each comppsite tube. Another feature is that this heating device of locally-heating traveling type can be made relatively small and simple in construction. Accordingly, the space occupied by the entire apparatus can be reduced, and the initial cost can be lowered. Furthermore, the work of maintenance of the apparatus is facilitated and made safe. Still another merit of this method is that, since the heating device is adapted to travel in the axial direction of the composite tube, the quantity of heat imparted to the outer tube 2 can be regulated by adjusting the traveling speed of the heating device, which is advantageous for control purposes. By such control, heating can be carried out in a concentrated manner in a short time. A further feature of this method is that, since a relatively low temperature for heating is sufficient to create a temperature difference between the two pipes, the product precision can be made high without causing deterioration of the properties of the outer tube, and there is no heating of the pressure applying liquid, whereby a separately provided cooling liquid is not necessary. In another embodiment of this invention as illustrated in FIG. 5, an inner tube 3 is inserted in an outer tube 2, which is then inserted and fixedly supported in a cylindrical steam heater 14. A mandrel 17 connected coaxially to one end of a connecting rod 16 is forcibly placed in one end (right end as viewed in FIG. 5) of the inner tube 3. The connecting rod 16 extends out from the interior of the inner tube 3 through a central hole in a seal cap 18 closing the other end of the inner tube 3 and is connected at the other end thereof to a drawing device 15 of hydraulic type. The opposite end of the inner tube 3 is closed by a seal cap 19. Chilled water 23 from a chilled water source 20 is supplied through passages 21 and 22 to fill the interior of the inner tube 3, which is thereby cooled and caused to contract. Steam from a boiler 24 is supplied to the steam heater 14 thereby to heat the outer tube 2 and to cause it to expand. Thus a difference between the inner and outer diameters of the outer and inner tubes 2 and 3 is established, and a clearance is formed between the tubes, the clearance serving to reduce heat transmission from the heated outer tube 2 to the cooled inner tube 3 thereby to establish a substantial temperature difference between the tubes. Then, with the tubes in the above described state, the mandrel 17 is drawn in the arrow direction by the drawing device 15 acting through the connecting rod 16, and the heating by the steam heater 14 is stopped, whereupon the mandrel 17 presses radially outward against the inner tube 3, causing it to yield and undergo plastic deformation to expand to an outer diameter greater than the initial inner diameter of the outer tube 2, prior to its heating and expansion, whereby the clearance between the tubes disappears and the inner tube 3 is placed in a tightly pressed state against the inner surface of the outer tube 2 as indicated on the right-hand side of the mandrel 17 in FIG. 5. During this action, the chilled water on the left side of the mandrel 17 is transferred to the right side via the passage 22. As a result, the outer tube 2 is cooled by heat transfer to the inner tube 3 and shrinks, whereby a tight interference fit between the tubes is obtained. Then, when the inner and outer tubes have been thus joined by the mandrel 17 over their entire length, the seal caps 18 and 19 are removed to discharge the cooling water, whereupon the interior of the inner tube 3 is exposed to the atmospheric air temperature, and its temperature thereby rises. As a consequence, the inner tube undergoes thermal expansion, whereby the interference fit with respect to the outer tube 2 is further increased by that much. Thus, a double-wall composite tube 1 of a very tight interference fit between its inner and outer tubes is obtained. In still another embodiment of the invention as illustrated in FIG. 6, inner and outer tubes 3 and 2 in mutually fitted state as in the preceding example are drawn in the longitudinal direction relative to heating and cooling means 14a and 30 and a mandrel 17a which are held stationary. The mandrel 17a is first placed in the inner tube 3 at one end (the right end as viewed in FIG. 6) thereof. The mandrel 17a is fixed to one end of a connecting rod 16a which is fixed at its other end to a stationary frame 25 and is passed through a seal cap 18a closing one end of the inner tube 3. The other end of the inner tube 3 is closed by a suitable seal clamp 26, 26a and is coupled by way of a crosshead 27 to a hydraulic drawing device 28. Chilled water 23 is supplied from a chilled water source 20, through a passage 21 and the seal cap 18a, into the inner tube 3 on one side of the mandrel 17a and then through passages 29 in the mandrel into the part of the inner tube 3 on the other side of the mandrel, the entire interior of the inner tube 3 being thus filled with the chilled water. The inner tube 3 is thus cooled and contracts in diameter. The above mentioned heating means is a steam heater 14a of annular shape encircling a local portion of the outer tube 2 and the mandrel 17a. Steam is supplied to the steam heater 14a from a boiler 24. Thus each part of the outer tube 2 passing by the steam heater 14a is successively heated thereby and undergoes thermal expansion as indicated in FIG. 6. Thus a clearance is formed between the outer and inner tubes. The above mentioned cooling means is a cooling device 30 of annular shape encircling a local portion of the Quter tube 2 at a position between the seal clamp 26, 26a and the steam heater 14a at a specific distance from the heater. This cooling device 30 is supplied with cooling water 23a at nearly atmospheric temperature from a cooling water source 20a through a pump 31 and a passage 21a and, by spraying this water onto the outer tube 2, cools the same. Then under these conditions, the drawing device 28 is operated to draw the outer and inner tubes 2 and 3 in the arrow direction. Successive portions of the outer tube 2 are thereby heated by the steam heater 14a and thermally expanded. At the same time, successive portions of the cooled and contracted inner tube 3 are expanded by the mandrel 17a, yield, and undergo plastic deformation, thereby expanding toward the expanded outer tube 2 and tightly fitting thereagainst the cooled and contracting outer tube in the region thereof cooled by the cooling device 30. Then, after the inner and outer tubes have been thus processed over their entire length, the seal cap 18a and the seal clamp 26, 26a are removed to discharge water from the interior of the inner tube 3 and permit atmospheric air to enter thereinto. As a consequence, the inner tube 3 absorbs heat and is thermally expanded to further increase the degree of interference fit, whereby a double-wall composite tube 1 of tightly fitted inner and outer tubes is obtained. It is to be understood that the modes of practice of this invention by using a mandrel are not limited to those of the above described two examples, various modifications being also possible. For example, the outer tube may be heated and thermally expanded prior to insertion thereinto of the inner tube. Furthermore, the inner tube may also be cooled and shrunk beforehand. These modes of practice of the method of this invention are not limited to the production of oil and gas well tubings but may be applied to that of a wide range of other pipes and tubes. A feature of these modes of practice of this invention through the use of a mandrel for mechanically expanding the inner tube inserted in the outer tube is that a temperature difference is established beforehand between the two tubes by selectively heating and expanding the outer tube and cooling and shrinking the inner tube either prior to or after the insertion of the inner tube into the outer tube, thus creating between the tubes a clearance which is useful to establish the temperature difference. This preparatory process enables a tight interference fit between the tubes in the final step. Then, by causing the mandrel and the composite tube thereafter to move axially relative to each other, the rate of expansion of the inner tube can be made constant over its entire length. Accordingly, even if there is an ununiformity in the heating of the outer tube, a constant degree of interference between the tubes can be attained. The modes of practice with the use of a mandrel can be carried out in the manner described above with reference to FIG. 5, which is advantageous for relatively short lengths of composite tubes, or in the manner illustrated in FIG. 6, which is advantageous for relatively long lengths of composite tubes. Furthermore, by selectively carrying out thermal shrinking of the outer tube and thermal expanding of the inner tube after tube expansion, a further increase in the degree of interference can be obtained, whereby a strong interference fit can be attained. In addition, since the axial force at the time of production is due only to the resistance to deformation of the inner tube, a relatively small tube-expanding device is sufficient even in the production of tubes of large diameter. In a further embodiment of this invention as illustrated in FIGS. 7 and 8, a die 32 for acting on the outer surface of the outer tube 2 is used in addition to a mandrel 17a for operating cooperatively therewith. In the example shown in FIG. 7, an inner tube 3 is closed at its two ends, filled with cooling water and caused to shrink in diameter, and inserted into an outer tube 2 of large diameter at atmospheric temperature thereby to form tentatively a composite tube, and the tooling water is then drained out of the inner tube 3. Then, into one end of the inner tube 3 in the composite tube la prepared in this manner, a mandrel 17a of a diameter greater by a specific amount than the inner diameter of the inner tube 3 is forcibly inserted. At the same time, a die 32 is forcibly pressed onto the outer tube 2. The mandrel 17a is fixed by way of a connecting rod 16a to a stationary frame part 25, while the die 32 is fixed to a stationary frame part 25 by way of a bracket 33. In front of the die 32, an annular induction heating device 11 connected to a control device 34 is installed to encircle the outer tube 2. At the same time, a cooling device 30 supplied with cooling water from a cooling water source 20 by way of a pump 31 is provided behind the die 32 to encircle the outer tube 2. Furthermore, a seal clamp device 26, 26a is attached to the rear end of the tubes and is coupled to a drawing device 28 such as a pinion-and-rack mechanism. Tap water 23b is supplied from a tap water source 20b through a flexible conduit 21b and a seal cap 18a, through which the above mentioned rod 16a is passed in a sealing state, to fill the interior of the inner tube 3, which is thereby cooled. The mandrel 17a is provided with through passage holes 29 for free passage of the tap water from the front side to the rear side of the mandrel within the inner tube 3. Then, when the drawing device 28 is operated to draw the composite tube la toward the right as viewed in FIG. 7, the inner tube 2 at its region acted upon by the mandrel 17a is mechanically expanded by it, since the mandrel and the die 32 are fixed in position, and yields to undergo plastic deformation along a stress-strain curve. On the other hand, the outer tube 2, which has been heated and expanded in diameter by the heating device 11 in front of the die 32, is subjected to a mechanical confining force by the die and is integrally fitted onto the inner tube 3. The outer tube 2 is then immediately cooled and shrunk by the cooling water from the cooling device 30, while the inner tube 2 is relieved of the expanding force and, in a tightly fitted state with the outer tube 2, is drawn rearward. By this operation wherein the composite tube la is drawn in this manner as it is heated, worked mechanically, and cooled, a tightly joined double-wall tube 1 is finally obtained. After the entire composite tube has been thus processed, the seal cap 18a is removed to discharge the water 23b out of the composite tube 1, which is then drawn away from the mandrel 17a and the die 32. By being removed from the seal clamp device 26, 26a the composite tube is exposed to the atmosphere, and the outer tube is cooled to the atmospheric temperature, whereby its shrinking in diameter is promoted. On the other hand, the inner tube 3 is no longer cooled by the water 23b, and its temperature therefore rises to the atmospheric temperature, whereby its increase in diameter is promoted. As a result of these two additive effects, an even greater interference fit is obtained, and a double-wall tube of tubes in a strongly joined state is finally produced. In the above described example, the double-wall composite tube is produced by drawing the tube past the mandrel, die, and heating and cooling devices. In a modification of this mode of practice, as shown in FIG. 8, the heating device 11, the mandrel 17a, the die 32, and the cooling device 30 are coupled by way of rods 16b to a forward drawing device 28a, while the composite tube la sealed at its ends by seal caps 18a and 18b and filled with water 23b is fixed to a stationary frame part 25 by a clamp device 26b. Thus, the die 32 and the mandrel 17a, as well as the heating device 11 and the cooling device 30, are caused to travel relative to the composite tube la. The operational effectiveness of this arrangement is substantially the same as that of the preceding example. It will be apparent that various modifications of the above described two examples are possible within the scope of this invention. For example, the entire front part of the outer tube may be heated; the heating device may be of the steam heated type; and the cooling water within the inner tube may be forced-fed cooling water. According to the above described modes of practice of the invention as illustrated in FIGS. 7 and 8, the inner tube inserted into the outer tube by a measure such as cooling is filled with cooling water, and a mandrel is placed in contact in a tube expanding state against the inner surface cf the inner tube, while a die is placed in a confining or squeezing state against the outer surface of the outer tube, whereby fundamentally, the inner tube is mechanically expanded while the outer tube is mechanically constricted. As a result, the two effects have an additive effect of producing an interference fit between the inner and outer tubes as they are moved relative to the mandrel and the die. Furthermore, since the inner tube is cooled, and the outer tube before passing by the die is heated and expanded, the outer tube at the time of passing by the mandrel and die is forcibly shrunk prior to the cooling and shrinking after this passing by and is tightly fitted against the inner tube of expanded diameter. The outer tube is thus subjected to the three shrinking steps of constriction by the die, forcible cooling and shrinking, and shrinking due to natural cooling. These effects combined with the increase in diameter of the inner tube due to natural temperature rise after plastic deformation thereof result in a very strong interference fit between the tubes. Another advantageous feature of this mode of practice of the invention is that, since it is necessary to heat only one portion of the outer tube during the production of long lengths of the composite tube, the heating means and measure are relatively simple. Moreover, tap water is sufficient for cooling the inner tube. Accordingly, the simple apparatus suffices, and the production cost can be kept low. Further preferred modes of practice of this invention will be described with reference to FIGS. 9 , 10, and 11. Referring first to FIGS. 9 and 10, the apparatus shown is designed to produce a composite tube 1 comprising an outer tube 2 and an inner tube 3 inserted in the outer tube. The composite tube 1 is supported at its front end by a seal head 36 and at its rear end by a holder 37. The seal head 36 and the holder 37 are, in turn, supported on brackets 38 and 39 respectively fixed to a base 35 and a stationary frame part 25. The seal head 36 is provided with a central bore 41 having a packing 40, through which a rod 47 to be described below is passed. The seal head 36 has at its rear end an annular countersunk surface 44 for confronting an annular beveled surface 43 of a clamp seal 42, as shown in detail in FIG. 10, and also has internal screw threads 45 meshed with external screw threads of the clamp seal 42. The front end of the inner tube 3 is clamp sealed between the inclined surfaces 44 and 43. The rod 47 passed through the central bore 41 in the seal head 36 has a liquid passage 46 throughout its length and has at its rear end a piston 48 provided with an annular packing 49 around its outer periphery and adapted to be slidable in the inner tube 3. A liquid pressure chamber 50 is formed between this piston 48 and the seal head 36. The liquid passage 46 is communicative at 46a with the liquid pressure chamber 50. The front end of the rod 47 is coupled by way of a head 52 of a drawing device 51 to a rack 53, which is meshed with a pinion 55 driven through a speed-reducing device by a motor 54 mounted on the base 35 and with an idler pinion 56. The head 52 is provided with a crosshead 57 extending downward and connected at its lower end to one end of a tie rod 58 which extends rearward and is coupled to a truck 60 riding on rollers 59 rolling along the base 35 at a position outside of the outer tube 2 slightly in front of the piston 48. The truck 60 supports an annular heating device 11 of a high-frequency induction heating coil type encircling the outer tube 2 at a position slightly in front of the piston 48. Cooling water from a cooling water source (not shown) is conducted through a hose pipe 64 which is connected at its downstream end to a cooling water header 61 and is suspended from rollers 63 riding on a rail 62 aligned parallelly with the axis of the rod 47. A long branch pipe 66 connected at its rear end to the cooling water header 61 extends forward therefrom into the interior of the inner tube 3 where it is connected to cooling water nozzles 65 for spraying cooling water against the inner surface of the inner tube 3. Another long branch pipe 68 also connected at its rear end to the cooling water header 61 extends forward therefrom outside of the holder 37 and the outer tube 2 and is connected at its front end to cooling water nozzles 69 disposed in a circle encircling the outer tube 2 for spraying cooling water thereagainst at a position rearward of the piston 48. The header 61 and the branch pipes 66 and 68 constitute an integral structure which is supported and rides on rollers 67 roll able on the base 35 and is connected by way of a joint 70 to the aforedescribed truck 60. The above described head 52 is provided with a liquid passage communicating with the front end of the aforedescribed liquid passage 46 and also with the downstream end of a hose pipe 71 which is suspended from rollers 63 rolling along a rail 62 and is connected at its upstream end via an accumulator 72 and a check valve 73 to a highTpressure liquid pressure source 74. The outer tube 2 is placed between the seal head 36 and the holder 37. At the same time, the inner tube 3 having a smaller diameter than the outer tube 2 is inserted from its front end through the holder 37 and loosely into the outer tube 2 to form q composite structure and is further clamped at its front end by the seal head 36 and the clamp seal 42 as indicated in FIG. 10. The composite combination of the outer and inner tubes is thus supported. The motor 54 is then operated to actuate the rod 47 via the pinion 55 and the rack 53 thereby to cause the piston 48 which has been within the seal head 36 to advance rearward to the holder 37, with the cooling water nozzles 65 and 69 being connected by way of the joint 70 to the drawing device 51. In this case, the packing 49 of the piston 48 has been made somewhat on the tight side. The heating device 11 is then operated, and the tube-expanding liquid is supplied from the high-pressure liquid pressure source 74 to fill and apply tubeexpanding pressure to the interior of the liquid pressure chamber 50. Then, when the motor 54 is operated normally, the inner tube 3 is expanded in diameter and is pressed into contact with the outer tube 2. Then, since the heating device is heating and expanding the outer tube 2 in front of the piston 48, the tube expansion is further amplified. This state is caused by the operation of the drawing device 51 to advance forward in concert with the piston 48, the heating device 11, the cooling water nozzles 65 and 69, and their related parts. Accordingly, the outer tube 2 of the integral doublewall tube heated and expanded in front of the piston 48 is immediately cooled rapidly by the cooling water sprayed from the cooling water nozzles 65 and 69 to the rear of the piston 48 and shrinks. The inner tube 3 is also cooled and shrinks, and, because of the difference in the shrinkages, a high degree of interference is obtained, whereby a self-tightening double-wall tube is continuously formed in an autofrettage manner. During this operation, the tube-expanding liquid within the liquid pressure chamber 50 is positively sealed by the clamp packing 40 between the seal head 36 and the rod 47 and the seal between the seal head 36 and the clamp seal 42 and by the packing 49 of the piston 48, and the rise in liquid pressure is fed back by the forward advance of the piston 48 and absorbed by the accumulator 72, whereby constant pressure is maintained. Then, when the piston 48 advances to the seal head 36, the supplying of the tube-expanding liquid is stopped; the joint 70 is disconnected and retracted rearward; the bracket 39 is moved rearward relative to the frame 25; and the holder 37 is removed from the end of the inner tube 3. Furthermore, the clamp seal 42 is turned in the disconnecting direction and thus disconnected from the seal head 36. In the example as shown in FIG. 11 of the apparatus a ccording to this invention, both ends7of the inner tube are left as they are in open state. A drawing device 51a comprising a chain 75 and a sprocket 76 driven by a motor 54 is used. The rear end of a rod 47a, corresponding to the rod 47 in the apparatus shown in FIG. 9 , is provided with a spool-like piston 48a having two spaced apart heads in tandem arrangement, the front head being a smaller diameter and the rear head being of larger diameter. These front and rear heads are provided respectively with annular packings 49 and 49a tightly contacting the inner surface of the inner tube 3. Between these two heads, an annular liquid pressure chamber 50a is formed. The rod 47a is also provided with a liquid passage 46 communicating at its rear end with the liquid pressure chamber 50a, which also communicates with a relief valve 77 at the rear end of the piston 48a. The relief valve 77 is provided in place of the accumulator 72 of the preceding example. At the time of assembly for operation, a compositely assembled double tube la, which has been mechanically expanded by a specific amount at its rear end is mounted between the brackets 38 and 39, and the rod 47a with the piston 48a is inserted from the rear side and coupled to the head 52 by means of a coupling or joint 78. The tie rod 58 coupled at its rear end to the truck 60 supporting the heating device 11 and to the inner and outer cooling water nozzles 65 and 69 is coupled by way of a joint 70a to the crosshead 57. Then, when the motor 54 is operated normally; the tube-expanding liquid is supplied through the hose pipe 71; the heating device 11 is operated; and cooling water is supplied, the tube-expanding liquid is supplied through the liquid passage 46 through the rod 47a into the pressure liquid chamber 50a, where it expands the inner tube 3. The portion of the outer tube 2 which has been heated and expanded by the heating device 11 is further expanded by the pressure of the tubeexpanding liquid and undergoes plastic deformation and assumes a shrunken state after the passing of the piston 48a, thereafter being cooled by the cooling water, whereby an interference fit is obtained to produce a selftightened double-wall tube. In this case, the packings 49 and 49a are capable of positively sealing the tube-expanding liquid. Upon completion of the tube expansion, the application of liquid pressure is stopped, and the bracket 39 is moved to remove the composite tube thereby to return the apparatus to its initial state. It will be seen various modifications can be made in the apparatuses described above and illustrated in FIGS. 9 , 10, and 11. For example, the cooling water nozzles within the inner tube may be omitted, and a lowtemperature liquid such as chilled water can be used for the tube-expanding liquid. In the above described modes of practice of this invention for producing multiple-wall composite tubes of an outer tube of carbon steel and an inner tube of stainless steel, for example, a piston for contacting the inner tube is provided on the rear end of a rod passed through a seal head and coupled to a drawing device, and at the same time a liquid pressure chamber is formed by the piston and the inner tube. A device for cooling the outer tube coupled to the drawing device is provided to the rear of the piston, and a heating device is provided in front of the piston, whereby, basically, the part of the outer tube being heated advances forward together with the forward advance of the piston. Moreover, by carrying out cooling immediately at each part by which the piston has passed, tube expansion can be accomplished with one pass, and a self-tightened multiple-wall composite tube can be produced. Accordingly, a merit of these modes of.practice is that once the two tubes in composite state are positioned therein, a multiple-wall tube can be produced with one process step in one apparatus from these tubes as they are. Furthermore, by forming a liquid pressure chamber between the piston and the seal head in front of the inner tube, a tube-expanding effect can be amply obtained beforehand in the forward advancing operation of the piston, and, with the heating device iF the forwardly advancing state, expansion in diameter can be immediately obtained. Still another advantageous feature of this method is that, since the heating device and the cooling device are intercoupled to advance forward together with the piston, a saving in heating energy can be attained, and the devices can be made compact. Furthermore, a small quantity of the cooling water is sufficient. A further merit of the method in the example shown in FIG. 11 is that, by forming a liquid pressure chamber in the annular concavity around the middle part of the piston, a further simplification of the construction is made possible, and at the same time tube expansion under liquid pressure can be accomplished over a zone of minimum extent, whereby the required power for tube expanding can be minimized and the operation is facilitated. It will be understood that contrary to the method described with reference to FIGS. 2 through 4, wherein substantial temperature difference is established between the outer and inner tubes even in the state where the tubes are in tight contact, some of the methods described with reference to FIGS. 5 through 11 necessitate an initial clearance between the outer and inner tubes, unless a high-frequency induction heating device is used, in order to create substantial temperature difference between the tubes which is a requisite for obtaining interference fit between the tubes. While this invention has been described above with respect to embodiments thereof in each of which two tubes are fitted together to form a dual or double-wall tube, it will be apparent that the principle of this invention can be advantageously applied to the production of other multiple-wall composite tubes formed from more than two tubes.

Claims: CLAIMS: 1. A method of producing multiple-wall composite tubes comprising the step of applying heat to an outer tube (2) and the step of applying pressure to the inner surface of an inner tube (3) inserted into the outer tube (2) thereby to cause the inner tube to plastically expand in diameter into tight contact with the outer tube, the heat and pressure being removed thereafter, characterized in that at least one of said steps is carried out with respect to a traveling local zone of the tubes t2 and 3) extending#fully transversely across the tubes substantially perpendicularly to the axis thereof, the local zone being caused to travel progressively from one end to the other end of the tubes thereby to cause the outer tube to successively expand locally in diameter in the traveling local zone and the inner tube to undergo plastic deformation in expansion to fit tightly against the outer tube. 2. A method of producing multiple-wall composite tubes according to claim 1, wherein the pressure is applied by a liquid (5) at a low temperature to obtain an increased temperature difference between the tubes. 3. A method of producing multiple-wall composite tubes according to claim 1, wherein the pressure is applied mechanically by a mandrel (17, 17a) drawn forcibly through the inner tube (3) from one end to the other end thereof. 4. A method of producing multiple-wall composite tubes according to claim 3, wherein the inner tube (3) is filled with a liquid (23) at a low temperature during the step of applying pressure. 5. A method of producing multiple-wall composite tubes according to claim 3, wherein a die ±32) for applying radially-inward constrictive pressure on the outer surface of the outer tube t2) is caused to be drawn forcibly together with the mandrel C17a) in substantially the same transverse plane, 6. A method of producing multiple-wall composite tubes according to claim 1 or 2, wherein the step of applying heat is carried out with respect to a traveling local zone encircling the outer part of the outer tube (2), the local zone being caused to travel progressively from one end to the other end of the outer tube. 7. A method of producing multiple-wall composite tubes according to claim 6, wherein the heat is applied by high-frequency induction heating only to the outer tube (2) in the state wherein the outer and inner tubes are closely fitted. 8. A method of producing multiple-wall composite tubes according to calim 6, wherein the heat is applied by means of a high-frequency induction heating device disposed in substantially annular arrangement around the outer tube and adapted to travel parallelly to the longitudinal axis of the outer tube from one end to the other end thereof. 9. A method of producing multiple-wall composite tubes according to claim 1 or 2, wherein the heat is applied by high-frequency induction heating to heat locally the outer tube along a helical path therearound with a helical pitch sufficient for full heating coverage of the outer tube. 10. A method of producing multiple-wall composite tubes according to calim 3, wherein the step of applying heat is carried out with respect to a local zone traveling in synchronism with the mandrel (17a) and encircling the outer tube (2) at a position immediately outside of the mandrel. 11. A method of producing multiple-wall composite tubes according to claim 5, wherein the step of applying heat is carried out with respect to a local zone traveling in synchronism with the mandrel (17a) and the die (32) relative to the outer tube and encircling the outer tube (2) at a position in front of the die with respect to the direction of relative travel thereof. 12. A method of producing multiple-wall composite tubes according to claim 11, wherein the outer part of the outer tube (2) is further cooled with a liquid (23a) at low temperature in a second local zone traveling in synchronism with the mandrel (17 a) and encircling the outer tube at a position to the rear of the mandrel with respect to the direction of relative travel thereof. 13. A method of producing multiple-wall composite tubes according to claim 1, wherein after applying heat to the outer tube C2), the outer surface of the outer tube (2) is further cooled with a liquid at low temperature in a local zone encircling the outer tube and traveling longitudinally thereof. 14. A method of producing multiple-wall composite tubes according to claim 1, wherein after applying pressure to the inner tube t3), the inner surface of the inner tube (3) is cooled with a liquid at low temperature in a circumferential local zone traveling longitudinally thereof. 15. A method of producing multiple-wall composite tubes according to claim 13 or 14, wherein the liquid at low temperature is supplied by means of nozzles onto the surface to be cooled. 16. A method of producing multiple-wall composite tubes according to claim 1, wherein the step of applying pressure to the inner tube (3) with respect to a traveling local zone of the tubes is carried out by moving a piston (48a) having therearound an annular liquid pressure chamber t50a2 defined between the outer surface of the piston and the inner surface of- the inner tube C3) in which the piston C48a# is axially slidable. 17. A method of producing multiple-wall composite tubes according to claim 6, wherein the heat is applied to the outer tube C2) to form or increase a clearance between the inner and outer tubes thereby to establish a substantial temperature difference between the tubes.

Inventors: ATSUTA, TOSHIO, MATSUI, SHIGETOMO, YOSHIDA, TOSHIO
Applicants: KAWASAKI JUKOGYO KABUSHIKI KAISHA
Application year: 1982
Main classification: B23P11
IPC codes: B23P11, B21D39