Ultra-narrow gap and ultra-low temperature pipeline circumferential weld stress reduction method

Abstract

The invention provides an ultra-narrow gap and ultra-low temperature pipeline circumferential weld stress reduction method. The method comprises the steps that heating belts are used at the positions, with a certain distance, of the two sides of a weld joint for heating, the heating, heat preservation and cooling processes are controlled, and stress reduction and stress homogenization are achieved. The device for realizing the method comprises a heating power supply, two thermal insulation layers and two heating mechanisms, the two heat preservation layers are arranged on the two sides of a pipeline welding seam correspondingly and wrap a pipeline. The two heating mechanisms are arranged on the two heat preservation layers correspondingly to form two heating areas. And the two heating mechanisms are connected with a heating power supply. The problems caused by wide heating band and high heating temperature of a traditional heat treatment method are effectively avoided, an anti-corrosion layer is effectively prevented from being damaged, and the method is more suitable for the site and higher in practicability; the heat treatment process is low in temperature, short in time, low in energy consumption and good in social and economic benefits, the stress level of the pipeline can be effectively regulated and controlled, stress distribution is uniform, and the stress reduction effect is good.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline residual stress reduction, and in particular to a method for reducing pipeline residual stress at an ultra-narrow gap and an ultra-low temperature. Background Art

[0002] In recent years, the number of pipelines in my country has increased rapidly and has been widely used. The presence of large residual stress will affect the mechanical properties of the pipeline and reduce its safety margin. It is an important reason for the brittle fracture or even failure of the welded joint. Therefore, it is very important to reduce the residual stress at the pipeline welded joint. Among the commonly used stress reduction methods, the hammer method, ultrasonic impact method and other methods have certain limitations due to the complex on-site conditions, high cost, high operation difficulty and unstable stress reduction degree. There are many problems when using traditional heat treatment methods for stress reduction, such as high heating temperature, long heating time, heating temperature bandwidth, organizational deterioration, unclear stress reduction on the inner wall and poor social and economic benefits. In order to avoid these problems, traditional high-temperature heat treatment methods are currently banned.

[0003] Based on the above problems, it is necessary to propose a new heat treatment method to relieve the stress of the pipeline. Summary of the invention

[0004] The purpose of the present invention is to solve at least one of the above-mentioned deficiencies in the prior art. For example, one of the purposes of the present invention is to provide a method for reducing residual stress in pipelines with a heating zone width of no more than 90 mm, a peak temperature of no more than 200° C., a heat treatment process of no more than 2 hours, and a significant reduction in stress level.

[0005] In order to achieve the above object, the present invention provides a pipeline residual stress reduction method.

[0006] The method comprises: heating both sides of the pipeline weld for heat treatment to achieve stress relief and stress homogenization; wherein the heating areas on both sides do not contact the weld.

[0007] Optionally, the width of the heating area does not exceed 90 mm.

[0008] Optionally, the peak temperature of the heating is not higher than 200°C.

[0009] Optionally, the heating time does not exceed 2 hours.

[0010] Optionally, the heating is performed by laying a heating tape or winding an induction coil.

[0011] Optionally, the heating area is an annular area, and the heating areas on both sides are symmetrically distributed around the center of the weld.

[0012] Optionally, the heating includes five stages: rapid heating, slow heating, heat preservation, rapid cooling and slow cooling.

[0013] Optionally, the position of the heating zone, the width of the heating zone and the process control parameters of the heat treatment are determined by numerical simulation.

[0014] Optionally, the numerical simulation process includes: establishing a finite element model of a pipeline welding joint; adding a heating area on both sides of the weld respectively, and the heating area does not contact the weld; selecting different heating area positions, heating area widths and heat treatment process control parameters to simulate the heat treatment process, and comparing the effects of different parameters on stress reduction; and determining appropriate parameters based on the effects while ensuring the stress reduction effect.

[0015] Optionally, the method further comprises: verifying the result determined by the numerical simulation through experiments.

[0016] Optionally, the method can be implemented by the following device, including a heating power supply, a first insulation layer, a first heating mechanism, a second insulation layer and a second heating mechanism; wherein the first insulation layer and the second insulation layer are respectively arranged on both sides of the pipeline weld and wrap the pipeline; the first and second heating mechanisms are respectively arranged on the first insulation layer and the second insulation layer to form two heating areas on both sides of the pipeline weld; the first heating mechanism and the second heating mechanism are both connected to the heating power supply.

[0017] Optionally, the device for implementing the method further comprises a temperature measuring mechanism, which can measure the temperature of the inner and outer surfaces of the pipeline at the heating area and the temperature of the anti-corrosion layer. Further, the temperature measuring mechanism may comprise a thermocouple.

[0018] Optionally, in the apparatus for implementing the method, the first heating mechanism and the second heating mechanism both comprise induction coils or heating belts.

[0019] Optionally, in the device for implementing the method, the heating power supply can control the heating processes of the two heating mechanisms.

[0020] Optionally, in the device for implementing the method, the heating power supply may include a medium frequency induction heating power supply.

[0021] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0022] (1) The present invention uses a narrow heating belt on both sides of the weld to perform local heat treatment. The heating process temperature is low, which effectively avoids the problems caused by the wide heating belt and high heating temperature of the traditional heat treatment method, effectively prevents the anti-corrosion layer from being damaged, is more suitable for on-site use, and is more practical.

[0023] (2) The present invention can effectively control the stress level of the pipeline and make the stress distribution uniform, and the stress reduction effect is good. The heat treatment process of the present invention has low temperature, short time, low energy consumption, good social and economic benefits, and good economy.

[0024] (3) The present invention can effectively solve the problem of stress reduction during local heat treatment of pipelines. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The above and other objects and / or features of the present invention will become more apparent through the following description in conjunction with the accompanying drawings, in which:

[0026] Figure 1A A simulated schematic diagram showing the location of the heating belt of the present invention.

[0027] Figure 1B for Figure 1A Corresponding physical picture.

[0028] Figure 2 The temperature cycle curve determined by the present invention is shown.

[0029] Figure 3 The temperature distribution cloud diagram for different heating zone widths and peak temperatures is shown.

[0030] Figure 4 The stress distribution diagram of each welding layer before and after heat treatment obtained by finite element simulation of the present invention is shown.

[0031] Figure 5 A schematic diagram of a device for implementing a pipeline residual stress reduction method according to the present invention is shown.

[0032] Figure 6 The stress distribution cloud diagram before and after heat treatment and the Von Mises stress distribution diagram at the root weld are shown.

[0033] Figure 7 The figure shows a comparison of the stress relief effects of the existing heat treatment method and this method for the same pipe with different diameters.

[0034] Figure 8 The figure shows the comparison of VonMises stress distribution cloud diagrams of the inner and outer walls and cross-sections of the same pipe before and after heat treatment using different parameters.

[0035] Description of main reference numerals:

[0036] 1-heating power supply, 2-insulation layer, 3-heating mechanism, 41-thermocouple, 42-thermocouple socket, 5-anti-corrosion layer, 6-weld, 7-welding heat affected zone. DETAILED DESCRIPTION

[0037] Hereinafter, the ultra-narrow gap and ultra-low temperature pipeline girth weld stress relief method of the present invention will be described in detail in conjunction with exemplary embodiments.

[0038] Exemplary Embodiment 1

[0039] After welding, there is a large residual stress in the pipeline. In order to reduce the stress, the present invention lays a heating belt at a certain distance on both sides of the weld for heat treatment. During the heat treatment process of the heating belt, stress reduction and homogenization are achieved through temperature and constraint.

[0040] The pipeline residual stress reduction method of the present invention is also called an ultra-narrow gap, ultra-low temperature pipeline residual stress reduction method, comprising: symmetrically setting a heating area on both sides of the pipeline ring weld to perform heat treatment, controlling its heating, insulation and cooling processes to achieve stress reduction and stress uniformization; wherein, the heating area is spaced a certain distance from the weld, and the heat treatment will not damage the anti-corrosion layer on both sides of the weld.

[0041] In this embodiment, the heating area is an annular area, and heating can be performed by laying a heating belt or winding an induction coil. The two heating areas can be symmetrically distributed relative to the weld.

[0042] In this embodiment, the width of the heating area does not exceed 90 mm, for example, 85, 80, 75, 70, 65, 55, 40 mm, etc.

[0043] In this embodiment, the heat treatment may include five stages: rapid heating, slow heating, heat preservation, rapid cooling and slow cooling. Among them, the peak temperature has a greater impact on the stress relief effect. To ensure that the anti-corrosion layer is not damaged, the peak temperature does not exceed 200°C, such as 85°C, 100°C, 110°C, 130°C, 150°C, 160°C, 170°C, 190°C, 195°C, etc.

[0044] The heat treatment time does not exceed 2 hours, for example 1 hour, 1.5 hours, etc.

[0045] In this embodiment, refer to Figure 5 The heat treatment process can use a pipeline residual stress reduction device. Taking the thermocouple, insulation blanket, heating belt or induction coil, thermocouple socket and medium frequency induction heating power supply of a specific structure as an example, after fixing the thermocouple at the position where temperature measurement is required, fix the insulation blanket, lay heating belts or wrap induction coils on both sides of the weld outside the insulation blanket; connect the heating belt or induction coil to the medium frequency induction heating power supply to control its heating, insulation and cooling processes.

[0046] In this embodiment, the position of the heating area, the width of the heating area and the process control parameters of the heat treatment may be determined by numerical simulation.

[0047] Numerical simulation can use SYSWELD software to establish a finite element model of the pipeline welding joint. The grids near the weld and the heat-affected zone are dense, and the grids far away from the weld are sparse, which shortens the time used while ensuring the simulation accuracy. A heating belt is added at a certain distance on both sides of the weld, and the pipeline is heat treated after welding is completed and cooled. Different parameters such as heating belt width, heat treatment peak temperature and holding time are selected to simulate the heat treatment process, and the effects of different parameters on stress reduction are compared. Determine the appropriate parameters under the premise of ensuring the stress reduction effect and complete the heat treatment temperature cycle curve.

[0048] Furthermore, the accuracy of the simulation results with the same parameters can also be verified by experimental verification: before heat treatment, the thermocouple is fixed to the heating belt and anti-corrosion layer on the inner and outer surfaces of the pipeline, and the temperature of each location on the inner and outer walls of the pipeline during the heat treatment process is determined. Wrap the insulation blanket at the location where the heat treatment is required on the outer surface of the pipeline and fix it, wrap the induction coil or lay the heating belt outside the insulation blanket, connect it to the induction heating power supply and heat treat it by inputting the temperature cycle curve. During the heat treatment process, the anti-corrosion layer is prevented from being damaged due to excessive temperature. After the heat treatment is completed, after the pipeline is cooled to room temperature, the stress conditions at 0, 3, and 6 points are measured respectively, and compared with the stress size before heat treatment after the welding is completed and cooled, to determine the degree of stress reduction. The experimental verification results are combined with the numerical simulation results, and the influence of various factors on the degree of stress reduction and the most suitable heat treatment process parameters are determined according to the stress relief effect under different processes, so as to verify the stress relief effect of the pipeline girth weld stress relief method proposed in the present invention. In addition, the experimental verification can also verify the stress relief effect achieved by the method of the present invention.

[0049] Exemplary Embodiment 2

[0050] The present invention provides a pipeline residual stress reduction method, which improves the stress distribution in the weld area by laying a narrow heating belt on both sides of the weld and heating it at low temperature for a short time, thereby achieving a significant reduction in residual stress. The method may specifically include the following steps:

[0051] (1) Determine the parameters of the pipeline that needs to be heat treated: determine the material, wall thickness, diameter, weld size, welding material and other related parameters of the pipeline, establish a model to simulate the welding process, and determine the stress when the welding is completed.

[0052] (2) Determine the method of heat treatment: Choose induction heating for heat treatment. This method is easy to achieve precise temperature control, the equipment and its operation are simple and convenient, the degree of automation is high, and it is easier to construct on site.

[0053] (3) Determine the position and size of the heating belt: including the distance between the heating belt and the weld and the width of the heating belt. The width of the heating belt shall not exceed 90 mm. Add a heating belt at a certain distance from the weld on both sides of the weld of the established model, and change the distance between the heating belt and the pipe ring weld, the width of the heating belt and other parameters respectively to determine the optimal position and width of the heating belt when using the same temperature cycle curve for heat treatment.

[0054] (4) Determine the local heat treatment process (heat treatment temperature cycle curve): It is necessary to determine the temperature and heating time of the rapid heating stage, the heating time of the slow heating stage, the peak temperature, the holding time, the temperature and cooling time of the rapid cooling stage, the slow cooling stage time and other parameters to complete the temperature cycle curve. Among them, the appropriate temperature cycle curve can be selected by numerical simulation under the premise of ensuring the stress reduction effect, the peak temperature does not exceed 200°C, the heat treatment process does not take more than 2 hours, and the anti-corrosion layer is not damaged during the heat treatment process.

[0055] (5) Arrangement of thermocouples: After the pipeline is welded and cooled to room temperature, select a suitable thermocouple before heat treatment. After grinding and rust removal of the surface, fix the thermocouple to the heat treatment area and anti-corrosion layer on the inner and outer surfaces of the pipeline. Connect the thermocouple to the induction power supply so that the temperature of each point can be monitored at all times during the heat treatment process.

[0056] (6) Arrangement of heat treatment equipment: including the arrangement of insulation layer and induction coil. The insulation layer shall be laid symmetrically on the outer surface of the pipeline with the weld as the center. The insulation material and thickness of the insulation layer shall comply with the provisions of the design documents, relevant standards and heat treatment process documents. The insulation layer shall be fixed tightly to the surface of the pipeline and shall not loosen or fall off during the heat treatment process. Select a suitable induction power supply and induction coil or heating belt, connect the induction coil or heating belt to the induction heating power supply, and program the temperature cycle curve of the heat treatment process into the induction heating power supply.

[0057] (7) Heat treatment to reduce stress: Heating is performed using the hysteresis thermal effect and eddy current thermal effect of induction heating. The temperature is raised at a certain rate and kept at this temperature for a certain period of time according to the heat treatment temperature cycle curve to reduce stress and make the stress distribution uniform.

[0058] Exemplary Embodiment 3

[0059] This exemplary embodiment provides a device for implementing the pipeline residual stress reduction method in exemplary embodiment 1 or 2. Figure 5 A schematic diagram of a device for implementing a pipeline residual stress reduction method is shown.

[0060] like Figure 5 As shown, the device includes a heating power supply 1, two heat-insulating layers 2, two heating mechanisms 3 and a temperature measuring mechanism.

[0061] Two insulation layers 2 are respectively arranged on both sides of the pipeline weld and wrap the pipeline; the insulation layer 2 may include an insulation blanket.

[0062] Two heating mechanisms 3 are respectively arranged on the two insulation layers 2 to form two heating areas on both sides of the pipeline weld. The heating mechanism 3 may include an induction coil or a heating belt.

[0063] The heating power supply 1 is connected to the two heating mechanisms 3, and the heating power supply 1 can control the heating, heat preservation and cooling processes of the two heating mechanisms. The heating power supply 1 may include a medium frequency induction heating power supply.

[0064] The temperature measuring mechanism can measure the temperature of the inner and outer surfaces of the pipeline at the heating area and the temperature of the anti-corrosion layer. The temperature measuring mechanism may include a plurality of thermocouples 41 and thermocouple sockets 42.

[0065] To further explain the installation process, after fixing the thermocouple at the position where temperature measurement is required, fix the insulation layer such as an insulation blanket, lay heating tape or wound induction coil on both sides of the weld outside the insulation layer, connect the heating tape or wound induction coil to a medium frequency induction heating power supply, and control its heating, insulation and cooling processes.

[0066] In order to better understand the above exemplary embodiments, they are further described below with reference to specific examples.

[0067] Example 1

[0068] The present invention provides a pipeline residual stress reduction method, which has the advantages of ultra-narrow gap and ultra-low temperature, and specifically comprises the following steps:

[0069] (1) Determine the parameters such as the size of the pipeline to be heat treated: the pipeline material is X70 pipeline steel, the diameter is 813 mm, and the wall thickness is 17.5 mm. Build a model, simulate the welding process, and determine the stress when the welding is completed.

[0070] (2) Determine the method of heat treatment: Choose induction heating for heat treatment, which is easy to achieve precise temperature control. Use medium frequency induction heating power supply, the equipment and its operation are simple and convenient, with a high degree of automation, and easier to construct on site.

[0071] (3) Determine the location and size of the heating belt: Figure 1A and Figure 1B A schematic diagram showing the location of the heating belt is shown, wherein: Figure 1A For the simulation diagram, Figure 1B For the real picture, Figure 1A The 200 in the figure means that the anti-corrosion layer is 200 mm away from the weld. Figure 1A and Figure 1BAs shown, the present invention lays heating mechanisms such as heating belts or winding induction coils on both sides of the weld, and the position and width of the heating mechanism are determined by simulating the stress relief effect of different parameters. Figure 1A As shown, a heating mechanism is added at a certain distance from the weld on both sides of the established model weld 6. The distance between the heating mechanism and the pipe ring weld, the width of the heating mechanism and other parameters are changed, and appropriate parameters are determined according to the stress reduction effect.

[0072] (4) Determine the local heat treatment process: Determine the parameters such as the time and temperature of the rapid heating stage, the time of the slow heating stage, the peak temperature, the holding time, the temperature and time of the rapid cooling stage, and the time taken for the slow cooling to room temperature, and draw a diagram such as Figure 2 The heat treatment temperature cycle curve is shown, where T1~T2 is the fast heating zone (fast heating), T2~T3 is the slow heating zone (slow heating), t2~t3 which keeps T3 is the insulation zone, T3~T4 is the fast cooling zone (fast cooling), and T4~room temperature (i.e. stage 5) is the slow cooling zone (slow cooling). The temperature distribution cloud diagrams obtained by simulation at different heating band widths and peak temperatures are shown in the figure below. Figure 3 As shown, Figure 3 The 50, 60, 70, 80, 90 in the first column represent the width of the heating zone, in mm, and the 90, 120, 150, 180 in the first row represent the temperature; because during the heat treatment process, the temperature of the anti-corrosion layer 200mm away from both sides of the weld should be lower than 80℃ to ensure that the anti-corrosion layer is not damaged by high temperature, so Figure 3 The parameters in the red box in the lower right corner do not meet the requirements, so it is determined that the peak temperature of the heat treatment process does not exceed 200℃ and the width of the heating zone does not exceed 90mm. After heat treatment, the stress reduction is obvious and the stress distribution is more uniform, especially for the root weld. Comparing the stress reduction effect under different parameters, the stress reduction effect is best when the edge of the heating zone is 10mm away from the edge of the weld, the width is 80mm, the peak temperature is 120℃, and the holding time is 2400s. The stress distribution before and after heat treatment is as follows Figure 4 As shown in the figure, after heat treatment, the axial stress reduction in the heat-affected zone of the root weld is the largest; as the distance from the weld increases, the stress reduction gradually decreases, and the high stress area transfers from the heat-affected zone to the parent material. The stress reduction of hot welding, filling welding and cap welding is less than that of the root weld, and the stress transfers from the inner surface to the outer surface.

[0073] (5) Arrangement of thermocouples: After the pipeline is welded and cooled to room temperature, the surface is polished and rust-free before heat treatment, and the thermocouples are fixed to the heat treatment parts and anti-corrosion layer on the inner and outer surfaces of the pipeline. The thermocouples are numbered and connected to the induction power supply through the thermocouple socket so that the temperature of each point can be monitored at all times during the heat treatment process. The thermocouple positions are as follows: Figure 5 shown.

[0074] (6) Arrangement of heat treatment equipment: including the arrangement of insulation layer and induction coil. Figure 5 The insulation layer and induction coil are arranged as shown. The insulation layer is laid symmetrically on the outer surface of the pipeline with the weld as the center. The insulation material and the thickness of the insulation layer should comply with the provisions of the design documents, relevant standards and heat treatment process documents. The insulation layer used this time has a zirconium-containing ceramic fiber inner layer and a high-silica cloth outer layer. The insulation layer should be fixed tightly to the surface of the pipeline and should not loosen or fall off during the heat treatment process. Select an induction coil with a diameter of 18mm and a length of 30m, connect it to the medium-frequency induction heating power supply, and write the temperature cycle curve of the heat treatment process into the induction heating power supply.

[0075] (7) Heat treatment to reduce stress: Heating is performed using the hysteresis thermal effect and eddy current thermal effect of induction heating. The temperature is raised at a certain rate according to the temperature cycle curve, and the temperature is kept at a certain time before cooling to reduce stress. The stress is measured and is close to the simulation result. After heat treatment, the stress distribution is uniform and the stress is reduced by about 40%.

[0076] Example 2

[0077] For a pipeline made of X70 pipeline steel, with a diameter of 1016 mm and a wall thickness of 21 mm, the pipeline residual stress reduction method of the present invention is used to reduce stress.

[0078] The pipeline model is established by using the finite element numerical simulation method. After completing the simulation of the pipeline girth weld welding part, the stress relief effect when using different parameters is simulated according to the pipeline girth weld heat treatment stress relief method provided by the present invention.

[0079] By comparing the residual stress distribution after heat treatment under different parameters, it is found that when the peak temperature is 140℃ and the heating zone width is 70mm, the stress reduction effect is the best. The stress distribution cloud diagram before and after heat treatment and the Von Mises stress distribution at the root weld are shown in the figure. Figure 6 As shown, it is obvious that the stress reduction effect at the root weld is obvious after heat treatment, and the overall stress distribution is more uniform.

[0080] It can be seen from this example that, compared with other post-weld stress relief methods and traditional high-temperature heat treatment methods, the heat treatment stress relief method provided by the present invention has the advantage of reducing stress at the root weld.

[0081] Comparative Example 1

[0082] For pipelines made of X80 pipeline steel and with diameters of 813mm and 1016mm, different heat treatment methods were used to simulate the stress conditions before and after heat treatment. The traditional heat treatment method is to perform local high-temperature heat treatment at the weld. After half an hour, the temperature is raised to 700°C and then kept warm for 2 hours, and then cooled to room temperature. The width of the heating zone is 242mm and 292mm respectively. The stress reduction method for the ultra-narrow gap and ultra-low temperature pipeline ring weld is to heat the temperature to 180°C after a rapid heating stage and a slow heating stage, quickly cool to a certain temperature, and then slowly cool to room temperature. The edge of the heating zone is 10mm away from the edge of the weld, and the width of the heating zone is 70mm. The stress distribution cloud diagram before heat treatment and after heat treatment by two methods is shown as follows Figure 7 shown.

[0083] Compared with traditional heat treatment methods, this method has low temperature, short time period, low energy consumption and is more economical; the stress reduction effect is better after heat treatment, especially at the root weld, where the stress reduction effect is obvious.

[0084] Comparative Example 2

[0085] The method of the present invention is simulated by selecting different heating zone temperatures and peak temperatures for a pipeline with a diameter of 813 mm, a wall thickness of 17.5 mm, and a material of X70 pipeline steel. The temperature distribution cloud diagram during the heat treatment process is shown as follows: Figure 3 As shown, the stress distribution cloud diagram before and after heat treatment is as follows Figure 8 As shown ( Figure 8 The stress distribution cloud corresponding to the heating zone width of 90 mm is not included), where: Figure 8 The 50, 60, 70, 80 in the leftmost column represent the width of the heating zone, in mm. The 90, 120, 150, 180 in the next row after the top heat treatment represent the temperature, in °C. The temperature of the anti-corrosion layer at 200mm away from the weld is measured. To ensure that the anti-corrosion layer is not damaged by high temperature, the temperature here should not be higher than 80°C. Figure 3 The results in the red box in the lower right corner do not meet the requirements. Figure 8 Corresponding Figure 3 The results outside the red frame are those in which the anti-corrosion layer is not damaged.

[0086] As the width of the heating zone increases, the temperature of the anti-corrosion layer gradually increases. When the width of the heating zone exceeds 90mm, under the condition of ensuring the stress reduction effect, the selected peak temperatures will lead to excessively high temperatures at the anti-corrosion layer, and the anti-corrosion layer will be damaged. As the peak temperature increases, the temperature at the anti-corrosion layer increases, and the stress reduction effect improves. When the temperature exceeds 200°C, the anti-corrosion layer is easily damaged, but the stress reduction effect is not significantly improved. Therefore, under the premise of ensuring that the anti-corrosion layer is not damaged, considering the stress reduction effect and economy of the heat treatment, the width of the heating zone should not exceed 90mm, and the peak temperature of the heat treatment should not exceed 200°C.

[0087] In summary, compared with the traditional heat treatment method, the present invention uses a narrow heating belt on both sides of the weld for local heat treatment, and the heating process temperature is low, which effectively avoids the problems caused by the wide heating belt and high heating temperature of the traditional heat treatment method, effectively prevents the anti-corrosion layer from being damaged, and is more suitable for the site and more practical. In addition, the heat treatment process has low temperature, short time, low energy consumption, good social and economic benefits, good economy, and can effectively regulate the pipeline stress level and make the stress distribution uniform, with good stress reduction effect.

[0088] Although the present invention has been described above in conjunction with the exemplary embodiments and the accompanying drawings, it should be apparent to those skilled in the art that various modifications may be made to the above-described embodiments without departing from the spirit and scope of the claims.

Claims

1. A pipeline residual stress reduction method, characterized in that: The method comprises: Heat treatment is performed on both sides of the pipeline weld to achieve stress relief and stress equalization, wherein the heated areas on both sides do not contact the weld.

2. The pipeline residual stress reduction method according to claim 1, characterized in that: The width of the heating area does not exceed 90 mm, the peak temperature of the heating is not higher than 200° C., and the heating time does not exceed 2 hours.

3. The pipeline residual stress reduction method according to claim 1, characterized in that: The heating is performed by laying a heating belt or winding an induction coil.

4. The pipeline residual stress reduction method according to claim 1, characterized in that: The heating area is an annular area, and the heating areas on both sides are symmetrically distributed around the center of the weld.

5. The pipeline residual stress reduction method according to claim 1, characterized in that: The heating includes five stages: rapid heating, slow heating, heat preservation, rapid cooling and slow cooling.

6. The pipeline residual stress reduction method according to claim 1, characterized in that: The position of the heating zone, the width of the heating zone and the control parameters of the heat treatment are determined by numerical simulation.

7. The pipeline residual stress reduction method according to claim 6, characterized in that: The numerical simulation process includes: Establish a finite element model of the pipeline welding joint; add a heating area on both sides of the weld respectively, and the heating area does not contact the weld; The heat treatment process was simulated by selecting different heating area positions, heating area widths and heat treatment process control parameters, and the effects of different parameters on stress relief were compared. According to the impact results, the appropriate parameters are determined under the premise of ensuring the stress reduction effect.

8. The pipeline residual stress reduction method according to claim 6, characterized in that: The method further comprises: verifying the result determined by the numerical simulation through experiments.

9. The method for reducing residual stress in pipelines according to any one of claims 1 to 8 is implemented by the following device: The device comprises a heating power source, a first heat-insulating layer, a first heating mechanism, a second heat-insulating layer and a second heating mechanism; in, The first thermal insulation layer and the second thermal insulation layer are arranged on both sides of the pipeline weld and wrap the pipeline; The first and second heating mechanisms are respectively arranged on the first insulation layer and the second insulation layer to form two heating areas on both sides of the pipeline weld; The first heating mechanism and the second heating mechanism are both connected to a heating power source.

10. The pipeline residual stress reduction method according to claim 9, characterized in that: The device also includes a temperature measuring mechanism, which can measure the temperature of the inner and outer surfaces of the pipeline at the heating area and the temperature of the anti-corrosion layer; The first heating mechanism and the second heating mechanism both include induction coils or heating belts.

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