Postweld heat treatment heating method for thick-wall horizontal pipe section

Abstract

The invention discloses a heating method for postweld heat treatment of a thick-wall horizontal pipe section, an induction heat treatment system is adopted, the induction heat treatment system comprises an induction cable, induction heating equipment, thermocouples, a heat preservation blanket and a heat insulation batten, a plurality of thermocouples are uniformly spot-welded on a weld joint in the circumferential direction, one thermocouple is spot-welded on the top of the weld joint and is arranged as a temperature control thermocouple, and the other thermocouple is arranged as a temperature control thermocouple. The heat preservation blanket is wound on the heat treatment pipe section, the heat insulation batten is arranged on the top of the heat preservation blanket, the induction cable is wound on the outer side of the heat preservation blanket and the outer side of the heat insulation batten, the induction heating device is connected with the induction cable, and heat treatment process parameters are controlled according to signals of the temperature control galvanic couple. The temperature is kept constant for 4-6 minutes every time the temperature is increased by one gradient. 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] The invention belongs to the technical field of pipeline welding, in particular to a post-weld heat treatment heating method for a thick-walled horizontal pipe section. Background Art

[0002] In recent years, there has been a lot of heat treatment work on large-diameter thick-walled pipes in major units in the petrochemical industry, and there are many horizontal pipes in the units, such as the ultra-high-pressure steam pipe P22 of the ethylene unit, with a maximum wall thickness of 79mm, and the thick-walled TP347 pipe of the hydrocracking unit with a maximum thickness of 78mm. At present, the post-weld heat treatment of process pipes in petrochemical units all adopts the resistance heating method. The traditional resistance heating is to heat the pipe through the heating plate, which has a slow transfer speed and serious heat loss. The temperature difference in the wall thickness direction is large, and a long constant temperature time is required to achieve the same temperature of the inner and outer walls; especially for stainless steel pipes with a wall thickness of 50mm or more, there is a risk of reheating cracks after post-weld stabilization heat treatment. In order to solve the shortcomings of the resistance heating heat treatment method for thick-walled pipes, the industry began to introduce induction heat treatment technology. The heat treatment method of induction heating technology is to wrap the induction cable around the pipe, and the energy directly acts on the workpiece. However, when the induction heat treatment is used for the heat treatment of thick-walled horizontal pipes, due to the upward conduction of the pipe heat, there is a temperature difference between the 12 o'clock position on the top of the pipe and the 6 o'clock position on the pipe circumference. Therefore, a method is also needed to solve the problem of circumferential temperature difference in thick-walled horizontal pipes. Summary of the invention

[0003] The present invention provides a post-weld heat treatment heating method for thick-walled horizontal pipe sections to solve the technical problems existing in the known technologies, which can reduce the circumferential temperature difference of the pipeline, quickly make the temperatures of the inner and outer walls consistent, and improve the heat treatment efficiency.

[0004] The technical solution adopted by the present invention to solve the technical problems existing in the known technology is: a post-weld heat treatment heating method for a thick-walled horizontal pipe section, adopting an induction heat treatment system, the induction heat treatment system comprising an induction cable, an induction heating device, a thermocouple, an insulation blanket and an insulation strip, a plurality of the thermocouples are provided, and are evenly spot-welded on the weld along the circumferential direction, wherein one of the thermocouples is spot-welded on the top of the weld and is set as a temperature-controlling thermocouple, the thermocouple is connected to the induction heating device through a compensation wire, the insulation blanket is wound on the heat-treated pipe section, symmetrically about the weld, the insulation strip is arranged on the top of the insulation blanket, the induction cable is wound on the outside of the insulation blanket and the insulation strip, the induction heating device is connected to the induction cable, and the heat treatment process parameters are controlled according to the signal of the temperature-controlling thermocouple, wherein the temperature is increased in a step-by-step manner, and the temperature is kept constant for 4-6 minutes during the temperature increase process.

[0005] The gap between the induction cable and the heat treatment pipe section at the top of the heat treatment pipe section is 30-50 mm higher than that at other positions.

[0006] The heat insulating strips are mica strips or ceramic strips.

[0007] The heat treatment process parameters are as follows: the heating rate is not controlled below 300°C; above 300°C, the heating rate is 5125 / δ (°C / h) and not more than 220°C / h; the cooling rate is 6500 / δ (°C / h) and not more than 260°C / h, where δ is the wall thickness of the pipe section; the final constant temperature time is 1 hour for every 25mm of wall thickness.

[0008] The winding width of the thermal insulation blanket is greater than or equal to the winding width of the induction cable plus 200 mm.

[0009] The winding thickness of the thermal insulation blanket is at least 30 mm.

[0010] The winding width of the induction cable is the width of the uniform temperature 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 uniform temperature 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 uniform temperature zone is 100mm.

[0011] For heat treatment of chrome-molybdenum steel and carbon steel, the constant temperature should be set within the range required by the material.

[0012] The induction cable is an air-cooled high-temperature resistant alloy cable or a water-cooled heating cable.

[0013] Each temperature ramp was 50°C or 100°C.

[0014] The advantages and positive effects of the present invention are: by adopting the induction heating method, the heating area of ​​the weldment is located in the surface layer of the weldment and the local area below, and heat is transferred to the inside of the workpiece and other parts through heat conduction, the temperature distribution is uniform, and the temperature gradient between the inner and outer walls is small. At the same time, by increasing the coupling spacing at the top of the pipe and combining the stage heating method, the circumferential temperature difference of the pipeline can be reduced, and the inner and outer wall temperatures can be quickly consistent, thereby improving the heat treatment efficiency. At the same time, the heat treatment efficiency is guaranteed by the highest temperature point control and temperature setting, and the heat treatment quality is guaranteed. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a structural schematic diagram of the application of the present invention;

[0016] Figure 2 It is a schematic diagram of the thermocouple arrangement in the present invention.

[0017] In the figure: 1. Induction cable; 2. Induction heating equipment; 3. Thermocouple; 4. Thermal insulation blanket; 5. Insulation strips; 6. Heat treatment pipe section; 7. Weld. DETAILED DESCRIPTION

[0018] In order to further understand the content, features and effects of the present invention, the following embodiments are given as examples and described in detail with reference to the accompanying drawings:

[0019] See also Figure 1 and Figure 2 A method for post-weld heat treatment of thick-walled horizontal pipe sections adopts an induction heat treatment system, the induction heat treatment system includes an induction cable 1, an induction heating device 2, a thermocouple 3, an insulation blanket 4 and an insulation strip 5. The thermocouple 3 is provided with a plurality of them, uniformly spot-welded on the weld 7 along the circumference, one of which is spot-welded on the top of the weld 7 and is set as a temperature-controlling thermocouple. The thermocouple 3 is connected to the induction heating device 2 through a compensation wire. The insulation blanket 4 is wound on the heat-treated pipe section 6, and is symmetrical about the weld 7 in the width direction. The insulation strip 5 is arranged on the top of the insulation blanket to play a role of padding. The induction cable 1 is wound on the outside of the insulation blanket 4 and the insulation strip 5. The induction heating device 2 is connected to the induction cable 1 and controls the heat treatment process parameters according to the signal of the temperature-control thermocouple. The temperature rise and temperature drop adopt a step-by-step method. During the temperature rise process, each temperature rise is a gradient and the temperature is kept constant for 4-6 minutes.

[0020] The induction cable is wound around the outside of the insulation blanket in the same way as in the prior art. Ignoring the insulation strips, the gap between the induction coil and the heat treatment pipe section 6 is ensured to be 10 mm to 80 mm. The insulation strips 5 are padded, and the induction coil is raised so that the gap between the induction cable 1 and the heat treatment pipe section 6 is higher than other parts at the 12 o'clock position on the top of the heat treatment pipe section 6. At the same time, combined with the stage heating method, each temperature is increased by a gradient, for example, 100 degrees, and the temperature is kept constant for 5 minutes. During the heat treatment process, the circumferential temperature of the pipeline is highly consistent, and the temperature inside and outside the pipe wall is consistent.

[0021] The more preferred solution of this embodiment is as follows:

[0022] The gap between the induction cable 1 and the heat treatment pipe section 6 is 30-50 mm higher at 12 o'clock on the top of the heat treatment pipe section 6 than other parts. The simulation test shows that during the heating process, the temperature inside and outside the pipe wall is consistent for every 100 degrees heating and 5 minutes of constant temperature, and during the heat treatment process, the circumferential temperature of the pipeline tends to be consistent.

[0023] The heat insulating strips 5 are made of mica strips or ceramic strips.

[0024] The heat treatment process parameters are as follows: the heating rate is not controlled below 300°C; above 300°C, the heating rate is 5125 / δ (°C / h) and not more than 220°C / h; the cooling rate is 6500 / δ (°C / h) and not more than 260°C / h, where δ is the wall thickness of the pipe section; the final constant temperature time is 1 hour for every 25mm of wall thickness.

[0025] The winding thickness of the thermal insulation blanket 4 is greater than or equal to 30 mm; the winding width is greater than or equal to the winding width of the induction cable plus 200 mm.

[0026] The winding width of the induction cable 1 is the average temperature zone width plus 50mm, and is 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 average temperature zone width is the weld width plus 2 times the wall thickness of the pipe section; when the nominal thickness is greater than 50mm, the average temperature zone width is 100mm. It is recommended that the induction cable 1 use air-cooled high-temperature resistant alloy cables or water-cooled heating cables.

[0027] For heat treatment of chrome-molybdenum steel and carbon steel, the constant temperature is set in the range of the constant temperature required for heat treatment of the material. If the constant temperature is required to be 700-750℃, then the constant temperature is set to 700-730℃ to avoid overheating.

[0028] The induction cable 1 is an air-cooled high-temperature resistant alloy cable or a water-cooled heating cable.

[0029] Each temperature ramp was 50°C or 100°C.

[0030] The application of the above heat treatment heating method is now described by taking the ultra-high pressure thick-walled P22 pipeline of an ethylene plant as an example. The pipeline material is P22, the pipe diameter is Ф610mm, and the thickness is 76mm. The above heat treatment heating method is used to perform stress relief heat treatment during the specific construction process.

[0031] The selected induction heat treatment equipment should be able to automatically perform temperature inspections and should 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 an over-temperature protection function.

[0032] First, arrange the thermocouples. The pipe diameter is 610mm. According to the specification, at least 3 thermocouples need to be arranged, and the horizontal pipe should be arranged with a temperature measuring point at the bottom of the weld. Arrange a thermocouple at the top. Therefore, at the 12 o'clock, 6 o'clock, and 3 o'clock positions of the heat treatment pipe section 6, a storage heat treatment electric welder is used to spot weld 3 thermocouples on the weld 7 of the heat treatment pipe section. Connect the compensation wire of the thermocouple 3 to the induction heat treatment equipment 2.

[0033] Arrange the thermocouple 3, with the heat treatment weld as the center, and the width of each layer of insulation blanket is the width of the heating belt plus 200mm. The wall thickness of this pipeline is greater than 50mm, and the width of the uniform temperature zone is 100mm. The width of the heating belt is 5 times the wall thickness of the pipe, that is, 380mm, and the width of all insulation cotton windings is at least 380+200=580mm. Therefore, with the weld as the center, the width of the insulation blanket on both sides is 290mm, and the thickness of the insulation blanket is 40mm. After the insulation blanket is wound, it is tied and fixed with a glass fiber tape.

[0034] Then a mica sheet with a thickness of 30 mm and a width of 50 mm is placed on top of the thermal insulation blanket 4 .

[0035] After the thermal insulation blanket 4 and the mica sheet are installed, the induction cable 1 is wound. The induction cable is wound around the weld joint and the heating width is 380 mm. After winding, it is connected to the induction heating device 2.

[0036] After arranging the thermocouple 3, the insulation blanket 4, and the induction cable 1, complete the following operations: 1) Set the heating rate, cooling rate, constant temperature and constant temperature time on the intelligent control panel of the induction heating equipment. According to the specifications, during heat treatment, there is no control below 300℃, and above 300℃, the heating rate is 5125 / δ(℃ / h), and not more than 220℃ / h, and the cooling rate is 6500 / δ(℃ / h), and not more than 260℃ / h, where δ is the pipe wall thickness; the constant temperature time is 1h for every 25mm wall thickness; after calculation, the heating rate of this pipe section is 67.5℃ / h, and the cooling rate is 85.5℃ / h. The constant temperature time is 3.1h. The P22 material specification requires the constant temperature of heat treatment to be 700-750℃. In order to avoid overheating, the constant temperature is set to 720±10℃. 2) Set the step-by-step heating parameters during the heating process, and set the constant temperature for 5 minutes at the temperature nodes of 100℃, 200℃, 300℃, 400℃, 500℃, etc. The simulation test shows that after the constant temperature time is greater than 5 minutes, there is no obvious change in the temperature difference between the inside and outside of the pipe wall. 3) Set the thermocouple at the 12 o'clock position of the weld as a temperature control thermocouple; after setting the above parameters, press the start button to start the heat treatment. The entire heat treatment process can be observed from the intelligent control panel of the heat treatment equipment.

[0037] The skin effect of induction heat treatment causes the induced current to be concentrated on and below the surface of the workpiece section, and the highest point of current density is related to many factors such as induction frequency and wall thickness, and there is no fixed rule. A large number of tests were conducted this time. When measuring the constant temperature of induction heat treatment, the highest point temperature in the direction of pipe wall thickness may be at the surface or 0mm-12mm below the surface. In order to avoid overheating below the surface during the heat treatment process, the temperature exceeds the critical temperature of the material, causing the pipe section to be scrapped, the constant temperature of heat treatment of chrome-molybdenum steel and carbon steel materials should be set according to the constant temperature range required by the material for heat treatment. If the constant temperature is required to be 700-750℃, the constant temperature is set to 700-730℃.

[0038] Due to the use of induction heating, the heating area of ​​the weldment is located on the surface of the weldment and the local area below. The above step-by-step heating method allows heat to be transferred to the inside of the workpiece through heat conduction, increasing the temperature of the inner wall. At 100°C, 200°C, and 300°C, there is no temperature difference between the inner and outer walls. At 400°C, the inner and outer walls are 8°C, and the inner and outer walls are 3°C after 5 minutes of constant temperature. At the final constant temperature time of 730°C, the temperature difference between the inner and outer walls is 6-12°C. At the same time, due to the installation of insulation strips on the top, the circumferential temperature difference of the pipe is also reduced, and the circumferential temperature difference is only 4-5°C. If the conventional method is used, the temperature difference between the inner and outer walls is 35-40°C, and the circumferential temperature difference is 20°C to 25°C. The quality of heat treatment of horizontal pipelines is better guaranteed.

[0039] 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 above-mentioned specific embodiments, which are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can make many forms without departing from the scope of protection of the present invention and the claims, all of which fall within the scope of protection of the present invention.

Claims

1. A post-weld heat treatment heating method for thick-walled horizontal pipe sections, characterized in that: An induction heat treatment system is used, which includes an induction cable, an induction heating device, a thermocouple, a thermal insulation blanket and thermal insulation strips. There are multiple thermocouples, which are spot welded evenly on the weld along the circumference. One of the thermocouples is spot welded on the top of the weld and is set as a temperature control thermocouple. The thermocouple is connected to the induction heating device via a compensation wire. The insulation blanket is wound around the heat-treated pipe section and is symmetrical about the weld. The insulation battens are arranged on top of the insulation blanket, The induction cable is wound around the outside of the thermal blanket and the insulation battens, The induction heating device is connected to the induction cable, and controls the heat treatment process parameters according to the signal of the temperature control thermocouple, wherein the temperature is increased and decreased in a step manner, and during the temperature increase process, each temperature increase is a gradient, and the temperature is kept constant for 4-6 minutes.

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

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

4. The post-weld heat treatment heating method for thick-walled horizontal pipe sections according to claim 1, characterized in that: The heat treatment process parameters are as follows: the heating rate is not controlled below 300°C; above 300°C, the heating rate is 5125 / δ (°C / h) and not more than 220°C / h; the cooling rate is 6500 / δ (°C / h) and not more than 260°C / h, where δ is the wall thickness of the pipe section; the final constant temperature time is 1 hour for every 25mm of wall thickness.

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

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

7. The post-weld heat treatment heating method for thick-walled horizontal pipe sections according to claim 1, characterized in that: The winding width of the induction cable is the width of the uniform temperature 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 uniform temperature 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 uniform temperature zone is 100mm.

8. The post-weld heat treatment heating method for thick-walled horizontal pipe sections according to claim 1, characterized in that: For heat treatment of chrome-molybdenum steel and carbon steel, the constant temperature should be set within the range required by the material.

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

10. The post-weld heat treatment heating method for thick-walled horizontal pipe sections according to claim 1, characterized in that: Each temperature ramp was 50°C or 100°C.

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