METHOD FOR PRODUCING A LARGE MULTILAYER PIPE

Abstract

A method for producing a multilayered large pipe out of an outer pipe which forms a supporting layer, and at least one inner pipe, which forms a lining layer and is bent from a lining sheet and welded along a longitudinal seam or is seamless, including the following sequence of method steps: preparing a wavy inner pipe which is bent from the lining sheet with a continuously rounded wavy contour extending transverse to a longitudinal axis of the large pipe and with wave troughs and wave crests extending continuously over a length of the wavy inner pipe where the maximum outer diameter of the wavy inner pipe is smaller than the inner diameter of the outer pipe; inserting the wavy inner pipe into the outer pipe; and expanding the wavy inner pipe by an expansion force acting in a radially outward direction until it assumes an almost round form and, after removal of the expansion force, is clamped in a nonpositive way in the outer pipe, and subsequent relaxation.

Claims

1. A method for producing a multilayered large pipe out of an outer pipe (1), which forms a supporting layer and is welded or seamless and thus closed on a casing side, and at least one inner pipe (2) which forms a lining layer and is bent from a lining sheet and welded along a longitudinal seam or is seamless, including the following sequence of method steps: preparing the wavy inner pipe (20) which is bent from the lining sheet or is seamless and is closed on the casing side, with a continuously rounded, wavy contour (22) extending transverse to a longitudinal axis of the large pipe and with wave troughs (21) and wave crests (23) extending continuously over a length of the wavy inner pipe (20), where a maximum outer diameter (OD.sub.L) of the wavy inner pipe (20) is smaller than an inner diameter (ID.sub.T) of the outer pipe (1); inserting the wavy inner pipe (20) into the outer pipe (1); and expanding the wavy inner pipe (20) by an expansion force acting in a radially outward direction until it assumes an almost round form and, after removal of the expansion force, is clamped in a nonpositive way in the outer pipe (1), and subsequent relaxation.

2. A method for producing a multilayered large pipe out of an outer pipe (1), which forms a supporting layer, and at least one inner pipe (2) which forms a lining layer, which is of a lining sheet or a plurality of partial lining sheets that are placed next to one another in a circumference direction, including the following sequence of method steps: preparing a supporting sheet which is for the supporting layer and is pre-bent to a predetermined initial bending radius, and at least one lining sheet, which is pre-bent to a predetermined initial bending radius, in which a continuously rounded wavy contour (22) extending transverse to the longitudinal axis of the large pipe to be produced has been or is formed, with wave troughs (21) and wave crests (23) extending continuously over a length of the inner pipe (2) to be produced; placing the at least one lining sheet which is pre-bent and has the wavy contour (22), on an inside of the supporting sheet through positioning and parallel orientation of its longitudinal edges extending in a direction of a longitudinal axis of the large pipe in order to form the supporting layer and at least one wavy lining layer; integrally joining at least the two longitudinal edges of the at least one lining sheet provided with the wavy contour (22) to the supporting sheet; molding the composite of the integrally joined supporting layer and at least one wavy lining layer to produce a slit multilayered large pipe with the outer pipe (1) and a wavy inner pipe (20); closing of a gap of the slit large pipe by longitudinal seam welding; and expanding the wavy inner pipe (20) by an expansion force acting in a radially outward direction until it assumes an almost round form and, after removal of the expansion force, is clamped in a nonpositive way in the outer pipe (1), and subsequent relaxation.

3. The method according to claim 2, wherein the wavy contour (20) is already molded into the lining sheet in the flat initial state.

4. The method according to claim 3, wherein in the unexpanded state before the expansion, an outer circumference length (Li) of the wavy inner pipe (20) measured in the circumference direction is selected, which is at least a length of a circle with a diameter that exceeds a diameter of the wavy inner pipe (20) at its wave crests, where Li>.Math.OD.sub.L and the outer circumference length (Li) is selected to be at least great enough that after expansion and removal of the expansion force, no fold formation occurs in the inner pipe (2).

5. The method according to claim 4, wherein before the expansion, the outer pipe (1) and the inner pipe (2) are closed by a longitudinal seam weld.

6. The method according to claim 5, wherein the length of the lining sheet or of the wavy inner pipe (20) is selected to be at most as great as a length of the outer pipe (1) and before the expansion, at first only end sections of the wavy inner pipe (20) are expanded to the inner circumference surface of the outer pipe (1) and are integrally joined to the outer pipe (1) at the ends.

7. The method according to claim 6, wherein with a shorter length of the wavy inner pipe (20) than the outer pipe (1), the remaining free section or sections of the inner circumference surface of the outer pipe (1) each is provided with a lining layer.

8. The method according to claim 7, wherein the large pipe has a corrosion protection on an outside through heat treatment, before or after the expansion procedure.

9. The method according to claim 8, wherein the expansion force for the expansion procedure is exerted by a mechanical or a hydraulic expansion device.

10. The method according to claim 9, wherein before the expansion, the cavity between the wavy inner pipe (20) and the outer pipe (1) is evacuated by a vacuum pump.

11. The method according to claim 10, wherein before expansion an adhesive layer is applied to a part or all of an area of the wavy inner pipe (20) and/or the outer pipe (1) on sides oriented toward each other and the adhesive layer is hardened during or after the expansion.

12. The method according to claim 2, wherein in the unexpanded state before the expansion, an outer circumference length (Li) of the wavy inner pipe (20) measured in the circumference direction is selected, which is at least a length of a circle with a diameter that exceeds a diameter of the wavy inner pipe (20) at its wave crests, where Li>.Math.OD.sub.L and the outer circumference length (Li) is selected to be at least great enough that after expansion and removal of the expansion force, no fold formation occurs in the inner pipe (2).

13. The method according to claim 2, wherein before the expansion, the outer pipe (1) and the inner pipe (2) are closed by a longitudinal seam weld.

14. The method according to claim 2, wherein the length of the lining sheet or of the wavy inner pipe (20) is selected to be at most as great as a length of the outer pipe (1) and before the expansion, at first only end sections of the wavy inner pipe (20) are expanded to the inner circumference surface of the outer pipe (1) and are integrally joined to the outer pipe (1) at the ends.

15. The method according to claim 2, wherein with a shorter length of the wavy inner pipe (20) than the outer pipe (1), the remaining free section or sections of the inner circumference surface of the outer pipe (1) each is provided with a lining layer.

16. The method according to claim 2, wherein the large pipe has a corrosion protection on an outside through heat treatment, before or after the expansion procedure.

17. The method according to claim 2, wherein the expansion force for the expansion procedure is exerted by a mechanical or a hydraulic expansion device.

18. The method according to claim 2, wherein before the expansion, the cavity between the wavy inner pipe (20) and the outer pipe (1) is evacuated by a vacuum pump.

19. The method according to claim 2, wherein before expansion an adhesive layer is applied to a part or all of an area of the wavy inner pipe (20) and/or the outer pipe (1) on sides oriented toward each other and the adhesive layer is hardened during or after the expansion.

20. The method according to claim 1, wherein the wavy contour (20) is already molded into the lining sheet in the flat initial state.

21. The method according to claim 1, wherein in the unexpanded state before the expansion, an outer circumference length (Li) of the wavy inner pipe (20) measured in the circumference direction is selected, which is at least a length of a circle with a diameter that exceeds a diameter of the wavy inner pipe (20) at its wave crests, where Li>.Math.OD.sub.L, and the outer circumference length (Li) is selected to be at least great enough that after expansion and removal of the expansion force, no fold formation occurs in the inner pipe (2).

22. The method according to claim 1, wherein before the expansion, the outer pipe (1) and the inner pipe (2) are closed by a longitudinal seam weld.

23. The method according to claim 1, wherein the length of the lining sheet or of the wavy inner pipe (20) is selected to be at most as great as a length of the outer pipe (1) and before the expansion, at first only end sections of the wavy inner pipe (20) are expanded to the inner circumference surface of the outer pipe (1) and are integrally joined to the outer pipe (1) at the ends.

24. The method according to claim 1, wherein with a shorter length of the wavy inner pipe (20) than the outer pipe (1), the remaining free section or sections of the inner circumference surface of the outer pipe (1) each is provided with a lining layer.

25. The method according to claim 1, wherein the large pipe has a corrosion protection on an outside through heat treatment, before or after the expansion procedure.

26. The method according to claim 1, wherein the expansion force for the expansion procedure is exerted by a mechanical or a hydraulic expansion device.

27. The method according to claim 1, wherein before the expansion, the cavity between the wavy inner pipe (20) and the outer pipe (1) is evacuated by a vacuum pump.

28. The method according to claim 1, wherein before expansion an adhesive layer is applied to a part or all of an area of the wavy inner pipe (20) and/or the outer pipe (1) on sides oriented toward each other and the adhesive layer is hardened during or after the expansion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] This invention is explained in greater detail in view of exemplary embodiments with reference to the drawings, wherein:

[0032] FIG. 1 shows an end view of a closed outer pipe with a closed, wavy inner pipe inserted into it before an expansion procedure;

[0033] FIG. 2 is a perspective depiction to illustrate the insertion of the closed, wavy inner pipe into the outer pipe;

[0034] FIG. 3 shows a partially cut-away side view of the end section of the outer pipe with the inserted wavy inner pipe, showing the end connection of the two pipe partners and the cladding of a remaining end section of the outer pipe by a lining layer (plating layer, alloying layer);

[0035] FIG. 4A shows an end view of the closed outer pipe with the inserted wavy inner pipe and a depiction of the expansion forces (arrows pointing radially outward) during the expansion procedure;

[0036] FIG. 4B shows an end view of the outer pipe with the inserted inner pipe after the wavy inner pipe has been expanded into the round shape; and

[0037] FIGS. 5 and 6 show depictions of the manufacture of a two-layered large pipe according to the prior art, with different stages of an expansion process in an outer die (FIG. 5) and an explanatory stress-strain diagram (FIG. 6) as described at the beginning.

DETAILED DESCRIPTION OF THE INVENTION

[0038] FIGS. 1 through 4 show essential processing steps in the manufacture of a multilayered, in this case two-layered, large pipe based on an exemplary embodiment. The term large pipe should be understood to mean pipes with diameters of at least 150 mm and an overall wall thickness of at least 5 mm. The at least two layers or plies that form the multilayered wall of the large pipe are of or composed of a first and a second metal sheet (and possibly others), which are bonded into a stable composite of or composed of a closed outer pipe (supporting pipe) and an inner pipe (liner pipe, liner). An integral connection of the two pipe partners is produced, for example, in both end sections of the large pipe. The wall thickness of the outer pipe is significantly larger, in most use instances by several times, than that of the inner pipe. The outer pipe is preferably of or composed of carbon steel. The inner pipe is advantageously of or composed, for example, of an austenitic material such as stainless 316L steel. But various metallic materials can be used, particularly for the inner pipe, in order to meet different requirements. The method for producing the multilayered large pipe includes a sequence of several method steps.

[0039] According to the exemplary embodiments shown in the figures, the above-mentioned pipe partners (outer pipe and inner pipe) are embodied in the form of closed pipes, with the outer pipe 1 at this stage embodied as a round outer pipe 1 and the inner pipe embodied as a wavy inner pipe 20 with a wavy contour 22, which extends transversely relative to the longitudinal axis of the pipe and has continuously rounded wave troughs 21 and wave crests 23 that continuously transition into one another and that extend in a steadily continuous fashion over the entire length of the wavy inner pipe, such as parallel to its longitudinal axis or in a helical fashion. The wavy contour can be embodied in different ways, such as with wave troughs and wave crests of uniform or different widths, a varying spatial frequency (number per unit length), and/or different wave height (amplitude), by which it is also possible to influence the expansion forces and bonding forces of the pipe partners. In order to be able to easily insert the wavy inner pipe 20 into the outer pipe 1, the maximum outer diameter of the inner pipe OD.sub.L is smaller than the inner diameter ID.sub.T of the outer pipe 1, as shown in FIG. 1.

[0040] The wavy inner pipe 20 is geometrically shaped so that its outer circumference length Li (perimeter) is greater than the circumference length (perimeter) of an enveloping circle with the diameter OD.sub.L (FIG. 1). The diameter OD.sub.L here is understood to be the diameter of the smallest possible circle that just envelops the wavy inner pipe. Preferably, the outer circumference length Li is at least as large as the inner circumference length Lo of the outer pipe 1.

[0041] The forming of the wavy inner pipe can, for example, take place before the round molding into the wavy inner pipe 20, already in the sheet (lining sheet) provided for this, which is flat or even pre-bent with a larger bending radius, by corresponding recesses and bulges, after which the lining sheet that has been provided with the wavy contour is then bent into the wavy inner pipe and is completely closed in the circumference direction by a longitudinal seam weld.

[0042] The outer pipe 1 is bent for example from a flat metal sheet (supporting sheet) into a round pipe and likewise completely closed in the circumference direction by a longitudinal weld seam.

[0043] In order to embody this invention, however, the outer pipe 1 and/or a pipe body for the inner pipe can, before the production of the pipe composite, exist in the form of (longitudinal seam- or helically) welded or seamless pipe bodies in any combination.

[0044] As shown in FIG. 2, the wavy inner pipe 20 is inserted into the round outer pipe 1. The length of the wavy inner pipe 20 can be less than the length of the outer pipe 1 so that the outer pipe 1 protrudes beyond the wavy inner pipe 20 at one or both of the end sections, as shown in FIG. 3. The ends of the inner pipe 20 (as is also the case in the equal-length outer pipe 1 and wavy inner pipe 20) are expanded with the aid of an expansion device, are pressed against the outer pipe 1, and at the ends of the thus-expanded inner pipe 20, are integrally joined to the outer pipe 1 by a connecting seam 3, for which purpose a fusion welding, for example, is used.

[0045] In another step, the remaining length of the outer pipe 1 at one or both of the end sections that is not covered by the wavy or expanded inner pipe has or is provided with a lining layer 3 (alloying layer, plating layer) so that the inside of the outer pipe 1 is completely protected with a lining layer (functional layer) that is adapted to the relevant requirements.

[0046] As demonstrated in FIG. 4A, in the next step, the wavy inner pipe 20 is radially expanded with an expansion force (in accordance with the arrows pointing radially outward) until it assumes the round shape shown in FIG. 4B and is clamped in the outer pipe 1. This step of the expansion of the wavy inner pipe 20 until the round shape is reached and thus the forming of the inner pipe 2 and possibly the further forming together with the outer pipe 1 can be carried out before or after the outside of the large pipe is coated with a corrosion protection. If the expansion of the inner pipe 20 is carried out after the coating with the corrosion protection has been completed and the pipe is cooled to the ambient temperature along with its pipe partners, then this prevents the bonding force between the two pipe partners from being negatively affected by a temperature increase during the coating procedure (which can reach a peak value of up to 270 C.), thus achieving a significant advantage of this invention in comparison to conventional methods for producing mechanically plated multilayered pipes (liner pipes).

[0047] After the expansion of the wavy inner pipe 20, possibly followed by expansion of the outer pipe 1, the expansion force is decreased, causing the pipe partners to relax and the nonpositive connection to be produced between the material layers functioning as the inner pipe 2 and the outer pipe 1. The nonpositive connection is produced when the inner pipe 2 is formed during the expansion and is at least partially swaged (in some sections), such as is displaced due to compressive stress, it being possible for the outer pipe 1 to remain under a tensile stress in the elastic range. This offers particular advantages in the event that the expansion takes place in a pipe that has already been externally provided with a coating that forms or constitutes a corrosion protection because in this case, no outer die that could damage the outer coating is required in order to contain the outer pipe 1. The outer pipe 1 can also, but does not have to, be expanded into the plastic range.

[0048] The recovery of the outer pipe 1 after the decrease in the expansion force is directed inward. The cumulative recovery of the inner pipe 2 can be considerably smaller toward the inside or can even be directed outward. The recovery can be directed outward if the outer circumference length Li of the wavy inner pipe 20 is selected to be greater than the inner circumference length Lo of the outer pipe 1.

[0049] The expansion of the wavy inner pipe 20 and possibly of the outer pipe 1 can, for example, be carried out by a mechanical device, for example a mechanical or hydraulic expander. Other types of expansion (flaring) are also possible, for example by electromagnetically, pneumatically, or explosively acting devices. In an embodiment of this invention, the expansion of the wavy inner pipe 20 and possibly also of the outer pipe 1 is carried out by an internally acting pressure for which purpose, a cold water testing machine (CWT) can advantageously be used.

[0050] In an additional method step, the cavity between the two pipe partners can be evacuated by a vacuum pump before the expansion in order to minimize the resistance of the air that must be compressed during the expansion of the wavy inner pipe 20 and thus to achieve a better bond between the two pipe partners after the expansion and relaxation.

[0051] In addition, the outside of the wavy inner pipe 20 and/or the inside of the outer pipe 1 can be partially or entirely provided with an adhesive layer that hardens after the expansion or after the relaxation of the pipe partners. The adhesive layer increases the bonding force between the two pipe partners in addition to the nonpositive connection.

[0052] An essential feature of this invention is also that the outer circumference length Li of the wavy inner pipe 20 can be greater than the inner circumference length Lo of the outer pipe 1. The greater the difference between the inner circumference length Lo and the outer circumference length Li, the greater the compressive force that is produced in the nonpositive connection of the pipe partners. On the other hand, the outer circumference length Li is restricted by the fact that a shaping of the wavy inner pipe 20 into the round inner pipe 2 also actually takes place inside the outer pipe 1, without the occurrence of fold formation. This condition for the minimum and maximum outer circumference length Li depends on material properties and geometrical properties and depending on the choice of these parameters, can also be established and optimized in combination with relevant parameters of the outer pipe 1 in each respective case, such as through calculation, so that a wide variety of options for adjusting to different use conditions is achieved.

[0053] The cumulative degree of swaging of the liner (such as a shaping determined by the circumference and wall thickness) can be estimated according to the following formula

[00001]$\mathrm{.Math.}=\frac{L_i-L_i^f}{L_i^f}$

where L.sub.i and L.sub.i.sup.f are the outer circumference lengths of the liner respectively before and after the expansion. The outer circumference length of the liner L.sub.i.sup.f after expansion correlates to the outer diameter of the outer pipe OD.sub.T.sup.f after expansion according to the following relation:

L.sub.i.sup.f=(OD.sub.T.sup.f2.Math.WT.sub.T),

where WT.sub.T represents the wall thickness of the outer pipe 1.

[0054] Under the condition that L.sub.i>L.sub.i.sup.f, regardless of its yield strength, the wavy inner pipe 20 or liner is subjected to a cumulative compressive stress in the circumference direction during expansion before the outer pipe 1 reaches its yield strength. This makes it possible to use various material combinations of outer pipe 1 and inner pipe 2, regardless of their yield strengths. This is an essential advantage as compared to conventional manufacturing methods of the kind mentioned above.

[0055] Another important feature of this invention is that the expansion or flaring of the wavy inner pipe 20 requires less pressure, such as produced by a cold water testing machine, than the yield load for the outer pipe 1, which forms or constitutes a fundamental difference in the present technology as compared to known hydroforming techniques. Usually, in the conventional procedure according to FIGS. 5 and 6, pressures are used, which cause the outer pipe to flow, thus requiring an outer die in order to protect the pipe from uncontrolled expansion and breakage.

[0056] The expansion of the inner pipe, preferably by a cold water testing machine after the coating with a corrosion protection on the outside, does not cause any loss in the nonpositive connection, which must be considered another significant advantage as compared to the known procedures.

[0057] In another embodiment for producing a multilayered, in particular two-layered, pipe using the principle according to this invention lies in a modification of the procedure for producing a multilayered large pipe taught in German Patent Reference DE 10 2013 103 811 B3 in which a supporting sheet that is pre-bent to a predetermined initial bending radius and a lining sheet that is pre-bent to a predetermined initial bending radius are welded to each other along the longitudinal edges of the lining sheet. Through the use of a lining sheet with a continuously rounded wavy contour of the kind that has been described in connection with the exemplary embodiment above, it is first possible to produce the composite of the pre-bent supporting sheet and the pre-bent lining sheet, with the pre-bent lining sheet having been provided with the wavy contour ahead of time. After this, the pre-bent wavy lining sheet is welded to the pre-bent supporting sheet along its longitudinal edges, then bent into a closed composite tube with a round cross-section, and completely closed by a longitudinal seam weld. After this, the above-described method steps of the expansion can be correspondingly carried out in order to produce the nonpositive connection in the regions that are not integrally joined. This also achieves a multilayered, in particular two-layered, large pipe with a stable connection between the inner pipe 2 and the outer pipe 1. With this procedure, instead of only one pre-bent lining sheet, it is also possible for a plurality of pre-bent lining sheets, with the lining surface that has been provided with the wavy contour and adjoining one another in the circumference direction, to be integrally joined to the pre-bent supporting sheet, followed by the shaping into the rounded composite pipe and the subsequent other steps with the longitudinal seam welding, expansion of the wavy inner pipe and possibly also of the outer pipe 1, and relaxation in order to produce the nonpositive connection.

[0058] With the above-described measures for producing the nonpositive connection using an inner pipe with a wavy contour, it is possible to already produce the nonpositive connection between the pipe partners at lower pressures by comparison to known methods. The possibility of producing the nonpositive connection between the pipe partners through expansion of the wavy inner pipe 20 against the outer pipe 1 regardless of the yield strengths of the inner pipe and outer pipe achieves the advantage that the yield strength of the liner can be selected to be either less than or greater than the yield strength of the outer pipe 1. This in turn makes it possible to use a broader spectrum of materials for the inner pipe 2 and thus affords improved possibilities for adjusting to different requirements. By comparison with metallurgically plated clad pipes, a significantly more reasonably priced production is achieved and on the other hand, a broader palette of materials is available, for example high-carbon, wear-resistant steels and highly corrosion-resistant duplex steels. Because the two material layers of the large pipe can be produced independently of each other (by contrast with metallurgically plated sheets, which must be rolled jointly), the production of the respective material partners can be optimized with regard to the desired mechanical properties and/or corrosion properties. Other advantages include greater availability and shorter delivery times of the respective sheets for the material layers as compared, for example, to metallurgically plated or explosively clad sheets.