EP2285507B1 - Method for producing a large steel tube - Google Patents

Abstract

A method for producing a steel tube, wherein a steel sheet is formed into tubular body having a round cross section in a bending process, welded in a subsequent welding process along longitudinal edges facing each other for producing a continuous longitudinal seam, and then subjected to a stress-relieving treatment. The production quality is improved, with reduced production time, because the stress-relieving treatment is performed in a process for concentrically truing along the circumference in at least one segment relative to the longitudinal axis thereof, while cold forming by compression (FIG. 1). The mechanical technological properties of the material are also thereby improved.

Description

The invention relates to a method for producing steel pipes, in which a sheet metal or coil formed in a bending process to a round tube in cross-section, welded in a subsequent welding along the longitudinal edges facing each other for producing a longitudinal seam and then subjected to a relaxation treatment.

A method of this kind is in the DE 10 2006 010 040 B3 specified. In this known method, the tube is compressed by means of a straightening machine from the outer circumference by means of a plurality of circumferentially offset, axially arranged rectilinear straightening for straightening, the straightening wear the straightening tube adapted to the shape of the tube outer cross section. The straightening can be individually or in dependence on each other z. B. are moved hydraulically, the operation can be controlled or regulated can. By means of the control axes, the straightening cylinders with the straightening shells can direct the tube up to its circular contour, the calibration taking place with respect to the diameter and / or the ovality. An upsetting of the material beyond the yield point is also possible by means of this so-called impanding there for the first time.

The EP 0 438 205 A2 shows a method and apparatus for straightening the ends of elongated workpieces. When the workpiece is stationary, at least one selected in the end region cross-section of a rising and falling bending bending stress is subjected, with a predetermined maximum deflection one or more times revolves around the workpiece axis. A rising or falling bending stress is chosen so that the selected cross section is deformed into the plastic region. The means for generating a deflection of the workpiece axis in an orbit beyond the elastic limit of the workpiece also have at least three symmetrically arranged about a common axis, movable in the radial direction plunger, which are each connected to a path and time-dependent controllable piston-cylinder unit and the rams out of phase with each other during the straightening process by means of a control connection of the piston-cylinder units to perform a sinusoidal lifting movement. This is done no judging roundness or ovality, but a correction of deviations in the straightness of the bent ends, ie it is about a longitudinal straightening.

Also with one in the FR 737 123 A shown straightening machine for pipes they are directed in their longitudinal direction, in a warm state. Here are two opposing straightening elements that receive the pipe between them and can be pressed against each other by means of a lever mechanism with drive, over the entire length of the tube. The straightening elements are z. B. rounded according to the diameter of the tube, wherein the inner part of the straightening elements can be interchangeable. Before the straightening process, the tubes are heated red and evacuated. After the longitudinal straightening thus carried out, the tubes are fed by means of an ejector to a cooling device. In particular, the straightening of large steel pipes is complicated with such measures, and problems and solutions to Rundricht do not go out of this document.

In the DE 196 02 920 A1 is a method for producing pipes, in particular large pipes, specified, in which the tubes are calibrated and straightened after the internal and external welding by cold expansion (expanding).

The DE 41 24 689 A1 shows a method and apparatus for eliminating molding defects and eliminating noxious residual stresses in longitudinally welded tubing also by expanding the tube using an internal mandrel. The expansion of the tubing takes place in such a measure that existing in the circumferential direction residual stresses should be largely eliminated.

When straightening pipes unevenness of the tube shape, such. B. local ovalities on the tubular body, eliminated by local material transformations. In this case, no uniform stress reduction over the pipe jacket, in particular pipe circumference made. Rather, the known local ovality eliminations produce further, undefined stresses in the material. A target diameter can be in this way with the straightening, although with a relatively high Set effort, but in particular over the pipe circumference thereby no compression strength of the material is achieved.

During expansion, the tools generate a uniform force on the inner side of the tube, which, when straightening, evenly guides the material into a circular shape. In this process, however, unfavorable stress conditions can be generated in the tubular body, whereby the compression strength and thus collapse resistance of the pipe can decrease. In the case of coated pipes (eg CLAD pipes), the material may also be damaged so that such pipes often can not be calibrated using this process. Such adverse effects can be further increased with increasing degree of expansion.

The invention has for its object to provide a method for producing large steel tubes, with which the production of high-quality pipes is achieved with the most accurate rounding and with the shortest possible production time, as well as appropriately trained pipes to provide, including the mechanical technological properties of the material to be improved.

This object is achieved with the features of claim 1. In the method with the features of the preamble of claim 1 it is provided that the relaxation treatment is performed in a step to Rundricht along the circumference at least partially with respect to the longitudinal axis of the tube under cold deformation by upsetting.

With the measures in the combination mentioned not only the target diameter can be set well, but in the process of Rundrichtens is also a Relaxation treatment performed. In this way, not only the pipe tolerance, in particular the ovality, improved by uniform plastic deformation of the material in a short time, but also the residual stress behavior of the tubular body. Not only are the stresses generated mechanically by the shaping of the sheet metal material in the base material reduced, but also the thermally generated stresses caused by the longitudinal seam welding of the sheet material formed to the tube are reduced. Overall, the mechanical properties of the pipe are improved by the method, namely z. B. the compression strength and the collapse resistance. As calculations in the research and development work prove, the residual stress behavior after impanding, depending on the degree of impact, is reduced to a minimum, whereby a virtually complete reduction in stress is made possible without a complex heat treatment (low-stress annealing at, for example, approx 600 ° C) is required, and disadvantages caused by the heat treatment can be avoided. Due to the uniform upsetting over the outer surface of the tube, the residual stresses generated by the manufacturing process in the longitudinal and circumferential direction in the base material and in the weld build off. As the investigations of the inventors have shown, a reason for the improvements obviously lies in the fact that the residual stress state is reversed, ie after the impanding there is tension on the inside of the tube and compressive stress on the outside of the tube. With raw materials clad on the inside, additional advantages result from the external impanation, since the sensitive inner surface is not damaged or loaded. As a result, the corrosion properties of the inner material are not weakened. For support materials z. For example, made of alloy 625, the corrosion resistance is even improved by internal residual stresses.

A measure which is advantageous for the straightening and the relaxation is that during straightening a plastic deformation of the tubular body is made over its entire circumference.

Vorteihafte embodiments for an exact Rundrichten consist in the fact that the circular alignment is done on predetermined pipe outside diameter or predetermined pipe inside diameter.

In order to improve the inherent stress behavior of the tubular body, the measures further contribute to the fact that circumferential straightening and hydraulic expansion (for example with hydrotester) are combined with each other during straightening for relaxation. In this case, the impanding and hydraulic relaxation can also be carried out alternately and repeatedly.

Furthermore, the straightening and the relaxation processes are facilitated by the fact that the straightening and relaxing is carried out by means of at least two straightening dies, which are pressed from outside in the radial direction to the tube axis and offset in the circumferential direction, with straightening cups which are adapted in sections to the peripheral contour of the tube.

A tube having advantageous properties is obtained by being produced by one of the above-mentioned methods.

Fig. 1

ein in einer Rundrichtmaschine angeordnetes Rohr in schematischer Querschnittsansicht und

Fig. 2

eine schematische Darstellung von Fertigungsschritten eines Rohres.

The invention will be explained below with reference to embodiments with reference to the drawings. Show it:

Fig. 1

a arranged in a rotary straightening tube in a schematic cross-sectional view and

Fig. 2

a schematic representation of manufacturing steps of a pipe.

Fig. 1 shows an axial plan view of a tube 1 of a round cross-section with an inner radius r _i and an outer radius r _a , through whose difference a wall thickness t is fixed. The tube 1 has a longitudinally extending weld seam 2. Mechanical or thermal stress regions 3, 3 'are present in the tube wall on the one hand as a result of the mechanical molding process and on the other as a result of the heat influences during welding.

The straightening machine or straightening device 10 has a plurality of circumferentially evenly distributed and arranged in the same direction in the axial direction of the directional stamp with respective straightening shells 11, 12, 13, 14, which are interchangeably mounted on a respective holder 15 and on its side facing the tube 1 with a are provided on the surface contour of the tube 1 adapted surface shape, which extends in the circumferential direction along the pipe surface, so that when concerns all straightening the tube surface is largely encompassed in the circumferential direction. In the axial direction, however, extend the straightening cups 11, 12, 13, 14 only over a short section of the tube 1, wherein a plurality of such units of straightening cups 11, 12, 13, 14 can be arranged in the longitudinal direction of the tube 1 on the outer surface. Due to the interchangeability straightening cups adapted to different tube diameters can be easily used or exchanged. The holder 15 of the straightening shells 11, 12, 13, 14 are along a Guide axis 17 hydraulically adjusted in radial, oriented to the center of the tube 1 direction in the carrier 16 to cause a compression of the tubular body and a hydraulic expansion in the opposite direction under control or regulation by means of a control device 20. In this case, a directing to predetermined inner or outer diameter can take place, wherein an absolute position can be specified via the control device.

Fig. 2 shows essential steps in the manufacture of the tube 1, namely a molding process a, in which a metal plate 4 is formed by means of a molding device 30 by means of dies under advancement of the metal plate 4 gradually to a bent part 1.1 and finally the circumferentially bent tubular body 1.2. Subsequently, the tubular body 1.2 is closed in a welding process b at its mutually facing edges, which were previously prepared for welding, by means of a longitudinal weld in a welding device 40. By the Einformvorgänge and welding results in mechanical and thermal stress areas 3, 3 ', as mentioned above. Subsequently, optionally followed by performing further processing and / or control steps a straightening process c under Rundrichten of the tube 1, in which at the same time also takes place a relaxation treatment. The relaxation treatment can additionally be combined in a subsequent step d with a hydrostatic relaxation, for example by means of hydrotester, wherein by means of a pressure medium in the pipe interior an outwardly directed pressure p is generated on the inner tube surface.

In the case of large pipes, ie in particular with wall thicknesses t ≥ 9 mm and diameters d ≥ 300 mm, eg up to t = 80 mm and d = 2000 mm, the rounding succeeds with uniform calibration over the circumference with the above-mentioned leveler, as mentioned in the introduction DE 10 2006 010 040 B3 is shown, with a upsetting of the material in the circumferential direction and a circular straightening can be achieved with high tolerance requirements, with a compression beyond the yield point addition is possible. By plastically deforming the circular straightening, a relaxation of both mechanical and thermal stress areas 3, 3 'over the entire circumference can be achieved simultaneously. As a result, the residual stress behavior of the tubular body is significantly improved without additional heat treatment, at the same time negative influences, such as can occur through a heat treatment, for. B. in low-voltage annealing, be avoided. Thus, not only the stresses caused by the molding of the sheet metal material are reduced, but also the thermally generated stresses caused by the longitudinal seam welding, degraded, wherein the plastic deformation of the tubular body 1.2 over the entire pipe circumference. Here, the straightening is achieved with the relaxation treatment by cold deformation.

By combining the impanding and hydraulic relaxation under control or regulation via the control device 20, the relaxation process can be specifically influenced. At the same time, pipe outside or inside pipe diameters can be set to specific values. By this method, the mechanical technological properties such as strength and thermal expansion coefficient of the pipe material can be positively influenced. Furthermore, the collapse behavior of the tube and the properties under fatigue stresses are improved. Overall, this makes it possible to produce high quality, virtually stress-free tubes with high tube tolerances in a much shorter time compared to conventional manufacturing processes. As in Research and development work has been demonstrated by calculations, the residual stress behavior can be minimized after impanding, depending on the degree of impact, and also a complete reduction of stress is possible.

Claims (5)

1. Method for producing a steel tube, in which method a plate or coil is formed into a tubular body (1.2) of round cross section in a bending operation, is welded in a subsequent welding operation (b) along the longitudinal edges facing one another to produce a continuous seam and is then subjected to a stressrelief treatment, characterized in that the stressrelief treatment is carried out during an operation for concentrically straightening (c) along the circumference in at least one section with respect to the longitudinal axis thereof while cold working by upsetting.
2. Method for producing a steel tube according to Claim 1, characterized in that plastic deformation of the tubular body is carried out over the entire circumference thereof during the concentric straightening.
3. Method according to Claim 1 or 2, characterized in that a predetermined tube outside diameter (r_a) or predetermined tube inside diameter (r_i) is set during the concentric straightening.
4. Method according to one of the preceding claims, characterized in that, for the stress relief, upsetting in the circumferential direction and hydraulic stress relief are combined with one another during the concentric straightening.
5. Method according to one of the preceding claims, characterized in that the concentric straightening and stress relief are carried out by means of two, in particular at least three straightening punches which press from the outside in the radial direction relative to the tube axis, are offset in the circumferential direction and have straightening shells (11, 12, 13, 14) adapted in sections to the circumferential contour of the tube (1).

Images