Medium-frequency induction heat treatment system and process for chromium-molybdenum heat-resistant steel pipeline welded junction

Abstract

The invention relates to the technical field of welding heat treatment, in particular to a medium-frequency induction heat treatment system and process for a chromium-molybdenum heat-resistant steel pipeline welded junction. The system comprises a medium-frequency power supply, the medium-frequency power supply is controlled by a control switch, the medium-frequency power supply is connected with a medium-frequency transformer, the medium-frequency transformer is connected with an induction coil through a compensation capacitor, the medium-frequency power supply is provided with a heat treatment parameter control and display, and the heat treatment parameter control and display is connected with a thermocouple through a compensation lead. According to the medium-frequency induction heat treatment system and process for the chromium-molybdenum heat-resistant steel pipeline welded junction, the process is high in practicability and accurate and reliable in result, and through medium-frequency induction heat treatment, it can be guaranteed that the pipeline heat treatment temperature is uniform, the temperature difference between the inner wall and the outer wall of the welded junction is small, the heat treatment area is uniform in metal structure, and weld strength, plasticity and toughness are good.

Description

Technical Field

[0001] The invention relates to the technical field of welding heat treatment, and in particular to a medium-frequency induction heat treatment system and process for a chromium-molybdenum heat-resistant steel pipeline weld. Background Art

[0002] When processing the weld, medium frequency induction heat treatment is often required. However, when heating the pipe weld, due to the different outer diameters and thicknesses of different pipes, a larger power is required to heat the pipe with a higher thickness, and the power needs to be adjusted accordingly when processing the pipe with a lower thickness. The power of pipe heating is controlled only by manual experience, so it is impossible to accurately adjust the medium frequency induction power supply to the appropriate heating power and the number of turns required by the induction coil, thereby increasing the process cost. Therefore, in view of the above shortcomings, a medium frequency induction heat treatment system and process for chromium-molybdenum heat-resistant steel pipe weld is proposed. Summary of the invention

[0003] 1. Technical issues to be resolved

[0004] The present invention provides a medium-frequency induction heat treatment system and process for chromium-molybdenum heat-resistant steel pipeline welds, thereby avoiding the defects in the prior art that the heating power of the medium-frequency induction power supply and the number of turns of the induction coil cannot be accurately obtained manually due to the different outer diameters and thicknesses of different pipelines, resulting in poor heat treatment effect and excessive process cost.

[0005] (II) Technical solution

[0006] In order to solve the above problems, the present invention provides a medium frequency induction heat treatment system for chromium-molybdenum heat-resistant steel pipeline welds, comprising:

[0007] An intermediate frequency power supply is controlled by a control switch, the intermediate frequency power supply is connected to an intermediate frequency transformer, the intermediate frequency transformer is connected to an induction coil via a compensation capacitor, the intermediate frequency power supply is provided with a heat treatment parameter control and display, and the heat treatment parameter control and display are connected to a thermocouple via a compensation wire.

[0008] The present invention provides a process based on a medium frequency induction heat treatment system for chromium-molybdenum heat-resistant steel pipeline welds, comprising:

[0009] Step S1: measuring the size specifications of the pipe weld to be heat treated, calculating the heating width according to the obtained size specification parameters, and presetting the heating parameters of the heat treatment;

[0010] Step S2: fixing the thermocouple on the pipe weld of step S1, and laying a thermal insulation layer on the outside of the pipe weld;

[0011] Step S3: winding an induction coil on the outer side of the insulation layer in step S2, and connecting the induction coil to a matching medium frequency power supply;

[0012] Step S4: Connect the thermocouple of step S2 to the compensation wire, input the heating parameters preset in step S1 into the heat treatment parameter control and display, and start the medium frequency power supply;

[0013] Step S5: heating the pipe weld. After the temperature of the pipe weld exceeds the calibrated control temperature, the heating speed is determined according to the specifications of the pipe weld. After reaching the specified constant temperature, the constant temperature time is determined according to the specifications of the pipe weld to keep the temperature stable.

[0014] Step S6: After the constant temperature time is reached, the pipe weld joint begins to be cooled. The cooling rate is determined according to the specifications of the pipe weld joint. After the temperature drops to the calibrated control temperature, the pipe weld joint begins to cool naturally.

[0015] Step S7: Wait for the temperature of the pipe weld to drop to room temperature, remove the outer coil and insulation layer of the pipe weld in sequence, and end the heat treatment.

[0016] Preferably, in step S1, the dimensional parameters of the pipe weld include outer diameter and wall thickness, the heating width: Y×70%≤heating width≤Y×140%, Y is a reference value, and its calculation formula is: Y=(outer diameter / wall thickness)0.5×4.5+wall thickness×5.3, unit: mm.

[0017] Preferably, in step S2, the cold end of the thermocouple is exposed to the insulation layer, the temperature of the outer surface of the insulation layer should not be higher than 60°C, the width of the insulation layer is greater than or equal to the heating width of the pipeline, and the thickness of the insulation layer is at least 5 cm.

[0018] Preferably, in step S5, the constant temperature time is optimally 2h to 4h, and when the weld heat treatment thickness is ≤50mm, the shortest insulation time = wall thickness / 25, unit: h, at least 0.5h; when the weld heat treatment thickness is greater than>50mm, the shortest insulation time = 2+(wall thickness-50) / 100, unit: h.

[0019] Preferably, in step S3, the output power of the medium frequency power supply is ≥ (outer diameter / wall thickness) 0.5×wall thickness×outer diameter ÷ 2.6 ÷ 1000, in units of KW, and the power supply oscillation frequency is 400 Hz to 10 kHZ.

[0020] Preferably, the calibration control temperature is a preset basic temperature, the heating rate = 5125 / wall thickness, in °C / h, and the heating rate is not more than 220 °C / h; during the heat treatment insulation period of the weld, the difference between the highest temperature and the lowest temperature of each temperature measuring point is not more than 30 °C; the cooling rate = 6500 / wall thickness, in °C / h, the cooling method is air cooling, and the cooling rate is not more than 260 °C / h.

[0021] Preferably, in step S1, the heating parameters include temperature, time, frequency, power and current, the temperature includes a specified constant temperature, the specified constant temperature is determined by the chromium content of the pipeline weld, and the range of the specified constant temperature is: Cr≤0.5% is 600-650°C, 0.5%﹤Cr≤2% is 650-700°C, 2.25%≤Cr≤3% is 700-760°C, 3%﹤Cr≤10% is 700-760°C; the frequency includes the frequency of alternating current, the frequency of alternating current is 1700-2000Hz; the current is direct current, and the direct current value is 100-180A.

[0022] Preferably, in step S3, the induction coil has 9 to 19 turns, the distance between turns of the induction coil is between 5 mm and 20 mm, and the diameter of the induction coil is 15 mm.

[0023] Preferably, the hot end points of the thermocouple are welded to the temperature sampling points of the weld.

[0024] (III) Beneficial effects

[0025] The medium frequency induction heat treatment system and process for chromium-molybdenum heat-resistant steel pipeline welds provided by the present invention have strong practicability and accurate and reliable results. Through this medium frequency induction heat treatment, it is possible to ensure that the pipeline heat treatment temperature is uniform, the temperature difference between the inner and outer walls of the weld is small, the metal structure in the heat treatment area is uniform, and the weld strength, plasticity and toughness are good. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic structural diagram of a medium frequency induction heat treatment system for a chromium-molybdenum heat-resistant steel pipeline weld according to an embodiment of the present invention;

[0027] Figure 2 The present invention is a flowchart of a medium frequency induction heat treatment process for a chromium-molybdenum heat-resistant steel pipeline weld.

[0028] Among them: 1-control switch; 2-intermediate frequency power supply; 3-intermediate frequency transformer; 4-compensation capacitor; 5-induction coil; 6-heat treatment parameter control and display; 7-compensation wire; 8-thermocouple. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Figure 1 Schematic diagram of the flow chart of the medium frequency induction heat treatment system for the weld of chromium-molybdenum heat-resistant steel pipeline according to an embodiment of the present invention. Figure 1 As shown, the present invention provides a medium frequency induction heat treatment system for chromium-molybdenum heat-resistant steel pipeline welds, comprising:

[0031] An intermediate frequency power supply 2 is controlled by a control switch 1, the intermediate frequency power supply 2 is connected to an intermediate frequency transformer 3, the intermediate frequency transformer 3 is connected to an induction coil 5 via a compensation capacitor 4, the intermediate frequency power supply 2 is provided with a heat treatment parameter control and display 6, and the heat treatment parameter control and display 6 is connected to a thermocouple 8 via a compensation wire 7.

[0032] In this heat treatment system, the intermediate frequency voltage of the intermediate frequency power supply 2 can be converted into the voltage required by the induction coil 5 through the intermediate frequency transformer 3, and the reactive power of the intermediate frequency power supply 2 can be reduced through the compensation capacitor 4. The heat treatment parameter control and display 6 can not only display the temperature sensed by the thermocouple 8 in real time, but also adjust and control related heat treatment parameters, including temperature, time, frequency, power and current.

[0033] Figure 2 Flow chart of the medium frequency induction heat treatment process of the chromium-molybdenum heat-resistant steel pipeline weld according to an embodiment of the present invention. Figure 2 As shown, the present invention provides a process based on a medium frequency induction heat treatment system for chromium-molybdenum heat-resistant steel pipeline welds, comprising:

[0034] Step S1: measuring the size specifications of the pipe weld to be heat treated, calculating the heating width according to the obtained size specification parameters, and presetting the heating parameters of the heat treatment;

[0035] Step S2: fixing the thermocouple on the pipe weld of step S1, and laying a thermal insulation layer on the outside of the pipe weld;

[0036] Step S3: winding an induction coil on the outer side of the insulation layer in step S2, and connecting the induction coil to a matching medium frequency power supply;

[0037] Step S4: Connect the thermocouple of step S2 to the compensation wire, input the heating parameters preset in step S1 into the heat treatment parameter control and display, and start the medium frequency power supply;

[0038] Step S5: heating the pipe weld. After the temperature of the pipe weld exceeds the calibrated control temperature, the heating speed is determined according to the specifications of the pipe weld. After reaching the specified constant temperature, the constant temperature time is determined according to the specifications of the pipe weld to keep the temperature stable.

[0039] Step S6: After the constant temperature time is reached, the pipe weld joint begins to be cooled. The cooling rate is determined according to the specifications of the pipe weld joint. After the temperature drops to the calibrated control temperature, the pipe weld joint begins to cool naturally.

[0040] Step S7: Wait for the temperature of the pipe weld to drop to room temperature, remove the outer coil and insulation layer of the pipe weld in sequence, and end the heat treatment.

[0041] In this heat treatment method, the size parameters of the pipe weld include the outer diameter and wall thickness. The heating width is the vertical distance from the top surface to the bottom surface of the cylinder formed by the induction coil. If the heating width is too narrow, the temperature difference between the inner and outer walls of the weld will be too large, and the stress elimination will not be complete. The range of the heating width is: Y×70%≤heating width≤Y×140%, Y is a reference value, and the calculation formula is: Y=(outer diameter / wall thickness)0.5×4.5+wall thickness×5.3, unit mm. The formula can be used to quickly determine the appropriate heating width. In practical applications, since the width of the insulation layer is greater than or equal to the heating width of the pipe, the heat loss of the pipe can be effectively prevented.

[0042] In practical applications, the thermocouple is fixed on the pipe weld. The thermocouple is made of nickel silicon. The hot end of the thermocouple is welded to the temperature sampling point of the weld. The cold end of the thermocouple is exposed to the insulation layer. The temperature of the outer surface of the insulation layer should not be higher than 60°C. The width of the insulation layer is greater than or equal to the width of the heated pipe. The thickness of the insulation layer is at least 5 cm.

[0043] It should be noted that the thermocouple has a wide temperature measurement range, relatively stable performance and high measurement accuracy. The thermocouple is in direct contact with the object being measured and is not affected by the intermediate medium. It has a fast thermal response time and is flexible to temperature changes. It has a large measurement range and can continuously measure temperature from -40 to +1600℃ with reliable performance.

[0044] In addition, the insulation layer is the insulation material wrapped around the pipeline weld. The insulation thickness should be determined according to the characteristics of the insulation material. The thickness of the outer surface of the insulation layer should not be higher than 60°C. The insulation material should be covered with a whole piece. When splicing, the overlap width of two adjacent insulation materials should be greater than 100mm. When laying multiple layers, the joints between each two layers should be staggered. It should be noted that the insulation material is tied and fixed with metal wire, most of which are high-temperature iron wire, and the insulation material mostly uses hard insulation cotton.

[0045] It should be noted that the induction coil has 9 to 19 turns, the turn-to-turn distance of the induction coil is between 5 mm and 20 mm, and the diameter of the induction coil is 15 mm. Table 1 is a power and induction coil selection table of the present invention. As shown in Table 1, the induction coil is wound around the outside of the insulation layer, and the number of turns of the induction coil is adjusted according to different powers.

[0046] Table 1 Power and induction coil selection table of the present invention

[0047] KW Induction coil turns <10 9 10-20 11 20-30 12 30-40 13 40-50 14 50-60 15 60-70 16 70-80 17 80-90 18 90-100 19

[0048] In practical applications, the output power of the medium frequency power supply is ≥ (outer diameter / wall thickness) 0.5 × wall thickness × outer diameter ÷ 2.6 ÷ 1000, unit KW, the power oscillation frequency is 400HZ ~ 10kHZ. In this heat treatment method, the output power of the medium frequency power supply is calculated by the formula, so that different output powers can be adjusted according to the outer diameters and wall thicknesses of different pipes to prevent excessive power from causing excessive heating speed and affecting the quality of the pipe weld, and to avoid too little power affecting the heating efficiency.

[0049] It should be noted that in terms of operation, the weld binding process of the medium frequency induction heating process is relatively simple. Secondly, in terms of heat treatment quality, the medium frequency induction heating is uniform, and the temperature difference between the inner and outer walls of the weld is low, and the heat treatment quality is good. The medium frequency induction heat treatment process is energy-saving and environmentally friendly, which greatly saves the company's production investment costs and has good economic benefits.

[0050] In this heat treatment method, the calibrated control temperature is the preset basic temperature of the pipe weld. After the temperature of the pipe weld after heating exceeds the calibrated control temperature, the heating rate = 5125 / wall thickness, in °C / h, and the heating rate is not more than 220 °C / h; during the heat treatment insulation period of the weld, the difference between the highest temperature and the lowest temperature of each temperature measuring point is not more than 30 °C; the cooling rate = 6500 / wall thickness, in °C / h, the cooling method is air cooling, and the cooling rate is not more than 260 °C / h; after the temperature of the pipe weld after cooling is less than the calibrated control temperature, natural cooling begins.

[0051] In practical applications, the best constant temperature time is 2h to 4h. When the weld heat treatment thickness is ≤50mm, the shortest insulation time = wall thickness / 25, unit h, at least 0.5h, and the insulation time can be adjusted according to the material-related heat treatment constant temperature requirements; when the weld heat treatment thickness is greater than>50mm, the shortest insulation time = 2+(wall thickness-50) / 100, unit h, and the insulation time can be adjusted according to the material-related heat treatment constant temperature requirements.

[0052] In addition, in the heat treatment method, the heating parameters are controlled and displayed by the heat treatment parameter control and display 6, and the heating parameters include temperature, time, frequency, power and current. The temperature includes a specified constant temperature, and the specified constant temperature is determined by the chromium content of the pipeline weld. The range of the specified constant temperature is: Cr≤0.5% is 600-650°C, 0.5%﹤Cr≤2% is 650-700°C, 2.25%≤Cr≤3% is 700-760°C, and 3%﹤Cr≤10% is 700-760°C; the frequency includes the frequency of alternating current, and the frequency of alternating current is 1700-2000Hz; the current is direct current, and the direct current value is 100-180A.

[0053] It should be noted that Cr is the chromium element of the chemical element. The content of chromium determines the heating temperature. The greater the content of chromium, the higher the heating temperature requirement. After heating to the target temperature, the heating temperature is kept constant. The constant temperature time is determined according to the wall thickness. After the constant temperature ends, cooling is carried out.

[0054] In practical applications, when the magnetic flux surrounded by the conductor loop changes, an induced potential will be generated in the loop. The conductor in the alternating magnetic field will also generate an induced potential due to electromagnetic induction, forming an induced current in the conductor. The induced current overcomes the resistance of the conductor itself and generates Joule heat. This heat is used to heat the conductor itself, causing it to heat up and achieve various thermal processing purposes.

[0055] The medium-frequency induction heat treatment system and process for the weld of the chromium-molybdenum heat-resistant steel pipeline provided by the present invention measures the size of the weld of the chromium-molybdenum heat-resistant steel pipeline to obtain the outer diameter and wall thickness of the pipeline, and then calculates the suitable output power and heating width of the medium-frequency power supply through a formula. At the same time, the number of turns of the induction coil can be adjusted accordingly according to the corresponding heating power value, so as to maximize the utilization of resources and reduce the process cost. At the same time, through this medium-frequency induction heat treatment, it can be ensured that the pipeline heat treatment temperature is uniform, the temperature difference between the inner and outer walls of the weld is small, the metal structure in the heat treatment area is uniform, and the weld strength, plasticity and toughness are good.

[0056] The following is a detailed description of the practical application of this heat treatment process:

[0057] Step S1: Measure the size specifications of the pipe weld to be heat treated, calculate the heating width based on the obtained size specification parameters, and preset the heating parameters for the heat treatment.

[0058] In this embodiment, the pipe weld is made of P22 chromium-molybdenum heat-resistant steel Ф323×48, that is, the outer diameter is 323mm and the wall thickness is 48mm. The reference value Y=(323 / 48) 0.5 ×4.5+48×5.3≈266mm, that is, 186.2mm≤heating width≤372.4mm.

[0059] It should be noted that in the pipe weld, the Cr content is 6%, that is, the heating temperature ranges from 700 to 760°C, the frequency of the AC power is 1800Hz, and the DC current value is 140A.

[0060] Step S2: Fixing the thermocouple on the pipe weld of step S1, and laying a thermal insulation layer on the outside of the pipe weld.

[0061] In this embodiment, the hot end of the thermocouple is fixed at the temperature sampling point of the weld by spot welding, and the thermocouple is tied and fixed together with the weld by high-temperature iron wire. In actual application, a thermal insulation layer is laid, and thermal insulation material is wrapped around the pipe weld. The thermal insulation material is made of hard thermal insulation cotton. At the same time, the cold end of the thermocouple is exposed to the thermal insulation layer. The thermal insulation thickness should be determined according to the characteristics of the thermal insulation material. The thickness of the outer surface of the thermal insulation layer should not be higher than 60°C. The thermal insulation material should be covered with a whole piece. When splicing, the overlap width of two adjacent thermal insulation materials should be greater than 100 mm. When laying multiple layers, the seams between each two layers should be staggered.

[0062] Step S3: Winding an induction coil on the outside of the thermal insulation layer in step S2, and connecting the induction coil to a matching medium frequency power supply.

[0063] In this embodiment, power calculation Y = (323 ÷ 48) 0.5 ×323×48÷2.6÷1000≈15.47KW, the medium frequency power supply power is 10KW<15.47KW<20KW, the number of induction turns is determined to be 11 turns, the coil spacing is 20mm, the diameter of the induction coil is 15mm, the induction coil is wound around the outside of the insulation layer and connected to the matching medium frequency power supply.

[0064] Step S4: Connect the thermocouple of step S2 to the compensation wire, input the heating parameters preset in step S1 into the heat treatment parameter control and display, and start the medium frequency power supply.

[0065] Step S5: heating the pipe weld. After the temperature of the pipe weld exceeds the calibrated control temperature, the heating speed is determined according to the specifications of the pipe weld. After reaching the specified constant temperature, the constant temperature time is determined according to the specifications of the pipe weld to keep the temperature stable.

[0066] In actual application, start the medium frequency power supply, connect the thermocouple compensation wire, set the heat treatment parameters through the heat treatment parameter control and display 6, and start the medium frequency power supply for heat treatment after confirmation. In this embodiment, the calibration control temperature is set to 300°C according to actual needs. After the pipe weld is heated to 300°C, according to the formula, the heating rate = 5125 / 48, the heating rate is 107°C / h, which is not greater than the required 220°C / h. After 4 hours, the temperature rises to 735°C. When the weld heat treatment thickness is ≤50mm, the shortest insulation time = wall thickness / 25, the weld insulation is 1.92h, and the maximum and minimum temperature difference between the temperatures of each temperature measuring point during the weld heat treatment insulation period is not greater than 15°C.

[0067] Step S6: After the constant temperature time is reached, the pipe weld begins to cool down. The cooling rate is determined according to the specifications of the pipe weld. After the temperature drops to the calibrated control temperature, the pipe weld begins to cool down naturally.

[0068] Step S7: Wait for the temperature of the pipe weld to drop to room temperature, remove the outer coil and insulation layer of the pipe weld in sequence, and end the heat treatment.

[0069] In actual application, after reaching the constant temperature time, the weld cooling begins, the cooling rate of the weld = 6500 / 48 (℃ / h), the cooling rate is 135℃ / h, the measured heat treatment temperature drops to the calibrated control temperature of 300℃, which is 4.3h, the actual cooling rate is 101℃ / h, and the heat treatment cooling method should be air cooling and not more than 260℃ / h. When the cooling rate is greater than the specified requirement, the heat treatment should be repeated. When the heat treatment temperature is reduced to 300℃, the weld should be kept in a slow cooling state until the temperature drops to room temperature, the outer coil and insulation cotton are removed, and the heat treatment process is completed.

[0070] In this embodiment, the hardness test after heat treatment shows that the minimum hardness value of the base material is 155HB, the maximum hardness value is 162HB, and the average value is 158.5HB; the minimum hardness value of the heat affected zone is 192HB, the maximum hardness value is 197HB, and the average value is 194.5HB; the minimum hardness value of the weld is 216HB, the maximum hardness value is 219HB, and the average value is 217.5HB. The hardness distribution of the base material, heat affected zone, and weld of the weld heat treatment weld is uniform, which meets the requirements of the design specifications and the hardness is qualified; after 24 hours of heat treatment, there are no reheating cracks and excessive defects through X-ray and ultrasonic testing, and the weld inspection is qualified; the metallographic structure of the weld is pearlite, the organization is evenly distributed, and the metallographic structure meets the design specifications and is qualified; the tensile strength of the weld joint mechanical properties test is 487-500MPa, the transverse surface bending is intact and crack-free, the mechanical properties meet the requirements of the design specifications, and the test is qualified.

[0071] In practical applications, medium-frequency induction causes a certain induced current to be generated on the surface of the workpiece. When the magnetic flux surrounded by the conductor loop changes, an induced potential will be generated in the loop. The conductor in the alternating magnetic field will also generate an induced potential under the action of electromagnetic induction, forming an induced current in the conductor. The induced current overcomes the resistance of the conductor itself and generates Joule heat. This heat is used to heat the conductor itself, causing it to heat up and melt, thereby achieving various thermal processing purposes.

[0072] The medium frequency induction heat treatment system and process for chromium-molybdenum heat-resistant steel pipeline welds provided by the present invention have strong practicability and accurate and reliable results. Through this medium frequency induction heat treatment, it is possible to ensure that the pipeline heat treatment temperature is uniform, the temperature difference between the inner and outer walls of the weld is small, the metal structure in the heat treatment area is uniform, and the weld strength, plasticity and toughness are good.

[0073] The above implementation modes are only used to illustrate the present invention, but not to limit the present invention. Ordinary technicians in the relevant technical field can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also belong to the scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A medium frequency induction heat treatment system for chromium-molybdenum heat-resistant steel pipeline welds, characterized in that: include: An intermediate frequency power supply (2) is controlled by a control switch (1), the intermediate frequency power supply (2) is connected to an intermediate frequency transformer (3), the intermediate frequency transformer (3) is connected to an induction coil (5) via a compensation capacitor (4), the intermediate frequency power supply (2) is provided with a heat treatment parameter control and display (6), and the heat treatment parameter control and display (6) is connected to a thermocouple (8) via a compensation wire (7).

2. A heat treatment process based on the medium frequency induction heat treatment system for chromium-molybdenum heat-resistant steel pipeline welds according to claim 1, characterized in that: include: Step S1: measuring the size specifications of the pipe weld to be heat treated, calculating the heating width according to the obtained size specification parameters, and presetting the heating parameters of the heat treatment; Step S2: fixing the thermocouple on the pipe weld of step S1, and laying a thermal insulation layer on the outside of the pipe weld; Step S3: winding an induction coil on the outer side of the insulation layer in step S2, and connecting the induction coil to a matching medium frequency power supply; Step S4: Connect the thermocouple of step S2 to the compensation wire, input the heating parameters preset in step S1 into the heat treatment parameter control and display, and start the medium frequency power supply; Step S5: heating the pipe weld. After the temperature of the pipe weld exceeds the calibrated control temperature, the heating speed is determined according to the specifications of the pipe weld. After reaching the specified constant temperature, the constant temperature time is determined according to the specifications of the pipe weld to keep the temperature stable. Step S6: After the constant temperature time is reached, the pipe weld joint begins to be cooled. The cooling rate is determined according to the specifications of the pipe weld joint. After the temperature drops to the calibrated control temperature, the pipe weld joint begins to cool naturally. Step S7: Wait for the temperature of the pipe weld to drop to room temperature, remove the outer coil and insulation layer of the pipe weld in sequence, and end the heat treatment.

3. The heat treatment process according to claim 2, characterized in that: In step S1, the dimension parameters of the pipe weld include outer diameter and wall thickness, the heating width: Y×70%≤heating width≤Y×140%, where Y is a reference value and the calculation formula is: Y=(outer diameter / wall thickness) 0.5 ×4.5+wall thickness×5.3, unit: mm.

4. The heat treatment process according to claim 3, characterized in that: In step S2, the cold end of the thermocouple is exposed to the insulation layer, the temperature of the outer surface of the insulation layer should not be higher than 60°C, the width of the insulation layer is greater than or equal to the heating width of the pipeline, and the thickness of the insulation layer is at least 5 cm.

5. The heat treatment process according to claim 3, characterized in that: In step S5, the optimal constant temperature time is 2h to 4h. When the weld heat treatment thickness is ≤50mm, the shortest insulation time = wall thickness / 25, unit: h, at least 0.5h; when the weld heat treatment thickness is greater than >50mm, the shortest insulation time = 2+(wall thickness-50) / 100, unit: h.

6. The heat treatment process according to claim 2, characterized in that: In step S3, the output power of the intermediate frequency power supply ≥ (outer diameter / wall thickness) 0.5 × wall thickness × outer diameter ÷ 2.6 ÷ 1000, unit KW, the power supply oscillation frequency is 400HZ ~ 10kHZ.

7. The heat treatment process according to claim 3, characterized in that: The calibration control temperature is the preset basic temperature, the heating rate = 5125 / wall thickness, in °C / h, and the heating rate is not more than 220 °C / h; during the weld heat treatment insulation period, the difference between the highest temperature and the lowest temperature of each temperature measuring point is not more than 30 °C; the cooling rate = 6500 / wall thickness, in °C / h, the cooling method is air cooling, and the cooling rate is not more than 260 °C / h.

8. The heat treatment process according to claim 2, characterized in that: In step S1, the heating parameters include temperature, time, frequency, power and current. The temperature includes a specified constant temperature, which is determined by the chromium content of the pipeline weld. The range of the specified constant temperature is: Cr≤0.5% is 600-650°C, 0.5%﹤Cr≤2% is 650-700°C, 2.25%≤Cr≤3% is 700-760°C, and 3%﹤Cr≤10% is 700-760°C; the frequency includes the frequency of alternating current, which is 1700-2000Hz; the current is direct current, and the direct current value is 100-180A.

9. The heat treatment process according to claim 2, characterized in that: In step S3, the induction coil has 9 to 19 turns, the distance between turns of the induction coil is between 5 mm and 20 mm, and the diameter of the induction coil is 15 mm.

10. The heat treatment process according to claim 4, characterized in that: The hot end point of the thermocouple is welded to the temperature sampling point of the weld.

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