Method for on-line production of an inner wall oxidation-resistant coating of seamless steel pipes

Abstract

This invention relates to an online method for preparing an anti-oxidation coating on the inner wall of a seamless steel pipe, comprising the following steps: placing a steel billet heated to 1000°C to 1300°C on a piercing platform; performing a first piercing by moving the mandrel relative to the steel billet; performing a second piercing on the steel billet after the first piercing; during the first piercing, when the mandrel is submerged in the steel billet, spraying anti-oxidation powder onto the inner wall of the steel pipe using a powder spraying device. Using this online method for preparing an anti-oxidation coating on the inner wall of a seamless steel pipe, anti-oxidation substances can be sprayed onto the inner wall of the steel pipe simultaneously with piercing, solving the technical problem of severe oxidation of the inner wall of the steel pipe during the piercing process through online preparation. This avoids the oxide scale generated damaging the quality of the inner wall of the seamless steel pipe in subsequent piercing processes, avoids the need for additional grinding processes, and even avoids the scrapping of the steel pipe.

Description

Technical Field

[0001] This invention belongs to the field of seamless steel pipe piercing, and particularly relates to the field of online preparation of anti-oxidation coating on the inner wall of seamless steel pipe. Background Technology

[0002] The piercing process for hot-rolled seamless steel pipes is as follows:

[0003] Solid round billet → heating → piercing → two-roll skew rolling, continuous rolling or extrusion → tube removal → sizing (or reduction) → cooling and tube return → straightening → hydrostatic test (or flaw detection) → marking → warehousing.

[0004] In this process, the solid round billet of steel pipe is generally heated to 1250℃. For products formed by one-time piercing, the oxidation of the outer surface of the round billet has little impact on the quality of the steel pipe.

[0005] However, the fabrication of large-diameter seamless steel pipes often requires two piercing processes, as follows:

[0006] Solid round billet → heating → piercing → secondary heating → secondary piercing → three-roll skew rolling, continuous rolling or extrusion → tube removal → sizing (or reduction) → cooling and tube return → straightening → hydrostatic test (or flaw detection) → marking → warehousing.

[0007] Because the billet temperature is high during the first piercing process, oxidation occurs on the inner wall of the steel pipe after the first piercing. Temperatures exceeding 1000℃ can lead to severe oxidation of the inner wall. During the second piercing, the oxide scale is crushed by the mandrel. Due to the extremely high hardness of the oxide scale, the broken scale will severely scratch the inner wall of the steel pipe during the second piercing process, reducing the quality of the seamless pipe's inner wall. While minor damage can be addressed by grinding the inner wall, this increases the workload and dust pollution. Severe scratches can render the steel pipe unusable. In existing technologies, the problem of oxide scale formation on the inner wall of the steel pipe during the first piercing is often addressed after the first piercing, as it is impossible to prevent or reduce oxide scale formation during the piercing process itself. Summary of the Invention

[0008] The purpose of this invention is to provide an online method for preparing an anti-oxidation coating on the inner wall of a seamless steel pipe. This method solves the technical problem of severe oxidation on the inner wall of the steel pipe while piercing, avoids the oxide scale generated from damaging the quality of the inner wall of the seamless steel pipe during the second piercing process, and avoids the need for additional grinding processes or even the scrapping of the steel pipe.

[0009] To achieve the above objectives, the specific technical solution of the online preparation method for the anti-oxidation coating on the inner wall of seamless steel pipe of the present invention is as follows:

[0010] An online method for preparing an anti-oxidation coating on the inner wall of a seamless steel pipe includes the following steps:

[0011] The steel billet heated to 1000°C to 1300°C is placed on the piercing platform;

[0012] The mandrel moves relative to the steel billet to perform the first piercing;

[0013] The steel billet is pierced a second time after the first piercing is completed;

[0014] During the first piercing, when the mandrel is inserted into the steel billet, an anti-oxidation powder is sprayed onto the inner wall of the steel pipe using a powder spraying device. The powder spraying device includes a mandrel, which is a hollow cylindrical shape. One end of the mandrel is connected to the mandrel. Multiple powder outlets are provided at the connection between the mandrel and the mandrel. The powder outlets are connected to the powder spraying machine through a powder feeding pipe set on the inner wall of the mandrel. When the mandrel moves inside the steel billet, the powder spraying machine conveys the anti-oxidation powder to the powder outlets through the powder feeding pipe and sprays the anti-oxidation powder in all directions. The anti-oxidation powder is composed of 40-45 parts of benzenesulfinic acid, 53-59 parts of graphite powder, and 1-2 parts of ethyl cellulose by weight. The anti-oxidation powder is pre-formed as a spherical mixture with a particle diameter of 0.1 mm-1.0 mm.

[0015] Furthermore, the powder feeding pipe is a single pipe, installed on the inner wall of the top rod, with one end connected to multiple powder outlets and the other end connected to the powder spraying machine.

[0016] Furthermore, the powder feeding pipe is configured with multiple pipes corresponding to the powder outlet. The powder feeding pipes are installed on the inner wall of the top rod, with one end of each powder feeding pipe connected to the corresponding powder outlet and the other end connected to the powder spraying machine.

[0017] Furthermore, the powder feeding pipe is a steel pipe.

[0018] Furthermore, the mandrel and the mandrel are connected by a connecting part.

[0019] Furthermore, there are 6 powder outlets, which are evenly distributed circumferentially on the connecting part.

[0020] Furthermore, the powder outlet is connected to a cover, on which multiple spray nozzles are evenly distributed.

[0021] Furthermore, the powder outlet diameter is 30mm-50mm, and the spray nozzle diameter is 2mm-10mm.

[0022] The online preparation method for the anti-oxidation coating on the inner wall of seamless steel pipe of the present invention has the following advantages over the prior art: while the seamless steel pipe is being pierced for the first time, an anti-oxidation powder is sprayed onto the inner wall of the steel pipe using a powder spraying device to form an anti-oxidation protective layer on the inner wall of the steel pipe. This online preparation method solves the technical problem of severe oxidation of the inner wall of the steel pipe during the piercing process, avoids the oxide scale generated from damaging the quality of the inner wall of the seamless steel pipe in subsequent piercing processes, avoids the need for additional grinding processes, and even avoids scrapping the steel pipe. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the powder spraying device structure in the first embodiment of the online preparation method of the anti-oxidation coating on the inner wall of seamless steel pipe of the present invention;

[0024] Figure 2 This is a schematic diagram of the powder spraying device structure in the second embodiment of the online preparation method of the anti-oxidation coating on the inner wall of seamless steel pipe of the present invention;

[0025] Figure 3 This is a schematic diagram of the powder outlet structure;

[0026] The markings in the diagram are as follows: 1. Top head; 2. Powder outlet; 21. Top cover; 22. Spray nozzle; 3. Top rod; 4, 4', Powder delivery pipe; 5. Powder sprayer; 6. Connecting part. Detailed Implementation

[0027] To better understand the purpose, structure, and function of this invention, the following detailed description, in conjunction with the accompanying drawings, provides a method for online preparation of anti-oxidation techniques for the inner wall of seamless steel pipes.

[0028] like Figure 1 and Figure 3 The diagram shows the structure of the powder spraying device and the powder outlet structure in the first embodiment of the online preparation method of the anti-oxidation coating on the inner wall of the seamless steel pipe of the present invention. The device has a top head 1, which is connected to one end of a top rod 3. The top rod 3 is a hollow structure with an internal accommodating space.

[0029] A powder outlet 2 is provided at the rear end of the joint between the top rod 3 and the top head 1. The powder outlet 2 is connected to the powder spraying machine through the powder feeding pipe 4.

[0030] The top head 1 and the top rod 3 can be freely connected or connected via the connecting part 6. When connected via the connecting part 6, the powder outlets 2 are located on the circumference of the connecting part 6. There are multiple powder outlets, each 30mm-50mm in size, evenly distributed circumferentially on the connecting part 6. In one embodiment, there are six powder outlets with a diameter of 40mm. A powder feeding pipe 4 is installed on the inner wall of the top rod 3. One end of the powder feeding pipe 4 is connected to all six powder outlets 2, and the other end is connected to the outlet of the powder spraying machine 5. The powder outlets 2 are designed as a spray nozzle structure, such as... Figure 3 As shown, each powder outlet 2 is equipped with a face cover 21, and the face cover 21 is provided with multiple spray nozzles 22 with a diameter of 2mm-10mm, preferably 5mm. Antioxidant powder is transported to the powder outlet 2 through the powder feeding pipe 4 and sprayed outwards from the spray nozzles 22 under the action of compressed air.

[0031] When the powder spraying machine 5 starts, it uses compressed air to transport the pre-made anti-oxidation powder through the powder feeding pipe 4 connected to it to the powder spraying port 2, and then sprays the powder in all directions through the spraying port 22. In one embodiment, the anti-oxidation powder is prepared into spherical particles with a diameter of 0.1mm-1.0mm. The diameter of the spraying port 22 is 5mm. The spherical powder has good flowability. Under the power provided by the compressed air, the anti-oxidation powder is sprayed out smoothly when it passes through the powder outlet 2 of the shower head structure, and the anti-oxidation powder has a good dispersion effect, which can make the anti-oxidation powder evenly adhere to the inner wall of the steel pipe.

[0032] In the processing of seamless steel pipes, especially large-diameter seamless steel pipes requiring secondary piercing, the powder spraying machine 5 is first prepared, and compressed air is connected to it. In one embodiment, the anti-oxidation powder is a mixture of 40% benzenesulfonic acid, 58% graphite powder, and 2% ethyl cellulose by weight, which is then prepared into spherical particles with a diameter of 0.1mm-1mm using a spray dryer. The solid round billet is heated to 1250℃ and held at that temperature. After the billet exits the furnace, it is pierced by an upper piercing machine. When the mandrel 1 is completely submerged in the billet, the powder spraying machine 5 is turned on to spray the powder. The anti-oxidation powder arrives at the powder outlet 2 through the powder feeding pipe 4. Under the action of compressed air and the powder outlet 2 with its spray nozzle structure, the anti-oxidation powder is sprayed outwards from the spray nozzle 22. The aforementioned anti-oxidation powder mainly consists of an antioxidant and graphite powder. The composition includes benzenesulfinic acid as an antioxidant, although other organic salts can be used instead. Organic salts have low softening points and good film-forming properties. The softening point of the aforementioned organic salts is approximately 750-900℃, which ensures that the coating can form and adhere to the inner wall of the steel pipe during the first piercing process, even when the pipe is cooled. Graphite has lubricating and anti-oxidation effects. Graphite is easily oxidized, preferentially consuming oxygen in the air that is in contact with the inner wall of the steel pipe. The remaining graphite powder can improve lubrication during the second piercing process. The billet from the first piercing is heated a second time, then passed through a piercing mill for a second piercing. The billet from the second piercing process undergoes subsequent processing steps, including three-roll skew rolling, continuous rolling or extrusion → pipe removal → sizing (or reduction) → cooling and straightening → hydrostatic testing (or flaw detection) → marking → warehousing. This process yields high-quality inner wall finish for large-diameter seamless pipes.

[0033] like Figure 2 and Figure 3The diagram shown illustrates the structure of the powder spraying device and the powder outlet structure in the second embodiment of the online preparation method for the anti-oxidation coating on the inner wall of seamless steel pipes according to the present invention. It includes a top head 1, one end of which is connected to a top rod 3. A powder outlet 2 is provided at the rear end of the joint between the top head 1 and the top rod 3. The top head 1 can be freely connected to the top rod 3, or it can be connected to the top rod 3 via a connecting part 6. Multiple powder outlets 2 are circumferentially formed on the connecting part 6. The top rod 3 has a hollow structure and multiple powder feeding pipes 4 and 4' are provided corresponding to the powder outlets 2. The powder feeding pipes are located on the inner wall of the top rod. One end of each powder feeding pipe 4 and 4' is connected to one of the multiple powder outlets 2, and the other end is connected to the outlet of the powder spraying machine 5. The method and working principle are the same in the piercing process of seamless steel pipes. The main difference between the second embodiment and the first embodiment lies in the number of powder feeding pipes. In the first embodiment, multiple powder outlets share one powder outlet pipe 4, while in the second embodiment, each powder outlet 2 corresponds to one powder outlet pipe. In the second embodiment, since the powder outlet and the powder feeding pipe correspond one-to-one, the air pressure in each powder outlet pipe is more stable, making the anti-oxidation substance sprayed from each powder outlet more uniform. However, the increase in the number of powder outlet pipes will also increase the cost.

[0034] Because large-diameter seamless steel pipes often require two piercing processes, the billet temperature is heated to 1000℃ to 1300℃ before the first piercing. If no anti-oxidation protection is applied to the inner wall, severe oxidation will occur. The secondary heating before the second piercing will also exacerbate the oxidation of the inner wall of the steel pipe, forming a hard oxide scale. During the second piercing, the oxide scale will crack, causing severe scratches on the inner wall of the steel pipe during the piercing process.

[0035] If the anti-oxidation coating is applied after the first piercing, the inner wall of the steel pipe will already be severely oxidized, which will not significantly improve the quality of the inner wall in the subsequent second piercing process. In the online preparation method of the anti-oxidation coating for the inner wall of seamless steel pipe of this invention, the anti-oxidation coating is prepared online using a powder spraying device simultaneously with the first piercing of the steel billet. In this method, the anti-oxidation powder used is a mixture of benzenesulfinic acid, graphite powder, and ethyl cellulose, in the following weight proportions: benzenesulfinic acid 40-50 parts, graphite powder 53-59 parts, and ethyl cellulose 1-2 parts. To improve the smoothness and uniformity of the anti-oxidation powder spraying, the powder needs to be prepared into spherical particles. These powders are mixed in a specific ratio, and pure water is added to form a slurry. Spherical particles are prepared using a spray dryer and then vacuum-dried at 500°C for 1 hour to obtain spherical particles with a diameter of 0.1 mm-1.0 mm. When the nozzle 1 is inserted into the steel billet, the powder spraying machine 5 is started. The powder spraying machine uses compressed air as power to transport the anti-oxidation powder to the powder outlet 2. The spherical powder has high fluidity, which improves the smoothness of powder spraying and is conducive to improving the dispersion effect of the powder when it comes out of the outlet, thus improving the uniformity of the coating on the inner wall of the steel pipe. The anti-oxidation powder is mainly composed of an antioxidant and graphite powder. The antioxidant is benzenesulfinic acid, but other organic salts can also be used instead. Organic salts have low softening points and good film-forming properties. The softening point temperature of the organic salts is about 750-900℃. This ensures that the coating can form a film when the steel pipe is cooled down during the first piercing. Graphite has the effects of lubrication and anti-oxidation. Graphite is easy to oxidize, so it preferentially consumes the oxygen in the air that is in contact with the inner wall of the steel pipe. The remaining graphite powder can improve the lubrication effect during the second piercing. Because the anti-oxidation coating isolates the steel pipe from air, it protects the inner wall from severe oxide scale formation during secondary heating. This prevents the inner wall from being scratched by oxide scale during secondary piercing. The billet after the second piercing then undergoes subsequent processing steps: three-roll skew rolling, continuous rolling, or extrusion → pipe removal → sizing (or reduction) → cooling and pipe return → straightening → hydrostatic testing (or flaw detection) → marking → warehousing. This process yields high-quality inner wall finish for large-diameter seamless steel pipes.

[0036] In one embodiment, when the online preparation method for the anti-oxidation coating on the inner wall of the seamless steel pipe of the present invention is used during the first piercing, the anti-oxidation coating is prepared online during the second piercing according to the online preparation method for the anti-oxidation coating on the inner wall of the seamless steel pipe during the first piercing. This will further improve the quality of the inner wall of the seamless steel pipe. However, this method will increase the cost. In actual production, it is necessary to comprehensively consider the balance between cost and quality and select a suitable online preparation method for the anti-oxidation coating on the inner wall of the seamless steel pipe.

[0037] The online preparation method for the anti-oxidation coating on the inner wall of seamless steel pipe of the present invention, compared with the existing seamless steel pipe preparation method, can prepare the anti-oxidation coating online at the same time as piercing due to the addition of a powder spraying device. This avoids severe oxidation on the inner wall of the steel pipe after piercing, and prevents quality problems on the inner wall of the steel pipe caused by oxide scale cracking during secondary piercing. It also eliminates the need for costly inner wall grinding operations, saves labor costs, improves production efficiency, and reduces environmental pollution caused by grinding dust.

[0038] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. An online method for preparing an anti-oxidation coating on the inner wall of a seamless steel pipe, comprising the following steps: The steel billet heated to 1000℃ to 1300℃ is placed on the piercing platform; The mandrel moves relative to the steel billet to perform the first piercing; The steel billet is pierced a second time after the first piercing is completed; Its features are, During the first piercing process, when the mandrel is inserted into the steel billet, an anti-oxidation powder is sprayed onto the inner wall of the steel pipe using a powder spraying device. The powder spraying device includes a mandrel, which is a hollow cylindrical shape. One end of the mandrel is connected to the mandrel. Multiple powder outlets are provided at the connection between the mandrel and the mandrel. The powder outlets are connected to the powder spraying machine through a powder feeding pipe set on the inner wall of the mandrel. When the mandrel moves inside the steel billet, the powder spraying machine conveys the anti-oxidation powder to the powder outlets through the powder feeding pipe and sprays the anti-oxidation powder in all directions. The anti-oxidation powder is composed of 40-45 parts of benzenesulfinic acid, 53-59 parts of graphite powder, and 1-2 parts of ethyl cellulose by weight. The anti-oxidation powder is pre-formed as a spherical mixture with a particle diameter of 0.1 mm-1.0 mm. The anti-oxidation powder softens into a film at a temperature of 750℃-900℃, adheres to the inner wall of the steel pipe, and plays a role in isolating oxygen and lubrication during the secondary perforation process.

2. The online preparation method for the anti-oxidation coating on the inner wall of a seamless steel pipe according to claim 1, characterized in that, The powder feeding pipe is a single pipe installed on the inner wall of the top rod, with one end connected to multiple powder outlets and the other end connected to the powder spraying machine.

3. The online preparation method for the anti-oxidation coating on the inner wall of a seamless steel pipe according to claim 1, characterized in that, The powder feeding pipe is configured with multiple pipes corresponding to the powder outlet. The powder feeding pipes are installed on the inner wall of the top rod. One end of each powder feeding pipe is connected to the corresponding powder outlet, and the other end is connected to the powder spraying machine.

4. The online preparation method for the anti-oxidation coating on the inner wall of a seamless steel pipe according to any one of claims 1-3, characterized in that, The powder delivery pipe is a steel pipe.

5. The online preparation method for the anti-oxidation coating on the inner wall of a seamless steel pipe according to any one of claims 1-3, characterized in that, The top head and the top rod are connected by a connecting part.

6. The online preparation method for the anti-oxidation coating on the inner wall of a seamless steel pipe according to claim 5, characterized in that, There are 6 powder outlets, which are evenly distributed circumferentially on the connecting part.

7. The online preparation method for the anti-oxidation coating on the inner wall of a seamless steel pipe according to any one of claims 1-3, characterized in that, The powder outlet is connected to a cover, on which multiple spray nozzles are evenly distributed.

8. The online preparation method for the anti-oxidation coating on the inner wall of a seamless steel pipe according to claim 7, characterized in that, The powder outlet diameter is 30mm-50mm, and the spray nozzle diameter is 2mm-10mm.

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