Tensile test specimens for thick-walled pipes and their processing methods
By machining parallel planes and tangent curved surfaces on thick-walled tubes to form axisymmetric tensile specimens, the problem of inaccurate testing in existing technologies is solved, and reliable evaluation of high-temperature long-term performance is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- TSINGHUA UNIVERSITY
- Filing Date
- 2023-06-20
- Publication Date
- 2026-07-17
Smart Images
Figure CN116754330B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of pipe performance testing technology, and in particular to a tensile test specimen for thick-walled pipes and its processing method. Background Technology
[0002] Thick-walled heat exchange tubes are widely used in thermal equipment such as steam generators and heat exchangers. The high-temperature long-term performance (including the measurement of high-temperature creep strength and creep strength) of these heat exchange tubes and their welded joints is one of the key factors affecting equipment safety and long service life. Reasonable and effective testing of the high-temperature long-term performance of heat exchange tubes and their welded joints is fundamental to improving equipment manufacturing levels and enhancing the safe and reliable operation of equipment.
[0003] The existing non-standard specimen forms for high-temperature creep performance testing of small-diameter thick-walled pipes mainly follow the following approaches: (1) By thinning the pipe as a whole, the stress level in the gauge length zone is higher than that in the non-gauge length zone, ensuring that the specimen breaks in the gauge length zone during the high-temperature creep test. The overall thinning scheme ignores the influence of the pipe surface quality on the high-temperature long-term performance. However, the surface quality of the pipe and joint is one of the key factors affecting its high-temperature long-term performance, and the extent to which the test data obtained by the overall thinning scheme covers the actual mechanical properties of the pipe is questionable. At the same time, after the pipe wall is thinned, the influence of metal oxidation in the high-temperature creep test will increase, introducing a large test deviation. (2) Cut sheet-like specimens from the pipe. The cross-sectional size of the parallel gauge length zone of the sheet-like specimen is smaller than that of the clamping end, so that the specimen also breaks in the gauge length zone during the high-temperature creep test. The sheet-like specimen is part of the cylindrical surface of the pipe. The specimen is loaded with an additional bending moment, which makes it easy to cause abnormal fracture during the test. (3) Clamp the pipe as a whole for high-temperature creep test. The clamping end and the surrounding area are in a triaxial stress state, which makes it easy to break outside the gauge length zone. (4) Given the additional bending moment of the sheet-like specimens, some have proposed an improved non-standard specimen form: the symmetrical double-strip high-temperature creep rupture specimen. The principle is approximately that two symmetrical sheet-like specimens are combined for a long-term high-temperature test, with their additional bending moments canceling each other out, ensuring the tensile load is distributed along the axis. The problem with the double-strip high-temperature creep rupture specimen is the severe stress concentration at the corners of the gauge length. During the high-temperature creep rupture test, numerous cracks appear at the corners of the gauge length, becoming a competing factor for creep rupture failure and interfering with the characterization of the pipe's creep rupture information. Secondly, to ensure that high-temperature creep failure occurs in the gauge length (where the stress is greater than in other parts of the specimen), the cross-sectional area of the gauge length portion of the double-strip high-temperature creep rupture specimen is only half the cross-sectional area of the pipe, making the specimen's geometric effects significantly influential on the high-temperature creep rupture test data.
[0004] For high-temperature long-term tensile testing of thick-walled pipes, there is currently a lack of better non-standard tensile specimen types that can meet the requirements of high-temperature long-term tensile testing of small-diameter pipes, so as to reasonably and effectively evaluate the high-temperature long-term performance of small-diameter pipes. Summary of the Invention
[0005] Therefore, it is necessary to provide a tensile specimen for thick-walled pipes and its processing method to address the above-mentioned technical problems.
[0006] A method for processing tensile specimens for thick-walled pipes, the method comprising:
[0007] A raw tubing is provided, the raw tubing comprising a first clamping section, a first transition section, a stretching section, a second transition section and a second clamping section distributed sequentially along the axial direction, wherein the surface of the stretching section has a first processing area and a second processing area distributed circumferentially along the raw tubing;
[0008] The first and second processing areas of the stretching section are cut to form a first and a second parallel plane on the stretching section. The first and second planes are symmetrically distributed on both sides of the axis of the original pipe and each has a preset distance from the inner wall of the original pipe.
[0009] The surfaces of the first transition section and the second transition section are cut to form a first curved surface tangent to the first plane on the first transition section and a second curved surface tangent to the second plane on the second transition section. The first curved surface and the corresponding second curved surface are symmetrically distributed on both sides of the original pipe axis.
[0010] In one embodiment, the cross-sectional area of the stretched section after processing is less than or equal to 90% of the cross-sectional area of the original pipe.
[0011] In one embodiment, the axial length of the stretching segment Where S0 is the cross-sectional area of the original pipe.
[0012] In one embodiment, the axial length of the first clamping segment is the same as the axial length of the second clamping segment.
[0013] In one embodiment, during the cutting of the stretching segment, a first clamping boss and a second clamping boss are respectively retained at both ends of the stretching segment along its axial direction, wherein the first clamping boss is formed on the first plane and / or the second plane, and the second clamping boss is formed on the first plane and / or the second plane.
[0014] In one embodiment, the outer diameter of the original pipe is 3mm to 42mm and the wall thickness is 0.8mm to 12mm.
[0015] A tensile test specimen for thick-walled pipes, wherein the tensile test specimen for thick-walled pipes is manufactured by the processing method described in any of the above claims, and includes a first clamping section, a first transition section, a tensile section, a second transition section and a second clamping section distributed sequentially along the axial direction.
[0016] The tensile section has a first plane and a second plane that are parallel to each other. The first plane and the second plane are symmetrically distributed on both sides of the axis of the tensile specimen, and there is a preset distance between the first plane, the second plane and the inner wall of the original tube.
[0017] The first transition segment has a first curved surface tangent to the first plane, and the second transition segment has a second curved surface tangent to the second plane.
[0018] In one embodiment, the cross-sectional area of the stretched section is less than or equal to 90% of the cross-sectional area of the original tubing.
[0019] In one embodiment, the axial length of the stretching segment Where S0 is the cross-sectional area of the original pipe.
[0020] In one embodiment, a first clamping boss and a second clamping boss are provided at both axial ends of the stretching segment, the first clamping boss being formed on the first plane and / or the second plane, and the second clamping boss being formed on the first plane and / or the second plane.
[0021] The tensile specimens and processing methods for the aforementioned thick-walled pipes preserve the original surface of the pipes to demonstrate the influence of surface quality on the instantaneous tensile properties and long-term high-temperature performance of the pipes. The processed structure is symmetrical, avoiding extra bending moments and local stress concentrations that could lead to fractures outside the gauge length and abnormal fractures. By maintaining appropriate distances between the first and second planes on the tensile section and the inner surface of the pipe, excessive stress concentrations at geometric corners and the characterization of persistent fracture information of the pipe can be avoided. By forming a first curved surface in the first transition section and a second curved surface in the second transition section, a suitable transition mode is achieved between the first and second transition sections to ensure a suitable stress distribution and avoid preferential damage failure. Attached Figure Description
[0022] Figure 1 This is a three-dimensional structural schematic diagram of a tensile specimen for thick-walled pipes provided in this application.
[0023] Figure 2A three-dimensional structural schematic diagram of another tensile specimen for thick-walled pipes provided in this application.
[0024] Figure 3 The stress distribution cloud diagram of the tensile section of the tensile specimen for thick-walled pipe provided in Embodiment 1 of this application.
[0025] Figure 4 The stress distribution cloud map of the tensile section of the double-strip high-temperature creep specimen provided in Comparative Example 1 of this application. Detailed Implementation
[0026] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.
[0027] In the description of this application, it should be understood that if terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" appear, these terms indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.
[0028] Furthermore, where the terms "first" and "second" appear, these terms are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, where the term "multiple" appears, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.
[0029] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.
[0030] In this application, unless otherwise expressly specified and limited, the use of descriptions such as "above" or "below" the second feature indicates that the first and second features are in direct contact or indirect contact via an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. Similarly, "below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.
[0031] It should be noted that if an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. If an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. If so, the terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used in this application are for illustrative purposes only and do not represent the only possible implementation.
[0032] One embodiment of this application provides a method for processing tensile specimens for thick-walled pipes, the method comprising:
[0033] Step S100: Provide the original tubing. See [link / reference] Figure 1 Both the original pipe and the tensile test specimen after processing include a first clamping section 100, a first transition section 200, a tensile section 300, a second transition section 400, and a second clamping section 500 distributed sequentially along the axial direction. Among them, the surface of the tensile section 300 has a first processing area Q1 and a second processing area Q2 distributed circumferentially along the original pipe.
[0034] Step S200: Cut the first processing area Q1 and the second processing area Q2 of the stretching section 300 to form a first plane 300a and a second plane 300b parallel to each other on the stretching section 300. The first plane 300a and the second plane 300b are symmetrically distributed on both sides of the original pipe axis, and the first plane 300a and the second plane 300b are both at a preset distance from the inner wall of the original pipe.
[0035] Step S300: Cut the surfaces of the first transition segment 200 and the second transition segment 400 to form a first curved surface 200a tangent to the first plane 300a on the first transition segment 200 and a second curved surface 400a tangent to the second plane 300b on the second transition segment 400.
[0036] It should be noted that, in order to clearly show the structure of the original pipe after processing, [the following text is missing]. Figure 1 and Figure 2 All of them have been rendered with a perspective effect.
[0037] The following describes each step of the above processing method:
[0038] In step S100, the provided raw pipe material can be a small-diameter, thick-walled heat exchanger tube commonly used in thermal equipment such as steam generators and heat exchangers, wherein the outer diameter of such pipe material is 3mm to 42mm and the wall thickness is 0.8mm to 12mm. Of course, this processing method can also be used to process tensile test specimens of small-diameter, thick-walled pipe materials in other fields of equipment.
[0039] In step S200, only the first processing area Q1 and the second processing area Q2 on the surface of the stretching section 300 are cut to form the first plane 300a and the second plane 300b, while the remaining surfaces of the stretching section 300 are not cut, thus preserving part of the original surface of the stretching section 300. This can reflect the influence of the surface quality of the pipe on the instantaneous tensile performance and high-temperature long-term performance of the pipe, and can also reduce the influence of metal oxidation in the high-temperature creep test. Moreover, the first plane 300a and the second plane 300b of the stretching area are both at a certain distance from the inner surface of the original pipe, which can avoid excessive stress concentration at the geometric corners and the characterization of the pipe's creep fracture information.
[0040] It is understandable that both the first plane 300a and the second plane 300b extend through the entire length of the stretching section 300.
[0041] It should be noted that, in order to ensure that the first plane 300a and the second plane 300b are symmetrically distributed on both sides of the original pipe axis, the axial length of the first plane 300a and the axial length of the second plane 300b are the same.
[0042] If the radial distance between the first plane 300a of the tension section 300 and the inner wall of the original pipe is too large, tensile fracture will not occur on the tension section 300. If the distance between the first plane 300a of the tension section 300 and the inner wall of the original pipe is too small, stress concentration areas will appear on the tension section 300. Therefore, numerical calculations and other methods are needed to optimize the distance between the first plane 300a and the inner wall of the original pipe. Specifically, the distance between the first plane 300a and the inner wall of the original pipe directly reflects the cross-sectional area of the tension section 300 after processing. Specifically, the cross-sectional area of the tension section 300 after processing should be less than or equal to 90% of the cross-sectional area of the original pipe (i.e., the cross-sectional area of the first clamping section 100 or the second clamping section 500), and the deviation between the maximum and minimum stresses and the average stresses of the tension section 300 after processing should not exceed 5%. Understandably, the minimum radial distance between the first plane 300a and the inner wall of the original pipe can be calculated by using stress constraints.
[0043] The tension section 300 should also have a suitable length to avoid the influence of the geometry and mechanical loading methods of the first and second transition sections and the first and second clamping sections on the measurement results. If the original pipe length allows the axial length L (original gauge length) of the tension section 300 to meet the relevant standard requirements, then... Where S0 is the cross-sectional area of the original pipe; if this is not met, the appropriate length of the stretching section 300 can be selected according to the specific circumstances.
[0044] During the cutting process of the tensile section 300, a first clamping boss 610 and a second clamping boss 620 can be retained at both axial ends of the tensile section 300, respectively. The first clamping boss 610 is formed on the first plane 300a and / or the second plane 300b, and the second clamping boss 620 is formed on the first plane 300a and / or the second plane 300b. Retaining the first clamping boss 610 and the second clamping boss 620 on the tensile section 300 allows for the clamping of related equipment, such as an extensometer, to obtain tensile curves, high-temperature creep curves, etc., of the tensile specimen. It is understood that the forms of the first clamping boss 610 and the second clamping boss 620 can be adjusted; for example, such as… Figure 2 As shown, a first clamping boss 610 is provided on the same end of the first plane 300a and the second plane 300b, and a second clamping boss 620 is provided on the other end of the first plane 300a and the second plane 300b.
[0045] Regarding step S300, a first curved surface 200a tangent to the first plane 300a is formed on the first transition segment 200 by cutting, and a second curved surface 400a tangent to the second plane 300b is formed on the second transition segment 400. This ensures that the first transition segment 200 and the second transition segment 400 have a suitable transition mode, thereby guaranteeing a suitable stress distribution and avoiding preferential damage failure. In other embodiments, the first curved surface 200a may also include a connecting plane that connects to the first plane 300a, and the second curved surface 40a may also include a connecting plane that connects to the second plane 300b.
[0046] It is understandable that there are two first curved surfaces 200a and two second curved surfaces 400a. The two first curved surfaces 200a are tangent to the two ends of the first plane 300a along its axial direction, and the two second curved surfaces 400a are tangent to the two ends of the second plane 300b along its axial direction. The first curved surfaces 200a and 400a are symmetrically distributed on both sides of the central axis of the original pipe. In addition, the first plane 300a and the second plane 300b are also symmetrically distributed on both sides of the central axis of the original pipe. This results in the original pipe having an axisymmetric structure after processing. This can avoid fractures outside the gauge length and abnormal fractures caused by additional bending moments and local stress concentrations.
[0047] The first clamping section 100 and the second clamping section 500 can be machined accordingly based on the method of mechanical loading. If the first clamping section 100 and the second clamping section 500 use a threaded method to mechanically load the tensile specimen, threads can be made on the inner or outer walls of the first clamping section 100 and the second clamping section 500. The first clamping section 100 and the second clamping section 500 need to have sufficient axial length to ensure the number of threads, so that the stress at the thread (calculated based on the minor diameter of the thread) is less than the stress of the parallel tensile section 300, that is, there will be no preferential failure at the thread. If the first clamping section 100 and the second clamping section 500 use a pin method to mechanically load the tensile specimen, pin holes can be radially made on the side walls of the first clamping section 100 and the second clamping section 500. The first clamping section 100 and the second clamping section 500 need to have sufficient axial length to ensure that there will be no preferential failure around the pin holes. Of course, in other embodiments, the clamping section can also be used to mechanically load the tensile specimen by means of a plug clamping, etc., where the clamping section should also have sufficient length to ensure that there is no preferential failure around the plug.
[0048] The axial length of the first clamping section 100 is the same as that of the second clamping section 500. This setting of the axial length relationship between the first clamping section 100 and the second clamping section 500 ensures uniform mechanical loading at both ends of the tensile specimen and guarantees that tensile fracture occurs in the tensile section 300 of the tensile specimen.
[0049] In summary, compared to existing overall thinning schemes, sheet-like specimen schemes, overall clamping schemes, and double-strip schemes, the local thinning scheme adopted in this application preserves the original surface of the pipe to reflect the influence of surface quality on the pipe's instantaneous tensile properties and high-temperature long-term performance. The processed structure is symmetrical, avoiding extra bending moments and local stress concentrations that could lead to extra-gauge-length fractures and abnormal fractures. By maintaining appropriate distances between the first and second planes on the tensile section 300 and the inner surface of the pipe, excessive stress concentrations at geometric corners and the characterization of persistent fracture information of the pipe can be avoided. By forming a first curved surface 200a in the first transition section 200 and a second curved surface 400a in the second transition section 400, the first transition section 200 and the second transition section 400 have a suitable transition mode, ensuring a suitable stress distribution between the first transition section 200 and the second transition section 400 and avoiding preferential damage failure.
[0050] On the other hand, see Figure 1 This application also provides a tensile specimen for thick-walled pipes, which is an axisymmetric structure processed from the original pipe by the processing method described in any of the preceding claims. The axisymmetric structure may include a first clamping section 100, a first transition section 200, a tensile section 300, a second transition section 400, and a second clamping section 500 distributed sequentially along the axial direction. The tensile section 300 has a first plane 300a and a second plane 300b that are parallel to each other. The first plane 300a and the second plane 300b are symmetrically distributed on both sides of the original pipe, and the first plane and the second plane are each at a predetermined distance from the inner wall of the original pipe. The first transition section 200 has a first curved surface 200a that is tangent to the first plane 300a, and the second transition section 400 has a second curved surface 400a that is tangent to the second plane 300b.
[0051] The local thinning scheme adopted in this application preserves the original surface of the pipe to reflect the influence of surface quality on the pipe's instantaneous tensile properties and long-term high-temperature performance. The processed structure is symmetrical, avoiding extra bending moments and local stress concentrations that could lead to fractures outside the gauge length and abnormal fractures. By maintaining appropriate distances between the first and second planes 300b on the tensile section 300 and the inner surface of the pipe, excessive stress concentrations at geometric corners and the characterization of persistent fracture information of the pipe can be avoided. By forming a first curved surface 200a in the first transition section 200 and a second curved surface 400a in the second transition section 400, the first transition section 200 and the second transition section 400 have a suitable transition mode, ensuring that the first transition section 200 and the second transition section 400 have a suitable stress distribution and avoiding preferential damage failure.
[0052] If the radial distance between the first plane 300a of the tension section 300 and the inner wall of the original pipe is too large, tensile fracture will not occur in the tension section 300. If the radial distance between the first plane 300a of the tension section 300 and the inner wall of the original pipe is too small, stress concentration areas will appear on the tension section 300. Therefore, numerical calculations and other methods are needed to optimize the distance between the first plane 300a and the inner wall of the original pipe. Specifically, the distance between the first plane 300a and the inner wall of the original pipe directly reflects the cross-sectional area of the tension section 300. Specifically, the cross-sectional area of the tension section 300 should be less than or equal to 90% of the cross-sectional area of the original pipe (i.e., the cross-sectional area of the first clamping section 100 or the second clamping section 500), and the deviation between the maximum and minimum stresses and the average stress of the tension section 300 should not exceed 5%. It is understandable that the minimum radial distance between the first plane 300a and the inner wall of the original pipe can be calculated by using stress constraints.
[0053] The tension section 300 should also have a suitable length to avoid the influence of the geometry and mechanical loading method of the first and second transition sections 400 and the first and second clamping sections 500 on the measurement results. If the original pipe length allows the axial length L (original gauge length) of the tension section 300 to meet the relevant standard requirements, then the axial length of the tension section 300... Where S0 is the cross-sectional area of the original pipe (i.e., the cross-sectional area of the first clamping section 100 or the second clamping section 500); if this cannot be satisfied, the appropriate length of the stretching section 300 can be selected according to the specific circumstances.
[0054] Figure 2 A schematic diagram of another tensile specimen for thick-walled tubing is shown; see [link / reference]. Figure 2The tensile section 300 has a first clamping boss 610 and a second clamping boss 620 respectively provided at both axial ends. The first clamping boss 610 is formed on the first plane 300a and / or the second plane 300b, and the second clamping boss 620 is formed on the first plane 300a and / or the second plane 300b. The retention of the first clamping boss 610 and the second clamping boss 620 on the tensile section 300 allows for the clamping of related equipment, such as an extensometer, to obtain tensile curves, high-temperature creep curves, etc., of the tensile specimen.
[0055] To clearly illustrate that the tensile test specimen for thick-walled pipes provided in this application has better measurement performance than existing tensile test specimens for thick-walled pipes, an embodiment and a comparative example are given below.
[0056] Example 1
[0057] This embodiment provides a tensile specimen for thick-walled tubing; see [link / reference]. Figure 1 The tensile test specimen for the thick-walled pipe is manufactured from an original pipe with dimensions of Φ19mm×3mm, and includes a first clamping section 100, a first transition section 200, a tensile section 300, a second transition section 400, and a second clamping section 500 distributed sequentially along the axial direction. The first clamping section 100 and the second clamping section 500 use threads to apply mechanical loading to the tensile test specimen. The distance between the first plane 300a and the second plane 300b of the tensile section 300 and the inner surface of the original pipe is 0.5mm. The first transition section 200 and the second transition section 400 both use arc surfaces with a radius of curvature of 150mm for transition. Figure 3 The stress distribution contour plot of the tensile specimen of the thick-walled pipe under tensile load is shown. Figure 3 As can be seen, the stress deviation on the tensile section 300 is within 1 MPa, which can be considered as a uniform stress distribution on the tensile section 300.
[0058] Comparative Example
[0059] This comparative example provides a bi-strip high-temperature durability specimen. Figure 4 The stress distribution contour plot of the tensile section 300 of the specimen under tensile load is shown. Figure 4 As can be seen, the stress deviation in the cross-section of the tensile section of the specimen is as high as 37 MPa, which causes stress concentration at the sharp parts of the double-strip high-temperature creep rupture specimen. This stress concentration, coupled with metal oxidation, can exacerbate the formation of notches in the double-strip high-temperature creep rupture specimen.
[0060] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0061] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.
Claims
1. A method for processing tensile test specimens for thick-walled pipes, characterized in that, The processing method includes: A raw tubing is provided, the raw tubing comprising a first clamping section, a first transition section, a stretching section, a second transition section and a second clamping section distributed sequentially along the axial direction, wherein the surface of the stretching section has a first processing area and a second processing area distributed circumferentially along the raw tubing; The first and second processing areas of the stretching section are cut to form a first and a second parallel plane on the stretching section. The first and second planes are symmetrically distributed on both sides of the axis of the original pipe and are both at a preset distance from the inner wall of the original pipe to avoid excessive stress concentration at the geometric corners and to characterize the pipe's persistent fracture information. The surfaces of the first transition section and the second transition section are cut to form a first curved surface tangent to the first plane on the first transition section and a second curved surface tangent to the second plane on the second transition section. The first curved surface and the corresponding second curved surface are symmetrically distributed on both sides of the original pipe axis. Wherein, the cross-sectional area of the stretched section after processing is less than or equal to 90% of the cross-sectional area of the original pipe.
2. The processing method according to claim 1, characterized in that, The axial length of the stretching section ,in The cross-sectional area of the original pipe is given.
3. The processing method according to claim 1, characterized in that, The axial length of the first clamping segment is the same as the axial length of the second clamping segment.
4. The processing method according to any one of claims 1 to 3, characterized in that, During the cutting process of the stretching segment, a first clamping boss and a second clamping boss are respectively retained at both ends of the stretching segment along the axial direction. The first clamping boss is formed on the first plane and / or the second plane, and the second clamping boss is formed on the first plane and / or the second plane.
5. The processing method according to any one of claims 1 to 3, characterized in that, The outer diameter of the original pipe is 3mm to 42mm, and the wall thickness is 0.8mm to 12mm.
6. A tensile specimen for thick-walled pipes, characterized in that, The thick-walled pipe tensile specimen is processed from the original pipe by the processing method described in any one of claims 1 to 5 above, including a first clamping section, a first transition section, a tensile section, a second transition section and a second clamping section distributed sequentially along the axial direction; The tension section has a first plane and a second plane that are parallel to each other. The first plane and the second plane are symmetrically distributed on both sides of the original pipe. The first plane, the second plane and the inner wall of the original pipe are all at a preset distance to avoid excessive stress concentration at the geometric corners and to characterize the pipe's persistent fracture information. The first transition segment has a first curved surface tangent to the first plane, and the second transition segment has a second curved surface tangent to the second plane; Wherein, the cross-sectional area of the stretched section is less than or equal to 90% of the cross-sectional area of the original pipe.
7. The tensile specimen for thick-walled tubing according to claim 6, characterized in that, The axial length of the stretching section ,in The cross-sectional area of the original pipe is given.
8. The tensile specimen for thick-walled tubing according to claim 6 or 7, characterized in that, The stretching section has a first clamping boss and a second clamping boss at its two axial ends, respectively. The first clamping boss is formed on the first plane and / or the second plane, and the second clamping boss is formed on the first plane and / or the second plane.