Postweld heat treatment method for pipeline with low local base metal hardness

Abstract

The embodiment of the invention provides a postweld heat treatment method for a pipeline with low local base metal hardness. The postweld heat treatment method comprises the steps that hardness values of to-be-detected areas on the two sides of a pipe fitting base metal weld joint are detected; delimiting a low-hardness area on the pipe fitting base material according to the detected hardness value; and whether the distance between the low-hardness area and the weld joint is within the range of a preset postweld heat treatment heating area or not is judged, and a corresponding heat preservation strategy is adopted for heat treatment according to the position relation between the low-hardness area and the preset postweld heat treatment heating area. According to the method, the hardness value of the base metal is detected to determine the low hardness degree and the distribution condition, the heat treatment heat preservation strategy of different heating heat input in different hardness areas is adopted, and on the premise that the parameter requirements of the weld joint heat treatment process are met, the heat input of local low-hardness area base metal heat treatment is reduced; the influence of postweld heat treatment on the low-hardness area of the base metal is reduced, and the situation that the hardness of the area is further reduced due to secondary heat treatment to affect the mechanical performance of the base metal is reduced, so that the reliability and safety are enhanced.

Description

Technical Field

[0001] The embodiments of the present disclosure belong to the technical field of post-weld heat treatment, and specifically relate to a post-weld heat treatment method for a pipeline with a relatively low local base material hardness. Background Art

[0002] Boiler pipes and pressure pipes made of alloy materials are widely used in engineering practice to transport fluid media and achieve production process performance. These pipes and their tees, elbows and other pipe fittings are connected by welding. Pipes, tees and elbows often require heat treatment during manufacturing and on-site welding. The purpose of the heat treatment process is to improve the welding process performance of the workpiece, the metallographic structure, mechanical properties and stress state of the weld. The hardness value is an intuitive representation of the impact performance, toughness, strength and other mechanical properties of metal materials. The hardness value is high, the metal material has good impact resistance and high strength, but poor toughness; the hardness value is low, the metal material has poor impact resistance and low strength, but good toughness. Therefore, it is necessary to find a balance in the hardness value. The general standard stipulates the upper and lower limits of the hardness value of the metal base material and its weld.

[0003] Due to some unit heat treatment process and quality control issues, the base material hardness of a large number of pipes and pipe fittings is close to or slightly lower than the lower limit of the hardness value specified in the regulations. We call this low hardness. When we weld or repair the above parts, it is inevitable to perform post-weld heat treatment again. Some of these base materials with low local hardness are close to the weld and are within the heating range of the post-weld heat treatment again. It is very important to avoid or reduce the hardness drop caused by heat treatment during the re-heat treatment of these base materials with low local hardness to ensure the quality of the base materials.

[0004] However, the conventional post-weld heat treatment method does not take into account the local low hardness differences of the parent material and adopts an indiscriminate heating method. As a result, after the heat treatment is performed again, the hardness of the low-hardness parts and the surrounding adjacent parent materials decreases by roughly the same amount, making the hardness of the local position lower than the lower limit of the parent material hardness value specified in the regulations, resulting in unqualified quality and affecting the safe operation of boiler pipes, pressure pipes, tees, elbows and other pipe fittings. Summary of the invention

[0005] The embodiments of the present disclosure aim to solve at least one of the technical problems existing in the prior art and provide a post-weld heat treatment method for a pipeline with a local base material having a low hardness.

[0006] One aspect of an embodiment of the present disclosure provides a post-weld heat treatment method for a pipeline with a local base material having a low hardness, comprising:

[0007] Detect the hardness value of the area to be inspected on both sides of the weld of the base material of the pipe fitting;

[0008] Delineate low hardness areas on the pipe base material according to the tested hardness values;

[0009] It is determined whether the distance between the low hardness area and the weld is within the predetermined post-weld heat treatment heating zone, and a corresponding insulation strategy is adopted for heat treatment according to the positional relationship between the low hardness area and the predetermined post-weld heat treatment heating zone.

[0010] Optionally, the predetermined post-weld heat treatment heating zone range and heating temperature are determined according to the material, specification and size of the pipe fitting and the size of the weld.

[0011] Optionally, the detection of the hardness values ​​on both sides of the weld of the pipe base material includes: using a Leeb hardness tester to measure the hardness values ​​at multiple positions on the surface of the pipe base material in the area to be inspected; wherein each position is measured at least once, and the average hardness value of the position is used as the basic hardness value of the base material.

[0012] Optionally, the step of defining a low hardness area on the pipe base material according to the detected hardness value includes:

[0013] Conduct hardness verification test on the surface of the pipe base material to be inspected to obtain the verified hardness value;

[0014] Compare the verified hardness value with the basic hardness value of the base material, and determine the lower hardness area and the interface between the lower hardness area and the normal base material according to the hardness difference between the two;

[0015] The low hardness area is defined on the pipe base material according to the interface between the lower hardness area and the normal base material.

[0016] Optionally, the hardness recheck test is performed on the surface of the to-be-tested area of ​​the pipe base material to obtain the rechecked hardness value, including:

[0017] Grind the surface of the pipe base material to be inspected;

[0018] A Leeb hardness tester is used to perform preliminary hardness measurement at several random locations on the surface of the area to be tested. The location with relatively low hardness is taken as the initial location. Two cross-shaped straight lines are drawn with the initial location as the center. The hardness values ​​of the two straight lines are tested at regular intervals along the intersection point. At least 3 hardness values ​​are tested at each location, and the average hardness value of the location is used as the verified hardness value.

[0019] Optionally, when the hardness difference between the verified hardness value and the base hardness value of the parent material is greater than or equal to 20HB, and the smaller hardness value is close to the lower limit of the parent material hardness value specified in the regulations, the area is divided into a lower hardness area;

[0020] When the hardness difference between the verified hardness value and the basic hardness value of the base material is less than or equal to 10HB, the area is regarded as the interface between the base material with lower hardness and the normal base material.

[0021] Optionally, demarcating a low-hardness area on the pipe fitting base material according to the interface between the low-hardness area and the normal base material includes: determining four interfaces on two cross straight lines respectively according to the hardness difference between the rechecked hardness value and the base material hardness base value, and drawing circles with each interface point as a point on the circumference. Among them, the range defined by the circles is the range of the low-hardness area of the pipe fitting base material.

[0022] Optionally, determining whether the distance between the low-hardness area and the weld is within the range of the post-weld heat treatment heating area includes: measuring the radius R1 of the circle of the low-hardness area; measuring the distance L1 from the center of the circle to the center of the weld and comparing it with the unilateral heating width L. If L1 + R1 ≤ L, the entire area of the low-hardness area falls within the range of the post-weld heat treatment heating area;

[0023] If L1 - R1 < L < L1 + R1, part of the area of the low-hardness area falls within the range of the post-weld heat treatment heating area; if L1 - R1 > L, the area of the low-hardness area falls outside the range of the post-weld heat treatment heating area.

[0024] Optionally, performing corresponding heat preservation strategies for heat treatment according to the positional relationship between the low-hardness area and the heating area includes: when the entire or part of the area of the low-hardness area falls within the range of the post-weld heat treatment heating area, taking twice the radius R1 of the low-hardness area as the radius R2 of the heat preservation layer shielding area and setting the heat preservation area.

[0025] Optionally, along the axial direction of the pipe fitting, in the direction where the center of the heat preservation area points to the weld, the thickness dimension of the heat preservation layer gradually increases.

[0026] The beneficial effects of the embodiments of the present disclosure include:

[0027] In the present disclosure, by detecting the hardness value of the base material, the low-hardness degree and distribution are determined, and targeted heat treatment heat preservation strategies with different heating heat inputs in different hardness areas are adopted. On the premise of meeting the requirements of the weld heat treatment process parameters, the heat input for heat treatment of the base material in the local low-hardness area is reduced, the influence of the post-weld heat treatment on the local low-hardness area of the base material is reduced, and the influence of further reducing the hardness of this area due to re-heat treatment on the mechanical properties of the base material is reduced, so as to enhance its safety and reliability during service. Description of the Drawings

[0028] Figure 1 It is a schematic flowchart of a post-weld heat treatment method for a pipeline with a locally lower hardness base material according to another embodiment of the present disclosure;

[0029] Figure 2 It is a schematic structural diagram of post-weld heat treatment of a pipe fitting base material according to an embodiment of the present disclosure.

[0030] In the figure, 1, pipe fitting; 2, weld; L, single-side heating width; S1, low hardness area; S2, insulation layer shielding area; 6, temperature control thermocouple; 7, monitoring thermocouple; 8, first comparison thermocouple; 9, second comparison thermocouple. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the technical solution of the present disclosure, the present disclosure is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0032] The following is a further detailed description of the implementation methods of the present application in conjunction with the accompanying drawings and examples. The detailed descriptions and drawings of the following examples are used to illustrate the principles of the present application, but cannot be used to limit the scope of the present application, that is, the present application is not limited to the described embodiments. In the description of the present application, it should be noted that, unless otherwise specified, the meaning of "multiple" is more than two; the orientation or position relationship indicated by the terms "upper", "lower", "left", "right", "inside", "outside", etc. is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. "Vertical" is not vertical in the strict sense, but within the error tolerance range. "Parallel" is not parallel in the strict sense, but within the error tolerance range.

[0033] In the description of this application, it should also be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0034] like Figure 1-2 As shown, a post-weld heat treatment method for a pipeline with a local base material having a low hardness comprises:

[0035] S101. Detect the hardness value of the area to be tested on both sides of the weld of the base material of the pipe fitting.

[0036] S102. Delineate a low hardness area on the pipe base material according to the detected hardness value.

[0037] S103, judging whether the distance between the low hardness area and the weld is within the predetermined post-weld heat treatment heating zone, and taking a corresponding heat preservation strategy for heat treatment according to the positional relationship between the low hardness area and the predetermined post-weld heat treatment heating zone. It can be understood that the heat preservation strategy is used to affect different heating heat inputs for different hardness areas.

[0038] In the present disclosure, the hardness value of the base material is detected to determine the degree and distribution of low hardness, and a targeted heat treatment insulation strategy with different heating heat inputs in different hardness areas is adopted. On the premise of meeting the requirements of the weld heat treatment process parameters, the heat input of the base material in the local low hardness area is reduced, and the impact of post-weld heat treatment on the local low hardness area of ​​the base material is reduced, and the impact on the mechanical properties of the base material due to further reduction of its hardness by re-heat treatment in this area is reduced, so as to enhance its safe service reliability and safety.

[0039] The parent materials of pipe fittings include boiler pipes, pressure pipes or pipe fittings such as elbows and tees.

[0040] In some embodiments, the predetermined post-weld heat treatment heating zone range and heating temperature are determined according to the material, specification and size of the pipe fitting and the size of the weld. The specification and size of the pipe fitting include diameter and thickness.

[0041] In some embodiments, the detection of the hardness values ​​on both sides of the weld of the pipe base material includes: using a Leeb hardness tester to measure the hardness values ​​at multiple positions on the surface of the pipe base material in the area to be inspected, wherein each position is measured at least once, and the average hardness value of the position is used as the basic hardness value of the base material.

[0042] In some embodiments, the step of defining a low hardness area on the pipe base material according to the detected hardness value includes: S1021, performing a hardness recheck test on the surface of the to-be-tested area of ​​the pipe base material to obtain a rechecked hardness value.

[0043] S1022. Compare the verified hardness value with the basic hardness value of the base material, and determine the lower hardness area and the interface between the lower hardness area and the normal base material according to the hardness difference between the two.

[0044] S1023. Delineate a low hardness area on the pipe base material according to the interface between the lower hardness area and the normal base material.

[0045] In some embodiments, the hardness verification test is performed on the surface of the to-be-tested area of ​​the pipe base material to obtain the verified hardness value, including:

[0046] S10211. Grind the surface of the pipe base material in the area to be inspected.

[0047] S10212. Use a Leeb hardness tester to perform preliminary hardness measurement at several points on the surface of the area to be tested. The position with relatively low hardness is taken as the initial position. Two cross-shaped straight lines are drawn with the initial position as the center. The two straight lines are used to measure the hardness values ​​at regular intervals along the intersection. At least three hardness values ​​are measured at each position, and the average hardness value of the position is used as the verification hardness value.

[0048] In some embodiments, when the hardness difference between the rechecked hardness value and the base hardness value of the base material is greater than or equal to 20 HB, and the smaller hardness value is close to the lower limit of the base material hardness value specified in the regulation, this area is divided into a low-hardness area.

[0049] When the hardness difference between the rechecked hardness value and the base hardness value of the base material is less than or equal to 10 HB, this area is used as the interface between the low-hardness area base material and the normal base material.

[0050] In some embodiments, demarcating the low-hardness area on the pipe fitting base material according to the interface between the low-hardness area and the normal base material includes: determining four interfaces on two cross straight lines respectively according to the hardness difference between the rechecked hardness value and the base hardness value of the base material, and drawing circles with the interface points as the points on the circumference. Among them, the range defined by the circles is the range of the low-hardness area of the pipe fitting base material.

[0051] In some embodiments, determining whether the distance between the low-hardness area and the weld is within the range of the post-weld heat treatment heating zone includes: measuring the circle radius R1 of the low-hardness area, measuring the distance L1 from the center of the circle to the center of the weld, and comparing it with the unilateral heating width L. If L1 + R1 ≤ L, the entire area of the low-hardness area falls within the range of the post-weld heat treatment heating zone.

[0052] If L1 - R1 < L < L1 + R1, part of the area of the low-hardness area falls within the range of the post-weld heat treatment heating zone. If L1 - R1 > L, the area of the low-hardness area falls outside the range of the post-weld heat treatment heating zone.

[0053] In some embodiments, taking corresponding heat preservation strategies for heat treatment according to the positional relationship between the low-hardness area and the heating zone includes: when the entire or part of the area of the low-hardness area falls within the range of the post-weld heat treatment heating zone, taking twice the radius R1 of the low-hardness area as the radius R2 of the heat preservation layer shielding area and setting the heat preservation area.

[0054] In some embodiments, along the axial direction of the pipe fitting, in the direction where the center of the heat preservation area points to the weld, the thickness dimension of the heat preservation layer gradually increases.

[0055] Reference Figure 2 , a specific example provided by the present disclosure includes:

[0056] 1. Detect the pipe fitting 1 to master the low-hardness degree and distribution within the range of its heat treatment heating zone, and whether the distance from the weld 2 is within the range of the post-weld heat treatment heating zone. The pipe fitting base material includes pipe fittings such as boiler pipes, pressure pipes, elbows, and tees.

[0057] 2. According to the material, specifications (diameter, thickness) of boiler pipes, pressure pipes, or pipe fittings such as elbows and tees. Determine the procedures and specifications for post-weld heat treatment according to the corresponding technical requirements, and determine the post-weld heat treatment temperature and the unilateral heating width L (refer to Figure 2 for the number 3 in it). The unilateral heating width L refers to the distance from the boundary of the post-weld heat treatment heating zone to the weld.

[0058] 3. Re-check and detect the local hardness of the pipe fitting base material previously mastered, and master its specific hardness value and the area of the low-hardness region.

[0059] 4. Detect the hardness of the pipe fitting base material. Grind the surface of the part to be inspected until it shows a metallic luster. Use a Leeb hardness tester to measure multiple points, with 3 points measured at each location, and take the average value as the base value of the base material hardness.

[0060] 5. Re-check and detect the surface of the part to be inspected above to obtain the re-check hardness value. Specifically, for the region to be re-checked for hardness, grind the surface to be inspected until it shows a metallic luster. Use a Leeb hardness tester. First, randomly select several points on the surface to be inspected for preliminary measurement. Select the position with relatively lower hardness as the initial position, draw two cross lines, and measure one point every certain distance (such as 10 mm - 20 mm) along each line outward. Take the average value of 3 points measured at each location as the re-check hardness value at that location.

[0061] 6. Compare the re-check hardness values measured along the two cross lines with the base value of the base material hardness. Among them, when the hardness difference between the two is more than 20 HB, and the smaller hardness value is close to the lower limit of the base material hardness specified in the regulations (such as a 10 HB difference) region, it is regarded as the low-hardness region. When the hardness difference between the two is reduced to within 10 HB, it can be used as the interface between the low-hardness region base material and the normal base material. When the hardness difference between the two is 5 HB, it can be used as the measurement error range.

[0062] 7. Measure 4 interfaces respectively on the two cross lines, and draw a circle with these four interface points as the points on the circumference. Among them, the range within the circle is the range of the low-hardness region of the base material, and the area of the low-hardness region S1 (refer to Figure 2 for the number 4 in it).

[0063] 8. Measure the radius R1 of the circle. Measure the distance L1 from the center of the circle to the center of the weld. Among them, measure the distance L1 from the weld along the axial direction of the pipe and pipe fitting, and compare it with the unilateral heating width L. If L1 + RI ≤ L, the range of the low-hardness region of the base material and the area S1 all fall within the post-weld heat treatment heating zone. If L1 - R1 < L < L1 + RI, part of the area S1 falls within the post-weld heat treatment heating zone. If L1 - R1 > L, the area S1 is outside the post-weld heat treatment heating zone.

[0064] 9. For S1 that is completely or partially in the post-weld heating zone, the following methods shall be used for post-weld heat treatment:

[0065] The first comparison thermocouple 8 is installed at the center of the circle S1. The second comparison thermocouple 9 is installed at a position 4 times R1 along the circumference of the boiler pipe, pressure pipe or tee or elbow pipe fitting, starting from the center of the circle.

[0066] With S1 as the center and R2 as the radius, draw a circle that represents the area S2 blocked by the insulation layer (reference Figure 2 Number 5) is used as the insulation cotton shielding area. The surface of the parent material in the S2 area is covered with 3mm-10mm insulation cotton to isolate the sheet heater or rope heater from direct contact with the parent material. Generally, L1 is small, close to the center of the weld, and the insulation cotton shielding thickness is thicker, and the shielding thickness is thinner if it is far from the center of the weld.

[0067] A temperature-controlling thermocouple is arranged at the 12 o'clock position of the weld center, and a monitoring thermocouple is set at a position about δ (pipe wall thickness) ≥50mm away from the weld center in the axial direction of the pipeline and pipe fittings.

[0068] After the temperature-controlling thermocouple 6, the monitoring thermocouple 7, the first comparison thermocouple 8 and the second comparison thermocouple 9 are installed and the shielding insulation cotton is arranged, the sheet heater or the rope heater is arranged according to the conventional post-weld heat treatment and tied firmly, and then covered with insulation cotton twice the width of the heating zone, and the post-weld heat treatment is carried out according to the parameters specified in the regulations.

[0069] The present disclosure first detects and grasps the degree and distribution of low hardness, and whether the distance from the weld is within the post-weld heat treatment heating zone.

[0070] The second is to define the low hardness area S1, the corresponding radius is R1, and twice R1 is used as the radius R2 of the insulation layer shielding area. The insulation area is S2 to set the insulation conditions to affect the different heating heat inputs in different hardness areas.

[0071] Third, a first comparison thermocouple 8 and a second comparison thermocouple 9 are respectively arranged at the center of S1 and in the same circumferential direction of the pipeline and the pipe fitting, at a distance of 4 times R1.

[0072] Fourth, according to the different distances of the low hardness area from the pipe and fittings along the axial direction to the weld, different thicknesses of insulation cotton are used for shielding, generally 3-10mm. The shielding thickness is thicker when it is close to the center of the weld, and thinner when it is far from the center of the weld.

[0073] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present disclosure, but the present disclosure is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and substance of the present disclosure, and these modifications and improvements are also considered to be within the scope of protection of the present disclosure.

Claims

1. A post-weld heat treatment method for pipelines with low local base material hardness, characterized in that: Including: Detecting the hardness values of the areas to be inspected on both sides of the weld of the pipe fitting base metal; Marking a low-hardness area on the pipe fitting base metal according to the detected hardness values; Judging whether the distance between the low-hardness area and the weld is within the range of the predetermined post-weld heat treatment heating zone, and adopting corresponding heat preservation strategies for heat treatment according to the positional relationship between the low-hardness area and the predetermined post-weld heat treatment heating zone.

2. A post-weld heat treatment method for pipelines with low local base material hardness according to claim 1, characterized in that: Determining the range and heating temperature of the predetermined post-weld heat treatment heating zone according to the material, specification dimensions and weld dimensions of the pipe fitting.

3. The post-weld heat treatment method for a pipeline with a local base material having a low hardness according to claim 1 is characterized in that: The detecting the hardness values of both sides of the weld of the pipe fitting base metal includes: using a Leeb hardness tester to measure the hardness values corresponding to multiple positions on the surface of the area to be inspected of the pipe fitting base metal; wherein, each position is measured at least once, and the average hardness value of this position is used as the base hardness value of the base metal.

4. A post-weld heat treatment method for pipelines with low local base material hardness according to claim 3, characterized in that: The marking a low-hardness area on the pipe fitting base metal according to the detected hardness values includes: Performing a hardness recheck on the surface of the area to be inspected of the pipe fitting base metal to obtain the recheck hardness value; Comparing the recheck hardness value with the base hardness value of the base metal, and determining the area with lower hardness and the interface between the area with lower hardness and the normal base metal according to the hardness difference between the two; Marking a low-hardness area on the pipe fitting base metal according to the interface between the area with lower hardness and the normal base metal.

5. A post-weld heat treatment method for pipelines with low local base material hardness according to claim 4, characterized in that: The performing a hardness recheck on the surface of the area to be inspected of the pipe fitting base metal to obtain the recheck hardness value includes: Grinding the surface of the area to be inspected of the pipe fitting base metal; Using a Leeb hardness tester to perform preliminary hardness measurements at several randomly selected positions on the surface of the area to be inspected; wherein, the position with relatively lower hardness is used as the initial position, and two cross lines are drawn with the initial position as the center. Two straight lines detect the hardness values at regular intervals outward along the intersection point. Each position is detected for at least 3 hardness values, and the average hardness value of this position is used as the recheck hardness value.

6. A post-weld heat treatment method for pipelines with low local base material hardness according to claim 5, characterized in that: When the hardness difference between the recheck hardness value and the base hardness value of the base metal is greater than or equal to 20 HB, and the smaller hardness value is close to the lower limit of the base metal hardness value specified in the regulations, this area is divided into the area with lower hardness; When the hardness difference between the recheck hardness value and the base hardness value of the base metal is less than or equal to 10 HB, this area is used as the interface between the base metal of the area with lower hardness and the normal base metal.

7. A post-weld heat treatment method for pipelines with low local base material hardness according to claim 6, characterized in that: The marking a low-hardness area on the pipe fitting base metal according to the interface between the area with lower hardness and the normal base metal includes: determining four interfaces on the two cross lines respectively according to the hardness difference between the recheck hardness value and the base hardness value of the base metal, and drawing circles with the interface points as the points on the circumference. Among them, the range defined by the circles is the range of the low-hardness area of the pipe fitting base metal.

8. The post-weld heat treatment method for pipelines with low local base material hardness according to claim 7, characterized in that: The judging whether the distance between the low-hardness area and the weld is within the range of the predetermined post-weld heat treatment heating zone includes: measuring the radius R1 of the circle of the low-hardness area; measuring the distance L1 from the center of the circle to the center of the weld and comparing it with the unilateral heating width L. If L1 + RI ≤ L, the entire area of the low-hardness area falls within the range of the post-weld heat treatment heating zone; If L1 - R1 < L < L1 + RI, part of the area of the low-hardness area falls within the range of the post-weld heat treatment heating zone; if L1 - R1 > L, the area of the low-hardness area falls outside the range of the post-weld heat treatment heating zone.

9. A post-weld heat treatment method for pipelines with low local base material hardness according to claim 8, characterized in that: The heat treatment is performed by adopting a corresponding insulation strategy based on the positional relationship between the low hardness area and the heating zone, including: when the area of ​​the low hardness area falls entirely or partially within the post-weld heat treatment heating zone, using twice the radius R1 of the low hardness area as the insulation layer shielding area radius R2 and setting an insulation area.

10. A post-weld heat treatment method for pipelines with low local base material hardness according to claim 9, characterized in that: Along the axial direction of the pipe, the center of the insulation area points in the direction of the weld, and the thickness of the insulation layer gradually increases.

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