DE102019103502A1 - Method of manufacturing seamless steel pipe, seamless steel pipe, and pipe product - Google Patents

Abstract

Rest: Eisen und unvermeidbare erschmelzungsbedingte Verunreinigungen. Zudem betrifft die Erfindung ein durch ein solches Verfahren hergestelltes nahtloses Stahlrohr (10) und ein Rohrprodukt (1), das aus einem solchen Stahlrohr hergestellt ist.

The present invention relates to a method for producing a seamless steel tube (10). The method is characterized in that a steel is used which, in percent by weight, consists of the following alloying elements: C. 0.06-0.15 Mn 1.5-4.0 Si Max. 0.1 Cr Max. 0.15 Mon 0.1-0.5 B. 0.001-0.005 Ti > 0.015 AI > 0.04 N > 0.001-0.1, where Ti / N> = 3.4 Remainder: iron and unavoidable impurities caused by the melting process. The invention also relates to a seamless steel pipe (10) produced by such a method and to a pipe product (1) produced from such a steel pipe.

Description

The present invention relates to a method for producing a seamless steel pipe, a seamless steel pipe produced by this method, and a pipe product produced from such a seamless steel pipe.

In the automotive industry in particular, the demands on the weight of motor vehicles are increasing. In order to reduce fuel consumption, it is necessary to keep the weight of the components, in particular the structural parts of the motor vehicle, as low as possible. Nevertheless, the costs should be kept low and the motor vehicles must meet the safety requirements. In particular, the structural parts must also be able to withstand dynamic loads. In addition, particularly in the case of components of a motor vehicle, it is necessary to be able to produce complex component geometries in a simple manner.

In other applications, too, such as pipe systems, it is necessary that the components have a high degree of strength. In the case of pipe systems, there is also the requirement that the individual pipe elements can be connected to one another. For this purpose, a connection geometry is usually to be formed at the pipe ends.

The present invention is therefore based on the object of creating a solution by means of which a pipe can be created which, on the one hand, has a high level of strength and, on the other hand, can reliably form complex geometries.

According to a first aspect, the object is achieved by a method for producing a seamless steel tube. The method is characterized in that a steel is used which, in percent by weight, consists of the following alloying elements: C. 0.06-0.15 Mn 1.5-4.0 Si Max. 0.1 Cr Max. 0.15 Mon 0.1-0.5 B. 0.001-0.005 Ti > 0.015 Al > 0.04 N > 0.001-0.1, where Ti / N> = 3.4 Remainder: iron and unavoidable impurities caused by the melting process.

The steel that is used in the method according to the invention is also referred to below as a steel alloy or material. Melting-related impurities are, in particular, impurities that get into the steel during steel production, in particular through materials added during the creation of the melt and treatment of the melt. In addition, impurities caused by the melting process are also impurities which, apart from silicon and chromium, are introduced into the melt by starting materials. Quantities or contents are given in percent by weight (% by weight) and are also referred to simply as percent or% in the following.

According to the invention, carbon (C) is present in the steel in an amount in the range from 0.06 to 0.15% by weight. With a carbon content of 0.06% by weight, sufficient strength can still be guaranteed and the formation of cementite Fe ₃ C in the steel can be kept to a minimum. In addition, sufficient toughness can be ensured. On the other hand, if the carbon content is too high, the carbide formation in the steel is favored, as a result of which the notched impact strength drops. According to the invention, the carbon content is therefore preferably limited to a maximum of 0.15%. According to one embodiment, the carbon content can be in a range from 0.08 to 0.12%.

According to the invention, manganese (Mn) is added in an amount in the range from 1.5 to 4% by weight. A manganese content of at least 1.5% by weight brings about a lowering of the bainite starting temperature. The bainite starting temperature can, for example, be reduced to below 600 ° C., preferably below 500 ° C. become. By lowering the bainite starting temperature, lower bainite can also be formed without isothermally holding it at a specified temperature. Without lowering the bainite start temperature, however, lower bainite can only be formed with complex process management. If the manganese content is too high, the bainite starting temperature is lowered further, but the bainite area is further narrowed. The area in the ZTU (time-temperature conversion diagram) in which bainite is formed is referred to as the bainite area. The bainite area is also known as the bainite nose. Reducing the size of the bainite nose therefore leads to an increased formation of a martensitic structure if the manganese content is too high.

According to one embodiment, manganese is contained in the steel alloy in an amount of at least 1.8% and preferably of at least 3%. According to a preferred embodiment, the manganese content is in a range from 3.0-3.5%.

In the case of the steel alloy used, silicon (Si) is not added as an alloying element but may be present when the steel alloy is melted from scrap. However, the steel alloy preferably has no silicon. If it contains silicon, the content is limited to a maximum of 0.1%. The absence of silicon or the very low content of silicon that may be present has the advantage that the steel pipe produced according to the invention can be galvanized, which is not possible with higher silicon contents.

Chromium (Cr) is also preferably not contained in the steel alloy used, or only in small amounts. Chromium can be present in small amounts, particularly when the steel alloy is melted from scrap. The chromium content is limited to a maximum of 0.1%. This ensures sufficient impact energy and toughness. In particular, it is possible to avoid nitride formation or carbide formation with these low chromium contents.

By adding molybdenum (Mo) in an amount of at least 0.1%, the ferrite area, which is also referred to as the ferrite nose, is shifted to the right in the ZTU diagram, i.e. to longer times. Since a bainitic structure is sought, such a displacement of the ferrite nose is advantageous. Even with 0.25% molybdenum, the ferrite range is shifted so far to longer times that ferrite formation is ruled out by air cooling. According to the invention, higher molybdenum contents are also possible. However, a higher molybdenum content brings with it a further shift in the ferrite range to longer times, which does not bring any further advantages in terms of avoiding the formation of ferrite, but leads to an increase in the cost of manufacturing the steel pipe. In addition, the strength increases with increasing molybdenum content and the notched impact strength decreases, and an undesirable formation of molybdenum carbides can occur.

Boron (B) is present in the alloy in an amount of at least 0.001%. In the alloy used, boron can lead to a further shift in the ferrite area to longer times, in particular because of the molybdenum also present, and ferrite formation can thus be further prevented at a slow cooling rate. A maximum of 0.005% of boron should be present, which in particular makes it possible to avoid the occurrence of boron carbides and too low a notched impact strength. According to one embodiment, the boron content is in a range from 0.0015-0.003%.

Titanium (Ti) is added in an amount greater than 0.015%. In the steel alloy used, titanium serves in particular to bind nitrogen and thereby in particular to prevent boron nitrides. For example, titanium can be present in an amount greater than 0.038%.

In addition, nitrogen is present in the steel alloy used in an amount in the range> 0.001-0.1%. The Ti / N ratio is greater than or equal to 3.4. According to one embodiment, the ratio Ti / N is at least 3.8. The specific setting of the Ti / N ratio in the stressed area ensures that the nitrogen is reliably bound.

The steel alloy also contains aluminum (AI). Aluminum is present in an amount of> 0.04% by weight. Aluminum is particularly preferably present in an amount of> 0.06% by weight. The bainitic transformation kinetics is accelerated by aluminum. If the aluminum content is too low, the bainitic transformation takes place too slowly, so that more martensite is formed, which has an unfavorable effect on the elongation at break and impact work as well as the local formability.

With the steel alloy used, a bainitic structure can thus be set in the steel pipe. Due to the alloying elements in the claimed amounts, the steel alloy shows The seamless steel pipe produced in particular has a high proportion of lower bainite and can therefore have a high hole expansion capacity, which is also referred to as hole expansion capacity, with high strength. Therefore, a pipe product with complex geometry can be manufactured from the steel pipe, which corresponds to the requirements given in the various applications. The tube is a seamless steel tube and can be produced, for example, by hot forming. The hot forming is preferably carried out at a temperature> Ac3 of the steel alloy. For example, hot forming takes place at> 900 ° C. After the hot forming, the steel pipe can be hardened and, if necessary, subjected to further annealing, such as stress-relieving annealing. The steel pipe is a seamless steel pipe. This has the advantage that, in contrast to a welded pipe, in which a flat steel product is rolled and then shaped and welded, the structure of the seamless steel pipe can be set directly after the hot forming can.

The steel can optionally contain at least one of the alloying elements niobium and vanadium. Here, the content of these optional alloy elements preferably fulfills the formula $$\text{Nb}+\text{Ti + V <= 0}\text{, 12 wt}\text{.-\%}$$

According to one embodiment, a steel is used which, in percent by weight, consists of the following alloy elements: C. 0.08-0.12 Mn 3.0-3.5 Si Max. 0.1 Cr Max. 0.13 Mon 0.2-0.3 B. 0.0015 - 0.003 Ti > 0.038 Al > 0.04 N > 0.0015, with Ti / N ranging from 3.8 to 4.5. Remainder: iron and unavoidable impurities caused by the melting process.

According to a preferred embodiment, the seamless tube is produced by hot forming with subsequent cooling in air. The cooling can take place in still or moving air. Due to the composition of the steel alloy that is used for the production of the seamless steel tube and the associated structural transformation, hardening takes place when it is cooled in air. The seamless steel pipe thus represents an air-hardened seamless steel pipe. Due to the composition of the steel alloy, a bainitic structure can be reliably produced and a high strength and a high hole expansion capacity can be achieved even with air hardening, i.e. cooling at low speed.

According to one embodiment, the cooling of the steel pipe in air is carried out in such a way that the temperature range between 800 ° C. and 500 ° C. is passed through at a cooling rate of 0.1 to 8.0 ° C./s. Since the hot forming is preferably carried out at a forming temperature of at least 800 ° C., the cooling is preferably carried out from the forming temperature, that is to say immediately after the forming at this cooling rate. With this cooling rate, the reliable setting of a bainitic structure, in particular a structure that mainly consists of lower bainite, can be ensured.

According to one embodiment, after cooling in air, the steel pipe is subjected to stress relief annealing. The stress relief annealing can take place at a temperature between 350 and 550 ° C., preferably at a temperature between 380 and 440 ° C., and can be carried out for a period of 30 minutes. However, it has been shown that a shorter glow time of, for example, 10 or 8 minutes can also be sufficient. The stress relief annealing can further increase the hole expansion capacity of the material of the seamless steel tube.

According to a further aspect, the present invention relates to a seamless steel tube which is produced by the method according to the invention.

According to one embodiment, the seamless steel tube consists of air-hardened steel with a bainitic structure, which has a tensile strength of Rm> 950 MPa and a hole expansion capacity of more than 80%.

With this high hole expansion capacity, the seamless steel tube can be used in a variety of ways. In particular, a pipe product can be produced from the seamless steel pipe which has widenings at one or both pipe ends.

The hole expansion capacity is a material property that describes the resistance of the material to crack formation and crack propagation when forming in areas close to edges, such as when pulling collars. The hole expansion capacity is determined in accordance with the international standard ISO 16630. In particular, a plate with a maximum thickness of 6mm is used here. The minimum edge length is 90mm. A hole with a diameter of 10mm is punched or wire-cut into this plate and then a cone is inserted. The hole expansion capacity is the change in the hole diameter related to the initial diameter at which the first crack in the plate occurs at the edge of the hole.

The hole expansion capacity of the steel pipe can be 100% +/- 20. In a further embodiment, the hole expansion capacity is 140% +/- 20. The steel preferably has a hole expansion capacity of 100% and more preferably 140%. A hole expansion capacity of 140% +/- 20 or exactly 140% can in particular be achieved by subjecting the air-hardened seamless steel tube to stress-relief annealing.

According to the invention, the seamless steel tube has a bainitic structure. A structure that has a bainite content of more than 80% is referred to as a bainitic structure. The structure particularly preferably has a proportion of lower bainite of more than 70%.

• Unterer Bainit > 70 %
• Oberer Bainit < 30 %
• Martensit < 30 %
• Restaustenit < 5 %.

According to one embodiment, the structure of the steel alloy in the steel pipe has the following structural components:

• Lower bainite> 70%
• Upper bainite <30%
• Martensite <30%
• Retained austenite <5%.

Due to the high proportion of lower bainite, which represents a fine-grain structure, the properties preferred according to the invention, in particular the high hole expansion capacity, can be achieved. The upper bainite, which is a coarser, needle-shaped or granular structure, is only present in smaller quantities.

According to one embodiment, the structure of the steel after the last hot forming step of the steel pipe has an average austenite grain size of <50 μm. As a result, a fine structure can be established after air hardening. The mean bainite packet width of the bainitic structure that is generated by air hardening, that is to say cooling in air, is preferably less than 25 μm.

The pipe preferably has a notched impact strength Av according to the ISO Charpy V notch impact test at -20 ° C. of at least 27 J.

According to a further aspect, the invention relates to a pipe product made from a seamless steel pipe according to the invention.

Advantages and features that are described with respect to the method according to the invention or the seamless steel tube according to the invention also apply - if applicable - to the tube product according to the invention and vice versa.

The seamless steel pipe produced according to the invention has a reduced edge crack sensitivity due to the high hole expansion capacity and pipe products can therefore be produced from the steel pipe which have a large expansion angle at one or both pipe ends.

The pipe product according to the invention can be used advantageously in particular for applications in which a pipe product is subjected to an internal pressure load. In particular, the high-strength pipe product has good fatigue strengths and the cracks normally to be expected at end widenings do not occur in the pipe product according to the invention.

According to one embodiment, the pipe product has a flange, a cutting ring contour in the pipe wall and / or a local flattening at one end. According to one embodiment, a flange, a cutting ring contour in the pipe wall and / or a local flattening can also be provided on the other pipe end. Because of the high hole expansion capacity that the seamless steel pipe has, these geometries can be formed on the pipe product without cracks occurring.

Flaring is a widening of the pipe end of the pipe product. This widening can be used, for example, to connect the pipe product to another pipe product. In addition, a cutting ring contour can be created at the pipe end through the pipe wall itself through the expansion. Here, the widening can represent a thickening of the pipe wall at the pipe end of the pipe product with an enlarged outer diameter. A cutting ring can then be placed from the outside on this thickened area and a thread can be cut into the pipe wall. A pipe connection system can thus also be created with the pipe product according to the invention.

According to one embodiment, the pipe product has an expansion of more than 15%, preferably more than 25%, at at least one pipe end. For example, the pipe end can have an expansion of 40%. The expansion of the pipe end is the difference between the largest outer diameter of the expanded pipe end and the outer diameter of the steel pipe from which the pipe product was made and the outer diameter of the steel pipe, in percent. These large expansions are possible with the steel pipe used according to the invention, since this has a high hole expansion capacity. The expansion of the pipes is measured according to the DIN EN 10305 standard.

According to one embodiment, the pipe product has a coating. The coating can be applied, for example, by cathodic dip painting or by galvanic coating. In particular, the pipe product can have a zinc layer. The galvanizing of the pipe product is possible in the present invention, since the steel from which the pipe and thus the pipe product is made has no or only a very low content of silicon. In addition, the pipe product is crack-free and preferably pore-free, so that the coating can be applied reliably.

The pipe product can represent, for example, a structural component of a motor vehicle. For example, the tubular product can represent part of a chassis component, in particular a stabilizer. In this case, the pipe product can also be referred to as a stabilizer pipe. A stabilizer generally comprises a tubular element, which is connected at its longitudinal ends to a connection component, in particular a torque lever. For this purpose, the stabilizer tube is welded to the connecting components. In addition, the tubular element of a stabilizer is generally designed in such a way that it is deformed, for example widened, at the longitudinal ends. These necessary widenings are possible in the steel pipe used according to the invention for producing the stabilizer without cracks occurring.

The pipe product may alternatively be a conduit pipe or a cylinder pipe or a piston pipe. Line pipes are used in shipbuilding, vehicle construction as well as in mechanical and plant engineering for media routing. Pistons and cylinder tubes can be part of a stationary or mobile hydraulic or pneumatic circuit. All of these pipe products have local sections with a high degree of deformation.

• 1: ein schematisches Diagramm des Lochaufweitungsvermögens über der Zugfestigkeit;
• 2: eine schematische Darstellung einer ersten Ausführungsform eines erfindungsgemäßen Rohrproduktes;
• 3: eine schematische Darstellung einer zweiten Ausführungsform eines erfindungsgemäßen Rohrproduktes;
• 4: eine schematische Darstellung einer dritten Ausführungsform eines erfindungsgemäßen Rohrproduktes;
• 5: eine schematische Darstellung einer vierten Ausführungsform eines erfindungsgemäßen Rohrproduktes; und
• 6: eine schematische Darstellung zur Bestimmung der Bainitpaketbreite.

In the following, exemplary embodiments are described with reference to the figures. Show it:

• 1 : a schematic diagram of the hole expansion capacity versus tensile strength;
• 2 : a schematic representation of a first embodiment of a pipe product according to the invention;
• 3 : a schematic representation of a second embodiment of a pipe product according to the invention;
• 4th : a schematic representation of a third embodiment of a pipe product according to the invention;
• 5 : a schematic representation of a fourth embodiment of a pipe product according to the invention; and
• 6 : a schematic representation for determining the bainite packet width.

In 1 the hole expansion capacity of various steel alloys of the prior art is plotted schematically over the tensile strength. In addition, in the diagram in 1 plotted the values for two exemplary embodiments of steel alloys of the invention. As can be seen from the diagram, higher-strength steels of the prior art with tensile strengths> 800 MPa can only achieve a hole expansion capacity of <60% and in particular <40%. With the steel alloy that is used according to the invention, however, in a first exemplary embodiment a hole expansion capacity of more than 100, in particular 108%, with a tensile strength of more than 1000 MPa, in particular 1050 MPa can be achieved. In the diagram, the tolerance of the hole expansion capacity of +/- 18 is shown schematically. The first embodiment of the steel alloy can have the following composition: C. 0.08-0.12 Mn 3.0-3.5 Si Max. 0.1 Cr Max. 0.13 Mon 0.2-0.3 B. 0.0015 - 0.003 Ti > 0.038 Al > 0.04 N > 0.0015, where Ti / N is in the range 3.8-4.5 Remainder: iron and unavoidable impurities caused by the melting process. In the first exemplary embodiment, this alloy is in the air-hardened state.

In the second exemplary embodiment, the steel alloy of the first exemplary embodiment is in an air-hardened and stress-relieved state. With a strength of> 1000 MPa, in particular 1050 MPa, a hole expansion capacity of 140% can be achieved. Also for the second embodiment is in the 1 a tolerance of +/- 18% is shown schematically.

In 2 is a first embodiment of a pipe product 1 according to the invention shown in sectional view. In this figure there is only one pipe end of the pipe product 1 shown. The pipe product 1 is from a pipe 10 manufactured that has an outer diameter AD0 having. At the pipe end shown, the pipe product has a widening 11 which is also referred to below as the expanded area. The expansion 11 has an outside diameter AD1 on. In the embodiment shown, the widening 11 a cylindrical shape. This means the outside diameter AD1 is present over a length at the pipe end. The expansion A, which can be calculated by the following formula 1, is 50% in the embodiment shown. $$\text{A}=\frac{\left(AD1-AD0\right)}{A\mathrm{<figure-callout\; id="0"\; label="D"\; filenames="DE102019103502A1\_0003.png"\; state="\{\{state\}\}">D</figure-callout>}0}\ast 100$$

In the cylindrical widened area 11 of the pipe product 1 For example, one pipe end of another pipe product (not shown) can be inserted. Alternatively, the pipe product 1 on a component, for example a plate with the widened area 11 be welded on.

In 3 is a second embodiment of the pipe product 1 shown. In this embodiment, the pipe product represents 1 a double bent pipe element of a pipeline. At each of the pipe ends there is a cutting ring 2 to the pipe 10 appropriate. The cutting ring 2 is preferably screwed onto a widened area (not visible) on the pipe end.

In 4th is a third embodiment of the pipe product 1 shown. In this embodiment the pipe is 10 from which the pipe product 1 manufactured is bent by 90 °. The pipe product has at both pipe ends 1 each have a widened area 11 on. In the expanded area 11 indicates the pipe product 1 an outside diameter AD1 on that is larger than the outside diameter AD0 of the pipe 10 is from which the pipe product 1 is made. The expanded area 11 can according to the expanded area 11 the first embodiment and in particular have a wall thickness that is equal to or less than the wall thickness of the pipe 10 is. But it is also possible that the wall thickness is in the widened area 11 in the third embodiment is greater than the wall thickness of the pipe 10 . Thus, the pipe end of the pipe product 1 be thickened. A thread can, for example, be cut inside or outside into this thickening.

In 5 is a fourth embodiment of the pipe product 1 shown in sectional view. In this embodiment, the widening 11 at the pipe end of the pipe product 1 different diameters. At the end of the widening 11 that lies in the end of the pipe is the outside diameter AD1 less than the outside diameter AD2 , which is spaced from the pipe end in the expansion 11 lies. Either AD1 as well as AD2 are larger than the outer diameter AD0 of the pipe 10 from which the pipe product 1 is made.

As in 6 is shown schematically, the bainite needles grow from the austenite grain boundaries into the austenite grain. Several needles are arranged side by side and in parallel as a package. Further packages with several bainite needles run at an angle to this package. The needles can be very short relative to the austenite grain, but also relatively elongated. The package width is the maximum distance between the opposing outer bainite needles measured perpendicular to the needle extension.

The present invention creates a high-strength, air-hardening bainitic steel material which, compared to conventional high-strength steels, has a significantly improved stretch flanging deformability with an average hole expansion capacity of 100% and thus allows geometrical changes in the component design and an improved lightweight construction potential. For seamless or cold-drawn tubes, the material can enable larger expansion angles due to the reduced sensitivity to edge cracks.

List of reference symbols

1

Pipe product

10

pipe

11

Widening

2

Cutting ring

AD0

Outer diameter pipe

AD1

Outside diameter expansion

AD2

Outside diameter expansion

Claims (18)

Method for producing a seamless steel tube (10), characterized in that a steel is used which, in percent by weight, consists of the following alloying elements: C. 0.06-0.15 Mn 1.5-4.0 Si Max. 0.1 Cr Max. 0.15 Mon 0.1-0.5 B. 0.001-0.005 Ti > 0.015 Al > 0.04 N > 0.001-0.1, where Ti / N> = 3.4 Remainder: iron and unavoidable impurities caused by the melting process. Procedure according to Claim 1 , characterized in that the manganese content is at least 1.8 wt .-%, preferably at least 3 wt .-%. Method according to one of the Claims 1 or 2 , characterized in that the ratio of titanium to nitrogen (Ti / N) is at least 3.8. Method according to one of the Claims 1 to 3 , characterized in that the aluminum content is at least 0.06% by weight. Method according to one of the Claims 1 to 4th , characterized in that the steel optionally contains at least one of the alloying elements niobium and vanadium, the content of these optional alloying elements satisfying the formula Nb + Ti + V <= 0.12% by weight. Method according to one of the Claims 1 to 5 , characterized in that a steel is used which, in percent by weight, consists of the following alloying elements: C. 0.08-0.12 Mn 3.0-3.5 Si Max. 0.1 Cr Max. 0.13 Mon 0.2-0.3 B. 0.0015 - 0.003 Ti > 0.038 Al > 0.04 N > 0.0015, where Ti / N is in the range 3.8-4.5 Remainder: iron and unavoidable impurities caused by the melting process. Method according to one of the Claims 1 to 6 , characterized in that the seamless steel tube (10) is produced by hot forming with subsequent cooling in air. Procedure according to Claim 7 , characterized in that the cooling is carried out in such a way that the temperature range between 800 ° C and 500 ° C is passed through at a cooling rate of 0.1 to 8.0 ° C / s. Procedure according to Claim 7 or 8th , characterized in that the seamless steel tube (10) is subjected to stress relief annealing after cooling in air. Seamless steel tube, characterized in that this according to a method according to one of Claims 1 to 9 is made. Seamless steel pipe after Claim 10 , characterized in that the seamless steel tube (10) consists of air-hardened steel with a bainitic structure, which has a tensile strength of Rm> 950 MPa and a hole expansion capacity of more than 80%. Seamless steel pipe after Claim 11 , characterized in that the hole expansion capacity is 100% and preferably 140%. Seamless steel tube according to one of the Claims 10 to 12th , characterized in that the structure has an average austenite grain size after the last hot forming step of <50 µm and the average bainite packet width of the bainitic structure after cooling in air is preferably less than 25 µm. Seamless steel tube according to one of the Claims 10 to 13th , characterized in that the structure of the steel alloy in the steel tube (10) has the following structural components: lower bainite> 70% upper bainite <30% Martensite <30% residual austenite <5%. Seamless steel tube according to one of the Claims 10 to 14th , characterized in that the steel has a notched impact strength Av at -20 ° C of at least 27 J. Pipe product, characterized in that this consists of a seamless steel pipe (10) according to one of the Claims 10 to 15th is made and at least one end has a flange, a cutting ring contour in the pipe wall and / or a local flattening .. Pipe product after Claim 16 , characterized in that the pipe product (1) has an expansion of more than 15%, preferably more than 25%, at at least one pipe end. Pipe product according to one of the Claims 16 or 17th , characterized in that the pipe product (1) is a stabilizer pipe.

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