An auxiliary structure, device and method for pipe tensile testing

Abstract

The present application belongs to the technical field of whole pipe tensile test, and particularly relates to a kind of pipe tensile test auxiliary structure, device and method;Including test pipe section and testing machine;Two ports of the test pipe section are inserted with metal plug respectively;The metal plug includes plug main body and boss;The plug main body is circular truncated cone, and the end with large diameter of plug main body is connected with boss;The metal plug is divided into N parts from the center axis, wherein N≥2;The testing machine clamps the two ends of the test pipe section with metal plug;By setting the plug main body as circular truncated cone, it is convenient to install the metal plug into the inside of test pipe section, and setting boss facilitates taking out the metal plug from the test pipe section.

Description

Technical Field

[0001] This invention belongs to the field of whole tube tensile testing technology, and specifically relates to an auxiliary structure, device and method for tube tensile testing. Background Technology

[0002] In engineering applications such as oilfields and urban pipeline networks, the mechanical properties of casing pipes or other pipe materials play a crucial role in engineering applications. Among these, tensile strength is the most important mechanical property indicator. Tensile testing of metal pipes to obtain parameters such as tensile strength, yield strength, and elongation after fracture can effectively verify material quality and provide important indicators of whether the material is suitable for application. Generally, tensile testing requires large-diameter metal pipes to be processed into standard shapes such as rods or plates. However, for smaller-diameter pipes, the entire pipe can be stretched directly, which can effectively obtain accurate strength properties of the original pipe. The apparatus and methods for stretching the entire pipe are relatively specialized and difficult, therefore, their research is of great significance. An auxiliary structure for pipe tensile testing is needed to address the problem of pipe segment flattening during clamping, which affects the test results. Summary of the Invention

[0003] To address the above problems, this invention proposes an auxiliary structure for pipe tensile testing, comprising a test pipe section and a testing machine; metal plugs are inserted into both ends of the test pipe section.

[0004] The metal plug includes a plug body and a boss; the plug body is frustoconical, and the end of the plug body with a larger diameter is connected to the boss; the metal plug is evenly divided into N single-lobed plugs from the central axis, where N≥2;

[0005] The testing machine clamps both ends of the test pipe section with metal plugs installed.

[0006] Furthermore, the outer ring of the plug body is wrapped with soft iron wire.

[0007] Furthermore, the diameter of the boss is greater than the maximum diameter of the plug body, and the diameter of the boss is smaller than the outer diameter of the test pipe section.

[0008] This invention proposes a pipe tensile testing device, including any of the auxiliary structures described above; it also includes a pull rod and a rope; the pull rod includes a horizontal bar and a vertical bar that are perpendicular to each other, and the two ends of the horizontal bar are provided with slots on the side walls facing the vertical bar; an extensometer is connected to the end of the vertical bar away from the test pipe section;

[0009] The two ends of the rope are connected to adjustment structures, which are detachably connected to the crossbar via slots.

[0010] Furthermore, the adjustment structure includes a porous sheet and a spring; one end of the porous sheet is connected to one end of the rope, and the other end of the porous sheet is connected to a slot on one side of the crossbar; one end of the spring is connected to the other end of the rope, and the other end of the spring is connected to a slot on the other side of the crossbar.

[0011] Furthermore, the slot is V-shaped.

[0012] This invention proposes a method for pipe tensile testing, employing a pipe tensile testing device as described in any one of the above-mentioned methods; specifically, it includes the following steps:

[0013] Cut the metal pipe into test sections of the appropriate length;

[0014] Obtain the outer diameter and wall thickness of the test pipe section;

[0015] Install the two metal plugs at both ends of the test pipe section respectively;

[0016] Dots are made on the outer wall of the test pipe section, and the two ends of the test pipe section are clamped by the clamps of the testing machine;

[0017] Install the extensometer on the test pipe section and obtain the extensometer deformation curve;

[0018] Remove the metal plug from the test section.

[0019] Furthermore, the acquisition of the outer diameter and wall thickness of the test pipe section is achieved through the following steps:

[0020] In the middle and both ends of the test pipe section, b points are measured along the circumference of each section, and the average value is taken as the outer diameter of the test pipe section.

[0021] Measure c points along the circumference at both ends of the test pipe section, and obtain the average value as the wall thickness of the test pipe section.

[0022] Furthermore, the installation of the two metal plugs onto both ends of the test pipe section is achieved through the following steps:

[0023] Connect N single-lobed plugs into a single metal plug;

[0024] Wrap soft iron wire around the outer wall of the plug body, and adjust the number of turns of soft iron wire according to the inner diameter of the test pipe section:

[0025] Insert the two plug bodies and the soft iron wire together into both ends of the test pipe section.

[0026] Furthermore, the installation of the extensometer on the test tube section is also achieved through the following steps;

[0027] Install and connect the extensometer to the longitudinal rod;

[0028] Connect the two ends of the rope to the spring and the porous sheet, respectively;

[0029] The rope is looped around the test tube section, the spring is fixed to the slot on one side of the crossbar, and the porous sheet is fixed to the slot on the other side of the crossbar.

[0030] Furthermore, the removal of the metal plug from the test pipe section is also achieved through the following steps;

[0031] Use a small-diameter rod to strike the plug body from the broken end of the test pipe section in the opposite direction;

[0032] Once one of the single-lobed plugs becomes loose, remove that single-lobed plug.

[0033] Then remove the other single-lobed plugs one by one.

[0034] Beneficial effects

[0035] 1. This application uses a frustum-shaped plug body to facilitate the installation of the metal plug into the test pipe section. The protrusion facilitates the removal of the metal plug from the test pipe section. The soft iron wire is wrapped around the outside of the plug body to adjust the tightness between the plug body and the test pipe section, and to avoid excessive compression of the plug body during the test, so that the metal plug can be reused. At the same time, it avoids excessive adhesion between the plug body and the test pipe section, making it easy to remove the metal plug.

[0036] 2. This application sets the pull rod as a horizontal bar and a vertical bar. The slot on the horizontal bar is connected to both ends of the rope through a porous sheet and a spring. The applicability to test tube sections with different outer diameters is adjusted by connecting the circular holes at different positions on the porous sheet to the horizontal bar. During the stretching process, the outer diameter of the test tube section becomes smaller, and the tension is adjusted by the spring to prevent the extensometer from slipping.

[0037] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1a A front view of the metal plug in an embodiment of the present invention is shown.

[0040] Figure 1b A top view of a metal plug in an embodiment of the present invention is shown.

[0041] Figure 2 A three-dimensional structural diagram of the segmented single-lobed metal plug in an embodiment of the present invention is shown.

[0042] Figure 3a A front view of the pull rod in an embodiment of the present invention is shown.

[0043] Figure 3b A top view of the pull rod in an embodiment of the present invention is shown.

[0044] Figure 4 A schematic diagram of the extensometer clamping device in an embodiment of the present invention is shown.

[0045] Figure 5 A schematic diagram of the overall structure of the test process in an embodiment of the present invention is shown.

[0046] Figure 6 A flowchart of a method according to an embodiment of the present invention is shown.

[0047] In the diagram, 1. Metal plug; 11. Plug body; 12. Boss; 2. Soft iron wire; 3. Rope; 4. Spring; 5. Porous sheet; 6. Longitudinal rod; 7. Cross rod; 8. Extensometer; 9. Testing machine; 10. Test tube section. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] This application provides an auxiliary structure for pipe tensile testing, with reference to... Figure 1a , Figure 1b , Figure 2 and Figure 5 It includes a test tube section 10 and a test machine 9; metal plugs 1 are inserted into the two ends of the test tube section 10 respectively;

[0050] The metal plug 1 includes a plug body 11 and a boss 12; the plug body 11 is frustoconical, and the end of the plug body 11 with a larger diameter is connected to the boss 12; the metal plug 1 is divided into four single-lobed plugs from the central axis.

[0051] The testing machine 9 clamps both ends of the test pipe section 10, which is equipped with metal plugs 1.

[0052] The plug body 11 is wrapped with soft iron wire 2 around its outer ring.

[0053] The diameter of the boss 12 is greater than the maximum diameter of the plug body 11, and the diameter of the boss 12 is less than the outer diameter of the test pipe section 10.

[0054] The existing metal pipe sections are directly clamped on the testing machine 9. During the tensile test, the clamping area is easily flattened or broken, and the fracture point is not in the middle of the specimen, which seriously affects the test data such as elongation after fracture. Therefore, metal mandrel plugs need to be placed at both ends of the pipe. To avoid the tensile test breaking at the clamping point, the mandrel plugs need to be processed from metal blanks with a lower hardness than the original pipe material. However, the plugs cannot be made of excessively soft materials such as copper or aluminum to prevent damage during clamping and affecting reuse. In the past, the original mandrel plugs were usually designed as uniform-diameter cylinders. However, due to processing errors and uneven inner diameter of the original pipe material, if the outer diameter of the cylindrical plug is too large, it is difficult to insert into the pipe body; if it is too small, it will fall out after insertion, affecting subsequent tests. Some mandrel plugs have a precision internal structure, which is too complex to design and process and is expensive. Due to the large clamping force of the clamp during the tensile test, the complex internal structure is flattened and damaged, making the plugs unusable. Therefore, they are not suitable for actual testing.

[0055] In the implementation of this application, the metal pipe is cut into test pipe sections 10 of corresponding length, and the metal plugs 1, which are divided into four equal parts, are spliced ​​together. The plug body 11 is made of metal blank with a hardness lower than that of the test pipe section 10. At the same time, the plug body 11 is not made of soft materials such as copper or aluminum. The outer diameter D1 of the plug body 11 is D1 = D - 2t - 1mm, where D is the outer diameter of the test pipe section 10 and t is the wall thickness of the test pipe section 10. The inner diameter D2 of the plug body 11 is D1 - D2 = 3~8mm. D3 is the outer diameter of the boss 12 (the length of the part of the boss 12 that exceeds D1), 2mm < D3 < t. L2 is the thickness of the boss 12, L2 ≈ 5mm. L1 is the length of the metal plug 1, L1 > La.

[0056] Next, wrap the soft iron wire 2 around the outer wall of the plug body 11. The soft iron wire 2 is selected with a diameter of about one millimeter. Then, place the plug body 11 with the soft iron wire 2 wrapped around it at the two ends of the test tube section 10. If it is too tight or too loose during the insertion process, you can take it out and adjust the number of turns of the soft iron wire 2 before putting it in again. If it is too tight, loosen a few turns of the soft iron wire 2. If it is too loose, wrap a few more turns of the soft iron wire 2.

[0057] The two ends of the test pipe section 10 are then clamped by the testing machine 9, and then the test is carried out. During the test, as the tensile loading force increases, the soft iron wire 2 will bear most of the deformation, thereby avoiding excessive compression of the metal plug 1 during the test, so that the metal plug 1 can be reused. The soft iron wire 2 is exposed about 3 to 5 mm from the end face of the test pipe section 10, while avoiding the plug body 11 from sticking too tightly to the inner wall of the test pipe section 10, so that the metal plug 1 can be removed after the test.

[0058] After repeated use, the metal plug 1 may be deformed or damaged to varying degrees. The severely damaged plug body 11 can be repaired or replaced appropriately. At the same time, the soft iron wire 2 can be used to wrap and adjust it to achieve convenient and quick reuse.

[0059] The side walls of the four-lobed metal plug 1 can be configured to slide vertically and vertically in pairs. Each of the two side walls of two lobe metal plugs 1 has a groove and a slider, respectively. One lobe has only a groove, and the other has only a slider. When assembling the four-lobed metal plug 1, first connect the metal plug 1 with both grooves and sliders to the metal plug 1 with only grooves via the groove and slider. Then, install the metal plug 1 with both grooves and sliders and the metal plug 1 with only sliders in sequence. When removing the metal plug 1, first remove the metal plug 1 with only sliders, then remove the two metal plugs with grooves and sliders in sequence, and finally remove the metal plug 1 with only grooves.

[0060] This application sets the plug body 11 in a frustum shape to facilitate the installation of the metal plug 1 into the test pipe section 10. The protrusion 12 facilitates the removal of the metal plug 1 from the test pipe section 10. The soft iron wire 2 is wrapped around the outside of the plug body 11. On the one hand, it can adjust the tightness between the plug body 11 and the test pipe section 10. On the other hand, it can avoid excessive compression of the plug body 11 during the test, so that the metal plug 1 can be reused. At the same time, it can prevent the plug body 11 from being overly adhered to the test pipe section 10, making it easier to remove the metal plug 1.

[0061] This application proposes a pipe tensile testing device, including any of the auxiliary structures mentioned above, with reference to... Figure 3a , Figure 3b , Figure 4 and Figure 5 It also includes a pull rod and a rope 3; the pull rod includes a crossbar 7 and a vertical bar 6, one end of the vertical bar 6 is connected to the middle of the crossbar 7, and both ends of the crossbar 7 are provided with slots on the side walls facing the vertical bar 6; the vertical bar 6 is connected to the extensometer 8;

[0062] The two ends of the rope 3 are connected to adjustment structures, which are detachably connected to the crossbar 7 via slots.

[0063] The adjustment structure includes a porous sheet 5 and a spring 4; one end of the porous sheet 5 is connected to one end of the rope 3, and the other end of the porous sheet 5 is connected to a slot on one side of the crossbar 7; one end of the spring 4 is connected to the other end of the rope 3, and the other end of the spring 4 is connected to a slot on the other side of the crossbar 7.

[0064] In one embodiment of the present invention, the card slot is "V" shaped.

[0065] In pipe stretching, due to the large outer diameter and significant differences in outer diameter, the existing extensometer 8 is clamped by binding the extensometer 8 to the pipe body with rubber bands. However, the installation process is time-consuming and labor-intensive, and the extensometer 8 tip is prone to slippage during stretching, resulting in slippage in the stretching curve, which in turn affects the accurate selection of the yield point. At the same time, the yield strength needs to be calculated based on the stretching curve, i.e., the force-extensometer 8 deformation curve. If the stretching curve is discontinuous yielding, i.e., for materials with a yield plateau, the upper or lower yield point can be easily determined by the yield plateau segment of the stretching curve. However, for continuous yielding, i.e. for materials without a yield plateau, the yield strength can only be obtained by specifying the plastic extension strength or the total extension strength. Therefore, if the extensometer 8 is not clamped and selected properly, an accurate and smooth force-extensometer 8 deformation curve cannot be obtained, which causes difficulties in calculating the yield strength.

[0066] In this application, the pull rod is made of metal, and the longitudinal rod 6 of the pull rod is inserted into the outer hole of the extensometer 8 and connected to the extensometer 8 by screws. During the test, the test tube section 10 is clamped axially on the testing machine 9, and the rope 3 is wrapped around the test tube. The rope 3 is a nylon rope with a length of 200-400 mm. One end of the nylon rope is connected to the ring on the spring 4 through a hook. The spring 4 has rings at both ends, and the other end of the spring 4 is connected to the V-shaped rod on the crossbar 7 through the ring. The nylon rope is connected to the ring on the porous sheet 5 via a hook. The porous sheet 5 has multiple holes, which are connected to the V-shaped slots on the crossbar 7. The crossbar 7 has a diameter of 2.3 mm, and the holes have a diameter of 2.5 mm. The holes can pass through the crossbar 7 and connect to the slots. The porous sheet 5 can fit the holes at different positions into the slots according to the outer diameter of the test tube section 10, making it suitable for test tube sections 10 with different outer diameters.

[0067] The extensometer 8 has two blades, one at the top and one at the bottom. Therefore, the two ends of the extensometer 8 body can be fixed to the test tube section 10 using two ropes 3 and two tie rods. This also fixes the upper and lower blades of the extensometer 8 to the test tube section 10, with the blades in contact with the test tube section 10. The changes in the distance between the two blades are then converted into deformation data. After the extensometer 8 is fixed to the test tube section 10, the pin of the extensometer 8 can be removed, and the tensile test can begin according to the normal procedure. During the test, when the tensile curve passes the yield force or the maximum force, the ropes 3 and the extensometer 8 must be removed promptly to prevent excessive vibration and damage to the extensometer 8 if the test tube section 10 breaks.

[0068] Meanwhile, during the tensile test, the outer diameter of the test tube 10 decreases, and the spring 4 can be adjusted accordingly to ensure that the extensometer 8 does not slip or fall off during the tensile test.

[0069] This application sets the pull rod as a horizontal bar 7 and a vertical bar. The slot on the horizontal bar 7 is connected to both ends of the rope body 3 through a porous sheet 5 and a spring 4. The application to test tube sections 10 with different outer diameters is adjusted by connecting the circular holes at different positions on the porous sheet 5 to the horizontal bar 7. During the stretching process, the outer diameter of the test tube section 10 becomes smaller, and the tension is adjusted by the spring 4 to prevent the extensometer 8 from slipping.

[0070] This application also proposes a method for tensile testing of pipes, referencing... Figure 6 The method employs a pipe tensile testing device as described in any one of the above-mentioned methods; specifically, it includes the following steps:

[0071] Cut the metal pipe into test pipe sections 10 of the corresponding length;

[0072] Obtain the outer diameter and wall thickness of test pipe section 10;

[0073] Install the two metal plugs 1 at both ends of the test pipe section 10 respectively;

[0074] Dots are made on the outer wall of the test tube section 10, and the two ends of the test tube section 10 are clamped by the clamps of the testing machine 9;

[0075] Install extensometer 8 on test pipe section 10 and obtain the deformation curve of extensometer 8;

[0076] Remove the metal plug 1 from the test pipe section 10.

[0077] In one embodiment of the present invention, obtaining the outer diameter and wall thickness of the test pipe section 10 is further achieved through the following steps:

[0078] In the middle and both ends of the test pipe section 10, b points are measured along the circumference of each section, and the average value is taken as the outer diameter of the test pipe section 10.

[0079] C points are measured along the circumference at both ends of the test pipe section 10, and the average value is taken as the wall thickness of the test pipe section 10.

[0080] In one embodiment of the present invention, the installation of the two metal plugs 1 to both ends of the test pipe section 10 is further achieved through the following steps:

[0081] The four single-lobed plugs are spliced ​​together to form a metal plug 1;

[0082] Soft iron wire 2 is wound around the outer wall of the plug body 11, and the number of turns of soft iron wire 2 is adjusted according to the inner diameter of the test pipe section 10:

[0083] Insert the two plug bodies 11 and the soft iron wire 2 together into both ends of the test pipe section 10.

[0084] In one embodiment of the present invention, the installation of the extensometer 8 on the test tube section 10 is further achieved through the following steps;

[0085] Install and connect the extensometer 8 to the longitudinal rod 6;

[0086] Connect the two ends of the rope 3 to the spring 4 and the porous sheet 5 respectively;

[0087] Rope 3 is wrapped around test tube section 10, spring 4 is fixed to the slot on one side of crossbar 7, and porous sheet 5 is fixed to the slot on the other side of crossbar 7.

[0088] In one embodiment of the present invention, the removal of the metal plug 1 from the test pipe section 10 is further accomplished through the following steps;

[0089] Use a small-diameter rod to strike the plug body 11 from the broken end of the test pipe section 10 in the opposite direction;

[0090] Once one of the single-lobed plugs becomes loose, remove that single-lobed plug.

[0091] Then remove the other three single-petal plugs one by one.

[0092] During the implementation process, the metal pipe is cut into test pipe sections 10 with a length of L = 2La + Le + 60 mm, where La is the length of the upper and lower clamps of the testing machine 9, and Le is the gauge length of the extensometer 8; La is 20 mm, Le is 50 mm, and the length L of the test pipe section 10 is 150 mm; the outer diameter is measured at three points at the middle and two ends of the test pipe section 10, with three points measured along the circumference at each point, for a total of nine points, and the average of the nine points is taken as the outer diameter D of the test pipe section 10; four points are measured along the circumference at each of the two ends of the test pipe section 10, for a total of eight points, and the average is taken to obtain the wall thickness T; then the cross-sectional area of ​​the test pipe section 10 is calculated according to S = π(Dt)t;

[0093] After wrapping the four-lobed metal plug 1 with soft iron wire 2, insert the plug body 11 into the test tube section 10. The boss 12 is located on the outside of the test tube section 10 to facilitate the removal of the metal plug 1 later. Use a dotting machine to make dots along the axial direction from one end to the other on the test tube section 10. The dotting interval is generally 10 mm. After dotting, select a testing machine 9 of appropriate size and clamp both ends of the test tube section 10 with the testing machine 9. When clamping, the dotting marks should face outward to prevent the clamping force of the testing machine 9 from being too large and damaging the dotting marks, which would affect the measurement of elongation after fracture.

[0094] An extensometer 8 is installed on the test tube section 10 to measure the yield strength. The extensometer 8 has an accuracy of 0.5 or higher and a gauge length of 50 mm. After clamping the extensometer 8, during the tensile process, the deformation of the extensometer 8 transmits the signal to the computer through the sensor element. On the computer interface, the curve of the relationship between the force value and the deformation of the extensometer 8 can be obtained. The stress can be obtained by dividing the force value by the cross-sectional area of ​​the test tube section 10, and the strain can be obtained by dividing the deformation of the extensometer 8 by the gauge length of the extensometer 8.

[0095] After the test pipe section 10 is pulled to break, the pipe tensile test is completed, and the test data such as yield strength and maximum force are recorded. After the broken test pipe section 10 is removed, the fracture ends are spliced ​​together, and the elongation after fracture is measured. After the measurement is completed, the metal plug 1 is removed.

[0096] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An auxiliary structure for pipe tensile testing, characterized in that, It includes a test tube section (10) and a testing machine (9); metal plugs (1) are inserted into both ends of the test tube section (10); The metal plug (1) includes a plug body (11) and a boss (12); the plug body (11) is frustum-shaped, and the end of the plug body (11) with a larger diameter is connected to the boss (12); the metal plug (1) is divided into N single-lobed plugs from the central axis, where N≥2; The testing machine (9) clamps both ends of the test pipe section (10) with metal plugs (1) installed.

2. The auxiliary structure for pipe tensile testing according to claim 1, characterized in that, The plug body (11) is wrapped with soft iron wire (2) around its outer ring.

3. The auxiliary structure for pipe tensile testing according to claim 1, characterized in that, The diameter of the boss (12) is greater than the maximum diameter of the plug body (11), and the diameter of the boss (12) is less than the outer diameter of the test pipe section (10).

4. A pipe tensile testing device, characterized in that, The auxiliary structure includes any one of claims 1-3; it also includes a pull rod and a rope (3); the pull rod includes a horizontal bar (7) and a vertical bar (6) that are perpendicular to each other, and the two ends of the horizontal bar (7) are provided with slots on the side walls facing the vertical bar (6); the end of the vertical bar (6) away from the test tube section (10) is connected to an extensometer (8); The two ends of the rope (3) are connected to adjustment structures, which are detachably connected to the crossbar (7) via slots.

5. The pipe tensile testing device according to claim 4, characterized in that, The adjustment structure includes a porous sheet (5) and a spring (4); one end of the porous sheet (5) is connected to one end of the rope (3), and the other end of the porous sheet (5) is connected to a slot on one side of the crossbar (7); one end of the spring (4) is connected to the other end of the rope (3), and the other end of the spring (4) is connected to a slot on the other side of the crossbar (7).

6. The pipe tensile testing device according to claim 4, characterized in that, The slot is "V" shaped.

7. A method for tensile testing of pipes, characterized in that, The pipe tensile testing apparatus according to any one of claims 4-6 specifically includes the following steps: The metal pipe was cut into test pipe sections of the corresponding length (10); Obtain the outer diameter and wall thickness of the test pipe section (10); Install the two metal plugs (1) at both ends of the test pipe section (10); Markings are made on the outer wall of the test tube section (10), and the two ends of the test tube section (10) are clamped by the clamps of the testing machine (9); Install the extensometer (8) on the test pipe section (10) and obtain the deformation curve of the extensometer (8); Remove the metal plug (1) from the test tube section (10).

8. The method for tensile testing of pipes according to claim 7, characterized in that, The outer diameter and wall thickness of the test pipe section (10) are obtained through the following steps: In the middle and both ends of the test pipe section (10), the outer diameter of b points along the circumference direction in each part is measured, and the average value is obtained as the outer diameter of the test pipe section (10); The wall thickness of the test pipe section (10) is measured at c points along the circumference at both ends, and the average value is taken as the wall thickness of the test pipe section (10).

9. The method for tensile testing of pipes according to claim 7, characterized in that, The installation of the two metal plugs (1) onto both ends of the test pipe section (10) is also achieved through the following steps: N single-lobed plugs are spliced ​​together to form a metal plug (1); Wrap soft iron wire (2) around the outer wall of the plug body (11), and adjust the number of turns of soft iron wire (2) according to the inner diameter of the test pipe section (10): Insert the two plug bodies (11) and the soft iron wire (2) together into both ends of the test tube section (10).

10. A method for tensile testing of pipes according to claim 7, characterized in that, The installation of the extensometer (8) on the test tube section (10) is also achieved through the following steps; Install and connect the extensometer (8) to the longitudinal rod (6); Connect the two ends of the rope (3) to the spring (4) and the porous sheet (5) respectively; The rope (3) is wrapped around the test tube section (10), the spring (4) is fixed to the slot on one side of the crossbar (7), and the porous sheet (5) is fixed to the slot on the other side of the crossbar (7).

11. A method for tensile testing of pipes according to claim 7, characterized in that, The removal of the metal plug (1) from the test tube section (10) is also achieved through the following steps; Use a small-diameter rod to strike the plug body (11) from the broken end of the test pipe section (10) in the opposite direction; Once one of the single-lobed plugs becomes loose, remove that single-lobed plug. Then remove the other single-lobed plugs one by one.

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