EP3033186B1 - Method for producing a quenched and tempered seamlessly hot-fabricated steel pipe - Google Patents

Description

The invention relates to a method for producing a quenched, seamless hot-rolled steel tube, in which a hollow block heated to forming temperature is rolled to a tube with a finished diameter after rolling in a rolling mill and subsequently annealed and the diameter of the tube grows during the annealing with corresponding compensation parameters ,

After the invention of the brothers Mannesmann to produce a thick-walled hollow block pipe from a heated block, there have been various proposals to stretch this hollow block pipe in the same heat in a further hot working stage, which is done reducing the outer diameter of the finished diameter of the rolling mill.

Keywords are the Kontiwalzverfahren, the Stoßbankverfahren, the plug rolling process and the Pilgerschrittverfahren ( Stahlrohr Manual, 10th edition, Vulkan-Verlag Essen 1986, III. Herstellverfahr s).

All these methods have their advantages for different dimensions and materials, although there are also overlaps. For the medium size range from 5 "to 18", the continuous and plug rolling process is used, for the size range up to 26 "the pilgrim stepping method is used.With thicker walls in the range of> 30 mm, the continuous and stopper rolling process are less suitable, while the pilgrimage process is has no wall thickness problems, but is slower in the production cycle.

In particular, for the use of pipes for the oil or gas industry, for example, from DE 3127373 A1 It is known to subject the tubes after finishing rolling to finished diameter to a tempering treatment to achieve the required mechanical properties such as strength, toughness and elongation. The tempering treatment itself is known to be heated to austenitizing temperature, quenching and tempering.

It is also known that in the course of this treatment, grain growth takes place in the structure of the steel, which leads to an increase in the diameter of the pipe and with respect to the required finished diameter of the finished pipe after the annealing must be observed.

Furthermore, the tube expands when heated and a subsequent obstruction of shrinkage, inter alia, in the structural transformation during the quenching process can also affect the diameter of the finished tube.

For Oilfield and Conduit pipes, standards such as API (American Petroleum Institute) specifications for diameter, tolerances, wall thickness tolerances, meter weight, drift, etc., are provided depending on the point of use and dimension for the finished pipe.

These specifications mean that for the production of the target diameter of the tube after rolling is not always the same for the same example given by a standard diameter, since this consists of a compromise between manufacturing capabilities and product specifications. In addition, depending on the material due to the grain size change and the shrinkage hindrance when tempering the pipe diameter grows more or less.

The simplest and most common method of dealing with this problem, in particular for diameters equal to or greater than 5 1/2 ", is to use a sizing mill to reduce the diameter slightly at tempering temperature JP 57155325 A or the JP 2006307245 A known. Such a sizing mill usually has three frameworks in which the required finished diameter are produced after tempering the tubes.

The disadvantages of this method are manifold. In addition to the investment and operating costs for the Maßwalzwerk incurred higher energy consumption, since for the sizing higher tempering temperatures are needed so that at the desired small diameter reduction in the sizing mill plastic deformation can take place. The higher tempering temperatures also cause an additional need for alloying in the material in order to achieve the required mechanical-technological properties.

Alternatively, even in the rolling mill, a pipe diameter adapted to the pipe after tempering could be rolled. However, this would lead to a significantly increased number of pipe diameters to be rolled and to a correspondingly extensive scaffolding park.

From the publication CN 101 993 991 A Already a method for heat treating seamless steel tubes from low-manganese steel is known. For this purpose, the steel pipes are classified in one of three categories, which refer to different areas of outside diameters of steel pipes and wall thicknesses of steel pipes. On the basis of statistical evaluations, a standard steel pipe is determined whose properties are stable, whose deviations are small and whose individual properties are in the middle range of the required standards. The manufacturing process in which this standard steel tube was made is defined as the standard manufacturing process and a standard meter weight of the associated standard steel tube is determined. On the basis of this standard meter weight and any deviations to the heat treatment is then assessed and regulated according to the amount of cooling water. With the method according to the invention, the yield strength of the steel tubes produced should be adjustable within a range of deviation of 80 MPa.

In the further disclosure US 2009/0038358 A1 - describes a method for the production of seamless tubes, wherein the tube have improved mechanical properties and a large-scale energy savings are to be made possible by a continuous process from the cross rolling to the heat treatment. For this purpose, a sizing roll is carried out at a temperature in the range of 600 to 800 degrees C and selected for subsequent reheating at least 440 degrees C as the inlet temperature of the steel pipe.

The object of the invention is to provide a production method for quenched seamlessly hot-rolled steel tubes, which allows a more economical production of such pipes while maintaining the geometric requirements for the quenched finished tube.

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

From the publication CN 101 993 991 A Already a method for heat treating seamless steel tubes from low-manganese steel is known. For this purpose, the steel pipes are classified in one of three categories, which refer to different areas of outside diameters of steel pipes and wall thicknesses of steel pipes. On the basis of statistical evaluations, a standard steel pipe is determined whose properties are stable, whose deviations are small and whose individual properties are in the middle range of the required standards. The manufacturing process in which this standard steel tube was made is defined as the standard manufacturing process and a standard meter weight of the associated standard steel tube is determined. On the basis of this standard meter weight and any deviations to the heat treatment is then assessed and regulated according to the amount of cooling water. With the method according to the invention, the yield strength of the steel tubes produced should be adjustable within a range of deviation of 80 MPa.

In the further disclosure US 2009/0038358 A1 - describes a method for the production of seamless tubes, wherein the tube have improved mechanical properties and a large-scale energy savings are to be made possible by a continuous process from the cross rolling to the heat treatment. For this purpose, a sizing roll is carried out at a temperature in the range of 600 to 800 degrees C and selected for subsequent reheating at least 440 degrees C as the inlet temperature of the steel pipe.

According to the teaching of the invention, a method for producing a quenched, seamless hot-rolled steel tube, in which a warmed to forming temperature hollow block is rolled into a tube with a finished diameter after rolling in a rolling mill and subsequently annealed and during the annealing with appropriate compensation parameters of the diameter the tube increases, thereby improving that, with knowledge of the diameter growth of the tube when tempering the finished diameter of the tube to be annealed after rolling in the rolling mill is adjusted, that the annealing consists of heating in a furnace, then continuous cooling in a cooling section and a tempering process , the compensation parameters are set on the basis of the range of previously determined relationships between diameter, pipe wall thickness, material quality, compensation parameters and diameter growth, and then based on the measured finished diameter of the currently rolled tube, the tempering parameters are finely adjusted with respect to the target diameter of the tube to be achieved after tempering. The innovative approach of the invention is that the knowledge of the influence of the compensation parameters on the diameter changes of the tube by the annealing for different material grades and dimensions (diameter, wall thickness) is used to determine the finished diameter for the rolling mill. This process is particularly advantageous and safe to manufacture if the tempering of the currently measured target diameter of the pipes to be coated is available in the pipe mill and the specifications for the selected manipulated variables are finely adjusted due to the dependencies of the diameter growth on the pipe material and the quenching parameters.

It is particularly advantageously provided that the compensation parameters are set in such a way that a pipe having a target diameter which corresponds to a finished diameter after tempering within a predetermined tolerance range is produced.
In particular, the parameters which have an influence on the cooling rate of the tube heated to austenitizing temperature are to be understood as the tempering parameters. The quenching of the heated tube is carried out according to the invention by means of a continuous cooling, as only in this type of cooling can be specifically influenced on the cooling rate and thus on the change in diameter. Also important is the measurement and control of the influencing cooling parameters. These growth rates are dependent on the one hand on the specific design of the quenching unit (for example, ring shower or annular gap shower), the Product parameters material, diameter / wall thickness ratio and on the other of the parameters of the quenching process (with and without internal cooling), pipe speed, water pressure, flow rate, etc.

A further simplification of the production process is achieved in that the finished diameter is achieved after tempering without the aid of mills. The proposed method has the advantage that can be dispensed with the method after the tempering of the pipe with this method, so that on the one hand significantly reduces the cost and on the other hand, the investment for the expensive sizing mill and the associated costs of maintenance and energy can be avoided. In addition, cheaper materials can be used for various material grades and lower tempering furnace temperatures can be achieved with correspondingly lower energy consumption. A higher tempering temperature is necessary for the sizing, because the tube must be plastically deformed and the elastic spring back is to be kept small. In order to be able to set the required material properties for the higher tempering temperatures, a so-called "richer" starting material with a higher content of alloy constituents must again be used than is necessary.

The setting of the target diameter after annealing is done as before. However, this is not achieved by a sizing after tempering but by a combination of finished diameter of the rolling mill after rolling and a targeted set diameter growth during annealing.

A particular simplification of the manufacturing process can be achieved in that, knowing the diameter growth of the tube when tempering a group of tube types with the same nominal diameter but different wall thicknesses, material grades or specifications is determined, set for a uniform finished diameter of the pipe to be tempered after rolling becomes. As a result, without a complicated conversion of the rolling mill different types of tubes can be rolled with a uniform finished diameter of the pipe to be tempered after rolling, although these types of tubes have different target diameter after tempering. At least the number of finished diameters of the tube to be coated after rolling can be minimized by a corresponding group formation of tube types and thus the frequency of retrofitting the rolling mill can be minimized.

It is particularly advantageously provided that the compensation parameters are set in such a way that, starting from the uniform finish diameter, a tube with its target diameter is produced for each tube type in the group.

In order to optimize the manufacturing process, the finished diameter of the tube is measured after rolling and used as an input for tempering.

It is particularly advantageously provided that the target diameter of the tube is adjusted after tempering by changing the cooling rate in the cooling section.

In the case of continuous cooling, the tube heated to austenitizing temperature and continuously transported via a roller table is usually quenched by means of stationary application of water to the final temperature to be reached. In addition to the pipe dimensions, the temperature of the cooling water, the intensity of the water cooling as quantity per unit of time, and the transport speed of the pipe via the roller table must be mentioned as significant factors influencing the height of the cooling rate.

It has proved to be advantageous for the parameters of the quenching process, if in the external cooling the amount of water applied to the pipe to be cooled controllably between 50 and 300m ³ / h, the cooling water temperature below 40 ° C and the transport speed of the tube in the cooling section to values between 0 , 1 and 1 m / s.

If necessary, in addition to the external cooling, an internal cooling of the pipe can take place, the amount of cooling water should be between 50 and 250 m ³ / h.

While the external cooling can advantageously take place via two or more annular showers or ring showers, the internal cooling is preferably realized via a lance insertable into the tube.

Alternatively, the heating for hardening or austenitizing also in take place an oven, which has at least two zones over the furnace length and of which the first serves for heating and the second for temperature compensation in the tube.

It is also advantageously provided that the heating takes place for hardening or austenitizing the tube in a first furnace and for equalizing the temperature in the tube in a second furnace.

In addition, it is economically particularly advantageous if the heating for hardening or austenitizing takes place in a lifting beam furnace with three zones, the first zone for preheating, the second zone for heating and the third zone for temperaure compensation in the pipe and wherein the different zones in one or more ovens can be located.

When tempering, the holding time should be at austenitizing temperature at least 3 minutes, with the holding time then begins when the lowest temperature reached in the pipe reaches the value "pipe set temperature minus 20 ° C". In this way, optimal starting conditions for homogeneous material properties of the tube are created after the subsequent quenching process.

• Figur 1 eine schematische Darstellung der Einflussfaktoren auf den Zieldurchmesser nach dem Vergüten,
• Figur 2 den Einfluss des Rohrdurchmessers auf das Wachstum mit Innenkühlung,
• Figur 3 den Einfluss des Rohrdurchmessers auf das Wachstum ohne Innenkühlung,
• Figur 4 den Einfluss der Durchlaufgeschwindigkeit auf das Wachstum ohne Innenkühlung,
• Figur 5 den Einfluss der Durchlaufgeschwindigkeit auf das Wachstum mit Innenkühlung.

The method according to the invention will be explained in more detail with reference to the figures shown in the appendix.
Show it:

• FIG. 1 a schematic representation of the factors influencing the target diameter after tempering,
• FIG. 2 the influence of pipe diameter on growth with internal cooling,
• FIG. 3 the influence of pipe diameter on growth without internal cooling,
• FIG. 4 the influence of the flow rate on growth without internal cooling,
• FIG. 5 the influence of throughput speed on growth with internal cooling.

In FIG. 1 shows schematically how the method according to the invention is applied to set a uniform finished diameter for the mill for different target diameter to be achieved after tempering. By target diameter is meant a target size. The finished diameter after the rolls or the finished diameter after tempering is understood as a certain actual size. The FIG. 1 shows diameter values or ranges of five exemplary tube types which are qualitatively defined by the influencing factors wall thickness W, material quality G and specification S. Under material quality G are essentially the material properties and S specification essentially the dimensions and tolerances to understand.

Whether different tube types can be rolled in a single finished diameter rolling mill in accordance with the present invention, although subsequent tempering results in a different diameter growth, will be readily appreciated FIG. 1 explained. For this purpose, for the five pipe types with the same nominal diameter in the sense of a nominal diameter, the different target diameters after tempering (see the places marked with "x" in FIG FIG. 1 ). These result from the specification S of the respective tube type, since all dimensions and tolerances are recorded there. Accordingly, the first and second or third and fourth pipe types having the same specification X or Y each have the same target diameter after tempering. Within the allowed tolerances of the specification, these could also be chosen slightly different from each other. Through experiments and production results, the minimum and maximum diameter growth in absolute values is now determined for each type of pipe and applied starting from the target diameter after tempering in the sense of a diameter reduction. The minimum diameter growth is registered in the form of the white area with the legend "minimum growth of the tube diameter during annealing" and results for this type of tube from the minimum required compensation parameters such as a minimum cooling rate to achieve the desired target structure during annealing. By varying the tempering parameters, starting from the area "minimum growth of the pipe diameter during tempering", it is possible to increase with the minimum diameter growth that results and, correspondingly, to achieve a larger diameter growth. This area of additional diameter growth is plotted as hatched area with the legend "area of influence of diameter growth". A comparison of the areas "Minimum Pipe Diameter Rewinding" and "Diameter Growth Influence Area" for the five pipe types shows that there is a kind of intersection area indicated by the arrow symbol and the legend "Pre-tempering diameter allowed range". The diameter before tempering corresponds to that previously described finished diameter after rolling. The "allowable diameter pre-tempering range" is limited upwards by the smallest diameter of the five areas "minimum pipe diameter growth during tempering" (see fourth pipe type from left, value between "minimum pipe diameter growth during tempering" and "influence range" of diameter growth "). At the bottom, the "allowable diameter range before annealing" is limited by the largest diameter of the respective lower limit of the five regions "diameter growth influence area" (see first pipe type from the left, lowest limit value from "diameter growth influence area").

On this basis, the finished diameter of the rolling mill is now set to a value within the "allowed range for the diameter before tempering", preferably in the middle of the "allowed range for the diameter before annealing". All five tube types can now be rolled uniformly on this rolling mill and the end diameters differing from each other after tempering are achieved by a corresponding adjustment of the tempering parameters. The "allowed range for the diameter before annealing" has a sufficient bandwidth to account for any manufacturing tolerances. For other groups of tube types of the same nominal diameter, it can be seen that the resulting "allowed range for the diameter before annealing" is very narrow or there is no corresponding area in the sense of a cut area. In this case, then the groups are to be chosen differently or to form subgroups of pipe types, for which then again results in a "permitted range for the diameter before annealing" with a sufficient bandwidth.

The FIGS. 2 to 5 show by way of example the dependence of the diameter growth of the tube on the tempering parameters, in particular the cooling parameters. With the help of the adapted quenching parameters, in particular the pipe speed, the volume flow and with or without internal cooling, it is possible for the same finished diameter of the rolling mill, which is within predetermined tolerances of, for example +/- 0.5%, the desired target diameter after tempering depending on the type of pipe to reach.

So shows FIG. 2 how the growth of the diameter during tempering depends on the diameter size increases at a constant pipe wall thickness for a material family A from the oil field pipe area (OCTG).

In this case, the throughput speed of the pipe through the cooling section is kept constant at 35% of the maximum value, the quenching conditions on the outside ie the amount of water, the number of ring showers and the water pressure. In addition, the pipes were also quenched inside with a constant amount of water per time.

FIG. 3 shows the same dependency as in FIG. 2 however, without additional internal cooling and for a selected flow rate of 22% of the maximum value.

In the FIGS. 4 and 5 It is shown how the selected flow rate influences the diameter growth of the pipe for the nominal dimension 406.4 x 14.6 mm from material group B. Again, the cooling conditions are kept constant outside. In the experiments according to FIG. 4 was worked without additional internal cooling, according to the experiments FIG. 5 but with internal cooling.

In the value tables of the FIGS. 4 and 5 For example, the minimum and maximum growth are shown within practicable values for the tempering parameters, such as flow rate and "with" or "without" internal cooling. For the nominal size 406.4 x 14.6 mm results FIG. 5 a minimum growth of the diameter of 0.9 mm and out FIG. 4 a maximum of 1.46 mm.

Claims (15)

1. Method for producing a tempered, seamlessly hot-rolled steel pipe in which a hollow block heated to forming temperature is rolled in a rolling mill to form a pipe with a finished diameter after rolling and is subsequently tempered, and the diameter of the pipe increases during tempering with appropriate tempering parameters, characterised in that with knowledge of the growth in diameter of the pipe during tempering, the finished diameter of the pipe to be tempered is adjusted after rolling in the rolling mill that the tempering consists of heating in a furnace, subsequent continuous flow cooling in a cooling path and an annealing process, the tempering parameters are adjusted on the basis of the band width of previously determined connections between diameter, pipe wall thickness, material quality, tempering parameters and diameter growth, and that subsequently on the basis of the measured finished diameter of the pipe being rolled the tempering parameters are finely adjusted with respect to the target diameter of the pipe to be achieved after tempering.
2. Method as claimed in claim 1, characterised in that the tempering parameters are adjusted in such a way that a pipe with a target diameter which corresponds to a finished diameter after tempering in a preset tolerance range is produced.
3. Method as claimed in claim 1 or 2, characterised in that without the assistance of sizing rolling the finished diameter is achieved after tempering.
4. Method as claimed in any one of claims 1 to 3, characterised in that with knowledge of the diameter growth of the pipe during tempering, a group of pipe types with the same nominal diameter but with wall thicknesses, material qualities or specifications which differ from each other is determined, for which a single finished diameter for the pipe to be tempered is adjusted after rolling.
5. Method as claimed in claim 4, characterised in that the tempering parameters are adjusted in such a way that starting from the single finished diameter for each pipe type in the group, a pipe is produced with its target diameter.
6. Method as claimed in any one of claims 1 to 5, characterised in that the finished diameter of the pipe after rolling is measured.
7. Method as claimed in any one of claims 1 to 6, characterised in that the target diameter of the pipe after tempering is adjusted by changing the cooling rate in the cooling path.
8. Method as claimed in claim 7, characterised in that in the case of external cooling of the pipe the change in the cooling rate is effected by means of varying the quantity of cooling water, the temperature of the cooling water and/or the transportation speed of the pipe in the cooling path.
9. Method as claimed in claim 8, characterised in that the water quantity poured onto the pipe to be cooled is controllably adjusted between 50 and 300m³/hr, the cooling water temperature is controllably adjusted to below 40°C and the transportation speed of the pipe in the cooling path is controllably adjusted to values between 0.1 m/s and 1m/s.
10. Method as claimed in claims 8 and 9, characterised in that in addition to the external cooling, internal cooling of the pipe takes place, wherein the quantity of cooling water amounts to between 50 and 250m³/hr.
11. Method as claimed in claims 8 to 10, characterised in that for the external cooling two or more annular showers or annular sprays are used.
12. Method as claimed in claims 1 to 11, characterised in that heating for hardening purposes, or for austenitisation, takes place in a furnace which has at least two zones over the furnace length, of which the first serves for heating purposes and the second for temperature equalisation in the pipe.
13. Method as claimed in claims 1 to 12, characterised in that the heating for hardening or austenitisation of the pipe, takes place in a first furnace and the temperature equalisation in the pipe takes place in a second furnace.
14. Method as claimed in claims 12 or 13, characterised in that the heating for hardening purposes, or for austenitisation, takes place in three zones, wherein the first zone serves for preheating, the second zone for heating and the third zone for temperature equalisation in the pipe, and wherein the different zones can be located within one or several furnaces.
15. Method as claimed in claims 1 to 14, characterised in that during tempering the time at which the temperature is held at austenitisation temperature is at least 3 minutes, wherein the holding time begins when the lowest temperature achieved in the pipe reaches the value of the "desired pipe temperature minus 20°C".

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