Heat treatment method for narrow-spacing welding seam of pipeline
By using asymmetric heating and temperature control to treat narrow weld seams in thermal power plant pipelines, the problem of heat treatment for narrow weld seams has been solved, achieving heat treatment standards and protecting the base material.
Patent Information
- Application Number
- CN202511004762.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-21
- Publication Date
- 2025-12-12
AI Technical Summary
In existing technologies, it is difficult to achieve asymmetric heating and temperature control in the heat treatment of narrow welds in thermal power plant pipelines, resulting in weld hardness not meeting standards and damage to the base material. In particular, there is a lack of mature heat treatment methods at the power plant site.
By measuring the spacing between two adjacent weld seams, pipe diameter and thickness, performing hardness testing, and arranging thermocouples, heating elements and insulation elements, and setting the heat treatment time and temperature, asymmetric heating and temperature control are achieved to avoid overheating and complete the heat treatment of narrow-spacing weld seams.
It enables simultaneous on-site heat treatment of narrow-gap welds, achieving heat treatment standards, saving time and reducing damage to the base material.
Smart Images
Figure CN121109728A_ABST
Abstract
Description
Technical Field
[0001] This disclosure belongs to the field of heat treatment technology for welding of metallic materials, and specifically relates to a heat treatment method for narrow-gap welds in pipelines. Background Technology
[0002] After the alloy steel pipelines in thermal power plants are welded, post-weld heat treatment is required to improve the weld microstructure and control the stress level at the weld. This is an essential and crucial step in pipeline installation or repair. Generally, the spacing between butt welds on large-diameter pipelines such as main / reheat steam and feedwater pipelines in thermal power plants is often greater than 500mm, which is easily achieved through on-site heat treatment or at the manufacturing plant. However, due to pipeline design or temporary repairs / replacements of low-hardness pipelines, there are cases where the spacing between one or two welds is between 200 and 500mm. For a single narrow weld, the temperature field is symmetrical due to the symmetrical heating of the weld and the base material on both sides, meeting the heat treatment requirements. For two welds, this type of weld can be heat-treated as a whole in a heat treatment furnace at the manufacturing plant. For example, a post-weld heat treatment method can be used to heat-treat both welds, but this requires two separate processes, and the heat treatment process will cause some damage to the base material. Therefore, two heat treatments are time-consuming and labor-intensive, and also cause additional damage to the material.
[0003] For power plant applications, the base material between two adjacent narrow welds is narrow and shared by both welds. When using conventional methods to heat treat the two narrow welds simultaneously after welding, the heating and temperature control on both sides of the weld are asymmetrical, which is quite difficult. Moreover, the base material area in the middle is prone to overheating. During the heat treatment process, it is very easy for one of the welds to fail to meet the standard hardness requirements. There is currently no mature heat treatment method for power plant applications. Summary of the Invention
[0004] This disclosure aims to at least solve one of the technical problems existing in the prior art, and to provide a heat treatment method for narrow-pitch welds in pipelines.
[0005] This disclosure provides a heat treatment method for narrow-gap welds in pipelines, the method comprising:
[0006] The spacing between two adjacent weld seams, pipe diameter, and thickness were measured.
[0007] Hardness tests were performed on the two welds, the base material around the welds, and the base material in the middle area between the two welds.
[0008] Thermocouples are placed at the hardness testing location;
[0009] The heating element is wrapped around both weld seams and their adjacent areas respectively;
[0010] Insulation components are arranged on the surface of each heating element, in the area between two weld seams where no heating element is arranged, and in the areas where two heating elements are opposite to each other.
[0011] Heat treatment time and temperature are set according to the pipe wall thickness and hardness test results;
[0012] After heat treatment, the hardness of the weld is tested to complete the heat treatment.
[0013] Optionally, when verifying the hardness of the two welds, hardness test points are selected along the circumferential direction of the pipe. When the pipe diameter is ≤700mm, a first hardness test point is selected every 90°. When the pipe diameter is >700mm, a first hardness test point is selected every 60°.
[0014] Optionally, when testing the hardness of the base material around the weld, a second hardness testing point is selected on both sides of the weld and in a direction parallel to the axial direction of the first hardness testing point. The distance between the second hardness testing point and the weld is 25-30 mm.
[0015] Optionally, when testing the hardness of the base material in the middle area between the two welds, one or two third hardness testing points can be selected on the base material between the two first hardness testing points along the pipe axis.
[0016] Optionally, when selecting inspection points in the base material in the middle area between two welds, if the distance between the two welds a ≥ 400, two inspection points are selected, with the inspection point 1 / 3a away from the weld, where a is the distance between the two welds.
[0017] If the distance a between two welds is less than 400, select one inspection point, and the inspection point is 1 / 2a away from the weld.
[0018] Optionally, the thermocouple is positioned at the same location as the hardness detection point.
[0019] Optionally, the heating element includes a first heating section, a second heating section, and a third heating section; wherein,
[0020] The first heating element covers the area where the two welds are close together, and the width of the first heating element is 1 / 4a.
[0021] The second heating element is wrapped around the weld, and the third heating element is wrapped around the area where the two welds are opposite to each other. The total width of the heating element is 8 to 10c, where c is the pipe thickness.
[0022] Optionally, the insulation component includes a first insulation part, a second insulation part, and a third insulation part; wherein,
[0023] The first insulation part covers the area between two weld seams where no heating element is arranged. The thickness of the first insulation part is 20-40mm and the width is 1 / 2a.
[0024] The second insulation part is wrapped around each weld seam, and the thickness of the second insulation part is 40-60mm and the width is 8-10cm.
[0025] The third insulation portion is wrapped around the opposite area of each heating element, and the thickness of the third insulation portion is 0-20mm and the width is 0-3c.
[0026] Optionally, the method further includes: adjusting the thickness and width of the insulation components in each region during the heat treatment process based on the temperature detected by the thermocouple.
[0027] If the thermocouple temperature exceeds the heat treatment temperature but the over-temperature is within 3°C, no adjustment is made. If it exceeds 3°C, the thickness of the second insulation part is reduced by 3mm for every 1°C of over-temperature, until the thickness of the insulation part is reduced to a minimum of 20mm. If the temperature still exceeds the limit, the width of the third insulation part is adjusted, reducing the width by 5mm each time, until it is reduced to 0. During the adjustment process, the thermocouple temperature is monitored and stopped when it meets the heat treatment temperature.
[0028] Optionally, the heat treatment temperature is 700-800℃ and the time is 5-10h.
[0029] This disclosure provides a heat treatment method for narrow-spacing welds in pipelines. The method includes: measuring the spacing between two adjacent welds, the pipeline diameter, and the thickness; performing hardness testing on the two welds, the base material surrounding the welds, and the base material in the area between the two welds; arranging thermocouples at the hardness testing locations; wrapping heating elements around the two welds and their adjacent areas; arranging insulation elements on the surface of each heating element, in the area between the two welds where no heating elements are arranged, and in the areas where the two heating elements are facing away from each other; setting the heat treatment time and temperature according to the pipeline wall thickness and hardness test results; and testing the weld hardness after heat treatment to complete the heat treatment. This disclosure, through the division of each area of the two welds, hardness testing, thermocouple arrangement, and insulation cotton arrangement, enables simultaneous on-site heat treatment of two welds with small spacing, meeting the heat treatment standard requirements, while also saving time and avoiding material damage. Attached Figure Description
[0030] Figure 1 A flowchart illustrating a method for heat treatment of narrow-pitch welds in pipelines according to a specific embodiment of this disclosure;
[0031] Figure 2 This is a schematic diagram of the pipe weld structure according to a specific embodiment of the present disclosure;
[0032] Figure 3 This is a schematic diagram of the hardness testing and thermocouple arrangement in a specific embodiment of the present disclosure.
[0033] Figure 4 For this disclosure Figure 3A schematic diagram of the cross-section of the central pipe;
[0034] Figure 5 This is a schematic diagram showing the arrangement of the heating element and the heat insulation element in a specific embodiment of this disclosure. Detailed Implementation
[0035] To enable those skilled in the art to better understand the technical solutions of this disclosure, the disclosure will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain this disclosure and represent a part of the embodiments of this disclosure, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the protection scope of this disclosure.
[0036] like Figure 1 As shown, this disclosure proposes a heat treatment method S100 for narrow-gap welds in pipelines, comprising the following specific steps S110 to S170:
[0037] S110. Measure the distance between two adjacent weld seams, the pipe diameter, and the thickness.
[0038] Specifically, combined Figure 2 As shown, the pipe 110 has two adjacent welds, namely the first weld 111 and the second weld 112, with a distance of a between the two welds, a diameter of b, and a thickness of c.
[0039] S120. Hardness testing is performed on the two welds, the base material around the welds, and the base material in the middle area between the two welds.
[0040] Specifically, such as Figure 3 and Figure 4 As shown, when performing hardness testing on the two welds, hardness testing points are selected on the first and second welds along the circumference of the pipe 110, and a hardness testing point is selected at an X-angle interval along the circumference. The specific settings can be based on the pipe diameter.
[0041] It should be noted that the hardness testing points in this embodiment include three types, including hardness testing points located in the weld, the periphery of the weld, and the middle area of the weld.
[0042] For example, such as Figure 3 and Figure 4 As shown, when the pipe diameter b ≤ 700 mm, a first hardness test point 101 is selected at an angle X = 90°. That is, a first hardness test point 101 is selected every 90° along the circumference of the pipe 110, for a total of four first hardness test points 101.
[0043] In some other preferred embodiments, when the pipe diameter b > 700 mm, a first hardness test point is selected at an angle X = 60°. That is, a first hardness test point is selected every 60° along the circumference of the pipe, for a total of six first hardness test points.
[0044] Note that if it is a pipe section replacement, weld hardness testing is not required, but hardness testing points still need to be selected.
[0045] Furthermore, combined Figure 3 As shown, when testing the hardness of the base material around the weld, a second hardness testing point 102 is selected on the base material around the weld. That is, a second hardness testing point is arranged on both the left and right sides of the weld and is axially parallel to the first hardness testing point. The distance of the second hardness testing point from the weld is d = 25~30mm. Similarly, a second hardness testing point is set every X angle. That is, the position and number of the second hardness testing points along the circumference of the pipe are the same as the first hardness testing points. For example, when four first hardness testing points are set along the circumference of the pipe, four second hardness testing points are set on the left and right sides of the first and second welds, respectively.
[0046] Furthermore, combine them together Figure 3 As shown, when testing the hardness of the base material in the middle area between the two welds, one or two additional third hardness testing points 103 are selected in the base material in the middle area between the two welds for hardness testing. The distance between the third hardness testing point 103 and the first weld 111 and the second weld 112 is e. That is to say, one or two third hardness testing points are set in the middle base material at a distance e from the first weld and the second weld.
[0047] It should be noted that the mention of setting one or two third hardness testing points here refers to setting one or two third hardness testing points between every two first hardness testing points in the radial direction of the pipe. In practice, these third hardness testing points also need to be arranged along the circumference of the pipe. For example, when a total of four first hardness testing points are set in the circumference of the weld, four or eight third hardness testing points need to be set in the circumference of the base material between the two welds. Note that the number of these third hardness testing points can be specifically set according to the weld spacing.
[0048] For example, such as Figure 3 As shown, if the distance a between two welds is less than 400, a third hardness test point 103 is set between every two first hardness test points 101 set radially along the pipe 110. The distance e from the third hardness test point 103 to the weld is 1 / 2a.
[0049] In other preferred embodiments, if the distance a between two welds is greater than or equal to 400, two third hardness testing points are set between every two first hardness testing points arranged radially, and the distance e from the third hardness testing point to the weld is 1 / 3a.
[0050] S130. Thermocouples are placed at the hardness testing location by spot welding.
[0051] It should be noted that since the thermocouple is arranged at the hardness detection position, the thermocouple arrangement position in this embodiment is consistent with the hardness detection position. For specific possible arrangement positions, please refer to the previous description.
[0052] S140, wrap the heating element around the two weld seams and their adjacent areas respectively.
[0053] Specifically, such as Figure 5 As shown, heating elements are wrapped around the periphery of the first weld 111 and the second weld 112. The wrapped area includes the positions of the two welds, the positions where the two welds are close together, and the positions where the two welds are away from each other, i.e., two heating elements are wrapped. Each heating element 120 includes a first heating part 121, a second heating part 122, and a third heating part 123. The first heating part 121 wraps around the area where the two welds are close together, and the width of the first heating part 121 is f, where f = 1 / 4a. That is, the width of the wrapping on the right side of the first weld 111 is f, and the width of the wrapping on the left side of the second weld 112 is f. No heating element is placed in the middle area between the two welds. The second heating part 122 wraps around the weld, and the third heating part 123 wraps around the area where the two welds are away from each other. The total width of the heating element wrapping is i = 8~10c, where c is the pipe thickness. In other words, a heating element is used to wrap around the two welds and their surrounding areas, including the inner area between the welds, the weld area, and the outer area of the weld, with a total width of 8-10c.
[0054] It should be noted that the heating element in this embodiment is preferably a ceramic heating rope or a ceramic heating plate. The function of the ceramic heating plate or ceramic heating rope is to heat the pipeline and raise its temperature, which, when used in conjunction with the insulation cotton, reaches the heat treatment temperature. The selection of its thickness and width enables asymmetrical heating, thereby completing the heat treatment of two welds simultaneously and avoiding overheating problems.
[0055] S150. Insulation components are installed on the surface of the heating element, in the area between two welds where no heating element is installed, and in the area where heating elements are installed opposite to each other, using wire binding.
[0056] It should be understood that, in addition to the heating element, there is also a position between the two welds where no heating element is arranged. Therefore, the insulation element in this embodiment is arranged between the positions where no heating element is arranged, the positions where heating element is arranged, and the side opposite to the heating element. In other words, insulation elements need to be arranged inside the heating element, above the heating element, and outside the heating element to improve the insulation effect.
[0057] Specifically, such as Figure 5 As shown, the insulation component 130 includes a first insulation portion 131, a second insulation portion 132, and a third insulation portion 133. The first insulation portion 131 covers the area between two weld seams where no heating element is located; specifically, the thickness g of the first insulation portion 131 located in the area between the first weld seam 111 and the second weld seam 112 where no heating element is located is 20-40 mm, and its width is 1 / 2a. The second insulation portion 132 covers the area above each weld seam; the thickness h of the second insulation portion 132 located in the area where heating elements are located at the first weld seam 111 and the second weld seam 112 is 40-60 mm, and its width i is 8-10c. The third insulation portion 133 covers the area opposite to each heating element 120; the thickness k of the third insulation portion is 0-20 mm, and its width j is 0-3c.
[0058] It should be understood that the insulation component consists of three parts. One part is a first insulation part, which wraps around the area in the middle of the two welds where no heating element is installed. Another part consists of two second insulation parts, which wrap around the heating elements corresponding to the first and second welds, respectively. The third part consists of two third insulation parts, which wrap around the opposite sides of the two heating elements, respectively.
[0059] It should be noted that the insulation component in this embodiment can preferably be insulation cotton. The function of this insulation cotton is to insulate the pipeline and prevent excessive heat loss, and it works in conjunction with the heating element to reach the heat treatment temperature. The selection of its thickness and width is also an important parameter for achieving asymmetric heating, thereby completing the heat treatment of two welds simultaneously.
[0060] S160. Based on the test results of pipe wall thickness and hardness, set the heat treatment time and temperature for heat treatment. During the heat treatment process, adjust the thickness and width of the insulation components in each area according to the temperature detected by the thermocouple.
[0061] In some preferred embodiments, the temperature range of the heat treatment is preferably 700-800°C, and the time is preferably 5-10 hours.
[0062] Specifically, the process of adjusting the thickness and width of the insulation components in each area based on the temperature detected by the thermocouple includes: no adjustment is made when the thermocouple temperature exceeds the heat treatment temperature but the over-temperature is within 3°C; when the thermocouple temperature exceeds the heat treatment temperature and exceeds 3°C, the thickness of the second insulation part is reduced by 3mm for every 1°C of over-temperature, until the thickness of the insulation component is reduced to a minimum of 20mm; if the detected temperature still exceeds the temperature, the width of the third insulation part is adjusted, reducing the width by 5mm each time, until it is reduced to 0mm. During the adjustment process, the adjustment is stopped when the thermocouple temperature meets the heat treatment temperature.
[0063] S170. After heat treatment, the weld hardness is tested to complete the heat treatment.
[0064] In this embodiment, by dividing the area of each of the two weld seams, testing the hardness, arranging thermocouples and arranging insulation cotton, the two weld seams with a small gap can be heat-treated on-site at the same time to meet the heat treatment standard requirements. The operation method is simple and can realize precise on-site heat treatment of narrow-gap weld seams in pipelines.
[0065] The heat treatment method for narrow-pitch welds in pipelines will be further explained below with reference to specific embodiments:
[0066] Example 1
[0067] This embodiment uses the heat treatment of P92 steel pipe welds as an example for illustration:
[0068] S1. Detailed dimensional measurements of the pipeline, including the weld size of the P92 steel pipeline as φ960×70mm, and the spacing between the two welds after the pipe section is replaced as 300mm.
[0069] S2. Hardness testing was performed on the base material around both sides of the pipe weld. Starting from the top, a hardness testing position was selected every 60° in the circumferential direction. The hardness of the base material was between 220-230 HBW. Hardness testing was also performed on the base material at the middle of the two welds. A hardness testing position was selected every 60° in the circumferential direction. The hardness was between 225 and 232 HBW.
[0070] S3. Thermocouples are placed at the hardness testing points using spot welding.
[0071] S4. Arrange ceramic heating elements on the weld, with a total width of 560mm and a width of 75mm for wrapping the middle side of the weld.
[0072] S5. Use wire binding to arrange the insulation cotton. Arrange the insulation cotton with a thickness of 50mm and a width of 560mm on the ceramic heating element. Arrange the insulation cotton with a thickness of 30mm and a width of 150mm in the area between the two welds where the heating element is arranged. Arrange the insulation cotton with a thickness of 20mm and a width of 140mm on the other side of the two welds.
[0073] S6. Set the constant temperature to 755℃ and the constant temperature time to 8 hours, then perform heat treatment.
[0074] S7. After heat treatment, the hardness of the weld and the base metal is tested. The hardness of the weld is 240-250 HBW, and the hardness of the base metal is between 215-225 HBW, which meets the standard requirements.
[0075] This disclosure proposes a heat treatment method for narrow-gap welds in pipelines, which has the following advantages over existing technologies: by measuring the dimensions of the two welds, arranging hardness testing points, setting up temperature measuring thermocouples, and arranging insulation cotton, the accuracy of heat treatment is improved, and the narrow-gap welds can be simultaneously heat treated on-site to meet the heat treatment standard requirements.
[0076] It is understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of this disclosure, and this disclosure is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this disclosure, and these modifications and improvements are also considered to be within the scope of protection of this disclosure.
Claims
1. A heat treatment method for narrow-gap welds in pipelines, characterized in that, The method includes: The spacing between two adjacent weld seams, pipe diameter, and thickness were measured. Hardness tests were performed on the two welds, the base material around the welds, and the base material in the middle area between the two welds. Thermocouples are placed at the hardness testing location; The heating element is wrapped around both weld seams and their adjacent areas respectively; Insulation components are arranged on the surface of each heating element, in the area between two weld seams where no heating element is arranged, and in the areas where two heating elements are opposite to each other. Heat treatment time and temperature are set according to the pipe wall thickness and hardness test results; After heat treatment, the hardness of the weld is tested to complete the heat treatment.
2. The heat treatment method for narrow-gap pipe welds according to claim 1, characterized in that, When verifying the hardness of two welds, hardness test points are selected along the circumferential direction of the pipe. When the pipe diameter is ≤700mm, a first hardness test point is selected every 90°. When the pipe diameter is >700mm, a first hardness test point is selected every 60°.
3. The heat treatment method for narrow-gap pipe welds according to claim 2, characterized in that, When testing the hardness of the base material around the weld, a second hardness testing point is selected on both sides of the weld and in a direction parallel to the first hardness testing point in the axial direction. The distance between the second hardness testing point and the weld is 25-30 mm.
4. The heat treatment method for narrow-gap welds in pipelines according to claim 3, characterized in that, When testing the hardness of the base material in the middle area between two welds, select 1 to 2 third hardness testing points on the base material between the two first hardness testing points along the pipe axis.
5. The heat treatment method for narrow-gap pipe welds according to claim 4, characterized in that, When selecting test points in the base material in the middle area of two welds, if the distance a between the two welds is greater than or equal to 400, two third hardness test points are selected. The distance between the third hardness test points and the welds is 1 / 3a, where a is the distance between the two welds. If the distance between two welds a < 400, select one third hardness test point, and the distance of the third hardness test point from the weld is 1 / 2a.
6. The heat treatment method for narrow-gap pipe welds according to any one of claims 1 to 5, characterized in that, The thermocouples are positioned in the same location as the hardness test.
7. The heat treatment method for narrow-gap welds in pipelines according to any one of claims 1 to 5, characterized in that, The heating element includes a first heating section, a second heating section, and a third heating section; wherein... The first heating element covers the area where the two welds are close together, and the width of the first heating element is 1 / 4a. The second heating element is wrapped around the weld, and the third heating element is wrapped around the area where the two welds are opposite to each other. The total width of the heating element is 8 to 10c, where c is the pipe thickness.
8. The heat treatment method for narrow-gap welds in pipelines according to any one of claims 1 to 5, characterized in that, The insulation component includes a first insulation section, a second insulation section, and a third insulation section; wherein... The first insulation part covers the area between two weld seams where no heating element is arranged. The thickness of the first insulation part is 20-40mm and the width is 1 / 2a. The second insulation part is wrapped around each weld seam, and the thickness of the second insulation part is 40-60mm and the width is 8-10cm. The third insulation portion is wrapped around the opposite area of each heating element, and the thickness of the third insulation portion is 0-20mm and the width is 0-3c.
9. The heat treatment method for narrow-gap pipe welds according to claim 8, characterized in that, The method further includes adjusting the thickness and width of the insulation components in each area based on the temperature detected by the thermocouples. If the thermocouple temperature exceeds the heat treatment temperature but the over-temperature is within 3°C, no adjustment is made. If it exceeds 3°C, the thickness of the second insulation part is reduced by 3mm for every 1°C of over-temperature, until the thickness of the insulation part is reduced to a minimum of 20mm. If the temperature still exceeds the limit, the width of the third insulation part is adjusted, reducing the width by 5mm each time, until it is reduced to 0. During the adjustment process, the thermocouple temperature is monitored and stopped when it meets the heat treatment temperature.
10. The heat treatment method for narrow-pitch pipe welds according to any one of claims 1 to 5, characterized in that, The heat treatment temperature is 700-800℃, and the time is 5-10h.