Hot expanding and upsetting composite molding process method for threaded end part of steel pipe

Abstract

The invention discloses a steel pipe threaded end hot expanding and upsetting composite forming process method, and relates to the technical field of steel pipe machining. The method comprises the steps that firstly, the end of a steel pipe is subjected to hot expanding treatment to form a primary expanding section; and then high-temperature heating is conducted on a local area which is a certain distance away from the pipe end, pressure is applied through combination of the upsetting outer mold and the upsetting inner mold, so that the material flows towards the pipe core direction under axial constraint, and upsetting and thickening of the step part are achieved. Through precise temperature gradient control and mold matching, the wall thickness of the step part can be increased, the sealing contact area is remarkably enlarged, and the sealing performance and the bearing strength of threaded connection are improved. The method is suitable for steel pipe connection under high-pressure working conditions such as oil drilling and deep well operation, and has the advantages of high machining precision, high reliability, long service life and the like.

Description

Technical Field

[0001] This invention relates to the field of steel pipe processing technology, and in particular to a composite forming process of hot expansion and upsetting at the threaded end of a steel pipe. Background Technology

[0002] In high-pressure environments such as oil drilling and deep well operations, the connection performance of steel pipes directly affects operational safety and efficiency. Traditional steel pipe connection methods mainly rely on external connectors such as clamps or flanges. While these methods achieve pipe connection to a certain extent, they increase structural complexity and installation time, and are prone to loosening and poor sealing at the connection points, making it difficult to meet the demands of high torque and high pressure conditions. To address this, existing technologies, such as the integrated heat-shrinking and expansion process for prefabricated steel pipe thread ends proposed in CN119407038A, use continuous operations of heat treatment, diameter reduction, and diameter expansion to form an inner wall step at the steel pipe end, facilitating direct threaded connection, simplifying the structure, and improving connection strength. This method first heats the steel pipe end, then uses an external mold to reduce the diameter, and then replaces the internal mold to expand the diameter, forming a stepped structure that allows the steel pipe to be directly connected to the external thread via internal threads, avoiding the drawbacks of traditional connectors.

[0003] However, this existing process has significant drawbacks in practical applications: because the wall thickness of the stepped section formed after diameter expansion is basically the same as the wall thickness of the steel pipe body, typically only about 10mm, the contact area between the end face and the stepped surface is small when another steel pipe is threaded together, resulting in a narrow sealing surface. This not only reduces the sealing reliability of the connection and easily leads to leakage risks under high-pressure environments, but also limits the load-bearing capacity of the threaded connection, failing to fully meet the requirements for connection strength and durability in harsh environments such as deep wells and oil wells. Furthermore, insufficient wall thickness at the stepped section may cause stress concentration at the root of the thread, easily leading to fatigue cracks during long-term use and affecting the overall structural integrity.

[0004] The root cause of the aforementioned defects lies in the fact that the existing process, with its single-stage expansion operation, can only change the shape of the steel pipe and cannot substantially increase the wall thickness of the stepped section. Although the integrated heat-shrink expansion process improves processing efficiency, the thin-walled nature of the stepped section restricts its widespread application in high-performance fields. Therefore, the industry urgently needs an innovative method that can significantly increase the stepped thickness, expand the sealing contact surface, and improve connection reliability and safety without weakening the overall strength of the steel pipe through process optimization. Summary of the Invention

[0005] The purpose of this invention is to provide a composite forming process for hot expansion and upsetting of the threaded end of a steel pipe, which overcomes the shortcomings of the prior art by locally thickening the stepped part.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a composite forming process of hot expansion and upsetting at the end of a steel pipe thread: firstly, the end of the steel pipe is subjected to hot expansion treatment to initially form an expanded section; then, a predetermined area at the end of the steel pipe is locally heated, and the area is upsetting in the presence of a mold to form a thickened stepped structure on the inner wall of the steel pipe.

[0007] Preferably, the hot expansion treatment includes heating the end of the steel pipe to above the austenitizing temperature and performing an expansion operation.

[0008] More preferably, the upsetting forming process includes high-temperature heating of a local area at the end of the steel pipe and applying pressure using a combination of an upsetting outer mold and an upsetting inner mold.

[0009] More preferably, the outer mold for upsetting is used to limit the radial deformation of the steel pipe, and the inner mold for upsetting has a pushing surface to promote the axial flow of material to achieve upsetting.

[0010] More preferably, the high-temperature heating temperature is higher than the heating temperature of the hot expansion treatment, and the local area is located at a predetermined distance behind the end of the steel pipe.

[0011] More preferably, the wall thickness of the thickened stepped structure is more than 50% greater than the wall thickness of the steel pipe body.

[0012] More preferably, in the upsetting forming process, the advancing speed of the upsetting inner mold is controlled within the range of 5-10 mm / s to ensure sufficient material flow.

[0013] More preferably, after the upsetting and forming process, the process also includes a step of cooling the steel pipe.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] By employing a localized upsetting process, the wall thickness of the stepped section is increased, thereby expanding the sealing contact area. This structural improvement results in a wider sealing band during threaded connections, significantly enhancing the sealing reliability of the joint, making it particularly suitable for the stringent sealing requirements of deep wells and high-pressure conditions. Furthermore, the upsetting process substantially thickens the stepped section, enhancing the load-bearing capacity of the threaded connection. The thickened stepped structure effectively disperses stress concentration at the thread root, avoiding fatigue cracking problems common in traditional thin-walled steps, and significantly extending the service life of the connection. In addition, the improved connection reliability reduces maintenance frequency and accident risks, lowering overall operating costs. Moreover, this process is suitable for retrofitting existing production lines; only upgrades to the mold system and temperature control are needed for industrial application, demonstrating promising prospects for widespread adoption. Attached Figure Description

[0016] Figure 1 This is a schematic cross-sectional view of the steel pipe after hot expansion treatment, which initially forms the expanded section in the embodiment.

[0017] Figure 2 This is a schematic diagram of the steel pipe undergoing upsetting and forming a thickened stepped structure on the inner wall of the steel pipe in the embodiment.

[0018] Figure 3 This is a cross-sectional structural diagram of the steel pipe, the outer formwork of the pier, and the inner formwork of the pier in the embodiment;

[0019] Figure 4 This is a schematic diagram of the overall structure of the inner mold for the piercing process in the embodiment;

[0020] In the picture:

[0021] 1. Steel pipe; 2. Outer formwork for piercing; 3. Inner formwork for piercing. Detailed Implementation

[0022] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention.

[0023] This embodiment takes high-strength steel pipes for oil drilling as an example, but the present invention is not limited to this and is also applicable to the processing of other pipes that require high-strength threaded connections.

[0024] The steel pipe thread end hot expansion and upsetting composite forming process method provided in this embodiment mainly involves first hot expanding the diameter of the steel pipe end to initially form an expanded section; then locally heating a predetermined area of ​​the steel pipe end, and upsetting the area with the help of a mold to form a thickened stepped structure on the inner wall of the steel pipe.

[0025] Preferably, the hot expansion treatment includes heating the end of the steel pipe to above the austenitizing temperature and then performing an expansion operation. Specifically, in this embodiment, the heating temperature is 820°C. This temperature ensures that the steel pipe material is fully austenitized, improving the material's plasticity and deformation capacity. This allows the subsequent expansion operation to proceed smoothly under lower resistance, avoiding defects such as microcracks that may occur during low-temperature expansion, and preventing grain coarsening and decreased mechanical properties caused by excessively high temperatures. It also ensures the stability of the pipe wall thickness after expansion, ensuring that the dimensional accuracy after expansion meets the reference requirements for secondary processing.

[0026] The upsetting process in this embodiment includes high-temperature heating of a local area at the end of the steel pipe and applying pressure using a combination of an outer upsetting mold 2 and an inner upsetting mold 3. Specifically, a local area 140mm from the pipe end is heated to 1250℃, which brings the material in this area to a superplastic state. When the outer upsetting mold 2 and the inner upsetting mold 3 apply pressure, the material in the high-temperature area undergoes significant plastic flow under axial pressure, while the adjacent low-temperature area maintains high strength and forms a natural constraint, effectively guiding the material to gather towards the core of the pipe. This achieves precise upsetting and thickening of the stepped section. This local superplastic forming method ensures a significant increase in the wall thickness of the stepped section (from 10mm to 25mm) while avoiding overall deformation of the steel pipe.

[0027] It should be noted that after the steel pipe 1 initially forms the expanded diameter section, it has an inclined convex surface on its outer periphery. The inner periphery of the upsetting outer mold 2 is provided with a matching limiting inclined surface. In this way, when the upsetting inner mold 3 pushes against the steel pipe 1, the steel pipe 1 will be blocked by the limiting inclined surface, thereby making the position of the steel pipe 1 more stable during the upsetting forming process.

[0028] The specific process methods described above are as follows:

[0029] First, preparatory work is carried out. The steel pipe 1 to be processed is fixed using two spaced clamps to ensure precise alignment between the centerline of the steel pipe 1 and the centerline of the mold. The clamps are hydraulically driven, and the upper clamp can move up and down for reliable clamping. The fixing device is equipped with a laser alignment system, which can monitor the position of the steel pipe in real time and make fine adjustments to ensure that the alignment accuracy is within the controllable range.

[0030] At the start of the process, during the hot expansion stage, a medium-frequency heating coil is used to heat a 200mm area at the end of the steel pipe. The heating temperature is precisely controlled at 820℃, and the holding time is adjusted according to the pipe wall thickness, typically 2-3 minutes. During heating, an infrared thermometer monitors the temperature distribution in real time to ensure uniform temperature across the entire heating area. Once the material reaches full austenitization, the hot expansion inner mold on the die advances at a constant speed to achieve the predetermined expansion amount, ensuring the required shape change and forming a shape like... Figure 1 The structure shown is as follows. Those skilled in the art should know that, since the thermally expanded tube end is actually quite short, the change in tube wall thickness is very small and can be ignored.

[0031] After the hot expansion process, the core upsetting and forming stage begins. A localized area 140mm from the pipe end is heated to 1250℃, while the pipe end and body remain unheated, creating a temperature gradient across the entire pipe. The length of the heated area is controlled within 40±5mm to ensure accurate positioning of the upsetting area.

[0032] In this embodiment, the mold used for upsetting and forming includes an inner upsetting mold 3 and an outer upsetting mold 2. The inner cavity surface of the outer upsetting mold 2 perfectly matches the target step structure on the outer periphery of the steel pipe. The structure of the inner upsetting mold 3 is as follows: Figure 4 As shown in the figure, its rear end has an annular stepped surface for contacting the end face of the steel pipe. Therefore, during the advancement process, as... Figure 3 As shown, the outer upsetting mold 2 provides rigid constraint to the steel pipe, limiting radial deformation, while the inner upsetting mold 3's pushing surface continues to advance steadily after contacting the end face of the steel pipe 1, promoting the flow of material in the high-temperature region towards the pipe core. After upsetting, the system automatically stops advancing. Cooling is performed after demolding.

[0033] The innovation of the composite forming process for hot expansion and upsetting of steel pipe thread ends provided in the above-described embodiments lies in the organic combination of hot expansion and upsetting processes. Through precise temperature field control and mold design, local thickening of the stepped area is achieved. Compared with traditional processes, this not only expands the sealing contact area but also significantly improves the connection strength and extends the fatigue life, fully meeting the usage requirements of harsh conditions such as deep wells and ultra-deep wells.

[0034] To facilitate understanding by those skilled in the art of the improvements of this invention over the prior art, some of the accompanying drawings and descriptions have been simplified. The above embodiments are preferred implementations of this invention. In addition, this invention can be implemented in other ways. Any obvious substitutions without departing from the concept of this technical solution are within the protection scope of this invention.

Claims

1. A composite forming process for hot expansion and upsetting of the threaded end of a steel pipe, characterized in that: First, the end of the steel pipe is thermally expanded to initially form an expanded section; then, a predetermined area at the end of the steel pipe is locally heated, and the area is upsetting and forming with the help of a mold, thereby forming a thickened stepped structure on the inner wall of the steel pipe.

2. The composite forming process of hot expansion and upsetting at the end of a steel pipe thread as described in claim 1, characterized in that: The hot expansion process includes heating the end of the steel pipe to above the austenitizing temperature and then expanding its diameter.

3. The composite forming process of hot expansion and upsetting at the end of a steel pipe thread as described in claim 1, characterized in that: The upsetting and forming process includes high-temperature heating of a local area at the end of the steel pipe and applying pressure using a combination of an outer upsetting mold and an inner upsetting mold.

4. The composite forming process of hot expansion and upsetting at the end of a steel pipe thread as described in claim 3, characterized in that: The outer mold for thickening is used to limit the radial deformation of the steel pipe, and the inner mold for thickening has a pushing surface to promote the axial flow of material to achieve thickening.

5. The composite forming process of hot expansion and upsetting at the end of a steel pipe thread as described in claim 4, characterized in that: The high-temperature heating temperature is higher than the heating temperature of the hot expansion treatment, and the local area is located at a predetermined distance behind the end of the steel pipe.

6. The composite forming process of hot expansion and upsetting at the end of a steel pipe thread as described in claim 1, characterized in that: The wall thickness of the thickened stepped structure is more than 50% greater than that of the steel pipe body.

7. The composite forming process of hot expansion and upsetting at the end of a steel pipe thread as described in claim 1, characterized in that: In the aforementioned upsetting and forming process, the advancing speed of the upsetting inner mold is controlled within the range of 5-10 mm / s to ensure sufficient material flow.

8. The composite forming process of hot expansion and upsetting at the end of a steel pipe thread as described in claim 1, characterized in that: After the upsetting and forming process, the steel pipe is also cooled.

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