A large-diameter-wall-ratio duplex stainless steel pipe and a piercing method thereof

Abstract

The application discloses a large-diameter-wall-ratio duplex stainless steel pipe and a piercing method thereof, and comprises the following steps: blank heating and rolling, the blank after cutting and removing the surface oxide skin is segmented heated, so that the rolling temperature rise and the heating temperature rise are offset to each other; hot piercing, the blank after the heating and rolling is arranged on a piercing mill to perform piercing, and a large-diameter-wall-ratio hollow shell pipe is obtained; water cooling, the obtained hollow shell pipe is water cooled and cold rolled, and a finished seamless steel pipe with smooth surface and no crack in the inner hole is obtained. Through the blank heating and rolling, heat treatment and water cooling mode, by adjusting the burner power, the blank is non-isothermally heated, the rolling temperature rise and the heating temperature difference are offset, the relatively constant temperature rolling is realized, the top head utilizing the cavity gap is arranged, and the process parameters suitable for the top head are selected, so that the stainless steel seamless pipe with the diameter-wall ratio greater than 15 can be pierced.

Description

Technical Field

[0001] This invention relates to the field of stainless steel profile technology, and in particular to a large-diameter duplex stainless steel pipe with a wall-to-diameter ratio and a perforation method thereof. Background Technology

[0002] Duplex stainless steel pipes have excellent mechanical properties, corrosion resistance, and good weldability, and are widely used in industries such as petroleum and natural gas, marine engineering, and chemical industry.

[0003] The diameter-to-wall ratio of piercing rough tubes is generally 8-12. Both excessively thick and thin walls pose significant challenges to the piercing process. Multiple piercing and rolling processes are required during piercing. Due to the multiple rolling and piercing passes, defects such as cracks, peeling, inclusions, folds, scratches, and pits may occur. In addition, there are disadvantages such as unstable quality, low yield, high cost per ton of steel, long delivery time, and high carbon emissions per ton of steel. Summary of the Invention

[0004] To address some or all of the technical problems existing in the prior art, this invention provides a large-diameter-to-wall-ratio duplex stainless steel pipe and its piercing method, which can achieve piercing of duplex stainless steel pipes with a diameter-to-wall ratio of 15 or higher, with stable quality and high yield.

[0005] The technical solution of the present invention is as follows:

[0006] In a first aspect, the present invention provides a method for piercing a large-diameter duplex stainless steel pipe with a wall-to-diameter ratio, comprising:

[0007] In the billet heating and rolling process, the billet after cutting and removing the surface oxide scale is heated in sections, so that the rolling temperature rise and the heating temperature rise of the billet cancel each other out.

[0008] Hot piercing involves placing a heated and rolled billet on a piercing mill for piercing to obtain a hollow tube with a large diameter-to-wall ratio.

[0009] Water cooling is performed on the hollow tube obtained, followed by cold rolling, to obtain a finished seamless steel pipe with a smooth surface and no cracks in the inner hole.

[0010] Furthermore, when heating the billet in stages, the heating temperature and heating time of the billet in different furnace doors are shown in the table below:

[0011] .

[0012] Furthermore, the material of the blank is 2205, the outer diameter of the blank is Φ200mm-Φ250mm, the multiple length is 2350mm, and the end face bevel is ≤3mm.

[0013] Furthermore, the surface roughness of the blank before hot piercing is ≤ Ra3.2.

[0014] Furthermore, the minimum value of the large diameter-to-wall ratio is 15.

[0015] Furthermore, during the water cooling process, a mandrel is used for cold rolling. The mandrel has a conical structure with a spherical apex and a radius of 2. The mandrel is 325 mm long and 190 mm in diameter. The surface roughness of the conical surface is Ra1.6.

[0016] Furthermore, the mandrel is made of alloy material and contains the following percentages of chemical elements: Mo: ≥96%, Ti: 1%-2%, Zr: 0.1%-0.5%, C: 0.1%-0.5%, and the remainder is 1%-5% of impurities and unavoidable elements contained in the raw materials.

[0017] Furthermore, during cold rolling, the roll gap is 198mm-203mm, the guide plate distance is 215mm-220mm, the mandrel lift is 50mm-80mm, the roll speed is 230r / min-260r / min, the feed angle is 8°-12°, the bite angle is 2.3°, and the ejection angle is 2.8°.

[0018] Furthermore, when the mandrel is set on the drilling machine for drilling, the dimensions of the mandrel set on the drilling machine are: 190mm×325mm, guide plate spacing: 210mm-220mm, mandrel length: 168mm, union size: 168mm, and inlet guide sleeve length: 235mm-260mm.

[0019] Secondly, the present invention also provides a large-diameter-to-wall-ratio duplex stainless steel pipe, which is prepared by the piercing method described above for large-diameter-to-wall-ratio duplex stainless steel pipes.

[0020] The main advantages of the technical solution of this invention are as follows:

[0021] The present invention discloses a piercing method for large-diameter-to-wall-ratio duplex stainless steel pipes. The method involves heating and rolling the billet, heat treatment, and water cooling. By adjusting the burner power, the billet is heated at different temperatures, so that the rolling temperature rise and the heating temperature difference cancel each other out, achieving relatively constant temperature rolling. At the same time, a mandrel utilizing the cavity gap is set up, and process parameters suitable for this mandrel are selected, thereby enabling the piercing of stainless steel seamless pipes with a diameter-to-wall ratio greater than 15. Attached Figure Description

[0022] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and constitute a part of this invention, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0023] Figure 1 This is a schematic flowchart of a perforation method for a large-diameter duplex stainless steel pipe with a wall ratio according to the present invention.

[0024] Figure 2 This is the temperature rise curve of the duplex stainless steel pipe being pierced and rolled in a piercing mill in a piercing mill, as described in the piercing method for a large-diameter duplex stainless steel pipe of the present invention.

[0025] Figure 3 This invention relates to a piercing method for large-diameter duplex stainless steel pipes, showing the temperature curves of the duplex stainless steel pipe at the beginning, middle, and end of the billet in the furnace during the piercing process. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0027] The technical solutions provided by the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0028] As attached Figure 1-3 As shown in the figure, an embodiment of the present invention provides a piercing method for large-diameter duplex stainless steel pipes with a wall-to-diameter ratio, the method comprising:

[0029] In the billet heating and rolling process, the billet after cutting and removing the surface oxide scale is heated in sections, so that the rolling temperature rise and the heating temperature rise of the billet cancel each other out.

[0030] Hot piercing involves placing a heated and rolled billet on a piercing mill for piercing to obtain a hollow tube with a large diameter-to-wall ratio.

[0031] Water cooling is performed on the hollow tube obtained, followed by cold rolling, to obtain a finished seamless steel pipe with a smooth surface and no cracks in the inner hole.

[0032] Specifically, when heating the billet in stages during the billet heating process, the heating temperature and heating time of the billet in different furnace doors are shown in the table below:

[0033] .

[0034] As an optional implementation method in this embodiment, the temperature of furnaces 12#-13# is controlled between 700℃ and 900℃, and the remaining temperatures are preferably between the temperatures of the adjacent furnace doors. The above temperature settings are determined according to process requirements.

[0035] As an optional implementation of this invention, the inclined bottom furnace has a single burner power of 1200 kW, with 15 burners in 5 rows of 3 burners each. The heating section has 9 burners in 3 rows, and the soaking section has 6 burners in 2 rows. Through multiple field tests, the power of burners No. 3 and No. 6 was adjusted to 1070 kW, and the power of burners No. 2 and No. 5 was adjusted to 1130 kW, achieving non-isothermal heating of the billet, so that the temperature at the tail end of the billet is 25°C lower than that at the head end.

[0036] Therefore, due to the temperature rise during hot piercing, defects occur at the tail of the blank due to the high temperature. In order to achieve relatively constant temperature rolling, the power of the burner is controlled by design and the heating process is changed to enable the blank to be heated in a non-isothermal manner, which complements the rolling temperature rise and keeps the rolling temperature within the process requirements.

[0037] It should be noted that: before rolling the billet, the billet needs to be cut according to the preset size, and centering holes are set at both ends of the cut billet. The size of the centering holes is Φ40×50mm. The inner and outer surfaces of the billet are free from visible defects such as cracks, peeling, scars, inclusions, folds, scratches, and pits. The curvature of the billet is ≤3mm / m, the total curvature is ≤0.3%L, and the bevel is ≤3mm.

[0038] As an optional implementation of this embodiment, in addition to the heating temperature and heating time of the billet in the different furnace doors listed above, the temperature in the furnace doors not listed is between the temperatures of two adjacent or neighboring furnace doors.

[0039] This configuration ensures that the temperature of the heated bidirectional pipe remains consistent throughout the rolling process.

[0040] It should be noted that, through the aforementioned non-isothermal heating method, the temperature of the bidirectional pipe is always maintained within a certain temperature range, thus offsetting the rolling temperature rise and the heating temperature difference, achieving relatively constant temperature rolling, and thereby ensuring the rolling effect. According to the structure of the heating furnace, as an optional implementation in this embodiment of the invention, the heating furnace is sloping, and the bidirectional pipes to be heated are sequentially heated along the order from #1 to #14. Furthermore, the temperature of the heating furnace is set from high to low according to the order from #1 to #14, thereby ensuring that the temperature of the heated bidirectional pipes remains consistent.

[0041] Specifically, the billet material is 2205 stainless steel, the outer diameter is Φ200mm-Φ250mm with a tolerance of -2mm to 0mm, the multiple length is 2350mm with a tolerance of 0 to +5mm, and the end face bevel is ≤3mm. The surface must not have any visible defects such as pits, grooves, cracks, scars, black skin, steps, or central porosity. Roughness: ≤R3.2um, no steps are allowed at transition points; Smoothness: no visible oil stains or other impurities are allowed on the surface.

[0042] Specifically, the minimum value for the large diameter to wall ratio is 15.

[0043] Specifically, during the water cooling process, a mandrel is used for cold rolling. The mandrel has a conical structure with a spherical apex and a radius of 2. The mandrel is 325mm long and 190mm in diameter. The surface roughness of the conical surface is Ra1.6.

[0044] Specifically, the mandrel is made of alloy material containing the following percentages of chemical elements: Mo: ≥96%, Ti: 1%-2%, Zr: 0.1%-0.5%, C: 0.1%-0.5%, with the remainder being 1%-5% of impurities and unavoidable elements contained in the raw materials.

[0045] Specifically, during cold rolling, the roll gap is 198mm-203mm, the guide plate distance is 215mm-220mm, the mandrel lift is 50mm-80mm, the roll speed is 230r / min-260r / min, the feed angle is 8°-12°, the bite angle is 2.3°, and the ejection angle is 2.8°.

[0046] Therefore, by modifying the mandrel structure and its coordination with the rolling mill, the original mandrel, being relatively short, was prone to forming cavities during rolling, resulting in high resistance and severe deformation. Extending the mandrel length and altering its curve reduces cavity formation, promotes uniform deformation, increases the number of rolling passes, and prevents internal defects. Simultaneously, combined with the aforementioned non-isothermal heating method, the narrow hot working temperature range of duplex steel leads to hot rolling defects when exceeded. The 25°C temperature rise during hot piercing offsets the temperature difference from the inclined hearth furnace heating, achieving relatively constant temperature rolling and ensuring hot rolling quality.

[0047] In summary, the piercing method for large-diameter-to-wall-ratio duplex stainless steel pipes of this invention utilizes billet heating and rolling, heat treatment, and water cooling. By adjusting the burner power, non-isothermal heating of the billet is achieved, canceling out the rolling temperature rise and heating temperature difference, thus achieving relatively isothermal rolling. Simultaneously, a mandrel utilizing the cavity gap is used, and suitable process parameters are selected for this mandrel, enabling piercing of seamless stainless steel pipes with a diameter-to-wall-ratio greater than 15. Specifically, the austenite-to-ferrite ratio of duplex steel at room temperature is 55:45. As the temperature increases, the ferrite ratio increases, and this change in the two-phase ratio directly affects the hot plasticity of the billet. Field tests show that when the austenite ratio is around 25, the hot plasticity is good enough to meet the requirements for hot rolling piercing deformation. However, changes in the phase ratio and temperature are quite sensitive. During the piercing of rough pipes with large diameter-to-wall-ratios, as the rolling temperature increases, hairline cracks appear on the surface of the duplex steel. To ensure the stability of the initial and final rolling temperatures, high-quality production is achieved through the aforementioned non-isothermal heating process, mandrel adjustment, and corresponding parameter adjustments. This enables the piercing of duplex stainless steel pipes with a diameter-to-wall ratio of 15 or higher, resulting in stable quality and high yield.

[0048] Example 2

[0049] This invention also provides a large-diameter-to-wall-ratio duplex stainless steel pipe, which is prepared by the piercing method for large-diameter-to-wall-ratio duplex stainless steel pipes described in Example 1 above. This method eliminates defects generated during hot rolling, resulting in stable quality in the large-diameter-to-wall-ratio duplex stainless steel pipe prepared by this invention.

[0050] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Additionally, the terms "front," "back," "left," "right," "upper," and "lower" in this document refer to the placement shown in the accompanying drawings.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A piercing method of a large-diameter-wall-ratio duplex stainless steel pipe, characterized by, The application relates to a large-diameter-wall-ratio duplex stainless steel pipe and a preparation method thereof. Blank heating, the material of the blank is 2205, the outer diameter of the blank is phi 200mm-phi 250mm, the length of the blank is 2350mm, the end surface cutting slope is less than or equal to 3mm, the blank after cutting and removing the surface oxide skin is segmented heated, the rolling temperature rise and the heating temperature rise of the blank are offset to each other, the tail temperature of the blank is 25 DEG C lower than the head temperature, the heating furnace is inclined, the duplex stainless steel pipe to be heated is sequentially heated along the furnace door 1# to 14#, the heating temperature and the heating time of the blank in different furnace doors during the segmented heating in the blank heating process are shown in the following table. ； Hot piercing, the blank after heating is arranged on a piercing machine to perform piercing, and a large-diameter-wall-ratio hollow pipe is obtained, the minimum value of the large-diameter-wall-ratio is 15, when a punch is arranged on the piercing machine to perform piercing, the size of the punch arranged on the piercing machine is 190mm*325mm, the guide plate spacing is 210mm-220mm, the length of the punch rod is 168mm, and the length of the inlet guide sleeve is 235mm-260mm. Water cooling and cold rolling are performed on the obtained hollow pipe to obtain a finished seamless steel pipe with smooth surface and no crack in the inner hole, when the cold rolling is performed, the roll distance is 198mm-203mm, the guide plate distance is 215mm-220mm, the roll rotating speed is 230r / min-260r / min, the feeding angle is 8 DEG -12 DEG, the biting angle is 2.3 DEG, and the throwing angle is 2.8 DEG.

2. The piercing method of a large-khck-wall-ratio duplex stainless steel pipe according to claim 1, characterized by, The surface roughness of the blank before the hot piercing is less than or equal to Ra3.

2.

3. The piercing method of a large-khck-wall-ratio duplex stainless steel pipe according to claim 2, characterized by, The punch is made of alloy material and contains the following chemical elements: Mo: greater than or equal to 96%, Ti: 1%-2%, Zr: 0.1%-0.5%, C: 0.1%-0.5%, and the rest is impurities and inevitable elements 1%-5% contained in the raw material.

4. A large-khck-wall-ratio duplex stainless steel pipe characterized by The duplex stainless steel pipe is prepared by the piercing method of the large-diameter-wall-ratio duplex stainless steel pipe according to any one of the above claims 1-3.

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