A pre-welding segment preheating process and device for straight seam welded pipes

Abstract

This invention discloses a segmented preheating process and apparatus for straight seam welded pipes. The process employs several heating components to preheat the straight seam welded pipes in segments before welding, with each heating component independently controlled and operated. The process includes the following stages: a low-power uniform heating stage, a high-power non-uniform heating stage, and a medium-power non-uniform heat preservation stage. The apparatus includes several heating components arranged sequentially along the weld seam extension direction of the straight seam welded pipe. Each heating component includes a heating blanket and a clamping device for ensuring the heating blanket adheres to the weld seam area of ​​the straight seam welded pipe. This invention targets the segmented preheating of the straight weld seam of thick-walled, long-length Q690D straight seam welded pipes. Compared to welding at room temperature and welding after overall preheating, this invention can maintain the temperature difference of the straight seam welded pipe at the weld point within 10°C during the welding process, achieving uniform preheating before welding. This significantly reduces the risk of pipe scrap due to weld seam cracking, thereby improving the yield rate.

Description

Technical Field

[0001] This invention relates to the field of steel pipe welding technology, and in particular to a preheating process before welding. Background Technology

[0002] With social development and technological advancements, my country's demand for structural steel pipes used in engineering machinery, wind power, and marine engineering is increasing. Straight seam welded pipes possess excellent mechanical properties. Through reasonable production processes and material selection, they exhibit high strength and toughness, capable of withstanding large loads and meeting the mechanical requirements of structural components under various working environments. The high dimensional accuracy of straight seam welded pipes, such as diameter and wall thickness, provides precise dimensional parameters for structural design and manufacturing, contributing to the stability and reliability of the structure. The relatively smooth surface of straight seam welded pipes reduces stress concentration caused by surface defects during use and facilitates subsequent treatments such as corrosion protection and painting.

[0003] Q690D steel is a high-strength structural steel widely used in coal mining machinery, engineering machinery, wind power, and metal structures. Its characteristics include ultra-high strength and good low-temperature performance. Therefore, the production of Q690D straight seam welded pipes, utilizing their high strength, large diameter, large wall thickness, and long length, has led to a year-on-year increase in their use as structural steel pipes for engineering machinery, wind power, and marine engineering. However, Q690D steel has relatively poor weldability. When welding large-walled Q690D straight seam welded pipes at room temperature, weld cracks are prone to occur, restricting the application of large-walled Q690D straight seam welded pipes. This is mainly because the straight weld length of large-walled and long Q690D straight seam welded pipes is 12~12.8m, the wall thickness is generally 22~40mm, the welding speed is 0.8~1.0m / min, and the welding time is 12~16 minutes per pipe. During the welding process, excessive residual stress in the weldment and the formation of brittle structures in the heat-affected zone of the weld lead to weld cracking.

[0004] Preheating is a crucial step in the welding process. Uniform preheating can reduce residual stress in the weldment, increase post-weld cooling time, and thus reduce the formation of hard and brittle structures in the heat-affected zone of the weld. Preheating also acts as a drying method, creating a localized dry area around the weld to reduce moisture content and prevent hydrogen embrittlement. However, due to the slow welding speed and long welding time of thick-walled and long-length Q690D straight seam welded pipes, and the large internal and external surface areas leading to rapid heat dissipation, a large preheating temperature difference exists between the initial and final weld ends. Currently, there is no suitable uniform preheating process for the straight weld seams of thick-walled and long-length Q690D straight seam welded pipes, either domestically or internationally. Summary of the Invention

[0005] This invention provides a segmented preheating process and apparatus for straight seam welded pipes before welding, in order to solve the technical problem mentioned in the background art that the existing preheating methods cannot meet the subsequent welding process requirements of Q690D straight seam welded pipes with large wall thickness and long length, and cannot guarantee the welding quality.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0007] A pre-welding segmented preheating process for a straight seam welded pipe involves using several heating components arranged sequentially along the weld extension direction of the straight seam welded pipe to preheat it in segments before welding. Each heating component is independently controlled and operated. The pre-welding segmented preheating of the straight seam welded pipe using the heating components includes the following stages:

[0008] Phase 1, Low-Power Uniform Heating Stage: The heating power of each heating component is controlled to be equal, and the weld of the straight seam welded pipe is uniformly heated with low heating power. The weld bevel of the Q690D straight seam welded pipe with large wall thickness and long length is characterized by large residual stress and significant Bauschinger effect. Low-power (usually not higher than 120kW) uniform heating can reduce residual stress and weaken the adverse effects of Bauschinger effect, and ensure the roundness of the weld bevel of the straight seam welded pipe.

[0009] Phase Two, High-Power Uneven Heating Stage: The heating power of each heating component is controlled to increase sequentially from the head to the tail of the straight seam welded pipe, resulting in uneven heating of the weld seam. For thick-walled and long-length Q690D straight seam welded pipes, the preheating temperature range is relatively small, and the welding time is relatively long. As welding progresses, a large temperature difference easily appears between the preheating positions at the head and tail. This large preheating temperature difference can easily lead to uneven distribution of welding stress, which in turn can cause welding cracks. By using high-power (usually not less than 150kW) uneven heating of the weld seam, the preheating temperature difference between the head and tail welding positions can be reduced, welding stress can be lowered, and welding cracks can be avoided.

[0010] Phase Three, Medium-Power Non-uniform Heat Insulation Phase: The heating power of each heating component is controlled to be lower than its corresponding heating power in Phase Two, and the heating power of each heating component is maintained to increase sequentially from the head to the tail of the straight seam welded pipe, thus performing non-uniform heat insulation on the weld seam of the straight seam welded pipe. As the wall thickness of the Q690D straight seam welded pipe increases, the temperature difference between the preheating temperature along the wall thickness direction and the length direction of the straight seam welded pipe increases. Medium-power (between low and high power) heat insulation can achieve a smooth transition of the temperature difference along the length direction of the straight seam welded pipe, and heat insulation can also achieve temperature uniformity along the wall thickness direction of the straight seam welded pipe. During welding, welding stress can be reduced, and welding cracks can be avoided.

[0011] As a further preferred embodiment of the above technical solution, in stage one, the heating rate of the heating component is controlled to be 0.3~0.45℃ / s, and the heating time is 1.5~3min. A high heating rate can easily lead to insufficient release of the residual stress in the weld bevel of the pre-bent Q690D straight seam welded pipe with large wall thickness and long length, resulting in insignificant reduction of the Bauschinger effect. A low heating rate cannot meet the production efficiency requirements of the production line.

[0012] As a further preferred embodiment of the above technical solution, after the first stage of heating, the weld surface temperature of the straight seam welded pipe rises to 60~80℃. A low preheating temperature cannot meet the production efficiency requirements of the production line.

[0013] As a further preferred embodiment of the above technical solution, in stage two, the heating rate of the heating components is controlled to be 0.24~0.42℃ / s, the difference in heating rate between adjacent heating components is controlled to be 0.012~0.022℃ / s, and the heating time for each heating component is 4.5~8 minutes. With the increase in heating rate, the release rate of residual stress in the weld bevel of the pre-bent Q690D straight seam welded pipe with large wall thickness and long length increases, significantly reducing the Bauschinger effect and easily leading to a decrease in the roundness accuracy of the straight seam welded pipe. To maintain the roundness of the straight seam welded pipe, the heating rate is appropriately reduced in stage two. An excessively low heating rate cannot meet the production efficiency requirements of the production line.

[0014] As a further optimization of the above technical solution, after the second stage of heating, the weld surface temperature in the corresponding area of ​​the heating component at the head of the straight seam welded pipe rises to 155~184℃. The preheating temperature range for thick-walled and long Q690D straight seam welded pipes is relatively small. High preheating temperatures can easily cause phase transformation in the pipe material, damaging its mechanical and microstructural properties. Low preheating temperatures can easily lead to high welding stress. With a relatively long welding time, a large temperature difference can easily occur between the preheating temperatures at the head and tail welding positions as welding progresses. This large temperature difference can easily lead to uneven welding stress distribution, resulting in welding cracks. By using unevenly heated welds, the preheating temperature difference between the head and tail welding positions can be reduced during welding, lowering welding stress and preventing welding cracks.

[0015] As a further optimization of the above technical solution, in stage three, when the heating power of each heating component is controlled to be lower than the corresponding heating power in stage two, the weld surface temperature of the corresponding area of ​​each heating component decreases by T℃ compared to the weld surface temperature in stage two, where T≤5℃; the holding time for each heating component is 3~5 minutes. As the wall thickness of the Q690D straight seam welded pipe increases, the temperature difference between the preheating temperature along the wall thickness direction and the length direction of the straight seam welded pipe increases. Holding the heat can achieve a smooth transition of the temperature difference along the length direction of the straight seam welded pipe, and it can also achieve temperature uniformity along the wall thickness direction. During welding, this can reduce welding stress and avoid welding cracks. Controlling the weld surface temperature to decrease by T℃ compared to the weld surface temperature in stage two, where T≤5℃, achieves uniform preheating welding of the straight seam welded pipe, ensuring the welding quality of the straight seam welded pipe.

[0016] As a further preferred embodiment of the above technical solution, the heating component is a flexible heating blanket, which covers the weld surface of the straight seam welded pipe to heat the weld. During heating, the heating power is adjusted by controlling the voltage and current of the flexible heating blanket.

[0017] As a further preferred embodiment of the above technical solution, the straight seam welded pipe is a Q690D straight seam welded pipe with a length of 12~12.8m, a wall thickness of 22~40mm, and a diameter of 912~1219mm; the number of heating components is 4, and the length of each heating component is 3~3.2m. If the length of the straight seam welded pipe is increased, heating components can be added directly at the rear.

[0018] As a further preferred embodiment of the above technical solution, the straight seam welded pipe that has undergone the preheating process before welding is sent to the welding process section for welding, and welding begins from the head of the straight seam welded pipe.

[0019] As a further preferred embodiment of the above technical solution, during the welding process of the straight seam welded pipe, the maximum temperature difference at various points along the weld seam of the straight seam welded pipe is less than or equal to 10°C.

[0020] Based on the same technical concept, the present invention also provides a preheating device for welded straight seam welded pipe, comprising a plurality of heating components arranged sequentially along the weld extension direction of the straight seam welded pipe; the heating components include a heating blanket and a pressing device for pressing the heating blanket against the weld area of ​​the straight seam welded pipe.

[0021] This invention provides the necessary hardware foundation for the preheating process described in the above technical solution. This enables the establishment and precise control of a temperature gradient along the weld length, fundamentally solving the core problem of uneven preheating of ultra-long welded pipes. The use of a clamping device ensures tight contact between the heating blanket and the weld surface, minimizing thermal resistance caused by air gaps. This not only improves heating efficiency and saves energy, but also ensures uniform and efficient heat transfer to the welded pipe base material, avoiding localized overheating or underheating, thus guaranteeing preheating quality from a hardware perspective.

[0022] As a further preferred embodiment of the above technical solution, the clamping device is positioned above the heating blanket and includes a telescopic rod and an arc-shaped pressure plate connected to the telescopic rod. The arc-shaped pressure plate moves vertically with the telescopic rod and applies pressure to the heating blanket. The shape of the arc-shaped pressure plate matches the outer surface shape of the straight seam welded pipe. The telescopic rod can be implemented using a cylinder, hydraulic cylinder, or electric push rod to achieve the telescopic function, providing a precisely controllable, vertically downward, stable pressure for the clamping device. This avoids the problem of inconsistent pressure in traditional binding methods. Compared to cumbersome binding and fixing, the telescopic rod drive can achieve rapid pressing and lifting of the heating component, greatly improving production speed and making it suitable for assembly line operations. The arc-shaped pressure plate matches the curvature of the pipe wall, ensuring that the pressure is evenly distributed along the weld area, preventing localized warping of the heating blanket, and further optimizing thermal contact. Furthermore, the above design has a certain tolerance for minor variations in the diameter and wall thickness of the welded pipe. By controlling the stroke of the telescopic rod, it is possible to quickly adapt to welded pipes of different specifications, enhancing the versatility of the device. The range of adaptability to welded pipe diameter can also be improved by replacing the arc-shaped pressure plate.

[0023] As a further preferred embodiment of the above technical solution, the heating blanket is suspended above the straight seam welded pipe via a rope box with a self-retracting function. The heating blanket does not contact the straight seam welded pipe when not under the pressure of the arc-shaped pressure plate. The self-retracting rope box allows the heating blanket to be suspended above the welded pipe without external force. On the one hand, it can be automatically and neatly retracted when not in use, maintaining the cleanliness of the work area and avoiding tangled cables and blankets, facilitating daily inspection, maintenance, and replacement. Simultaneously, the suspended state provides operators with a clear visual space, facilitating observation and positioning, and also facilitating the movement and transportation of the straight seam welded pipe. On the other hand, it ensures rapid separation of the heating blanket from the welded pipe before and after the preheating process. This effectively prevents long-term baking and aging of the heating blanket material by residual heat, and also avoids accidental scratches and damage to the heating blanket caused by pipe movement or other on-site operations, extending the service life of the equipment.

[0024] As a further preferred embodiment of the above technical solution, the preheating device for straight seam welded pipes also includes a frame that can move vertically and horizontally, with the clamping device and heating blanket both mounted on the frame. The entire heating assembly, as a whole, can move rapidly and over a wide range in space to precisely align the weld seam, greatly reducing downtime caused by tooling adjustments. This is particularly suitable for flexible production modes with multiple specifications and small batches. One movable preheating device can serve multiple welding stations or welded pipes in different locations, reducing redundant equipment investment and lowering costs. Simultaneously, the movable frame is easy to integrate with the upper-level control system, laying the hardware foundation for a fully automated positioning-clamping-heating-releasing-removal work cycle. It can even be further developed into a continuous production line, where after heating one section, the heating assembly is moved to another straight seam welded pipe for continuous operation.

[0025] As a further preferred embodiment of the above technical solution, a support assembly is also included for supporting the straight seam welded pipe, which rotates axially under the drive of the support assembly. The support assembly can adjust the weld position of the straight seam welded pipe, reducing the initial transfer operations.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] This invention addresses the segmented preheating of straight seams in thick-walled, long-length Q690D straight seam welded pipes before welding. Compared to welding at room temperature or welding after overall preheating, this invention maintains a temperature difference of less than 10°C at the weld joint, achieving uniform preheating and significantly reducing the risk of pipe scrap due to weld cracking, thereby increasing the yield (by 72-85%). Simultaneously, this invention provides an efficient, reliable, intelligent, and cost-optimized advanced preheating device, ensuring effective preheating while improving the device's operational flexibility and reducing production costs. Attached Figure Description

[0028] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0029] Figure 1 This is a three-dimensional structural diagram of the preheating device for straight seam welded pipe before welding in Example 1.

[0030] Figure 2 This is a schematic diagram (front view) of the preheating device for straight seam welded pipe before welding in Example 1.

[0031] Figure 3 for Figure 2 A cross-sectional view of the device along the AA direction.

[0032] Legend:

[0033] 1. Heating component; 11. Heating blanket; 12. Pressing device; 121. Telescopic rod; 122. Arc-shaped pressure plate; 123. Rope box; 124. Spring; 13. Frame. Detailed Implementation

[0034] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0035] The present invention will now be described in further detail with reference to the accompanying drawings.

[0036] Example 1:

[0037] like Figure 1 , Figure 2 and Figure 3 As shown, the preheating device for straight seam welded pipe in this embodiment includes several heating components 1 arranged sequentially along the weld extension direction of the straight seam welded pipe. The heating component 1 includes a heating blanket 11 and a pressing device 12 for pressing the heating blanket 11 against the weld area of ​​the straight seam welded pipe. The pressing device 12 is fixed on a movable frame 13. The heating blanket 11 is suspended and fixed on the frame 13 by several rope boxes 123 with self-winding function (such as coil springs, wire take-up devices and other commonly used self-winding structures, and can also be further increased with adjustment knobs to adjust the winding tension to adapt to the operation requirements of different working conditions). The pressing device 12 is located above the heating blanket 11 and includes a telescopic rod 121 and an arc-shaped pressure plate 122 connected to the telescopic rod 121. The arc-shaped pressure plate 122 moves vertically with the telescopic rod 121 and applies pressure to the heating blanket 11. The shape of the arc-shaped pressure plate 122 matches the outer surface shape of the straight seam welded pipe. The telescopic rod 121 is fixed on the frame 13, and a spring box (with built-in spring 124) is provided between the two to assist the retraction of the telescopic rod 121.

[0038] The preheating device for straight seam welded pipe in this embodiment also includes a support component for supporting the straight seam welded pipe. The support component can be designed as two parallel and spaced rotating rollers that can rotate axially. The straight seam welded pipe can rotate axially under the drive of the two rotating rollers.

[0039] Example 2:

[0040] The pre-welding segmented preheating process for straight seam welded pipe in this embodiment is carried out using Q690D straight seam welded pipe, which is 12 m long, 22 mm thick, and 912 mm in diameter. The pre-welding segmented preheating process for straight seam welded pipe described in Embodiment 1 includes the following steps:

[0041] S1. The straight seam welded pipe is transported laterally to the carrier component of the preheating station using the pipe delivery trolley. The straight weld seam of the straight seam welded pipe is rotated to the 12 o'clock position using the rotating roller of the carrier component. The arc-shaped pressure plate 122 is lowered by the telescopic rod 121, and four flexible heating blankets 11 with a length of 3m above the preheating station are covered on the straight weld seam, so that the heating blankets 11 fit the weld seam area of ​​the straight seam welded pipe.

[0042] S2. The straight weld seam is preheated using a flexible heating blanket 11, which includes three stages:

[0043] Phase 1: Low-power uniform heating phase

[0044] The four flexible heating blankets 11 use the same power for heating. The voltage of the flexible heating blankets 11 is set to 750V, the initial heating current is 120A to start heating, the average heating rate is about 0.44℃ / second, and the heating takes about 1.5 minutes to raise the surface temperature of the welded pipe (weld seam) to about 60℃.

[0045] Phase Two: High Power, Uneven Heating Stage

[0046] ① Set the voltage of the first flexible heating blanket 11 to 750V, increase the heating current from 120A to approximately 200A, with a heating current increase rate of approximately 17.8A / minute, an average temperature rise rate of approximately 0.352℃ / second, and heating for approximately 4.5 minutes. The surface temperature of the straight weld seam rises to approximately 155℃.

[0047] ② Set the voltage of the second flexible heating blanket 11 to 750V, increase the heating current from 120A to approximately 220A, with a heating current increase rate of approximately 22.2A / minute, an average temperature rise rate of approximately 0.374℃ / second, and heating for approximately 4.5 minutes. The surface temperature of the straight weld seam rises to approximately 161℃.

[0048] ③ Set the voltage of the third flexible heating blanket 11 to 750V, increase the heating current from 120A to approximately 240A, with a heating current increase rate of approximately 26.7A / minute, an average temperature rise rate of approximately 0.396℃ / second, and heat for 4.5 minutes. The surface temperature of the straight weld seam rises to approximately 167℃.

[0049] ④ Set the voltage of the fourth flexible heating blanket 11 to 750V, increase the heating current from 120A to approximately 260A, the heating current increase rate is approximately 31.1A / minute, the average temperature rise rate is approximately 0.418℃ / second, and heating lasts for 4.5 minutes. The surface temperature of the straight weld seam rises to approximately 173℃.

[0050] Phase Three: Medium-Power Uneven Heat Insulation Phase

[0051] ① Set the voltage of the first flexible heating blanket 11 to 750V, reduce the heating current from 200A to approximately 130A, and maintain the temperature for approximately 3.0 minutes. The surface temperature at the straight weld seam is maintained at approximately 152℃.

[0052] ② Set the voltage of the second flexible heating blanket 11 to 750V, reduce the heating current from 220A to approximately 140A, and maintain the temperature for approximately 3.0 minutes. The surface temperature at the straight weld seam is maintained at approximately 158℃.

[0053] ③ Set the voltage of the third flexible heating blanket 11 to 750V, reduce the heating current from 240A to approximately 150A, and maintain the temperature for approximately 3.0 minutes. The surface temperature at the straight weld seam is maintained at approximately 164℃.

[0054] ④ Set the voltage of the fourth flexible heating blanket 11 to 750V, reduce the heating current from 260A to approximately 160A, and maintain the temperature for approximately 3.0 minutes. The surface temperature at the straight weld seam is maintained at approximately 170℃.

[0055] After each of the above heating stages is completed, the telescopic rod 121 of the pressing device 12 retracts, and the heating blanket 11 returns to its initial position.

[0056] S3. After completing the above-mentioned preheating process in segments before welding, the heating blanket 11 stops heating, the telescopic rod 121 of the pressing device 12 retracts, and the heating blanket 11 returns to its initial position to wait for the next welded pipe to be heated; the straight seam welded pipe is sent into the welding station, and welding begins from the end of the straight seam welded pipe corresponding to the first flexible heating blanket 11. The temperature of the welded part of the straight seam welded pipe entering the welding station is 140~150℃ throughout the welding process, and no cracks are found in the straight seam welded pipe after welding.

[0057] Example 3:

[0058] The pre-welding segmented preheating process for straight seam welded pipe in this embodiment is performed on Q690D straight seam welded pipe with a length of 12.5m, a wall thickness of 33.1 mm, and a diameter of 1016 mm. The pre-welding segmented preheating process for straight seam welded pipe described in Example 1 can be implemented, including the following steps:

[0059] S1. The straight seam welded pipe is transported laterally to the carrier component of the preheating station using a pipe delivery trolley. The straight weld seam of the straight seam welded pipe is rotated to the 12 o'clock position using the rotating roller of the carrier component. The arc-shaped pressure plate 122 is lowered by the telescopic rod 121, and four flexible heating blankets 11 with a length of 3.2m above the preheating station are covered on the straight weld seam, so that the heating blankets 11 fit the weld seam area of ​​the straight seam welded pipe.

[0060] S2. The straight weld seam is preheated using a flexible heating blanket 11, which includes three stages:

[0061] Phase 1: Low-power uniform heating phase

[0062] The four flexible heating blankets 11 use the same power for heating. The voltage of the flexible heating blankets 11 is set to 750V, the initial heating current is 140A to start heating, the average heating rate is about 0.34℃ / second, and the heating takes about 2 minutes to raise the surface temperature of the welded pipe (weld seam) to about 71℃.

[0063] Phase Two: High Power, Uneven Heating Stage

[0064] ① Set the voltage of the first flexible heating blanket 11 to 750V, increase the heating current from 140A to approximately 200A, with a heating current increase rate of approximately 9.2A / minute, an average temperature rise rate of approximately 0.248℃ / second, and heating for approximately 6.5 minutes. The surface temperature of the straight weld seam rises to approximately 168℃.

[0065] ② Set the voltage of the second flexible heating blanket 11 to 750V, increase the heating current from 140A to approximately 220A, with a heating current increase rate of approximately 12.3A / minute, an average temperature rise rate of approximately 0.262℃ / second, and heating for approximately 6.5 minutes. The surface temperature of the straight weld seam rises to approximately 173℃.

[0066] ③ Set the voltage of the third flexible heating blanket 11 to 750V, increase the heating current from 140A to approximately 240A, with a heating current increase rate of approximately 15.4A / minute, an average temperature rise rate of approximately 0.277℃ / second, and heat for 6.5 minutes. The surface temperature of the straight weld seam rises to approximately 179℃.

[0067] ④ Set the voltage of the fourth flexible heating blanket 11 to 750V, increase the heating current from 140A to approximately 260A, with a heating current increase rate of approximately 18.5A / minute, an average temperature rise rate of approximately 0.291℃ / second, and heat for 6.5 minutes. The surface temperature of the straight weld seam rises to approximately 184℃.

[0068] Phase Three: Medium-Power Uneven Heat Insulation Phase

[0069] ① Set the voltage of the first flexible heating blanket 11 to 750V, reduce the heating current from 200A to approximately 140A, and maintain the temperature for approximately 4.0 minutes. The surface temperature at the straight weld seam is maintained at approximately 163℃.

[0070] ② Set the voltage of the second flexible heating blanket 11 to 750V, reduce the heating current from 220A to approximately 150A, and maintain the temperature for approximately 4.0 minutes. The surface temperature at the straight weld seam is maintained at approximately 168℃.

[0071] ③ Set the voltage of the third flexible heating blanket 11 to 750V, reduce the heating current from 240A to approximately 160A, and maintain the temperature for approximately 4.0 minutes. The surface temperature at the straight weld seam is maintained at approximately 174℃.

[0072] ④ Set the voltage of the fourth flexible heating blanket 11 to 750V, reduce the heating current from 260A to approximately 170A, and maintain the temperature for approximately 4.0 minutes. The surface temperature at the straight weld seam is maintained at approximately 180℃.

[0073] After each of the above heating stages is completed, the telescopic rod 121 of the pressing device 12 retracts, and the heating blanket 11 returns to its initial position.

[0074] S3. After completing the above-mentioned preheating process in segments before welding, the heating blanket 11 stops heating, the telescopic rod 121 of the pressing device 12 retracts, the heating blanket 11 returns to its initial position to wait for the next welded pipe to be heated, the straight seam welded pipe is sent into the welding station, and welding begins from the end of the straight seam welded pipe corresponding to the first flexible heating blanket 11. The temperature of the welded part of the straight seam welded pipe entering the welding station is 150~165℃ throughout the welding process. The straight seam welded pipe after welding is found to have no cracks.

[0075] Example 4:

[0076] The pre-welding segmented preheating process for straight seam welded pipe in this embodiment is performed on Q690D straight seam welded pipe with a length of 12.8m, a wall thickness of 40mm, and a diameter of 1219mm. The pre-welding segmented preheating process for straight seam welded pipe described in Example 1 can be implemented, including the following steps:

[0077] S1. The straight seam welded pipe is transported laterally to the carrier component of the preheating station using a pipe delivery trolley. The straight weld seam of the straight seam welded pipe is rotated to the 12 o'clock position using the rotating roller of the carrier component. The arc-shaped pressure plate 122 is lowered by the telescopic rod 121, and four flexible heating blankets 11 with a length of 3.2m above the preheating station are covered on the straight weld seam, so that the heating blankets 11 fit the weld seam area of ​​the straight seam welded pipe.

[0078] S2. The straight weld seam is preheated using a flexible heating blanket 11, which includes three stages:

[0079] Phase 1: Low-power uniform heating phase

[0080] The four flexible heating blankets 11 use the same power for heating. The voltage of the flexible heating blankets 11 is set to 750V, the initial heating current is 160A to start heating, the average heating rate is about 0.323℃ / second, and the heating takes about 3 minutes to raise the surface temperature of the welded pipe (weld seam) to about 80℃.

[0081] Phase Two: High Power, Uneven Heating Stage

[0082] ① Set the voltage of the first flexible heating blanket 11 to 750V, increase the heating current from 160A to approximately 200A, with a heating current increase rate of approximately 5A / minute, an average temperature rise rate of approximately 0.306℃ / second, and heating for approximately 8 minutes. The surface temperature of the straight weld seam rises to approximately 184℃.

[0083] ② Set the voltage of the second flexible heating blanket 11 to 750V, increase the heating current from 160A to approximately 220A, with a heating current increase rate of approximately 7.5A / minute, an average temperature rise rate of approximately 0.325℃ / second, and heating for approximately 8 minutes. The surface temperature of the straight weld seam rises to approximately 189℃.

[0084] ③ Set the voltage of the third flexible heating blanket 11 to 750V, increase the heating current from 160A to approximately 240A, with a heating current increase rate of approximately 12.5A / minute, an average temperature rise rate of approximately 0.344℃ / second, and heat for 8 minutes. The surface temperature of the straight weld seam rises to approximately 195℃.

[0085] ④ Set the voltage of the fourth flexible heating blanket 11 to 750V, increase the heating current from 160A to approximately 260A, with a heating current increase rate of approximately 12.5A / minute, an average temperature rise rate of approximately 0.363℃ / second, and heat for 8 minutes. The surface temperature of the straight weld seam rises to approximately 200℃.

[0086] Phase Three: Medium-Power Uneven Heat Insulation Phase

[0087] ① Set the voltage of the first flexible heating blanket 11 to 750V, reduce the heating current from 200A to approximately 150A, and maintain the temperature for approximately 5 minutes. The surface temperature at the straight weld seam is maintained at approximately 180℃.

[0088] ② Set the voltage of the second flexible heating blanket 11 to 750V, reduce the heating current from 220A to approximately 160A, and maintain the temperature for approximately 5 minutes. The surface temperature at the straight weld seam is maintained at approximately 185℃.

[0089] ③ Set the voltage of the third flexible heating blanket 11 to 750V, reduce the heating current from 240A to approximately 170A, and maintain the temperature for approximately 5 minutes. The surface temperature at the straight weld seam is maintained at approximately 190℃.

[0090] ④ Set the voltage of the fourth flexible heating blanket 11 to 750V, reduce the heating current from 260A to approximately 180A, and maintain the temperature for approximately 5 minutes. The surface temperature at the straight weld seam is maintained at approximately 195℃.

[0091] After each of the above heating stages is completed, the telescopic rod 121 of the pressing device 12 retracts, and the heating blanket 11 returns to its initial position.

[0092] S3. After completing the above-mentioned preheating process in segments before welding, the heating blanket 11 stops heating, the telescopic rod 121 of the pressing device 12 retracts, and the heating blanket 11 returns to its initial position to wait for the next welded pipe to be heated; the straight seam welded pipe is sent into the welding station, and the temperature of the welded part of the straight seam welded pipe entering the welding station is 175~185℃ throughout the welding process. The straight seam welded pipe after welding is found to have no cracks.

[0093] Comparative Example 1:

[0094] This comparative example shows a straight seam welded pipe being welded at room temperature. The straight seam welded pipe is a Q690D straight seam welded pipe with a length of 12.8m, a wall thickness of 40mm, and a diameter of 1219mm. After welding at room temperature, cracks appeared in the weld, causing the welded pipe to be scrapped and unusable.

[0095] Comparative Example 2:

[0096] This comparative example compares straight seam welded pipes that were uniformly preheated before welding. The straight seam welded pipe was a Q690D straight seam welded pipe with a length of 12.8m, a wall thickness of 40mm, and a diameter of 1219mm. It was uniformly preheated to 190℃ before welding. After welding, cracks appeared in the weld, causing the welded pipe to be scrapped and unusable.

[0097] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention. The above are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. For those skilled in the art, improvements and modifications obtained without departing from the technical concept of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A segmented preheating process for straight seam welded pipes before welding, characterized in that, A number of heating components arranged sequentially along the weld extension direction of the straight seam welded pipe are used to perform segmented preheating of the straight seam welded pipe before welding. Each heating component is independently controlled and operated. The straight seam welded pipe is a Q690D straight seam welded pipe with a length of 12~12.8m, a wall thickness of 22~40mm, and a diameter of 912~1219mm. The number of heating components is 4, and the length of each heating component is 3~3.2m. The segmented preheating of the straight seam welded pipe before welding using the heating components includes the following stages: Phase 1, Low-Power Uniform Heating Stage: The heating power of each heating component is controlled to be equal, and the weld seam of the straight seam welded pipe is uniformly heated with low heating power; in Phase 1, the heating rate of the heating component is controlled to be 0.3~0.45℃ / s, and the heating time is 1.5~3min; after the heating in Phase 1 is completed, the surface temperature of the weld seam of the straight seam welded pipe rises to 60~80℃; Phase Two, High-Power Non-uniform Heating Stage: The heating power of each heating component is controlled to increase sequentially from the head to the tail of the straight seam welded pipe, resulting in non-uniform heating of the weld seam. In Phase Two, the heating rate of the heating components is controlled to be 0.24~0.42℃ / s, the heating rate difference between adjacent heating components is controlled to be 0.012~0.022℃ / s, and the heating time of each heating component is 4.5~8min. After the heating in Phase Two is completed, the weld surface temperature in the area corresponding to the heating component at the head of the straight seam welded pipe rises to 155~184℃. Phase 3, Medium-Power Uneven Heat Insulation Phase: The heating power of each heating component is controlled to be lower than the corresponding heating power in Phase 2, and the heating power of each heating component is kept to increase sequentially from the head to the tail of the straight seam welded pipe, so as to perform uneven heat insulation on the weld of the straight seam welded pipe.

2. The pre-welding segmented preheating process for straight seam welded pipe according to claim 1, characterized in that, In Phase 3, when the heating power of each heating component is controlled to be lower than the corresponding heating power in Phase 2, the surface temperature of the weld seam in the area corresponding to each heating component decreases by T compared to the surface temperature of the weld seam in Phase 2, where T≤5℃; the holding time of each heating component is 3~5min.

3. The pre-welding segmented preheating process for straight seam welded pipe according to claim 1 or 2, characterized in that, The straight seam welded pipe that has undergone the preheating process is sent to the welding station for welding, and welding begins from the head of the straight seam welded pipe.

4. The pre-welding segmented preheating process for straight seam welded pipe according to claim 3, characterized in that, During the welding process of the straight seam welded pipe, the maximum temperature difference at various points along the weld seam is less than or equal to 10°C.

5. The pre-welding segmented preheating process for straight seam welded pipe according to claim 1 or 2, characterized in that, The preheating device for welded straight seam welded pipe is adopted. The preheating device for welded straight seam welded pipe includes several heating components (1) arranged sequentially along the weld extension direction of the straight seam welded pipe. The heating components (1) include a heating blanket (11) and a pressing device (12) for pressing the heating blanket (11) against the weld area of ​​the straight seam welded pipe.

6. The pre-welding segmented preheating process for straight seam welded pipe according to claim 5, characterized in that, The pressing device (12) is positioned above the heating blanket (11). The pressing device (12) includes a telescopic rod (121) and an arc-shaped pressure plate (122) connected to the telescopic rod (121). The arc-shaped pressure plate (122) moves vertically with the telescopic rod (121) and applies pressure to the heating blanket (11). The shape of the arc-shaped pressure plate (122) matches the outer surface shape of the straight seam welded pipe.

7. The pre-welding segmented preheating process for straight seam welded pipe according to claim 5, characterized in that, The heating blanket (11) is suspended above the straight seam welded pipe by a rope box (123) with a self-winding function. The heating blanket (11) does not contact the straight seam welded pipe when it is not subjected to pressure from the arc-shaped pressure plate (122).

8. The pre-welding segmented preheating process for straight seam welded pipe according to claim 5, characterized in that, The preheating device for welding also includes a frame (13) that can move in both vertical and horizontal directions, and the clamping device (12) and the heating blanket (11) are both installed on the frame (13).

9. The pre-welding segmented preheating process for straight seam welded pipe according to claim 5, characterized in that, It also includes a support assembly for supporting the straight seam welded pipe, which rotates axially under the drive of the support assembly.

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