EP3174647A1

EP3174647A1 - Method for producing hot-rolled seamless pipes having thickened ends

Info

Publication number: EP3174647A1
Application number: EP15742044.9A
Authority: EP
Inventors: Rolf Kümmerling; Henrike BRÖKER; Thorsten ANKE
Original assignee: Vallourec Deutschland GmbH
Current assignee: Vallourec Deutschland GmbH
Priority date: 2014-08-01
Filing date: 2015-07-28
Publication date: 2017-06-07
Anticipated expiration: 2035-07-28
Also published as: DE102014110980B4; US10695809B2; DE102014110980A1; EP3174647B1; JP6623211B2; JP2017522190A; WO2016016224A1; US20170216896A1

Abstract

The invention relates to a method for producing hot-rolled seamless pipes having at least one thickened wall portion that can be arranged at arbitrary positions across the length of the pipe, wherein by means of a multi-stand rod rolling mill having at least three roll stands and at least two rollers per stand, the rollers roll a hollow block pipe on a rolling rod as an internal tool to a required nominal wall thickness, and at pre-determined positions across the length of the pipe produce a required thickened wall portion on the outside of the pipe as compared to the nominal thickened wall portion by driving the rollers in the roll stands. In order to provide a method for producing hot-rolled seamless pipes by means of a rod rolling mill, with which at least one thickened wall portion at the pipe end or at a defined position on the pipe, of optimal roundness without the need for a subsequent compression process, can be produced, according to the invention the thickened wall is produced and roll-finished at the predetermined positions with only the two roll stands that are successive as viewed in the direction of rolling, wherein deviations of the finished contour of the thickened portion from an ideal circular cross section resulting from driving the rollers through the roller contours become minimal. The roll stands located in front thereof as viewed from the direction of rolling are likewise driven on for a required wall thickness gradation of the roll stands, and all subsequent roll stands are at least driven on such that a contact of the rollers of said roll stands with the previously produced thickened portion, and thus a subsequent reduction of the produced thickened wall portion is avoided. Fig. 2:

Description

Method for producing hot-rolled seamless tubes with thickened ends

description

The invention relates to a method for the production of hot-rolled seamless tubes with thickened ends according to the preamble of claim 1.

After the invention of the brothers Mannesmann from a heated block to produce a thick-walled seamless hollow block pipe, there have been various proposals to stretch this hollow block pipe in the same heat in another hot work stage. Keywords are, for example, the well-known Kontiwalz-, Stoßbank-, Stoppfenwalz- and Pilgerschrittverfahren. All the above methods have different dimensions and dimensions

Materials their advantages, whereby there are also overlaps. For the medium dimension range from 5 "to 18" the continuous and plug rolling process is used, for the size range up to 26 "the pilgrim step method is used.The three steps punching - stretching - reducing rolls with a characteristic feature for the production of seamless pipes from a heated block by hot rolling In the case of pipes that are connected by a welded connection to form a continuous strand, it is important to be able to weld them together as quickly as possible and without internal misalignment of the pipes mechanical internal machining of the pipe to a tightly tolerated inside diameter, so that it does not fall below the prescribed minimum wall thickness, it is helpful if these pipes are thickened at the ends before machining on the inside.

Another example is oil field pipes, in which the individual pipes are connected by a screw to a continuous strand. The pipes are provided with an integral thread and thus without additional sleeve with each other screwed. The threads introduced into the pipe weaken the pipe so that the bolting points can take up less load than the pipe body. Ends thickened on the outer and inner circumference allow this defect to be compensated in whole or in part.

It is known that such pipes are therefore often thickened in a separate process at their ends by hot dipping.

Such a method is known, for example, from Applicant's EP 2 170 540 B1 for the manufacture of hot-finished seamless tubes, which produces tubes with optimized fatigue properties in the welded state and automates them on a laying vessel or on land to conduits

be welded. In this known method, a larger wall thickness is generated in a region in a region in a first step than at the other in a first step

Pipe body. The wall thickening of the respective pipe end region is generated by a hot dipping of the pipe end, wherein the transitions to the pipe body generated during upsetting on the outer and inner circumference are arranged offset relative to the tube longitudinal axis.

In a second step, the required pipe cross-section is produced in this area by mechanical processing and provided the transition from machined to unprocessed area of the pipe paragraph-free with such a large radius or radius combinations that a smooth and notch-free transition results and the finished contour in originally thickened End portion of the tube has an outer diameter corresponding to the original diameter of the tube.

Similar methods in which thickening of the pipe ends are generated inwardly and outwardly by hot dipping and machining are

For example, also known from the published patent application DE 10 2004 059 091 A1 and the patent EP 0 756 682 B1.

Other ways of producing thickening by means of rolling technology are known for hot pilgering. On the one hand can by rolling up the rollers of the nip enlarged and thus a thicker wall pilgrimage. Pilger rollers are calibrated so that the circular arc cut in the smoothing part has its center on the rolling axis and the radius of the circular arc corresponds to the warm diameter of the pipe to be pilgered. The circular arc covers about a circumference of 150 ° per roller. When rolling up the rollers, however, creates a high oval (see the explanation below to Figure 1), resulting in a pinching of the rolling stock and a thinned in the flank area wall piled in comparison to the wall in the roll base. For this reason, only thickenings of a few millimeters can be achieved with this method.

In addition, hot pilots are not economically viable for the main dimension range of oilfield and conduit because of the low volume of about 10 tubes / run of the mill. In the patent application DE 31 29 903 Alwird for the production of

Wall thickening by means of cold pilgrims proposed to provide the two pilgrim rolls with two or even three calibers, each for the pilgrimage of the

be provided with different diameters. Cold pilgering represents an additional processing step, which causes significantly more costs than, for example, a separate hot swaging of the pipe ends and therefore also does not represent a suitable alternative for producing thickened pipe ends. In addition, the pipe is thickened only to the outside, and thus also for the welding

Connection of pipes unsuitable. For economic reasons, oil field and pipes are therefore

mainly on high performance plants, i. on bar rolling mills, rolled.

Rod rolling mills have the task to strip a hot hollow block previously produced by means of oblique rolling on a rolling rod to a mother tube. This mother tube is then reduced in a Maß- or stretch-reducing mill to the desired final size.

Modern bar rolling mills have in the draw unit, the actual

Bar mill, via hydraulic units, which control the positions of the rollers via servo valves in order to be able to perform position changes very quickly. This is already being used today, for example with slightly reduced pipe ends Thickness produced by the process-related reduced longitudinal train when filling and emptying the rolling stands of the downstream Reduzierbzw. Stretch reducing mill are upset again and so at least partially for the Gutrohr again available and thus minimize the head and foot scrap.

So far, however, it has not yet succeeded in relation to the required

Nominal wall thickness of the pipe targeted to produce wall thickening over a certain length at the end of the pipe by means of a bar mill, as existing during pilgrim problems when driving the rollers are also present in bar rolling mills. In addition, it is desirable to produce wall thickening at predetermined positions on the pipe, for example, at double lengths on half the pipe length by rolling, so that even with double lengths at the ends of both pipes thickenings are available.

Furthermore, European Patent EP 1 779 939 B1 already discloses a rolling control method of a multi-stand rod rolling mill for pipes. In the usual way, the bar rolling mill knows a finishing stand. In order to counteract known effects which result in rolled tubes with end regions of lesser wall thickness compared to the central regions of the tube, the rolling control process converts the rolls of the finishing stand and the rolling stand upstream in the rolling direction with the same rolling reduction direction as the finish rolling stand ascended a predetermined amount.

Furthermore, from the German patent DE 1 1 2013 004 557 T5 another

Control method for a pipe rod rolling mill is known in which the length of the rolling stock is measured and / or calculated and adjusted in the range of a predetermined distance to the end of the rolling stock, the setting of the rolling stands in such a way that the thickness of the pipe along the rolling axis so constant as possible and as equal as possible to a desired thickness.

The object of the invention is therefore to provide a process for the preparation of

Specify hot-rolled seamless tubes by means of a bar mill, with the wall thickening at the pipe end or at a defined position on the pipe with optimized roundness without downstream of a separate compression process can be produced.

In a further object, the method should be designed so flexible that the wall thickening of the tube can be made both on the inside and on the outside of the tube variable by means of the necessary for the production of the finished tube forming units.

This object is achieved by a method having the features of claim 1. Advantageous developments are the subject of dependent claims.

According to the teachings of the invention, a method for producing hot-rolled seamless tubes is provided with arbitrary positions over the pipe length wall thickening, in which by means of a multi-stand rod rolling mill with at least three rolling stands and at least two rollers per stand, the rollers on a hollow block pipe one

Rolling rod as an internal tool to a required nominal wall thickness and produce at predetermined positions over the pipe length by driving the rollers in the rolling stands on the outside of the pipe a required wall thickening compared to the nominal wall thickness, which is characterized in that the thickened wall only with the two stands on the predetermined positions generated and finish rolled, in which the resulting when driving up the rollers by the roll contours deviations of the finished contour of the thickening of an ideal circular cross-section are minimal, where seen in the rolling direction before rolling stands for a required Wanddickenstufung the

Rolling mills are also raised and all subsequent rolling mills are at least as far ascended that a contact of the rolls of this

Rolling stands with the previously generated thickening and thus a subsequent reduction of the wall thickening generated is avoided with certainty.

For the production of wall thickening are always offset by the arrangement of the rollers over the circumference two consecutive rolling stands required because only so the entire circumference of the tube comes into contact with the parts of the roll calibration, which should form the outer end geometry of the tube. The big advantage of the invention is that for the production of

Wall thickening on the one hand a powerful rod rolling aggregate after the Kontiwalzverfahren for oil field and pipes is used, on the other hand but on a subsequent hot swaging process for generating the

Wall thickening can be dispensed with at the pipe end. In addition, wall thickenings can be produced with this method by targeted movement of the rolls in the stands at arbitrary positions over the pipe length, so that, for example, when rolling double lengths, ie twice the length of the required

Finished pipe length, wall thickening in the center of the pipe and at the pipe ends can be generated. After dividing the tube in the central wall thickening then both tubes at the ends of the required wall thickening. In the same way, the wall thickenings at the pipe ends can also be produced in rolling of multi-length pipes. The determination of the two scaffolds, which are to roll the wall thickening, can be done in a first embodiment of the invention by simple experimental rolling, in which first a tube without thickening is rolled with the selected rolling rod. In subsequent pilot rolling, tubes with wall thickenings are then rolled with the same rod and selected for the rolling parameters selected for this purpose (selected rolling stands for rolling the thickening,

Roller adjustment and speed, time sequences for all scaffolds) determines the deviations of the finished contour of the generated wall thickening from the ideal circular cross-section. The two rolling mills, which, taking account of the later use and the pending forming in the final production produce the lowest geometric deviations, are then selected below for rolling the thickening.

In a preferred embodiment of the invention, the test rolls are formed by a computational determination and evaluation of the producible

Replaced cross-sectional geometries on the thickening of each scaffold, so that the optimal optimal circular cross section rolling scaffolds predestined in a simple and cost-effective manner and so costs for the experimental rolling can be saved. For this purpose, a closer described in the following examples Assessment number BWV, i introduced for the mathematical determination of the two stands for rolling the rolling thickening, wherein the rolling stand with the

absolute least geometric deviation from an ideal one

Circular cross-section, which was determined on the basis of a for each scaffold i

Evaluation parameter BWV, i is determined, which is selected as the framework for finish rolling the wall thickening and is selected as the second frame, the roll stand arranged in front of it in the rolling direction.

In a further advantageous embodiment of the invention, the rod diameter is selected for rolling the nominal tube wall thickness at the outlet of the rod rolling mill, that resulting from the roll contours deviations from an ideal circular cross section with the nominal tube wall thickness of the last two rolling stands in combination with the rating index BWV, i for the rolling of the thickening becomes minimal and the determination of the bar diameter DST is determined by a determined rating index BWR for rolling the bar

Pipe nominal wall thickness occurs. In this case, the smaller the rating number BWR, the smaller are the geometrical deviations of the nominal tube wall thickness from the ideal circular ring. A BWR value of zero stands for the ideal case.

The core idea of the proposed hitherto unusual method for producing wall thickening in bar rolling mills is that for each stand of the rolling mill resulting from roll geometry and inner tool

Different geometric contours of the pipe cross-section produced in the caliber base and the caliber edges are specifically evaluated. The targeted use of only the two stands for finish rolling the required wall thickening, which give the least geometric deviations from a circle, can now roll wall thickening, which were previously not feasible on bar rolling mills.

As a result, previously not producible wall thickening at the pipe end or at predetermined positions on the pipe produced and so minimizes the known problems when driving the rollers and a maximum of roundness at the thickened points on the pipe can be realized.

Depending on the requirements of the roundness of the tube in the range of nominal wall thickness and / or thickening, this can be advantageous with reference to the invention Evaluation parameters BWV, i and BWR are optimized accordingly during rolling.

The fundamental problem when raising or lowering the stands when rolling pipes by means of a bar rolling mill is shown again below.

In contrast to rolling thinned ends in which the nip is reduced, the result, as already described above, when opening the roll gap, the problem that the further you look in the incised roll profile from the center, the

Roll ground, moved towards the flank, the radial distance from the roll to the

Roll axis increases less than the Auffahrmaß, so that a high oval is formed. As previously described, this problem occurs not only in pilgrim rolling but also in continuous rolling with bar rolling mills. Due to the calibration of the rolls fall only in the roll base, the direction of Auffahrmaßes, which is perpendicular to the roll axis, and the radial direction, which is relevant to the wall thickness together.

1 a, 1 b and 1 c show by way of example for a roll 3 of a three-roll bar rolling mill the geometric situations for the zero position (see FIG. 1 a) and for the closing and driving of the rolls 3 (see FIGS. 1 a and 1 b) ), wherein simplified, the roller contour of the roller 3 is shown as a circular arc. In the figure 1 a are in the neutral position or in the neutral position, the rolling rod 2 in cross section, the rolling axis 1 and a part of a roller 3 shown. The rolling axis 1 and the axis of the rolling rod are superimposed. The nip appears as

Circular ring. The gap between the roller 3 and roll bar 2 is equal to the roll base SGrund and the roll edge SFIanke.

When driving up the rollers (see FIG. 1 b), a larger gap results for the roller base than for the edge, ie SGround> SFIanke. The rolling axis 1 is shifted with respect to the axis of the rolling rod upwards.

If the roller 3 is fed in (see FIG. 1 c), the conditions are reversed and for the base of the roller a smaller gap results than for the roller flank, ie SGround <SFIanke. The rolling axis 1 is opposite to the axis of the rolling rod after moved down.

A smaller nip in the flank compared to the roll base is critical, since the peripheral speed of the roll increases from the bottom to the flank. In

Combined with the edge of the gap becoming smaller roll gap, this can lead to thin drawing of the material on the flank, which can lead to holes in extreme cases.

In order for these deviations to remain manageable, the roll calibration is typically composed of two circular arcs. FIG. 2 shows that the

Caliber Grundradius R1 has a center M1, which is around a

Center offset e is attached to the rolling axis 1 and the

Caliber base radius R1 at the angle alpha merges tangentially into the edge radius R2 with the center M2. The center offset e corresponds to the vertical distance between the rolling axis 1 and the center M1. Since the rollers 3 are arranged rotated in the successive stands each by the angle beta to each other, resulting in the same calibration of two successively arranged scaffolding a contour formed for an angle alpha = beta / 2 only from the caliber parts with the caliber base radius R1 becomes. For example, results for a scaffold with three rolls an angle alpha of 30 °.

For a center shift of e = 0, this results in an exact circle. In practice, however, the angle alpha is chosen slightly larger than half the angle beta. However, this supplement delta alpha should not be greater than 5% of the angle beta.

As a zero position of the rollers, the position is referred to, in which the

Center shift e corresponds to the setpoint specified by the caliber. The minimum size of the factor C with R2 = C x R1 for the calculation of the

Flank radius R2 from the basic radius R1 also results from geometrical considerations. Even at the maximum intended driving the roller should take place on the flank no decrease in the incoming wall thickness there but even an air gap may be present. For this reason, C-values greater than 2 are common in the three-roller bar mill, for example. FIG. 3 shows, for various caliber diameters, the roll gap change, which is set by way of example for a three-roll bar rolling mill at an alpha = 30 ° circumferential position for different caliber diameters and e dimensions.

In order to overcome the problem explained when driving up the rollers to produce wall thickenings, according to the invention, the geometries of the wall thickenings produced with the individual scaffolds and their deviation from an ideal circular cross section are evaluated. Starting from the wall thicknesses in the

Caliber base is determined at the outlet of all scaffolding, in which frameworks the required wall thickening during rolling of the pipe is already undercut.

The two frameworks that give the smallest geometric deviations from a circle, are now used for rolling the wall thickening. The

Employment of the rollers of the remaining frameworks and the rolls of the framework, which falls below the required wall thickening first, are then selectively targeted. This approach must meet the following two criteria according to the invention. Criterion 1: The two chosen frameworks finish in the caliber base the desired thickened wall thickness. You will be driven accordingly. All remaining stands in front of it are also raised, so that a suitable wall thickness grading per framework for the rolling of the thickening results. Suitable in this context means that the wall thickness decreases in the frameworks, which are required for rolling the thickened wall, behave relatively similar to the rolling of the pipe nominal wall thickness. All subsequent stands are raised so far that contact of the rolls with the pipe at the point of thickening and thus a subsequent reduction of the wall thickening generated are avoided with certainty.

Criterion 2: The scaffolds responsible for the finish rolling of the wall thickening are determined using the evaluation number BWV, i. The smaller the evaluation number BWV, i the better the desired finished contour of the thickened pipe part corresponds to an exact circular ring. The following examples illustrate the selection of the stands for finish rolling the desired wall thickening.

example 1

For stretching and rolling the wall thickening, a bar mill with 5 stands and 3 rolls / stand is used.

The following applies:

i = serial number of the scaffolding, starting with 1 and ascending in the rolling direction i-max = serial number of the last scaffold

Number of scaffolds = 5

s-R = tube wall thickness at the outlet of the bar rolling mill

s-V = thickened wall Furthermore, for every framework i:

s, i = wall thickness in the caliber base of framework i

e, i = eccentric displacement of the center of the caliber base radius R1 in the zero position of the rolls in the framework i. The zeroing of the rolls is the position which the caliber has set for defining the caliber contours, i. The specified caliber contour and actual contour are identical when the rollers are reset in the framework.

DSTideal = ideal roll bar diameter with the roll position in

Zeroing the tube wall s-R is rolled

DSTist = used roll bar diameter for rolling s-R

A-ges. = same Anstellmaß for all roller positions, so that with the actual rod diameter, the pipe wall thickness s-R can be rolled,

+ = Rolls have moved up to the zero position,

- = rollers are closed against the zero position.

The approach or Zufahrmaße are defined as radial distances.

A-ges. = ^_1/2 x (DSTist - DSTideal) eR, i = actual center point shift of the caliber base radius R1, i in comparison to the rolling axis (+ = over rolling center, - = under roller center during rolling of the pipe wall sR)

A, i = theoretical drive-up distance of framework i in order to roll the thickened wall in the caliber base

A, i = s-V -s, i ev, i = center point displacement of the caliber base radius R1, i in comparison to the rolling axis (+ = over roller center, - = under roller center during rolling of the thickened wall s-V)

ev, i = eR, i + A, i

BWR = rating code for rolling the nominal pipe wall thickness in the form of an absolute amount

BWR = IeR, i-max-1 + eR, i-max I for i-max = 5

BWV, i = evaluation index for rolling the thickened wall s-V in the form of an absolute amount

BWV, i = I ev, i-1 + ev, i I for i = 2 to i-max (5)

MIN BWV, i = lowest value, from the evaluation codes BWV, i determined for all from the second framework with the respective serial numbers i

Variant Basis Example 1 Example 2

s-R 10 10 10

s-V 1 1 1 1

DST is DSTideal DSTideal DSTideal - 2

A-tot 0 0 -1

Scaffold i s, i e, i eR, i A, i BWR ev, i BWV, i eR, i A, i BWR ev, i BWV, i

1 18.5 -3.0 -3.0 -7.5 -10.5 -4.0 -7.5 -1 1, 5

2 14.0 -1, 0 -1, 0 -3.0 -4.0 14.5 -2.0 -3.0 -5.0 16.5

3 1 1, 0 0.0 0.0 0.0 0.0 4.0 -1, 0 0.0 -1, 0 6.0

4 10.0 0.0 0.0 1, 0 1, 0 1, 0 -1, 0 1, 0 0.0 1, 0

5 10.0 0.0 0.0 1, 0 0.0 1, 0 2.0 -1, 0 1, 0 2.0 0.0 0.0

All dimensions in mm Table 1: Basic configuration of a 5-stand rod mill and Examples 1 and 2 for rolling thickening

Variant Basis Example 3 Example 4

s-R 10 10 10

s-V 13 18

DST is DSTideal DSTideal - 2 DSTideal - 3

A-tot 0 -1 -1, 5

Scaffold i s, i e, i eR, i A, i BWR ev, i BWV, i eR, i A, i BWR ev, i BWV, i

1 18.5 -3.0 -4.0 -5.5 -9.5 -4.5 -0.5 -5.0

2 14.0 -1, 0 -2.0 -1, 0 -3.0 12.5 -2.5 4.0 1, 5 3.5

3 1 1, 0 0.0 -1, 0 2.0 1, 0 2.0 -1, 5 7.0 5.5 7.0

4 10.0 0.0 -1, 0 3.0 2.0 3.0 -1, 5 8.0 6.5 12.0

5 10.0 0.0 -1, 0 3.0 2.0 2.0 4.0 -1, 5 8.0 3.0 6.5 13.0 all dimensions in mm

Table 2: Basic configuration of a 5-stand rod mill and Examples 3 and 4 for rolling thickening

The starting position indicated in Tables 1 and 2 as the base shows the

Roller positions in zero position, the rolling rod used corresponds to the ideal rod for rolling a nominal pipe wall thickness of 10 mm at the outlet of the

Rod rolling mill.

In Example 1 of Table 1, the thickened wall 1 to be produced is 1 mm. So it should be produced a wall thickening of 1 mm. Since the roll bar used corresponds to the ideal roll bar, the roll total (A-ges) is zero and the center offsets eR, i are identical to the roll zero values. For rolling a wall thickness of 1 1 mm, the rolls must be raised by 1 mm compared to the nominal pipe wall thickness of 10 mm.

The smallest absolute value for the weighting index MIN BWV, i, stands 4 with a value of 1, 0, that is, when rolling the thickening with scaffold 4 occur the slightest deviations from an ideal annulus. Since stand 4 has the smallest value MIN BWV, i, the thickening with that in the rolling direction before standing frame 3 and the already determined framework 4 finish-rolled, since the framework 4 in terms of a finished scaffold, a tube with the smallest geometric deviations of an ideal circular ring results. Thus, only the first 4 scaffolds for generating the wall thickening are needed, with the stands 3 and 4 finish said wall thickness of 1 1 mm. Frame 5 is then only needed for rolling the tube nominal wall thickness of 10 mm.

Example 2

In Example 2 of Table 1 is rolled with a nominal tube wall thickness of 10 mm and a required wall thickening by 1 mm with a diameter smaller by 2 mm rod, so DSTideal minus 2 mm. Here, the lowest valuation MIN BWV, i is 0.0 for scaffold 5. Thus, in this variant, all 5 scaffolds for rolling the thickening is needed, the last two scaffolds, so scaffold 4 and 5, the thickening of 1 1 mm wall thickness finish rolling.

Examples 3 and 4

Examples 3 and 4 of Table 2 show the situation for a thickened tube wall of 13 or 18 mm with a nominal tube wall thickness of 10 mm. Here, with a wall thickening to 13 mm (Example 3), only the first 3 stands are required, since for framework 3 the lowest BWV value MIN BWV, i of 2.0 results. In Example 4 for a thickening of the pipe wall to 18 mm, scaffold 2 with 3.5 has the lowest BWV value, so that only the first two stands finish the wall thickening.

Furthermore, it can be seen from Table 2 that positive ev, i values can not be avoided in all cases. This theoretically also results in areas in which the desired thickening can not be achieved. FIG. 4 shows, in the case of a three-roll bar rolling mill and thus matching the examples given, which wall thickness deviations are relative (FIG. 4a) and absolute (FIG. 4b) for different center displacements ev, i (in the range from -2.0 mm to + 5.0 mm) of the caliber base radii.

Since the contour of the rollers determines the outer contour of the tube and the wall thickness is formed over the rod diameter, the absolute Wall thickness deviations when opening or closing the rollers are always the same. This results in a wall dilution of about 0.13 mm when driving up by 1 mm and at 5 mm by about 0.69 mm thinner wall. When approaching by 1 mm, the maximum deviation is + 0.14 mm. The relative values become smaller and smaller with increasing wall thickness. The representation with curves composed of straight sections was chosen only for the sake of simplicity.

Ultimately, the type of processing and the method used to calibrate the pipe ends decide on the still tolerable

Wall thickness variations.

Theoretically, thickened walls can be produced with the described method which correspond at most to the hollow block wall thickness. In the examples according to Table 1, the hollow block wall thickness is 25 mm.

As described above, the rod diameter DSTist is set for optimum roundness for rolling the pipe nominal wall thickness over a determined evaluation index BWR. In Examples 1 and 2 of Table 1 are otherwise the same geometric

Specifications for the pipe to be rolled, the evaluation parameters BWR in Example 1 with 0.0 and in Example 2 with 2.0 on the formula BWR = I eR, imax-1 + eR max I for i-max = 5 calculated. As described, the smaller the BWR value, the smaller the geometrical deviations of the nominal tube wall thickness from the ideal annulus. In the present case, one would therefore choose the rod diameter DSTideal according to Example 1.

However, there is the requirement for the wall thickness tolerances of the tube, rolling technical aspects and the requirements of the

Weigh the wall thickness uniformity of the thickenings against each other in order to determine the most suitable bar diameter and thus the BWR value, and applicable for the thickening BWV, i and thus the required for rolling thickening scaffolding. A BWR value of zero is theoretically the best, but because of the

Longitudinal tensile stresses in the sidewall region can represent negative eR, max and eR, imax-1 leading to a non-zero BWR while improving BWV, i values are the better solution. In practice, Example 2 with a bar diameter DSTist = DSTideal minus 2mm will therefore provide the better rolling results for thin wall thicknesses where the longitudinal courses can become critical.

However, the rolling rod still has to be removed from the so-called continuous pipe, as the pipe is called in the rod rolling mill after rolling. Usually referred to as a Kontirohr the tube behind bar rolling mills with two rolls / frame. Here, however, the term generally refers to a tube rolled in bar rolling mills, regardless of how many rolls / stand are used. The removal of the rolling rod from the Kontirohr by pulling in the

Creek over a chain after rolling done. However, the common method is a so-called Ausziehwalzwerk, which draws the Kontirohr in the rolling line from the bar and can be used advantageously to the at the

Outside of the wall, the thickening towards the inside of the pipe should be shifted.

For this purpose, three three-roll stands are generally used, which minimally reduce the diameter of the continuous pipe by about 2.5%. The removal of the pipe by means of Ausziehwalzwerks already begins when the pipe head the

Ausziehwalzwerk reached. At this time, in the vast majority of cases, rolling in the bar mill is not over. Rolling in the bar mill ends at the latest when the bar head comes to a stop shortly before the extracting mill. The extractor then pulls off the remaining part of the tube, which is still on the rod, from this. The maximum values of diameter reduction are about 4.5% in total over all three frameworks. For example, if a 1 1 mm Kontirohrwanddicke rolled and the thickening should be 10 mm, this means an increase in

Outer diameter reduction by 20 mm, which already accounts for 10% with a caliber of 200 mm. Since the employment of the rollers of the Ausziehgerüste are usually not changeable, for larger wall thickening is an adaptation of the Calibration required. This has to be done so that the minimum decrease for the fillet part takes place only in a maximum of two stands, preferably only in the last. Thus, the two front each make the additional necessary diameter decrease, however, should not exceed 4.5% per scaffold.

In a further variant, no pull-out is used to pull the rod but the extraction of the rod is done by a Maß- or

Stretch. Here is the extraction of the rod easier than the Ausziehwalzwerk, since only in front of the scaffolding, which are needed for reducing the Filetteile, still depending on the thickening of the pipe ends one or more

Additional scaffolding must be set. As Filetteile the pipe sections are referred to, which have the nominal wall thickness.

The decrease in diameter in the extraction or stretch-reducing mill causes the thickenings to be pressed inwards and the outside of the pipe has a constant outside diameter. This has the advantage that both the transport of the tubes as well as the necessary heat treatment in most cases can be carried out without additional measures. But it is also possible to distribute the wall thickening to Rohraußen- and -innenseite as desired.

When used in the production line for pipeline and oilfield pipes, the ends are then calibrated via a sizing press or another suitable unit so that a wall thickness profile of the pipe ends results to the specifications. The required forming and the customer specification with regard to permitted deformations in the cold state and residual stresses can lead to the pipe ends having to be preheated and / or reheated. Thereafter, the further steps are performed to ultimately achieve the desired

to produce specification-compliant end product. Depending on the specification, the water pressure test prescribed in most cases takes place before or after calibrating the pipe ends.

To produce thickened ends, the procedure according to the invention is therefore as follows:

1 . Specification of the wall thickness profile at the pipe ends of the finished pipe and the tolerances to be maintained before the mechanical processing such as indoor and or external machining, thread cutting or the like.

2. Specification of the length range with the tube end wall, the fillet part, and the tolerances to be maintained.

3. Conversion of the wall thickness curve on the finished pipe in a wall thickness curve with wall thickness increase outwards for the pipe in the outlet of the bar mill, the Kontirohr, taking into account the extension and the

Wall thickness change by the dimensional or stretch reduction mill and the Ausziehwalzwerk, if available, and the necessary Schopfschnitte. The Kontirohr may optionally contain multiple lengths of the finished tube.

4. Calculation of the specifications for the roll adjustment of the individual scaffolds matching the precalculated geometry of the continuous pipe in all scaffolds taking into account the introduced rating number BWV, i and BWR for determining the stands for finish rolling the desired thickening and the resulting geometry in the raised state as described above , Scaffolding, which is no longer required for rolling the thickening or the transition, are so far ascended that they certainly no longer accomplish wall deformation.

5. Calculation of the cross sections of the continuous pipe over the length with the associated area contents at the outlet of each stand. 6. Specification of the desired exit velocity of the continuous pipe behind the last stand. If the contra-piping runs out at a constant speed, the rolling speeds of the extracting mill need not be controlled.

7. Calculation of roll adjustments over time for all scaffolds matching points 5 and 6.

8. Calculation of the continuous pipe speeds over time at the outlet of each stand to match point 7. 9. Calculation of the rolling speeds over time for all stands. 10. Generate the necessary for the control of the bar mill

Setting specifications and datasets for controlling the roll adjustments and the rolling speeds.

1 1. rolling the heat-finished tube in Maß- or stretch-reducing, in which due to the reduction of Au ßendurchmessers now all wall thickening are inside and performing the necessary crumb and partial cuts.

12. If necessary, temper the pipe with verification of the mechanical technological properties.

13. Specification-compliant non-destructive testing of the pipe.

14. Calibrate the pipe ends, if necessary with heating to avoid strain hardening and residual stress.

15. Perform the water pressure test and further steps to produce the final product that meets the specification.

LIST OF REFERENCE NUMBERS

1 roll axis

2 roller bar 3 roll

Claims

claims

1 . A method for the production of hot-rolled seamless tubes with at least one can be arranged at any position over the tube length wall thickening, wherein by means of a multi-stand rod mill with at least three

Rolling stands and at least two rolls per framework, the rollers roll a hollow block tube on a rolling rod as an internal tool to a required nominal wall thickness and at predetermined positions over the pipe length by driving the rollers in the rolling stands a required wall thickening on the outside of the tube

Generate comparison to the nominal wall thickness, characterized in that the thickened wall is produced and finished only with the two seen in the rolling direction successive rolling stands at the predetermined positions, in which resulting when driving the rollers by the roll contours deviations of the finished contour of the thickening of a ideal circular cross-section to be minimal, with the seen in the rolling direction preceding rolling stands for a required Wanddickenstufung the rolling stands are also driven and all subsequent rolling stands are at least as far ascended that contact the rolls of these rolling stands with the previously generated thickening and thus a subsequent reduction of generated Wall thickening is avoided.

2. The method according to claim 1, characterized in that the two

Rolling mills, which roll the wall thickening, are determined by experimental rolling, initially rolled with the selected roll bar a tube without thickening and rolled in other test rolling with the same roll tubes with wall thickening and for the selected rolling parameters, the deviations of the finished contour of the wall thickening produced by the ideal

Circular cross-section measured and then the two rolling mills, which produce the least deviation of the finished contour to the ideal circular cross-section, are selected.

3. The method according to claim 1, characterized in that the two

Rolling mills, which roll the wall thickening, by a calculated

Assessment number BWV, i are determined, wherein the rolling stand with the smallest amount of geometric deviation from an ideal

Circular cross section and thus the smallest rating number BWV, i first Framework for finish rolling the wall thickening is selected and, secondly, the mill stand arranged in front of it in the rolling direction is selected, wherein the evaluation index BWV, i is defined as follows: BWV, i = I ev, i-1 + ev, i | for i = 2 to i-max

with i = serial number of the scaffold, starting with 1 and ascending in

Rolling direction,

i-max = serial number of the last framework

in which

ev, i = center point shift of the caliber base radius R1, i in comparison to

Rolling axis (+ = over roll center, - = below roll center during rolling of the thickened wall s-V)

With

ev, i = eR, i + A, i,

in which

eR, i = actual center point shift of the caliber base radius R1, i in comparison to the rolling axis (+ = over roller center, - = under roller center) during rolling of the

Pipe nominal wall thickness s-R

and

A, i = theoretical Auffahrmaß of framework i, around the thickened wall s-V in

to roll groove base,

With

A, i = s-V -s, i

in which

s, i = wall thickness in the caliber base of framework i.

4. The method according to claim 3, characterized in that for the rolling of the pipe nominal wall thickness s-R at the outlet of the rod rolling mill, the rod diameter DST is chosen so that the resulting by the roll contours

Deviations from an ideal circular cross-section with the nominal tube wall thickness s-R of the last roll stand become minimal and the determination of the

Bar diameter DST is calculated using a calculated BWR rating for rolling the nominal tube wall thickness, which is defined as an amount as follows: BWR = IeR, i-max-1 + eR, i-max I for i = i-max with i-max = serial number of the last framework

5. The method according to claims 1 to 4, characterized in that after rolling in the bar mill, the roll bar pulled out of the pipe and then the wall thickenings are pressed on the pipe outside by subsequent rolling to the pipe inside, so that a tube with a constant outer diameter over the length is generated.

6. The method according to claim 5, characterized in that the wall thickenings are completely pressed by means of a rod rolling mill downstream rod extracting mill or a stretch-reducing mill to the tube inside.

7. The method according to claim 6, characterized in that the pressed to the inside of the pipe wall thickenings are subsequently pressed by means of a sizing partially back to the pipe outside.

8. The method according to claims 1 to 7, characterized in that the wall thickenings produced extend in the tube longitudinal direction to a length of at least 300mm.