EP3288695B1 - Method for induction bend forming a compression-resistant pipe having a large wall thickness and a large diameter - Google Patents

Description

The invention relates to a method for induction bending forming a pressure-resistant tube with large wall thickness and large diameter, in particular on a power plant and pipeline pipe, having the features of the preamble of claim 1.

For the passage of liquid and gaseous media under pressure tubes of steel are required, which have a large wall thickness to withstand the stresses. Such requirements apply, for example, to the transport of superheated steam in power plants, where pipe bends are required to adapt the pipelines to the structural conditions, or for the transport of crude oil in pipelines over long distances, where compensators, so-called lye arcs, are used at regular intervals, to compensate for thermal changes in length. In order to enable a large throughput, a large opening cross-section and accordingly a large pipe outside diameter is required. Tubes to which the present method pertains usually have nominal diameters greater than 300 mm and a diameter to wall thickness ratio of from 10: 1 to 100: 1, typically from 20: 1 to 70: 1.

Such a method for Induktionsbiegeumformen has long been known, for example from the DE 2513561 A1 and has been continually upgraded to despite the enormous dimensions to produce very dimensionally stable pipe bends. The transformation of such massive tubes succeeds only by inductive heating of a narrow annular zone up to a forming temperature above 850 ° C. In the heat-affected zone, structural changes occur in the material, which is usually fine-grained steel. In order to homogenize the microstructure after hot working and thus improve the mechanical properties of the steel, the pipe bend is often subsequently heat treated at a temperature of about 600 ° C. The straight pipe sections that connect before and after the pipe bend and are also called tangents are also affected by the subsequent heat treatment. However, since they were not previously heated to high temperature in the course of the forming process and their structure therefore remained unchanged, the subsequent heat treatment has a negative effect on these sections; they become brittle. These sections must therefore be separated and the pipe bend produced by induction bending must be welded to new tangents.

This is disadvantageous because of the high workload, especially when several pipe bends, also in different directions, are made successively on the same piece of pipe, as determined by the in the DE 10 2010 020 360 A1 described device is made possible. The thus achieved simplification and acceleration of the line construction by producing a three-dimensional pipe structure in only one operation is nullified if the straight Tangentenstücke must be replaced, because to achieve certain strength values post heat treatment of the pipe structure is required. In order to avoid this, it is only possible to use pipes of higher strength steels and / or with greater wall thickness in order to retain the mechanically required minimum strength values for the overall structure after the post-heat treatment at the tangents. However, this way out is also disadvantageous due to the considerably higher material prices.

The object of the present invention is thus to improve the method of the type mentioned above so that negative influences of the forming process on the strength values of the material in the adjacent to the pipe bend tangents are avoided.

To solve the invention, the method with the features of claim 1 before.

The solution according to the invention is based on subjecting the tangents in front of and behind the bend to an exactly same heat treatment as the section of the tube must undergo during bending during the deformation, ie to guide the tangents through the induction device at the same throughput speed as in the case of FIG to be bent pipe section, and also apply the same temperature in the induction device as well as the same cooling parameters subsequently. The difference in the passage of the tangents is therefore only that the tube is not clamped in the bending buckle during the treatment of the tangent and therefore have no counter-forces during the feed.

The sole clamping at the rear end of the tube without further support makes it possible to operate independently of the clamping of the front end in the bending buckle, and further allows to move the inductor unhindered by support means along the tube wall in the direction of the rear end.

Fig. 1

eine Induktions-Rohrbiegevorrichtung in schematischer Ansicht;

Fig. 2a - 2d

jeweils die Induktions-Rohrbiegevorrichtung in verschiedenen Stellungen während der Durchführung des Verfahrens; und

Fig. 3, 4

je ein Ablaufdiagramm, in welchem Bewegungsgeschwindigkeiten über dem Weg aufgetragen sind.

The solution according to the invention provides an exact tuning of the movements of the feed unit and the inductor, which are executed and monitored by a control unit. These steps are explained in more detail below with reference to the drawings. The figures show in detail:

Fig. 1

an induction tube bending apparatus in a schematic view;

Fig. 2a - 2d

in each case the induction tube bending device in different positions during the implementation of the method; and

Fig. 3, 4

each a flowchart in which movement speeds are plotted over the path.

FIG. 1 shows an induction tube bending apparatus 100, which includes a stationary machine bed 10, on which a holding device 11 is arranged for a tube 1. The holding device 11 engages the tube 1 at its rear end and clamps it firmly. In addition, the holding device 11 in the direction of a pipe center axis 2, which at the same time indicates the feed direction, relative to the machine bed 10 slidably. The feed takes place via a hydraulic unit 12.

An induction device comprises an annular inductor 20, which is positioned with its center in the region of the tube center axis 2. According to the invention, a linear adjustment device 21 is provided in order to be able to move the inductor 20 relative to the machine bed 10.

A bending arm 30 is pivotally mounted on a vertical bending axis 32, wherein the distance of the bending axis 32 can be adjusted perpendicular to the tube center axis 2 to specify the desired bending radius. On the bending arm 30, a bending lock 31 is arranged, with which the tube 1 can be gripped and clamped.

Relatively close to the inductor 20 and the heat-affected zone, a cooling device 40 is arranged, with the z. B. with water, a cooling of the surface temperature is effected as soon as the corresponding length section has emerged from the forming zone.

For carrying out the method according to the invention, sensors for receiving the path and speed of the tube 1 and the inductor ring 20 are provided and control modules in a control unit with which the paths and speed and the connection and disconnection of the inductor are brought into the inventively provided relationships.

In the FIGS. 2a to 2d Different stages are shown during the execution of the procedure. FIG. 3 shows the to the representations in the FIGS. 2a to 2d associated times or phases t1 to t6 in a diagram in which the upper graph indicates the speed of the feed device or the longitudinal feed v _{R of} the tube 1 over the path and the lower graph indicates the travel speed vI of the inductor over the path. Positive speed values correspond to a movement in the feed direction; negative values indicate an opposite movement.

To the in Fig. 2a shown starting time, the front end of the tube is pushed into the inductor ring 20, which is located at its axial starting position. Unlike induction bending of the prior art, this is front pipe end, which also later forms the front tangent 3 on the deformed pipe bend, not yet fixed in the bending lock 31.

The induction device 20 and the cooling device are switched on and the axial feed of the tube 1 takes place in a first phase (see Fig. 3 ) with a constant pipe feed speed v _R. This is typically 3 mm - 200 mm per minute. As a result, the tangent 3 on the tube 1 is just as heat treated as in the subsequent forming, but without actually forming takes place. This phase is referred to as t1 in the time-velocity diagram in FIG. As can also be seen therefrom, there is no travel speed vI of the inductor 20; this is stationary.

In order to start the bending process, the bending lock 31 on the bending arm 30 must grip and clamp the tube 1, so that the forces that lead to the bending can be introduced. However, the closing of the flexure 31 and the application of the clamping forces takes a certain amount of time. During the approach but a relative movement between the flexure 31 and tube 1 must be avoided. The bending arm 30 with its bending buckle 31 but on the other hand can not be moved parallel to the feed of the tube 1, because the design effort for such a longitudinal displacement of the bearing of the bending arm 30 would be much too high and because then also the distance of the flexure 31 of the Heating zone on the inductor ring 20 would change.

Therefore, according to the invention in a short phase t2 (see. Fig. 3 ) provided to cancel the relative movement between the pipe 1 and bending lock 31, that the pipe feed is stopped, ie the pipe feed speed v _R = 0, and at the same time maintain the feed of the tube 1 relative to the inductor 20 that this with a travel speed v _I opposite to the feed direction and with the same amount of speed v _R as the pipe feed is moved. Insofar as a gradual, linear braking of the mechanical pipe feed is necessary, the retrograde motion of the inductor 20 already begins at the same time, so that the relative velocity is always constant, which is the same distance between the two graphs for v _R and v _I in FIG FIG. 3 is recognizable.

With the stoppage of the tube 1, the bending lock 31 can be closed, as FIG. 2b shows. Meanwhile, the inductor 20 performs its opposite movement Continuing at constant travel speed vI. Once the bending buckle 31 has clamped the tube 1, the inductor speed v _I is returned to zero in the phase t3 and at the same time the tube feed speed v _{R of} the tube 1 is increased linearly. The speed difference Δv = v _R - v _I is always the same, so that the flow rate of each differential length section on the tube 1 through the inductor 20 is the same and thus always the same energy input from the inductor into the tube jacket. The inductor 20 moves during the phase t3 back to its original position, which corresponds to the working position for the bending operation.

If a pipe bend is now to be produced, the initial point of the bend, which is present at the end of the phase t3, can lie arbitrarily on the longitudinal axis 2 of the pipe 1. On the other hand, at t1, t2 and t3, the operations described above must be started with a precisely calculated fore-run so that a given axial pipe position for the beginning of the bend is reached when the bend is started.

During phase t4, the induction bending process known per se is used to produce a pipe bend 4 with constant pipe feed speed V _R and stationary inductor 20, as in FIG Figure 2c shown.

In order to subject after completion of the pipe bend 4, a rear tangent 5 on the tube 1 of the same heat treatment as the other lengths on the pipe 1, the movements of the tube 1 and inductor 20 are opposite to the starting process described above.

Shortly before reaching the intended arc length, the tube feed is gradually decelerated at the speed v _R in phase t5 and at the same time starts the opposite movement of the inductor 20, with such a travel speed v _I that the relative movement between tube 1 and inductor 20 remains constant. As a result, the residence time of each longitudinal section of the tube 1 in the traveling heat-affected zone also remains constant. At standstill of the tube 1, the bending lock 31 can be opened. Thus, the tube 1 is now completely unhindered by the bending arm 30th

In order to treat only a short end-side tangent 5 on the tube 1, the inductor 20 can easily in phase t6 at a constant speed v _I to his Machine bed 10 facing end position are moved, see Figure 2d , There, the inductor 20 is then stopped and turned off the induction device. The non-heat-treated residual piece on the tube 1 is characterized and separated directly, but at the latest after the heat treatment of the pipe bend 3 thus produced with its end-side tangent sections 3, 4th

In order to obtain a longer tangent 5, in particular a tangent 5, which is followed immediately by another pipe bend, the method can be continued as shown in the further flow diagram FIG. 4 seen. For this purpose, in the phase t7, in the same way as in phase t3, the longitudinal feed of the tube 1 are gradually absorbed and the inductor 20 is returned to its initial position. Now, in phase t8, at a constant pipe advance speed v _R, the heat treatment of the tangent 5 can be continued as long as necessary to obtain a sufficiently long, heat-treated tangent 5. The flexure 31 is uninvolved in this phase. The phase t8 thus corresponds to the phase t1.

Claims (5)

1. Method for induction bend forming a pressure-tight pipe (1) having a large wall thickness and a large diameter, in particular on a power-station and pipeline pipe;
   said method comprising at least the following steps:

   - mounting the unprocessed pipe (1) on a machine bed (10);

   - advancing the pipe (1) through an annular inductor (20) of an electrical induction unit at a pipe advancement speed v_R;

   - clamping the front pipe portion (3) in a bending lock (31), which is mounted on a bending arm (30), which is pivotable about a vertical rotation axis (32) that is disposed laterally of the pipe (1);

   - energizing the induction unit with a current, in order for a pipe portion that lies within the inductor (20) to be heated;

   - deflecting the bending arm (30) by longitudinally advancing the pipe (1) up to the completion of a pipe elbow (4);

   characterized in that

   - the pipe (1) by way of the rear end thereof is chucked in a holding device (11) which is mounted so as to be displaceable in the direction of a pipe longitudinal axis (2);

   - an initial tangent (3) of the pipe (1) in an initial phase t1 is heat treated in that the initial tangent (3) is pushed through the inductor (20) without engagement of the bending lock (31);

   - the pipe advancement is stopped at a point in time t2 at the end of the initial tangent (3), and the inductor (20) is moved along the pipe (1) counter to the advancement direction, while the bending lock (31) on the pipe (1) is closed;

   - in order for bending of the pipe (1) to be initiated, the displacement speed a v_I of the inductor (20) in a phase t3 is reduced to zero, and the latter is moved into the bending position thereof, and that the advancement of the pipe (1) is simultaneously started until a process pipe advancement speed v_R is attained;

   - a pipe elbow (4) is produced at a constant pipe advancement speed v_R of the pipe (1) in a phase t4;

   - the pipe advancement speed v_R is reduced in a phase t5, and the inductor (20) is accelerated counter to the advancement direction, wherein the bending lock (31) is opened;

   - an end tangent (5) is heated in a phase t6 by further advancing the inductor in the opposite direction.
2. Method according to Claim 1, characterized in that the inductor (20) is moved into a starting position which when viewed in the advancement direction lies ahead of a bending position.
3. Method according to Claim 2, characterized in that the inductor (20) prior to the start of phase t1 is displaced from a position which when viewed in the advancement direction is a rearward position to the initial position of said inductor (20).
4. Method according to Claim 2, characterized in that the inductor (20) during phase t1 is displaced from a position which when viewed in the advancement direction is a rearward position to the initial position of said inductor (20), wherein the pipe advancement speed v_R is increased by the displacement speed v_I of the inductor (20).
5. Method according to one of Claims 1 to 4, characterized in that the relative speed as the differential between the pipe advancement speed v_R and the displacement speed v_I of the inductor (20) is constant in phases t1 to t6.

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