Preparation method of uniaxial tensile sample for sulfide stress corrosion cracking test

Abstract

The invention relates to the technical field of sulfur-resistant drill rod testing, in particular to a method for preparing a uniaxial tensile sample for a sulfide stress corrosion cracking test, which comprises the following steps of: polishing the uniaxial tensile sample along the axial direction of the uniaxial tensile sample, so that axial scratches with uniform surface quality are formed on the polished surface; performing anti-hydrogen sulfide coating spraying treatment on the surface of the clamping section of the uniaxial tensile sample; the uniaxial tensile sample is polished in the axial direction of the uniaxial tensile sample, so that annular machining traces are avoided, meanwhile, the surface of the clamping section is subjected to hydrogen sulfide resistant coating spraying treatment, and breakage of the uniaxial tensile sample caused by surface quality defects such as transverse machining traces and transverse scratches in the scale distance and transition arc area is effectively avoided; and meanwhile, the risk of invalid fracture at the sealing part of the clamping section due to crevice corrosion is avoided.

Description

Technical Field

[0001] This invention relates to the field of sulfur-resistant drill pipe testing technology, and in particular to a method for preparing uniaxial tensile specimens for sulfide stress corrosion cracking tests. Background Technology

[0002] The 105SS sulfur-resistant drill pipe, which is the highest strength grade specified in the current standard, has problems such as insufficient mechanical performance and low efficiency in these special well conditions, which seriously restricts the large-scale and high-efficiency development of sulfuric acid-containing oil and gas fields. Therefore, most drill bit manufacturers at home and abroad have successively developed high-strength sulfur-resistant drill pipes such as 120ksi, 125ksi, and 135ksi.

[0003] Currently, the qualification of sulfur-resistant drill pipes must be determined by passing the uniaxial sulfide stress corrosion cracking test (Method A) in the NACE TM0177 standard. The uniaxial tensile specimen consists of a threaded section, a clamping section, a transition arc section, and a gauge length section. Essentially, this test involves immersing the uniaxial tensile specimen in an aerated hydrogen sulfide solution, applying a constant tensile load, and determining product qualification based on whether hydrogen sulfide stress corrosion cracking occurs after 720 hours.

[0004] However, the current method for preparing uniaxial tensile specimens according to NACE TM0177 standard method A has the following main problems: 1. During the machining of uniaxial tensile specimens, the transition arc and gauge length areas are typically machined using external cylindrical grinding, leaving circumferential machining marks in these areas. Subsequent grinding and polishing usually involves manual circumferential grinding, which is insufficient to completely eliminate these machining marks and can easily result in defects such as transverse scratches.

[0005] 2. The uniaxial tensile specimen is installed in the test container, and the clamping area of ​​the specimen is sealed with a sealing ring to ensure that the solution in the test container is in an oxygen-free environment. Therefore, crevice corrosion is prone to occur in this area.

[0006] 3. For high-strength steel anti-sulfur drill pipes, especially those with a strength grade of ≥135ksi, which are made of high-strength steel, higher loads make them more sensitive to sulfide stress corrosion. Even small defects and crevice corrosion can easily cause cracking and fracture.

[0007] As the strength grade of sulfur-resistant drill rods increases, the applied load also increases. Defects such as fine transverse scratches on round rods lead to a significant increase in the probability of fracture, and the proportion of invalid fractures in the clamping section is also increasing. This has a great influence on the test results, making it impossible to accurately determine the qualification of the material products and greatly affecting the technicians' evaluation of the product's reliability. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing uniaxial tensile specimens for sulfide stress corrosion cracking tests, in order to solve the technical problems in the prior art where uniaxial tensile specimens have circumferential machining marks left during processing, and crevice corrosion reaction easily occurs in the clamping section area, leading to an increased probability of fracture, an increased proportion of invalid fractures in the clamping section, interference with test results, and affecting the evaluation of product reliability by test technicians.

[0009] The present invention provides a method for preparing a uniaxial tensile specimen for sulfide stress corrosion cracking test, comprising the following steps; S100. Samples are taken from the anti-sulfur drill pipe product, sawed and rough-machined as blanks, and then the blanks are finished using an external cylindrical grinding machine to prepare a uniaxial tensile specimen having a first threaded section, a first clamping section, a first transition arc section, a gauge length section, a second transition arc section, a second clamping section and a second threaded section in sequence along its axial direction. S200. Polish the uniaxial tensile specimen along its axial direction to form axial scratches with uniform surface quality on the polished surface. S300. Apply an anti-hydrogen sulfide coating to the surface of the clamping section of the uniaxial tensile specimen.

[0010] Furthermore, the processing area for polishing the uniaxial tensile specimen along its axial direction includes the uniaxial tensile specimen surface between the thread root of the first thread segment and the thread root of the second thread segment.

[0011] Furthermore, the polishing process of the uniaxial tensile specimen along its axial direction includes the following steps; S210. The uniaxial tensile specimen is fixed horizontally between two drive motors of the longitudinal polishing machine, and an abrasive belt is placed on one side of the uniaxial tensile specimen. A force is applied to the abrasive belt by weights so that the abrasive belt comes into contact with the uniaxial tensile specimen. The drive motor drives the uniaxial tensile specimen to move horizontally so that it rubs and polishes with the abrasive belt. S220. Rotate the drive motor around the axial direction of the uniaxial tensile specimen to make the uniaxial tensile specimen rotate around its axial direction by a preset angle, and then drive the uniaxial tensile specimen to move along its axial direction again through the drive motor so that it rubs and polishes with the sanding belt. S230. Repeat S220 until the uniaxial tensile specimen has rotated a preset number of times.

[0012] Furthermore, the speed at which the uniaxial tensile specimen moves in the horizontal direction is set to 0.5 cm / s to 1.5 cm / s, the preset angle is 1° to 15°, and the preset number of revolutions is 10 to 50.

[0013] Furthermore, the polishing process along the axial direction of the uniaxial tensile specimen also includes: S240, Replace the sanding belt and repeat S210, S220 and S230; The mesh size of the abrasive belt is selected as 800 mesh and 2000 mesh respectively.

[0014] Furthermore, when the uniaxial tensile specimen is polished with the 800-grit abrasive belt, the preset angle is preferably 7°, 11°, 13° or 14°. When the uniaxial tensile specimen is polished with the 2000-grit abrasive belt, the preset angle is preferably 3.5°, 5.5°, 6.5° or 7°.

[0015] Furthermore, before each polishing process along its axial direction, the uniaxial tensile specimen is polished in a direction perpendicular to its axial direction.

[0016] Furthermore, when polishing the uniaxial tensile specimen along a direction perpendicular to its axial direction, the mesh size of the abrasive belt is selected as 240 mesh and 1200 mesh respectively; When polishing the uniaxial tensile specimen with a 240-mesh screen along a direction perpendicular to its axial direction, the number of polishing cycles is set to 25 to 40. When polishing the uniaxial tensile specimen with 1200 grit along a direction perpendicular to its axial direction, the number of polishing times is set to 15 to 30.

[0017] Furthermore, the process of applying an anti-hydrogen sulfide coating to the surface of the clamping section of the uniaxial tensile specimen includes: Clean with acetone and air dry, then uniformly spray an anti-hydrogen sulfide coating onto the surface of the sample clamping section and heat to cure. The coating is cured at a temperature of 120°C to 160°C for 30 to 60 minutes.

[0018] Furthermore, the thickness of the hydrogen sulfide-resistant coating is set to be between 0.05 mm and 0.1 mm.

[0019] Compared with the prior art, the present invention provides a method for preparing a uniaxial tensile specimen for sulfide stress corrosion cracking testing, comprising sampling, sawing, and rough turning a specimen blank from a sulfur-resistant drill pipe product; finishing the blank specimen using an external cylindrical grinding machine to prepare a uniaxial tensile specimen having, sequentially along its axial direction, a first threaded section, a first clamping section, a first transition arc section, a gauge length section, a second transition arc section, a second clamping section, and a second threaded section; polishing the uniaxial tensile specimen along its axial direction to form axial scratches with uniform surface quality on the polished surface; and applying a hydrogen sulfide resistant coating to the surface of the clamping section of the uniaxial tensile specimen. Coating treatment: By polishing the uniaxial tensile specimen along its axial direction to avoid leaving circumferential machining marks, and by applying an anti-hydrogen sulfide coating to the surface of the clamping section, the technical problems in the prior art that leave circumferential machining marks during the processing of uniaxial tensile specimens, and that the clamping section area is prone to crevice corrosion, leading to an increased probability of fracture and a higher proportion of invalid fractures in the clamping section are solved. This effectively avoids fractures caused by surface quality defects such as transverse machining marks and transverse scratches in the gauge length and transition arc area of ​​the uniaxial tensile specimen, and also avoids the risk of invalid fractures due to crevice corrosion at the clamping section seal. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific 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 from these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the uniaxial tensile specimen provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the polishing process for a uniaxial tensile specimen provided in an embodiment of the present invention. Figure 3 This is a process flow diagram of the method for preparing uniaxial tensile specimens for sulfide stress corrosion cracking test provided in an embodiment of the present invention. Figure 4 This is a processing effect diagram of the first group in the comparative experiment of uniaxial tensile specimens provided in the embodiments of the present invention; Figure 5 This is a processing effect diagram of the second group in the comparative experiment of uniaxial tensile specimens provided in the embodiments of the present invention; Figure 6 This is a processing effect diagram of the third group in the comparative experiment of uniaxial tensile specimens provided in the embodiments of the present invention; Figure 7 This is a processing effect diagram of the fourth group in the comparative experiment of uniaxial tensile specimens provided in the embodiments of the present invention.

[0022] Figure label: 10. Uniaxial tensile specimen; 100, First threaded section; 200, First clamping section; 300, First transition arc section; 400, Gauge length section; 500, Second transition arc section; 600, Second clamping section; 700, Second threaded section; 20. Sanding belt; 30. Drive motor. Detailed Implementation

[0023] 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, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0024] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0025] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0026] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use. These terms are used only for the convenience of describing the invention and for 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. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0027] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0028] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; 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; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0029] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0030] In this embodiment of the invention, since the uniaxial tensile specimen is set vertically in the test field, as is well known to those skilled in the art, the axial direction of the uniaxial tensile specimen is taken as the longitudinal direction, and the direction perpendicular to the axial direction of the uniaxial tensile specimen is taken as the transverse direction.

[0031] Example 1 like Figures 1 to 3 As shown, this embodiment of the invention provides a method for preparing a uniaxial tensile specimen for sulfide stress corrosion cracking test, which includes the following steps: S100. Samples are taken from the anti-sulfur drill pipe product, sawed and rough-machined as blanks, and then the blanks are finished using an external cylindrical grinding machine to prepare a uniaxial tensile specimen having a first threaded section, a first clamping section, a first transition arc section, a gauge length section, a second transition arc section, a second clamping section and a second threaded section in sequence along its axial direction. S200. Polish the uniaxial tensile specimen along its axial direction to form axial scratches with uniform surface quality on the polished surface. S300. Apply an anti-hydrogen sulfide coating to the surface of the clamping section of the uniaxial tensile specimen.

[0032] Specifically, a sample blank needs to be obtained from the sulfur-resistant drill pipe product to be tested. In this embodiment, a portion of the sulfur-resistant drill pipe is cut by sawing and processed using an external cylindrical grinding machine to produce a first threaded section, a first clamping section, a first transition arc section, a gauge length section, a second transition arc section, a second clamping section, and a second threaded section. The uniaxial tensile specimen is then arranged longitudinally along its axial direction and polished along its axial direction to create uniform axial scratches on the polished surface, preventing specimen fracture caused by circumferential defects. Subsequently, an anti-hydrogen sulfide coating is sprayed onto the surface of the clamping section of the uniaxial tensile specimen to form an anti-hydrogen sulfide stress corrosion coating, preventing ineffective fracture of the clamping section.

[0033] Preferably, the processing area for polishing the uniaxial tensile specimen along its axial direction includes the surface of the uniaxial tensile specimen between the thread root of the first thread segment and the thread root of the second thread segment.

[0034] Specifically, in this embodiment, the polishing treatment area extends from 50-150mm from the thread root of the first thread segment to 50-150mm before the thread root of the second thread segment, encompassing the entire transition arc and gauge length segment, ensuring that the surfaces of the clamping segment, transition arc, and gauge length segment after polishing form axial scratches with uniform surface quality.

[0035] Furthermore, the polishing process for uniaxial tensile specimens along their axial direction includes the following steps; S210. Fix the uniaxial tensile specimen horizontally between the two drive motors of the longitudinal polishing machine, and set the sand belt on one side of the uniaxial tensile specimen. Apply force to the sand belt with weights so that the sand belt abuts against the uniaxial tensile specimen. Drive the uniaxial tensile specimen to move horizontally through the drive motors so that it rubs and polishes against the sand belt. S220, a drive motor rotates around the axial direction of the uniaxial tensile specimen to make the uniaxial tensile specimen rotate around its axis by a preset angle, and then the drive motor drives the uniaxial tensile specimen to move along its axis again, so that it is rubbed and polished with the sanding belt. S230, repeat S220, until the uniaxial tensile specimen has rotated the preset number of times.

[0036] Specifically, in this embodiment, the uniaxial tensile specimen is first fixed horizontally between the two drive motors of the longitudinal polishing machine, and the uniaxial tensile specimen is clamped and fixed horizontally by the clamping heads of the drive motors. The drive motors of the longitudinal polishing machine can drive the uniaxial tensile specimen to move horizontally and rotate around its axial direction. The abrasive belt is set vertically on one side of the uniaxial tensile specimen and abuts against it. The magnitude of the force applied by the abrasive belt to the uniaxial tensile specimen can be adjusted by adjusting the weights on the abrasive belt. At this time, by driving the uniaxial tensile specimen to move horizontally, the abrasive belt can rub and polish the uniaxial tensile specimen horizontally, that is, axially, to form axial scratches with uniform surface quality on its surface. After one horizontal polishing cycle, the drive motor can be rotated around the uniaxial tensile specimen's axial direction to rotate the uniaxial tensile specimen around its axial direction by a preset angle, and the uniaxial tensile specimen can be polished again, so that the abrasive belt polishes the unpolished areas. Then, the specimen is rotated and polished repeatedly until it has rotated several times, at which point the polishing of the uniaxial tensile specimen is complete.

[0037] Furthermore, the polishing process for the uniaxial tensile specimen along its axial direction also includes: S240, changing the abrasive belt and repeating S210, S220 and S230; the mesh size of the abrasive belt is selected as 800 mesh and 2000 mesh respectively.

[0038] Specifically, to ensure the polishing effect of the uniaxial tensile specimen, it is necessary to grind the specimen multiple times from coarse to fine. In this embodiment, the grinding and rotation steps described above need to be repeated by changing the abrasive belt. In this embodiment, the grit of the abrasive belt used for axial polishing is selected as 800 grit and then 2000 grit.

[0039] Preferably, when grinding a uniaxial tensile specimen with an 800-grit abrasive belt, the preset angle is preferably 7°, 11°, 13° or 14°; when grinding a uniaxial tensile specimen with a 2000-grit abrasive belt, the preset angle is preferably 3.5°, 5.5°, 6.5° and 7° respectively.

[0040] Specifically, in this embodiment, the preset angle is selected as an angle value that is not divisible by 360°, such as 7°, 11°, 13°, or 14°. This ensures that the rotation angles can overlap and avoid repeated grinding at the same position. Furthermore, the rotation angle of the grinding pass of the 800-grit abrasive belt is twice that of the grinding pass of the 2000-grit abrasive belt, thereby reducing the rotation angle during fine grinding and obtaining more uniform longitudinal polishing marks. That is, when grinding a uniaxial tensile specimen with an 800-grit abrasive belt at a preset angle of 7°, the preset angle for grinding a uniaxial tensile specimen with a 2000-grit abrasive belt is selected as 3.5°.

[0041] Preferably, the speed at which the uniaxial tensile specimen moves in the horizontal direction is set to 0.5 cm / s to 1.5 cm / s, the preset angle is 1° to 15°, and the preset number of revolutions is 10 to 50.

[0042] Specifically, excessively low grinding speeds affect the grinding efficiency of the specimen, while excessively high grinding speeds can cause the specimen to overheat. To ensure the grinding quality of the uniaxial tensile specimen, the horizontal movement speed is set to 0.5 cm / s to 1.5 cm / s. A preset angle of 1° to 15° and a preset number of passes of 10 to 50 ensure that the uniaxial tensile specimen is thoroughly ground, forming fine axial scratches. In this embodiment, the 800-grit grinding passes require 20 to 35 passes with a grinding force of 1.5 kg to 2.5 kg. The 2000-grit grinding passes require 10 to 20 passes with a grinding force of 2.5 kg to 3.5 kg. The grinding force increases by 0.3 kg to 0.6 kg with increasing grit number of passes, ensuring complete coverage of longitudinal scratches from the previous pass while reducing the number of grinding passes and improving longitudinal polishing efficiency.

[0043] Furthermore, before each polishing treatment along its axial direction, the uniaxial tensile specimen is polished in a direction perpendicular to its axial direction.

[0044] Specifically, if a uniaxial tensile specimen is polished only along its axial direction, it is relatively easy to leave deep axial scratches. To avoid leaving deep scratches, it is necessary to polish the specimen perpendicular to its axial direction before polishing it along its axial direction each time. This alternating horizontal and vertical polishing ensures a good polishing effect. In this embodiment, when polishing the uniaxial tensile specimen perpendicular to its axial direction, an external cylindrical grinder is used to rotate the specimen around its axial direction. Pressure is then applied to the specimen with sandpaper to polish it. After polishing one revolution in the area covered by the sandpaper, the specimen is moved horizontally to adjust the polishing position. Pressure is then applied again with sandpaper until the specimen is polished. The start and end positions of the horizontal movement of the sandpaper are the number of polishing passes.

[0045] Preferably, when polishing a uniaxial tensile specimen in a direction perpendicular to its axial direction, the mesh size of the abrasive belt is selected as 240 mesh and 1200 mesh respectively; when polishing a uniaxial tensile specimen in a direction perpendicular to its axial direction with 240 mesh, the number of polishing times is set to 25 to 40; when polishing a uniaxial tensile specimen in a direction perpendicular to its axial direction with 1200 mesh, the number of polishing times is set to 15 to 30.

[0046] Specifically, to ensure the polishing effect of the uniaxial tensile specimen, it is necessary to polish the specimen multiple times from coarse to fine. Therefore, the polishing treatment perpendicular to the axial direction, i.e., the transverse polishing, performed before polishing the uniaxial tensile specimen along its axial direction, requires coarser sandpaper than the longitudinal polishing. The polishing proceeds sequentially from coarse to fine, alternating between transverse and longitudinal. In this embodiment, the grit of the sandpaper used for the axial polishing treatment is selected as 240 grit and 1200 grit respectively. Based on this, the parameters for the 240 grit transverse polishing pass are set as follows: the number of polishing passes is preferably 25 to 40, and the applied polishing force is preferably 1.0 kg to 2.0 kg. In this embodiment, in the 240 grit pass, the specimen rotation speed is 0.6 r / s, the horizontal movement distance of the specimen is 2 cm, the total number of polishing passes is 35, and the applied polishing force is 1.5 kg. The parameters for the 1200 grit transverse polishing pass are set as follows: the number of polishing passes is preferably 15 to 30, and the applied polishing force is preferably 2.0 kg to 3.0 kg. In this embodiment, in the 1200-mesh pass, the sample rotation speed is 0.8 r / s, the sample horizontal movement distance is 2 cm, the total number of grinding passes is 25, and the grinding force is 2.5 kg.

[0047] Furthermore, the treatment of the clamping section surface of the uniaxial tensile specimen with an anti-hydrogen sulfide coating includes: cleaning with acetone and air drying, then uniformly spraying the anti-hydrogen sulfide coating onto the clamping section surface and heating to cure; the coating curing temperature is 120°C to 160°C and the curing time is 30 min to 60 min.

[0048] Specifically, by spraying an anti-hydrogen sulfide coating onto the surface of the clamping section of the uniaxial tensile specimen and then heating and curing it, the coating surface can be made uniform and free of defects such as blistering.

[0049] Preferably, the thickness of the hydrogen sulfide resistant coating is set to 0.05 mm to 0.1 mm.

[0050] Example 2 This embodiment is a comparative test between a uniaxial tensile specimen prepared by the above-described method for preparing uniaxial tensile specimens for sulfide stress corrosion cracking tests and a conventional uniaxial tensile specimen.

[0051] In this embodiment, 135MS sulfur-resistant drill pipe body (nominal yield strength 930MPa) material was selected, and three samples were prepared for each group of uniaxial tensile specimens. The first group consisted of machined specimens. The second group consisted of specimens prepared using the conventional manual grinding and polishing process, which involved machining on a machine tool, followed by transverse grinding and polishing at 240 grit, 800 grit, 1200 grit, and 2000 grit, and then polishing with W2.5 metallographic polishing paste to achieve a mirror finish. The third group of samples underwent an alternating horizontal and vertical grinding process, using 240-grit, 800-grit, 1200-grit, and 2000-grit sandpaper. Starting 100mm from the thread root, the 240-grit sandpaper was used with a rotation speed of 0.6 r / s, a horizontal movement distance of 2 cm, a total of 35 grinding passes, and an applied force of 1.5 kg, grinding along the direction perpendicular to the uniaxial tensile sample axis. The 800-grit sandpaper was used with a horizontal movement speed of 0.8 cm / s, a rotation angle of 7°, and 3 grinding passes. 0 passes: Grinding with a force of 2.0 kg along the axial direction of the uniaxial tensile specimen; 1200-grit passes: specimen rotation speed of 0.8 r / s, specimen horizontal movement distance of 2 cm, total number of grinding passes of 25, grinding force of 2.5 kg, grinding along the direction perpendicular to the uniaxial tensile specimen; 2000-grit passes: sandpaper horizontal movement speed of 1.0 cm / s, specimen rotation angle of 3.5°, number of grinding passes of 20, grinding force of 3.0 kg, grinding along the uniaxial tensile specimen. After grinding and polishing, a uniform hydrogen sulfide-resistant coating is sprayed onto the clamping section, cured at 130℃ for 40 min, with a thickness of 0.06 mm. The fourth group of samples underwent an alternating horizontal and vertical grinding process, using 240-grit, 800-grit, 1200-grit, and 2000-grit sandpaper. Starting 100mm from the thread root, the 240-grit sandpaper was used with a rotation speed of 0.6 r / s, a horizontal movement distance of 2 cm, a total of 35 grinding passes, and an applied force of 1.5 kg, grinding along the direction perpendicular to the uniaxial tensile sample axis. The 800-grit sandpaper was used with a horizontal movement speed of 0.8 cm / s, a rotation angle of 13°, and 3 grinding passes. 0 passes: Grinding with a force of 2.0 kg along the axial direction of the uniaxial tensile specimen; 1200-grit passes: specimen rotation speed 0.8 r / s, specimen horizontal movement distance 2 cm, total grinding 25 passes, grinding with a force of 2.5 kg, grinding along the direction perpendicular to the uniaxial tensile specimen; 2000-grit passes: sandpaper horizontal movement speed 1.0 cm / s, specimen rotation angle 6.5°, grinding 20 passes, grinding with a force of 3.0 kg, grinding along the uniaxial tensile specimen. After grinding and polishing, a uniform hydrogen sulfide-resistant coating is sprayed onto the clamping section, cured at 130℃ for 40 min, with a thickness of 0.06 mm.

[0052] Figures 4 to 7These are processing effect diagrams for the first, second, third, and fourth groups of test samples, respectively. Figures 4 to 7 It can be seen that the machining process on the machine tool produces transverse scratches of varying depths. Compared with external cylindrical grinding, the traditional manual grinding and polishing process significantly reduces the surface roughness, but the scratches are more irregular in direction, with some deeper transverse scratches. The longitudinal polishing process exhibits clearly uniform longitudinal scratches.

[0053] Three groups of samples of 135MS sulfur-resistant drill pipe were subjected to SSC tests in a solution environment according to NACE TM0177 standard A method. The concentration of hydrogen sulfide introduced was 100%, the pH was 6.5±0.1, and the load was 85% of the nominal minimum yield strength. The test results are shown in the table below.

[0054] Table 1. Results of uniaxial tensile test on sulfide stress corrosion cracking of 135ksi sulfur-resistant drill pipe body material.

[0055] As shown in Table 1, in the first group of machined specimens, 2 specimens broke at the gauge length and 1 specimen broke at the clamping section; in the second group of specimens prepared by the prior art transverse grinding and polishing, 1 specimen passed the test, 1 specimen broke at the gauge length, and 1 specimen broke at the clamping section; all 6 specimens in the two groups of tests prepared by the uniaxial tensile specimen preparation method for sulfide stress corrosion cracking test in the above embodiment passed the test.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; 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 or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing uniaxial tensile specimens for sulfide stress corrosion cracking tests, characterized in that, Includes the following steps; S100. Samples are taken from the anti-sulfur drill pipe product, sawed and rough-machined as blanks, and then the blanks are finished using an external cylindrical grinding machine to prepare a uniaxial tensile specimen having a first threaded section, a first clamping section, a first transition arc section, a gauge length section, a second transition arc section, a second clamping section and a second threaded section in sequence along its axial direction. S200. Polish the uniaxial tensile specimen along its axial direction to form axial scratches with uniform surface quality on the polished surface. S300. Apply an anti-hydrogen sulfide coating to the surface of the clamping section of the uniaxial tensile specimen.

2. The method for preparing uniaxial tensile specimens for sulfide stress corrosion cracking tests according to claim 1, characterized in that, The processing area for polishing the uniaxial tensile specimen along its axial direction includes the surface of the uniaxial tensile specimen between the thread root of the first thread segment and the thread root of the second thread segment.

3. The method for preparing uniaxial tensile specimens for sulfide stress corrosion cracking tests according to claim 1, characterized in that, Polishing the uniaxial tensile specimen along its axial direction includes the following steps: S210. The uniaxial tensile specimen is fixed horizontally between two drive motors of the longitudinal polishing machine, and an abrasive belt is placed on one side of the uniaxial tensile specimen. A force is applied to the abrasive belt by weights so that the abrasive belt comes into contact with the uniaxial tensile specimen. The drive motor drives the uniaxial tensile specimen to move horizontally so that it rubs and polishes with the abrasive belt. S220. Rotate the drive motor around the axial direction of the uniaxial tensile specimen to make the uniaxial tensile specimen rotate around its axial direction by a preset angle, and then drive the uniaxial tensile specimen to move along its axial direction again through the drive motor so that it rubs and polishes with the sanding belt. S230. Repeat S220 until the uniaxial tensile specimen has rotated a preset number of times.

4. The method for preparing uniaxial tensile specimens for sulfide stress corrosion cracking tests according to claim 3, characterized in that, The speed at which the uniaxial tensile specimen moves horizontally is set to 0.5 cm / s to 1.5 cm / s, the preset angle is 1° to 15°, and the preset number of revolutions is 10 to 50.

5. The method for preparing uniaxial tensile specimens for sulfide stress corrosion cracking tests according to claim 4, characterized in that, Polishing the uniaxial tensile specimen along its axial direction also includes: S240, Replace the sanding belt and repeat S210, S220 and S230; The mesh size of the abrasive belt is selected as 800 mesh and 2000 mesh respectively.

6. The method for preparing uniaxial tensile specimens for sulfide stress corrosion cracking tests according to claim 5, characterized in that, When grinding the uniaxial tensile specimen with the 800-grit abrasive belt, the preset angle is preferably 7°, 11°, 13° or 14°. When the uniaxial tensile specimen is polished with the 2000-grit abrasive belt, the preset angle is preferably 3.5°, 5.5°, 6.5° or 7°.

7. The method for preparing uniaxial tensile specimens for sulfide stress corrosion cracking tests according to claim 6, characterized in that, Before each polishing process along its axial direction, the uniaxial tensile specimen is polished in a direction perpendicular to its axial direction.

8. The method for preparing uniaxial tensile specimens for sulfide stress corrosion cracking tests according to claim 7, characterized in that, When polishing the uniaxial tensile specimen along a direction perpendicular to its axial direction, the mesh size of the abrasive belt is selected as 240 mesh and 1200 mesh respectively. When polishing the uniaxial tensile specimen with a 240-mesh screen along a direction perpendicular to its axial direction, the number of polishing cycles is set to 25 to 40. When polishing the uniaxial tensile specimen with 1200 grit along the direction perpendicular to its axial direction, the number of polishing times is set to 15 to 30.

9. The method for preparing uniaxial tensile specimens for sulfide stress corrosion cracking tests according to any one of claims 1-8, characterized in that, Applying an anti-hydrogen sulfide coating to the surface of the clamping section of the uniaxial tensile specimen includes: Clean with acetone and air dry, then uniformly spray an anti-hydrogen sulfide coating onto the surface of the sample clamping section and heat to cure. The coating is cured at a temperature of 120°C to 160°C for 30 to 60 minutes.

10. The method for preparing uniaxial tensile specimens for sulfide stress corrosion cracking tests according to claim 9, characterized in that, The thickness of the hydrogen sulfide-resistant coating is set to 0.05 mm to 0.1 mm.

Images