METHOD FOR INDUCTION BEND FORMING OF A COMPRESSION-RESISTANT PIPE HAVING A LARGE WALL THICKNESS AND A LARGE DIAMETER, AND INDUCTION PIPE BENDING DEVICE

Abstract

A method for induction bend forming of a compression-resistant pipe (1) having a large wall thickness and a large diameter, in particular, for use in power plants and pipelines, comprises: horizontal placement of the unprocessed pipe (1); feeding the pipe (1) to the passage of a front pipe section through an annular inductor (20) of an electrical induction unit; clamping the front pipe section in a bending lock (31) that is mounted on a bending arm (30), which is pivotable around a vertical axis of rotation (32) arranged laterally to the pipe; current supply to the induction unit for heating a pipe section; and deflecting the bending arm (30) by longitudinal feeding of the pipe (1) until the completion of the pipe bend (3).

The pipe (1) is compressed vertically in a pressing unit (50) prior to introduction into the inductor (20), such that a cross-section of the pipe (1) is forced into the shape of a lying oval, and a temperature profile with a lower temperature at an outer side of the bend (3.2) and with a higher temperature at an inner side of the bend (3.1) is set at least during a portion of the pipe bending process by means of a transverse movement of the inductor (20) relative to the pipe (1).

Claims

1. In a method for induction bend forming of a compression-resistant pipe having a large wall thickness and a large diameter, in particular, for use in power plants and pipelines, said method comprising the following steps; horizontal placement of an unprocessed pipe; feeding a front pipe section of the pipe through an annular inductor of an electrical induction unit; clamping the front pipe section in a bending lock that is mounted on a bending arm, which is pivotable around a vertical axis of rotation arranged laterally to the pipe; supplying current to the induction unit for heating a pipe section; deflecting the bending arm by longitudinal feeding of the pipe until the completion of the pipe bend; the improvement comprising the steps of compressing the pipe vertically in a pressing unit prior to introduction into the inductor, such that a cross-section of the pipe is forced into the shape of a lying oval, and setting a temperature profile with a lower temperature at an outer side of the bend and with a higher temperature at an inner side of the bend at least during a portion of the pipe bending process by means of a transverse movement of the inductor relative to the pipe.

2. Method as in claim 1, further comprising the step of continuously compressing the pipe during the longitudinal feed.

3. Method as in claim 2, wherein the degree of the pipe compression is progressively increased from an initial tangent to the center of the pipe bend and then reduced again to an end tangent.

4. Method as in claim 1, wherein the temperature profile is adjusted by an increased local energy supply at one side of the bend.

5. Method as in claim 4, wherein the distance between the inductor and the inside of the bend is reduced and at the same time is increased at the outside of the bend, and wherein the absolute temperature level is adjusted by adapting the electrical current flowing in the inductor.

6. Method as in claim 1, wherein the temperature profile is adjusted by an increased local energy removal at one side of the bend.

7. Method as in claim 6, wherein the temperature at the inner side of the bend is reduced by means of a cooling device and wherein the absolute temperature level is adjusted by adaptation of the electrical current flowing in the inductor.

8. Induction pipe bending device for compression-resistant pipes having a large wall thickness and a large diameter, in particular for use in power plants and pipelines, said device comprising, in combination: a machine bed for horizontal positioning of an unprocessed pipe; a feed unit configured to act along the pipe axis; an electrical induction unit with an annular inductor for heating a pipe section; a bending arm that is pivotable around a vertical axis of rotation and has a bending lock for clamping the pipe as well as an adjustment device for adjusting the distance between the axis of rotation and the bending lock; a pressing unit arranged upstream of the inductor in the feed direction having at least one punch acting vertically on the pipe and a counter support for the punch wherein the inductor is mounted such that it can be moved transversely to the feed direction, and a control unit for adjusting the electrical power of the induction unit as a function of a transverse offset of the inductor or vice versa.

9. Induction pipe bending device as in claim 8, wherein the pressing unit has at least two hydraulically driven punches that act upon the pipe in opposition to each other.

10. Induction pipe bending device as in claim 8, wherein at least one punch and counter-support each have at least one pressure roller having the shape of a double cone or a rotational hyperboloid.

11. Induction pipe bending device as in claim 8, wherein the at least one punch and counter support are arranged at the top and at the bottom in a closed rack, and wherein at least one lateral guide roller is arranged on both sides of the rack.

Description

[0022] Details of the invention are explained in more detail below with reference to the drawings. The figures show in detail:

[0023] FIG. 1 a schematic view of an induction pipe bending device:

[0024] FIG. 2 a top view of a pipe bend;

[0025] FIG. 3 cross-sections according to the prior art in the cross-sectional planes marked in FIG. 2;

[0026] FIG. 4 cross-sections according to the invention in the cross-sectional planes marked in FIG. 2;

[0027] FIG. 5 a cross-section of the different wall thickness distribution in the center of the pipe bend;

[0028] FIG. 6 a longitudinal section of the different wall thickness distribution in the center of the pipe bend, and

[0029] FIG. 7 a pressing device for the pre-ovalization.

[0030] FIG. 1 shows an induction pipe bending device 100 comprising a stationary machine bed 10 on which a holding device 11 for a pipe 1 is arranged. The holding device 11 grips the pipe 1 at its rear end and clamps it securely. In addition, the holding device 11 is movable in relation to the machine bed 10 in the direction of a pipe center axis 2, which at the same time indicates the feed direction. The feed is carried out via a hydraulic unit 12.

[0031] A bending arm 30 is pivotably mounted on a vertical bending axis 32, wherein the distance of the bending axis 32 can be adjusted perpendicular to the pipe center axis 2 in order to set the desired bending radius. A bending lock 31 with which the pipe 1 can be gripped and clamped is arranged on the bending arm 30.

[0032] Relatively close to the inductor 20 and to the heat-affected zone, a cooling device (not shown here) is arranged, with which, for example, cooling of the surface temperature is effected using water as soon as the corresponding length section has emerged from the forming zone.

[0033] An induction device comprises an annular inductor 20, which is positioned with its center in the region of the pipe center axis 2.

[0034] While the aforementioned features are also a component of the known induction pipe bending devices, according to the invention, on the one hand, a transverse adjusting device 21 is provided in order to be able to move the inductor 20 transversely to the longitudinal axis 2 of the pipe 1 being processed.

[0035] On the other hand, a pressing unit 50 is provided, of which a preferred embodiment is illustrated in FIG. 7 in a view from the front, viewed from the machine bed 10 in the feed direction. In a rack 51, at least one hydraulic punch 52, 53 is arranged at the top and at the bottom, each of which being provided with a pressure roller 54, 55 in the form of a double cone or a rotational hyperboloid or an otherwise concave, rotationally symmetrical body. Through these forms, a load distribution is achieved with only one roller each on each side of the pipe 1 on two sufficiently spaced apart lines on the outer circumference of the pipe 1. This avoids running marks on the pipe jacket due to excessive surface pressure. The hydraulic punches 54, 55 are operated with the same stroke after a single adjustment to a center located on the tube center axis 2, such that the pressure rollers 54, 55 simultaneously contact the pipe jacket and then effect the forming procedure with equal forces. The pipe thus remains centered in the vertical plane during the entire execution of the bend forming process.

[0036] Two further hydraulic punches 56, 57, each having at least one guide roller 58, 59 at their end, are mounted on the right and left sides of the rack 51. In this way, the pipe 1 is also centered in the horizontal direction in such a way that it is compressed precisely with the pressure rollers 54, 55 on the middle axis 2 by means of the punches 52, 53 arranged above and below, and no eccentricities occur. By means of the hydraulic punches 56, 57 on the side, only the guide rollers 58, 59 are positioned and held, but no forming force is exerted by them on the pipe. The lateral guide rollers 58, 59 are preferably convex-crowned or cylindrical, in order to prevent shape-dependent securing of the pipe 1 on the guide rollers in the vertical direction.

[0037] This arrangement on the horizontal and vertical axes applies to a pipe bend that is carried out in a horizontal plane.

[0038] As FIG. 7 shows, the compression occurs exclusively in the vertical direction, so that the cross-section of the pipe 1 takes the form of an oval, i.e., the long diameter axis extends horizontally. The ovality is shown overemphasized for illustrative purposes in the presentation according to FIG. 7 as well as in FIG. 3, which is explained below. In reality, the forced out-of-roundness is only about 1% of the pipe diameter at the beginning, 1.5% at the end, and up to 4% of the pipe diameter in the center of the pipe bend so that it is barely visible to the naked eye.

[0039] The rack 51 of the press unit 50 is of annular design, in the sense that it is closed in itself, i.e., unending. The outer shape is preferably diamond-shaped in the top view, with one of the punches 52, 53, 55, 56 being arranged at each corner point.

[0040] FIG. 2 shows a pipe bend 3 with a beginning tangent 2 and a tangent 4. Three different section planes A-A, B-B and C-C are marked in FIG. 2, with the section plane B-B being arranged in the center of the pipe bend 3 because the greatest deviations of the wall thicknesses on the inner and outer parts of the bend are present there.

[0041] The cross-sections at the locations marked in FIG. 2 that would result in an induction bending process according to the prior art are shown in FIG. 3. Accordingly, the cross-section is circular only in the area A-A, i.e., at the end tangent 4 on the non-formed pipe 1 being processed. As a result of the forming process, a so-called standing ovality is obtained as the cross-section B-B in the middle of the bend 3, which also results in a lying ovality in the area C-C, that is, at the transition to the starting tangent 2.

[0042] By using the induction bending method according to the invention, on the other hand, circular shapes are formed for all three cross-sections A-A, B-B and C-C as shown in FIG. 4.

[0043] FIG. 5 shows the different wall thickness distributions on the pipe bend 3 in a further cross-sectional drawing in the plane B-B. The wall thickness is considerably thicker on the inner pipe bend 3.2 than on the outer pipe bend 3.1. A vertical axis 3.3 that characterizes the neutral zone is not at the center of the pipe cross-section but instead, is offset toward the outside of the pipe bend 3.1 according to the invention. According to the invention, this is achieved, for example, by the following asymmetrical temperature distribution in the forming zone:

[0044] Outside of the pipe bend 3.1 850 C.

[0045] Inside of the pipe bend 3.2 1000 C.

[0046] The inductor adjustment path at this point is only about 10 mm out of the center. This small adjustment path relative to the other geometrical dimensions is already sufficient to achieve the effects according to the invention.

[0047] FIG. 6 shows the wall thickness distribution in a horizontal longitudinal section through the pipe bend 3. The dash-dotted line in the center represents the center axis 2 of the pipe. The neutral zone 3.3 runs parallel to it. The dashed lines in the area of the inner pipe bend 3.2 and the outer pipe bend 3.1 represent the wall thicknesses on the non-formed pipe 1. The solid lines show the wall thicknesses that arise after the bend forming is carried out. Again, the deviations are shown over-emphasized.

[0048] Examples of the wall thickness distribution for a processed pipe with a nominal wall thickness of 10 mm are shown below:

a) Induction Bend Forming According to the Prior Art:

[0049]

TABLE-US-00001 Outside of the bend 3.1 7.5 mm (25%) Inside of the bend 3.2 15.0 mm (+50%) Change to the inner pipe 1.25 mm diameter (constriction):

b) Induction Bend Forming According to the Invention:

[0050] By suitably adapted temperatures, a shift of the neutral zone 3.3 inwards or outwards can be achieved. In general, an outward shift is aimed for according to the invention in order to halve the decrease:

TABLE-US-00002 Outside of the bend 3.1 8.75 mm (12.5%) Inside of the bend 3.2 17.50 mm (+75%) Change of inner pipe approx. diameter (constriction): 3.125 mm

[0051] Thus, the weakening of the outer side of the bend 3.1 has been reduced by half. The simultaneous increase in the wall thickness at the inner side of the bend 3.2 does, however, lead to a slight reduction in the inner diameter. The resulting reduction in the clear pipe cross-section by about 2 mm is negligible in light of the large diameters of the pipes used.