Heating system for postweld heat treatment of thick-wall horizontal pipe section

Abstract

The utility model discloses a thick-wall horizontal pipe section postweld heat treatment heating system which comprises an induction cable, induction heating equipment, a plurality of thermocouples, a heat preservation blanket and a heat insulation batten, the thermocouples are evenly spot-welded on a weld joint in the circumferential direction, one of the thermocouples is spot-welded on the top of the weld joint and is arranged to be a temperature control galvanic couple, and the other thermocouple is arranged to be a temperature control galvanic couple. The thermocouple is connected with the induction heating equipment through a compensation lead, the heat preservation blanket is wound on a heat treatment pipe section and is in bilateral symmetry about a welding seam, the heat insulation batten is arranged at the top of the heat preservation blanket, and the induction cable is wound on the outer sides of the heat preservation blanket and the heat insulation batten. And the induction heating equipment is connected with the induction cable, and heat treatment process parameters are controlled according to signals of the temperature control galvanic couple. By increasing the coupling distance between the tops of the pipes and combining a stage heating mode, the circumferential temperature difference of the pipeline can be reduced, the temperatures of the inner wall and the outer wall can be rapidly consistent, and the heat treatment efficiency is improved.

Description

Technical Field

[0001] This utility model belongs to the field of pipeline welding technology, and in particular to a heating system for post-weld heat treatment of thick-walled horizontal pipe sections. Background Art

[0002] In recent years, heat treatment of large-diameter, thick-walled pipes has become increasingly common in petrochemical plants, particularly for horizontal pipes. Examples include the P22 ultra-high-pressure steam pipe in an ethylene plant, with a maximum wall thickness of 79mm, and the TP347 thick-walled pipe in a hydrocracking unit, reaching a maximum thickness of 78mm. Currently, post-weld heat treatment of process pipes in petrochemical plants typically employs resistance heating systems. Traditional resistance heating heats the pipe through heat conduction via heating elements, resulting in slow heat transfer, significant heat loss, and large temperature differences along the wall thickness. This necessitates prolonged isothermal treatment to achieve uniform temperature between the inner and outer walls. This is especially problematic for stainless steel pipes with a wall thickness of 50mm or more, which risk reheat cracking after post-weld stabilization heat treatment. To address the shortcomings of resistance heating for thick-walled pipes, the industry has begun introducing induction heat treatment technology. Induction heating involves wrapping an induction cable around the pipe, directly applying energy to the workpiece. However, when induction heat treatment is applied to thick-walled horizontal pipes, the upward conduction of heat creates a temperature difference between the top 12 o'clock position and the 6 o'clock position along the circumference of the pipe. Therefore, a method is needed to solve the problem of circumferential temperature difference in thick-walled horizontal pipes. Summary of the Invention

[0003] This utility model provides a heating system for post-weld heat treatment of thick-walled horizontal pipe sections to solve the technical problems existing in the prior art. It can reduce the circumferential temperature difference of the pipe and make the inner and outer wall temperatures quickly uniform, thereby improving the heat treatment efficiency.

[0004] The technical solution adopted by this utility model to solve the technical problems existing in the prior art is as follows: a heating system for post-weld heat treatment of thick-walled horizontal pipe sections, including an induction cable, an induction heating device, thermocouples, a thermal insulation blanket, and thermal insulation strips. Multiple thermocouples are provided and evenly spot-welded to the weld along the circumference. One thermocouple is spot-welded to the top of the weld and is set as a temperature-controlling thermocouple. The thermocouple is connected to the induction heating device through a compensating wire. The thermal insulation blanket is wrapped around the heat-treated pipe section, symmetrically about the weld. The thermal insulation strips are arranged on top of the thermal insulation blanket. The induction cable is wrapped around the outside of the thermal insulation blanket and the thermal insulation strips. The induction heating device is connected to the induction cable and controls the heat treatment process parameters according to the signal from the temperature-controlling thermocouple.

[0005] The coupling distance between the induction cable and the heat treatment pipe section at the top is 30-50mm higher than in other parts.

[0006] The insulation strips are made of mica strips or ceramic strips.

[0007] The wrapping width of the insulation blanket is greater than or equal to the wrapping width of the induction cable plus 200mm.

[0008] The thickness of the insulation blanket is at least 30 mm.

[0009] The winding width of the induction cable is the width of the temperature equalization zone plus 50mm, and not less than 5 times the wall thickness of the pipe section. When the nominal thickness of the pipe section is less than or equal to 50mm, the width of the temperature equalization zone is the weld width plus 2 times the wall thickness of the pipe section; when the nominal thickness is greater than 50mm, the width of the temperature equalization zone is 100mm.

[0010] The induction cable is either an air-cooled high-temperature resistant alloy cable or a water-cooled heating cable.

[0011] The advantages and positive effects of this invention are as follows: Using an induction heating system, the heating area of ​​the weldment is located in a localized area below the surface of the weldment. Heat is transferred to the interior and other parts of the workpiece through heat conduction, resulting in uniform temperature distribution and a small temperature gradient between the inner and outer walls. Simultaneously, by increasing the coupling distance at the top of the pipe and combining it with a staged heating method, the circumferential temperature difference of the pipe can be reduced, and the inner and outer wall temperatures can be quickly made uniform, thus improving heat treatment efficiency. Attached Figure Description

[0012] Figure 1 It is a structural diagram of the utility model;

[0013] Figure 2 This is a schematic diagram of the thermocouple arrangement in this utility model.

[0014] In the diagram: 1. Induction cable; 2. Induction heating equipment; 3. Thermocouple; 4. Insulation blanket; 5. Insulation strips; 6. Heat treatment pipe section; 7. Weld. DETAILED DESCRIPTION

[0015] To further understand the invention content, features, and effects of this utility model, the following embodiments are provided, and detailed descriptions are given below in conjunction with the accompanying drawings:

[0016] Please see Figure 1 and Figure 2A heating system for post-weld heat treatment of a thick-walled horizontal pipe section includes an induction cable 1, an induction heating device 2, thermocouples 3, an insulation blanket 4, and insulating strips 5. Multiple thermocouples 3 are evenly spot-welded circumferentially onto the weld seam 7, with one thermocouple 3 spot-welded to the top of the weld seam 7 and serving as a temperature-controlling thermocouple. The thermocouples 3 are connected to the induction heating device 2 via compensating wires. The insulation blanket 4 is wrapped around the heat-treated pipe section 6, symmetrically positioned about the weld seam 7 in its width direction. The insulating strips 5 are positioned on top of the insulation blanket, serving to elevate the pipe. The induction cable 1 is wrapped around the outside of the insulation blanket 4 and the insulating strips 5. The induction heating device 2 is connected to the induction cable 1 and controls the heat treatment process parameters based on the signals from the temperature-controlling thermocouple.

[0017] The induction cable is wound around the outside of the insulation blanket using the same method as existing technology. Ignoring the insulation strips, the gap between the induction coil and the heat treatment pipe section 6 is ensured to be 10mm to 80mm. Insulation strips 5 are used to raise the induction coil, ensuring that the gap between the induction cable 1 and the heat treatment pipe section 6 is higher at the top 12 o'clock position than at other locations. Simultaneously, combined with a staged heating method, each temperature gradient, for example, 100 degrees Celsius, is maintained for 5 minutes. During the heat treatment process, the circumferential temperature of the pipe is highly consistent, and the temperature inside and outside the pipe wall is uniform.

[0018] The more preferred solution in this embodiment is as follows:

[0019] The gap between the induction cable 1 and the heat treatment pipe section 6 is 30-50mm higher at the top 12 o'clock position of the heat treatment pipe section 6 than at other parts. Simulation tests show that during the heating process, for every 100 degrees Celsius increase, the temperature inside and outside the pipe wall is consistent after 5 minutes of constant temperature. Furthermore, during the heat treatment process, the circumferential temperature of the pipe tends to be consistent.

[0020] The insulating strip 5 is made of mica strip or ceramic strip.

[0021] The insulation blanket 4 has a winding thickness of 30 mm or more and a winding width of 200 mm or more than the winding width of the induction cable.

[0022] The winding width of the induction cable 1 is the width of the temperature equalization zone plus 50mm, and not less than 5 times the pipe section wall thickness. When the nominal thickness of the pipe section is less than or equal to 50mm, the width of the temperature equalization zone is the weld width plus 2 times the pipe section wall thickness; when the nominal thickness is greater than 50mm, the width of the temperature equalization zone is 100mm. It is recommended that the induction cable 1 be an air-cooled high-temperature resistant alloy cable or a water-cooled heating cable.

[0023] The induction cable 1 is an air-cooled high-temperature resistant alloy cable or a water-cooled heating cable.

[0024] Taking an ultra-high pressure, thick-walled P22 pipeline in an ethylene plant as an example, the application of the above-mentioned heat treatment heating method is illustrated. The pipeline material is P22, with a diameter of Ф610mm and a thickness of 76mm. In the specific construction process, the above-mentioned heat treatment heating method is used for stress-relieving heat treatment.

[0025] The selected induction heat treatment equipment should be able to automatically monitor temperature and preferably have the function of automatically selecting the highest temperature measurement point for temperature control. In constant temperature mode, the induction heating power supply should have over-temperature difference protection.

[0026] First, the thermocouples are arranged. The pipe diameter is 610mm, and according to specifications, at least three thermocouples are required. For horizontal pipes, one temperature measuring point should be prioritized at the bottom of the weld. One thermocouple is placed at the top. Therefore, at positions 12, 6, and 3 on the heat-treated pipe section 6, three thermocouples are spot-welded onto the weld 7 of the heat-treated pipe section using an energy storage type heat treatment welding machine. The compensating wires of the thermocouples 3 are then connected to the induction heat treatment equipment 2.

[0027] Arrange thermocouple 3, centering on the heat-treated weld joint. The width of each layer of insulation blanket should be the width of the heating band plus 200mm. Since the pipe wall thickness is greater than 50mm, the equipotential bonding band width is 100mm. The heating band width is 5 times the pipe wall thickness, which is 380mm. Therefore, the total insulation blanket wrapping width should be at least 380 + 200 = 580mm. Thus, centering on the weld joint, the insulation blanket wrapping width on both sides should be 290mm, and the insulation blanket thickness should be 40mm. After wrapping, secure the insulation blanket with fiberglass tape.

[0028] Then place a mica sheet with a thickness of 30mm and a width of 50mm on top of the thermal blanket 4.

[0029] After the insulation blanket 4 and mica sheet are installed, the induction cable 1 is wound around it. The induction cable is wound with the weld joint as the center, and the width is the heating width, which is 380mm. After winding, it is connected to the induction heating device 2.

[0030] After arranging thermocouples 3, insulation blankets 4, and induction cables 1, complete the following operations: I) Set the heating rate, cooling rate, constant temperature, and constant temperature time on the intelligent control panel of the induction heating equipment. According to specifications, during heat treatment, temperatures below 300℃ are not controlled; above 300℃, the heating rate is 5125 / δ (℃ / h), not exceeding 220℃ / h, and the cooling rate is 6500 / δ (℃ / h), not exceeding 260℃ / h, where δ is the pipe wall thickness; the constant temperature time is 1 hour for every 25mm of wall thickness. Calculations show that the heating rate for this pipe section is 67.5℃ / h, and the cooling rate is 85.5℃ / h. The constant temperature time is 3.1 hours. The P22 material specification requires a constant temperature of 700-750℃ for heat treatment; to avoid overheating, the constant temperature is set to 720±10℃. (ii) Set step-by-step heating parameters during the heating process, and maintain a constant temperature for 5 minutes at temperature nodes such as 100℃, 200℃, 300℃, 400℃, and 500℃. Simulation tests show that after a constant temperature duration of more than 5 minutes, there is no significant change in the temperature difference between the inside and outside of the pipe wall. (iii) Set the thermocouple at the 12 o'clock position of the weld as a temperature-controlled thermocouple; after setting all the above parameters, press the start button to begin heat treatment. The entire heat treatment process can be observed from the intelligent control panel of the heat treatment equipment.

[0031] The skin effect in induction heat treatment causes the induced current to concentrate at and below the surface of the workpiece cross-section. The point of highest current density is related to multiple factors, including the induction frequency and wall thickness, and there is no fixed rule. Extensive experiments were conducted, and during induction heat treatment at constant temperature, the highest temperature point along the pipe wall thickness could be at the surface or 0-12 mm below the surface. To avoid overheating below the surface during heat treatment, exceeding the material's lower critical temperature and causing pipe section scrap, the constant temperature for heat treatment of chromium-molybdenum steel and carbon steel should be set within the required range. For example, if the required constant temperature is 700-750℃, then the constant temperature should be set to 700-730℃.

[0032] Because induction heating is used, the heating area of ​​the weldment is located in a localized area below the surface. The stepped heating method allows heat to be conducted to the interior of the workpiece, increasing the inner wall temperature. At 100℃, 200℃, and 300℃, there is no temperature difference between the inner and outer walls. Starting at 400℃, the temperature difference between the inner and outer walls is 8℃, and after 5 minutes of holding at this temperature, it is 3℃. At the final holding time of 730℃, the temperature difference between the inner and outer walls is 6-12℃. Furthermore, the insulation strips at the top further reduce the circumferential temperature difference of the pipe, to only 4-5℃. With conventional methods, the temperature difference between the inner and outer walls is 35-40℃, and the circumferential temperature difference is 20℃-25℃. This significantly improves the quality of the heat treatment of the horizontal pipe.

[0033] Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and these all fall within the protection scope of the present invention.

Claims

1. A heating system for post-weld heat treatment of thick-walled horizontal pipe sections, characterized in that, Includes induction cables, induction heating equipment, thermocouples, insulation blankets, and insulation strips. Multiple thermocouples are provided and are evenly spot-welded to the weld along the circumference. One of the thermocouples is spot-welded to the top of the weld and is configured as a temperature-controlling thermocouple. The thermocouple is connected to the induction heating device via compensating wires. The insulation blanket is wrapped around the heat-treated pipe section, symmetrically about the weld seam. The insulation strips are arranged on top of the insulation blanket. The induction cable is wound around the outside of the insulation blanket and the insulation strips. The induction heating device is connected to the induction cable and controls the heat treatment process parameters according to the signal from the temperature control coupler.

2. The heating system for post-weld heat treatment of thick-walled horizontal pipe sections according to claim 1, characterized in that, The coupling distance between the induction cable and the heat treatment pipe section at the top is 30-50mm higher than in other parts.

3. The heating system for post-weld heat treatment of thick-walled horizontal pipe sections according to claim 1, characterized in that, The insulation strips are made of mica strips or ceramic strips.

4. The heating system for post-weld heat treatment of thick-walled horizontal pipe sections according to claim 1, characterized in that, The wrapping width of the insulation blanket is greater than or equal to the wrapping width of the induction cable plus 200mm.

5. The heating system for post-weld heat treatment of thick-walled horizontal pipe sections according to claim 1, characterized in that, The thickness of the insulation blanket is at least 30 mm.

6. The heating system for post-weld heat treatment of thick-walled horizontal pipe sections according to claim 1, characterized in that, The winding width of the induction cable is the width of the temperature equalization zone plus 50mm, and not less than 5 times the wall thickness of the pipe section. When the nominal thickness of the pipe section is less than or equal to 50mm, the width of the temperature equalization zone is the weld width plus 2 times the wall thickness of the pipe section; when the nominal thickness is greater than 50mm, the width of the temperature equalization zone is 100mm.

7. The heating system for post-weld heat treatment of thick-walled horizontal pipe sections according to claim 1, characterized in that, The induction cable is either an air-cooled high-temperature resistant alloy cable or a water-cooled heating cable.

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