Oil pipe threaded connection structure and waste oil pipe recycling and remanufacturing method

Abstract

The present invention discloses an oil pipe threaded connection structure and a method for recycling and remanufacturing waste oil pipes. The oil pipe threaded connection structure includes an oil pipe and a coupling connected to the oil pipe by threaded rotation. An external thread, an external sealing surface, an external transition surface, and an end face shoulder are sequentially arranged on the outer surface of one end of the oil pipe, and the end face shoulder is located at the end face of the end of the oil pipe where the external thread is arranged; an internal thread, an internal sealing surface, an internal transition surface, and a torque shoulder are sequentially arranged on the inner surface of the coupling. The external sealing surface and the internal sealing surface are interference-fitted to form a sealing structure for preventing external fluid from entering the oil pipe; the end face shoulder and the torque shoulder are top-fitted. Therefore, the sealing structure formed by the interference fit of the external sealing surface and the internal sealing surface in the present invention is close to the internal and external threads and is located on the side of the internal and external transition surfaces away from the shoulder, which is not easy to cause bruises and does not easily cause failure of the threaded connection structure.

Description

Technical Field

[0001] The invention relates to the technical field of oil pipes, and in particular to an oil pipe threaded connection structure and a recycling and remanufacturing method for waste oil pipes. Background Art

[0002] Oil pipes are the only channel for oil and gas production in oil and gas development. With the continuous commissioning of a large number of new oil and gas wells in the oil and gas industry, the use of oil pipes has been increasing year by year. In specific applications, the oil pipe is screwed to a coupling with an internal thread through an external thread, so that multiple oil pipes are connected through couplings to form an oil pipe string. The oil pipe string acts as a closed space to transmit oil or natural gas with high pressure from underground to the ground. The threaded connection part is the weakest link in the oil pipe string. The load and stress concentration it bears during service are relatively large, and most failures occur at the threaded connection part. Therefore, the design of the threaded connection structure is crucial. In the existing threaded connection structure, the shoulder and the thread are only connected through the sealing surface, and the sealing surface is very easy to be bruised, which can easily lead to the failure of the threaded connection structure.

[0003] Therefore, the prior art still needs to be improved and developed. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide an oil pipe threaded connection structure and a method for recycling and remanufacturing of waste oil pipes, aiming to solve the problem that in the existing threaded connection structure, the shoulder and the thread are connected only by a sealing surface, the sealing surface is easily scratched, and the threaded connection structure may fail.

[0005] The technical solution of the present invention is as follows:

[0006] In a first aspect of the present invention, there is provided a threaded connection structure for an oil pipe, comprising an oil pipe and a coupling rotatably connected to the oil pipe by threads, wherein an outer surface of one end of the oil pipe is provided with an external thread, an outer sealing surface, an outer transition surface, and an end face shoulder in sequence, and the end face shoulder is located at the end face of the end of the oil pipe provided with the external thread;

[0007] The inner surface of the coupling is provided with an internal thread, an inner sealing surface, an inner transition surface, and a torque stop shoulder in sequence.

[0008] The outer sealing surface and the inner sealing surface are interference-fitted to form a sealing structure for preventing external fluid from entering the oil pipe;

[0009] The end face shoulder is top-matched with the torque stop shoulder.

[0010] Optionally, a gap is formed between the outer transition surface and the inner transition surface.

[0011] Optionally, the angle between the outer transition surface and the middle diameter line of the oil pipe is 10±5°C, and the angle between the inner transition surface and the middle diameter line of the oil pipe is 0±5°C.

[0012] Optionally, the taper of the outer sealing surface and the inner sealing surface is (1±0.001):(6±0.001); the interference compression amount between the outer sealing surface and the inner sealing surface is 0.3±0.05mm.

[0013] Optionally, the length of the outer sealing surface is 3.5 mm, and the length of the inner sealing surface is 3 mm.

[0014] Optionally, the external thread and the internal thread are both trapezoidal threads, the angles between the bearing surfaces of the external thread and the internal thread and the center diameter of the oil pipe are both 90°, the angles between the guiding surfaces of the external thread and the internal thread and the center diameter of the oil pipe are both 45°, and the tooth heights of the external thread, the internal thread and the external thread are all 1.1 mm.

[0015] A second aspect of the present invention provides a method for recycling and remanufacturing waste oil pipes, which comprises the following steps:

[0016] Provide waste oil pipes;

[0017] The waste oil pipes are sequentially subjected to preliminary selection, cleaning, endoscope inspection, steel grade sorting, non-destructive testing, pipe end cutting, thread processing, thread inspection, hydrostatic pressure test, pipe body diameter, coupling screwing, appearance marking, and finished product storage;

[0018] The thread processing is performed so that when the threaded oil pipe is screwed with the coupling, the oil pipe threaded connection structure as described above is formed.

[0019] Optionally, the step of steel grade sorting specifically includes:

[0020] Establish a database of parameter indicators of oil pipes from different manufacturers, different types and different steel grades;

[0021] Conduct Leeb hardness test, direct reading spectrum test and on-site metallographic test on waste oil pipes to obtain test data;

[0022] The detection data is compared with the database to identify the steel grade of the pipe body.

[0023] Optionally, the cleaning step specifically includes: using a metal brush to remove oil and rust from the outer wall of the preliminarily selected waste oil pipe;

[0024] Then, the inner wall of the waste oil pipe after the preliminary selection is sprayed with NaOH hot solution for cleaning, and at the same time, a reamer is used to scrape and a metal brush is used to scrub the inner wall to remove scale and rust;

[0025] The waste oil pipe is then placed in a combustion furnace for combustion, and the inner wall of the burned waste oil pipe is sandblasted and the outer wall is brushed to obtain an oil pipe free of oil stains, scaling and corrosion products.

[0026] Optionally, the combustion temperature is 360-400° C., and the combustion time is 1-2 hours.

[0027] Beneficial effect: The outer sealing surface on the outer surface of one end of the oil pipe in the present invention is connected to the end face shoulder via an outer transition surface, and the inner sealing surface on the inner surface of the coupling is connected to the torque shoulder via an inner transition surface. Therefore, the sealing structure formed by the interference fit between the outer sealing surface and the inner sealing surface in the present invention is close to the inner and outer threads and is located on the side of the inner and outer transition surfaces away from the shoulder, which is not easy to cause scratches and failure of the threaded connection structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the structure of the oil pipe threaded connection structure in an embodiment of the present invention.

[0029] Figure 2 Schematic diagram of the exploded structure of the oil pipe threaded connection structure in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The present invention provides a threaded connection structure for an oil pipe and a recycling method for waste oil pipes. To make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0032] The embodiment of the present invention provides a threaded connection structure of an oil pipe, such as Figure 1 and 2 As shown, it includes an oil pipe 1 and a coupling 2 which is rotatably connected to the oil pipe 1 through a thread, wherein:

[0033] The outer surface of one end of the oil pipe 1 is provided with an external thread 11, an external sealing surface 12, an external transition surface 13, and an end face shoulder 14 in sequence, and the end face shoulder 14 is located at the end face of the oil pipe 1 at the end provided with the external thread 11;

[0034] The inner surface of the coupling 2 is provided with an internal thread 21, an inner sealing surface 22, an inner transition surface 23, and a torque shoulder 24 in sequence;

[0035] The outer sealing surface 12 and the inner sealing surface 22 are interference-fitted to form a sealing structure 3, which is used to prevent external fluid (including liquid and gas) from entering the oil pipe;

[0036] The end face shoulder 14 is in abutment with the torque stop shoulder 24 .

[0037] The embodiment of the present invention screws the oil pipe into the coupling to form an oil pipe threaded connection structure, in which the external thread cooperates with the internal thread, the external sealing surface cooperates with the internal sealing surface in an interference fit, the external transition surface cooperates with the internal transition surface, and the end face shoulder cooperates with the twist stop shoulder.

[0038] In the embodiment of the present invention, the outer sealing surface on the outer surface of one end of the oil pipe and the end face shoulder are connected by an outer transition surface, and the inner sealing surface on the inner surface of the coupling and the torque shoulder are connected by an inner transition surface. Therefore, the sealing structure formed by the interference fit between the outer sealing surface and the inner sealing surface in the embodiment of the present invention is close to the inner and outer threads and is located on the side of the inner and outer transition surfaces away from the shoulder, which is not easy to cause scratches and failure of the threaded connection structure.

[0039] In some embodiments, a gap 4 is formed between the outer transition surface 13 and the inner transition surface 23. This gap can effectively accommodate metal protrusions caused by damage to the outer transition surface of the oil pipe, and at the same time relieve material strain when the end face shoulder and the torque stop shoulder are butt-matched.

[0040] In some embodiments, the angle α between the outer transition surface 13 and the middle diameter of the oil pipe is 10±5°C, and the angle between the inner transition surface 23 and the middle diameter of the oil pipe is 0±5°C. This ensures that a gap is formed between the outer transition surface and the inner transition surface to accommodate metal protrusions caused by the impact of the outer transition surface of the oil pipe, and at the same time relieves the material strain when the end face shoulder and the torque shoulder are butt-matched.

[0041] In some embodiments, the taper of the outer sealing surface 12 and the inner sealing surface 22 is (1±0.001):(6±0.001); the interference compression amount of the outer sealing surface 12 and the inner sealing surface 22 is 0.3±0.05mm. The length of the outer sealing surface 12 is 3.5mm, and the length of the inner sealing surface 22 is 3mm. When the outer sealing surface and the inner sealing surface are in interference fit, the friction length is moderate, and the formed sealing structure is very stable, insensitive to bending and axial loads, and is not prone to sticking.

[0042] In some embodiments, the external thread and the internal thread are both trapezoidal threads, the angle γ between the bearing surface 5 of the external thread 11 and the internal thread 21 and the center diameter of the oil pipe is 90°, the angle β between the guide surface 6 of the external thread 11 and the internal thread 21 and the center diameter of the oil pipe is 45°, and the tooth height h of the external thread 11 and the internal thread 21 is 1.1 mm.

[0043] In some embodiments, the tooth top clearance between the internal thread and the external thread is 0.03 mm ( Figure 1 not shown).

[0044] In some embodiments, a backing groove 25 is further provided between the internal thread 21 and the internal sealing surface 22 of the coupling 2 .

[0045] In some embodiments, the processing parameters of the external thread, external sealing surface, external transition surface, and end shoulder of the oil pipe are shown in Table 1 below.

[0046] Table 1 Processing parameters of external thread, external sealing surface, external transition surface and end shoulder of oil pipe

[0047]

[0048] In some specific implementations, the processing parameters of the external thread, external sealing surface, external transition surface, and end shoulder of the oil pipe are shown in Table 2 below.

[0049] Table 2 Specific processing parameters of external thread, external sealing surface, external transition surface and end shoulder of oil pipe

[0050]

[0051]

[0052] In some embodiments, the processing parameters of the internal thread, the internal sealing surface, the internal transition surface, and the torque shoulder of the coupling are shown in Table 3 below.

[0053] Table 3 Processing parameters of the coupling's internal thread, internal sealing surface, internal transition surface, and torque shoulder

[0054]

[0055] In some specific implementations, specific processing parameters of the internal thread, internal sealing surface, internal transition surface, and torque shoulder of the coupling are shown in Table 4 below.

[0056] Table 4 Specific processing parameters of the internal thread, internal sealing surface, internal transition surface and torque shoulder of the coupling

[0057]

[0058] Oil pipes are the only channel for oil and gas production in oil and gas development. With the continuous commissioning of a large number of new oil and gas wells in the oil and gas industry, the use of oil pipes has been increasing year by year. The number of oil pipes scrapped in domestic oil and gas fields is about 7×10 5 t, of which about 70% of the oil pipes can be repaired and reused using remanufacturing technology to reduce consumption and save costs. Based on this, an embodiment of the present invention also provides a recycling and remanufacturing method for waste oil pipes, which includes the following steps:

[0059] S1. Providing waste oil pipes (the waste oil pipes are waste oil pipes recovered from different areas of oil and gas fields and oil and gas wells);

[0060] S2. The waste oil pipes are subjected to preliminary selection, cleaning, endoscope inspection, steel grade sorting, non-destructive testing, pipe end cutting, thread processing, thread inspection, hydrostatic pressure test, pipe body diameter, coupling screwing, appearance marking, and finished product storage.

[0061] The method provided in this embodiment can realize the recycling and remanufacturing of old oil pipes, which can not only meet production needs but also has good economic benefits.

[0062] Step S2 includes:

[0063] S20, preliminary selection; S21, cleaning; S22, endoscopic inspection; S23, steel grade sorting; S24, non-destructive testing; S25, pipe end cutting; S26, thread processing, thread inspection; S27, hydrostatic pressure test; S28, pipe body diameter; S29, coupling screwing, appearance identification, finished product storage.

[0064] Step S20 performs preliminary screening on the waste oil pipes to remove waste oil pipes with serious defects. In some embodiments, during the preliminary screening, waste oil pipes with at least one of the following defects are screened and removed to obtain the waste oil pipes after the preliminary screening:

[0065] The pipe body is spirally bent, the bending radius of the pipe body is greater than 100mm, cracks are visible to the naked eye, and the pipe wall is corroded, perforated and ruptured.

[0066] In step S21, the waste oil pipes after the preliminary selection are cleaned to remove oil stains, corrosive substances, etc. The cleaning of waste oil pipes is a basic process in the oil pipe remanufacturing process. The cleaning quality not only has an important impact on the subsequent processes, but also is related to the cost of oil pipe repair and environmental issues. The cleaning process requires the corrosion products, oil film, scaling, rust, etc. on the inner and outer surfaces of the oil pipe to be cleaned in the most economical way, while not damaging the oil pipe and being environmentally friendly. However, traditional chemical cleaning methods, physical cleaning methods, and heating cleaning methods have problems such as low cleaning efficiency, poor cleaning effect, and environmental pollution. Therefore, the present invention adopts a new physical cleaning + chemical cleaning process. Specifically, in some embodiments, the cleaning steps specifically include:

[0067] S221, using a metal brush to remove oil and rust from the outer wall of the preliminarily selected waste oil pipe;

[0068] S222, then spraying NaOH hot solution onto the inner wall of the preliminarily selected waste oil pipe for cleaning, while performing reaming and scraping with a metal brush to remove scale and rust from the inner wall;

[0069] S223, placing the waste oil pipe in a combustion furnace for combustion, sandblasting the inner wall and brushing the outer wall of the burned waste oil pipe to obtain an oil pipe free of oil stains, scaling and corrosion products.

[0070] The cleaning method provided in this embodiment changes the traditional repair cleaning method, has a good cleaning effect, and effectively increases the remanufacturing utilization rate of waste oil pipes.

[0071] In step S221, the outer wall of the waste oil pipe can be degreased and derusted by four groups of copper brushes rotating in opposite directions in cooperation with the transmission roller.

[0072] In step S222, the inner wall of the waste oil pipe passes through a double-layer rotating pipe (the pipe end is equipped with a reamer, a copper brush, and a rotating jet hole starting from the front of the pipe), and the inner wall is scraped by the reamer, brushed by the copper brush, and cleaned by a 360° rotating jet of a hot NaOH solution to remove scale and rust. Through steps S221 and S222, the overall rust and scaling of the waste oil pipe are cleaned. The hot NaOH solution is recycled during the entire cleaning process, and the waste gas generated is treated by special equipment for volatile organic compounds (VOCs). The final solid waste is transferred through hazardous waste and treated in an environmentally friendly manner.

[0073] In step S223, the waste oil pipe treated in step S222 is placed in a combustion furnace for combustion to remove the oil stains that may remain on the inner and outer wall surfaces, and then the outer wall of the burned waste oil pipe is brushed and the inner wall is sandblasted to obtain a cleaned oil pipe. In some embodiments, the temperature used for the combustion is 360-400°C, such as 360, 370, 380, 390 or 400°C, and the time used for the combustion is 1-2h, such as 1, 1.5 or 2h.

[0074] After the cleaning in step S21, a reselection step may be further included to remove the cleaned oil pipes that are severely corroded or severely worn.

[0075] In step S22, the cleaned oil pipe is inspected by endoscope to confirm that there is no corrosion or wear inside the pipe body.

[0076] Waste oil pipes are waste oil pipes recovered from different areas of oil and gas fields and oil and gas wells. Due to long-term use or management reasons, oil pipes of different materials, steel grades and newness are often mixed together for a long time. If they are to be reused, the oil pipe materials, steel grades, newness, etc. must be identified and graded. Therefore, in order to solve the problem that waste oil pipes generated by oil fields are mixed in the same area for a long time and cannot be used according to grade, step S23 proposes to sort the steel grades of the waste oil pipes after endoscope inspection. Specifically, in some embodiments, the steel grade sorting step specifically includes:

[0077] S231. Establish a database of parameter indicators of oil pipes of different manufacturers, different types and different steel grades;

[0078] S232, performing Leeb hardness test, direct reading spectrum test, and on-site metallographic test on the waste oil pipe to obtain test data;

[0079] S233, comparing the detection data with the database to identify the steel grade of the pipe body.

[0080] In this embodiment, integrated standard product parameter indicators are used to establish a database of parameter indicators of oil pipes of different manufacturers, different varieties, and different steel grades (including oil pipe steel grades and corresponding related parameter indicators). The waste oil pipes are tested for Leeb hardness, direct reading spectrum, and on-site metallographic testing to obtain test data (hardness data, component content data, and metallographic data in sequence), and the test data are entered into a computer, and the steel grade of the pipe body is identified through automatic comparison by the computer.

[0081] In step S24, non-destructive testing is performed on the oil pipes after the grade sorting.

[0082] The threaded connection is the weak link of the oil pipe. It is subjected to high load and stress concentration during service, and most failures occur at the threaded connection. The threads of most waste oil pipes have been damaged, and the old threads need to be cut off and new threads need to be reprocessed during the repair process. Therefore, in step S25, the undamaged oil pipe is cut off at the end to cut off the old threads. Then, thread processing and thread inspection are performed in step S26. In step S26, the thread processing can be API standard thread or special thread, preferably special thread.

[0083] The requirement for the new thread is that the strength of the threaded connection after repair must reach the level of the pipe body strength. However, at present, the vast majority of oil pipe thread repair processes are the original threads, and the strength of the threaded connection after repair is greatly reduced, which affects the normal use of the oil pipe. In order to solve the problem of oil pipe thread failure caused by the combined effect of axial load and up-tightening force, and to replace the thickened oil pipe, a special threaded connection structure is adopted in the present invention to ensure that the strength of the special threaded connection structure is greater than or equal to the connection strength of the thickened oil pipe, thereby reducing the energy consumption caused by the thickened oil pipe. Therefore, in other embodiments, thread processing is performed so that when the oil pipe after the thread processing is screwed with the coupling, the oil pipe threaded connection structure as described above in the embodiment of the present invention is formed. The processing parameters can be found in the above description and will not be repeated here.

[0084] The conical-conical sealing in this oil pipe thread connection structure, the sealing surface is close to the thread (the sealing surface is located between the transition surface and the thread), it is not easy to be damaged, the impact of the shoulder is reduced, the sealing performance is insensitive to bending and axial loads, the tensile strength reaches or even exceeds the requirements of thickened oil pipe threads, and the thickened oil pipe can be replaced (the strength of this thread connection structure is greater than or equal to the connection strength of the thickened oil pipe), reducing the energy consumption caused by the thickened oil pipe. This oil pipe thread connection structure can meet the requirements of multi-stage fracturing tests, repeated buckling and anti-sticking, meet the requirements of harsh on-site operating environments, and can replace thickened oil pipes.

[0085] Therefore, the present invention provides a green recycling and remanufacturing method for oil pipes, which is also a manufacturing method to replace traditional thickened oil pipes, solving the problem that oil pipes cannot be effectively and greenly reused, while reducing energy consumption caused by repeated smelting and repeated upsetting.

[0086] It should be understood that the application of the present invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A threaded connection structure for an oil pipe, comprising an oil pipe and a coupling connected to the oil pipe by thread rotation, characterized in that: The outer surface of one end of the oil pipe is provided with an external thread, an external sealing surface, an external transition surface, and an end face shoulder in sequence, and the end face shoulder is located at the end face of the end of the oil pipe provided with the external thread; The inner surface of the coupling is provided with an internal thread, an inner sealing surface, an inner transition surface and a torque stop shoulder in sequence; The outer sealing surface and the inner sealing surface are interference-fitted to form a sealing structure for preventing external fluid from entering the oil pipe; The end face shoulder is in abutment with the torque stop shoulder; A gap is formed between the outer transition surface and the inner transition surface; The angle between the outer transition surface and the middle diameter line of the oil pipe is 10±5°, and the angle between the inner transition surface and the middle diameter line of the oil pipe is 0±5°; The taper of the outer sealing surface and the inner sealing surface is (1±0.001):(6±0.001); the interference compression amount between the outer sealing surface and the inner sealing surface is 0.3±0.05mm; The length of the outer sealing surface is 3.5 mm, and the length of the inner sealing surface is 3 mm; The external thread and the internal thread are both trapezoidal threads, the angles between the bearing surfaces of the external thread and the internal thread and the mid-diameter line of the oil pipe are both 90°, the angles between the guiding surfaces of the external thread and the internal thread and the mid-diameter line of the oil pipe are both 45°, and the tooth heights of the external thread and the internal thread are both 1.1 mm; A cutter groove is also provided between the internal thread and the inner sealing surface of the coupling; The tooth top clearance between the internal thread and the external thread is 0.03 mm.

2. A method for recycling and remanufacturing waste oil pipes, characterized in that: The waste oil pipe recycling and remanufacturing method comprises the following steps: Provide waste oil pipes; The waste oil pipes are subjected to preliminary selection, cleaning, reselection, endoscope inspection, steel grade sorting, non-destructive testing, pipe end cutting, thread processing, thread inspection, hydrostatic pressure test, pipe body diameter, coupling screwing, appearance marking, and finished product storage in sequence; Wherein, thread processing is performed so that when the threaded oil pipe is screwed with the coupling, the oil pipe threaded connection structure according to claim 1 is formed; The steps of steel grade sorting specifically include: Establish a database of parameter indicators of oil pipes from different manufacturers, different types and different steel grades; Conduct Leeb hardness test, direct reading spectrum test and on-site metallographic test on waste oil pipes to obtain test data; Comparing the test data with the database to identify the steel grade of the pipe body; The cleaning step specifically includes: Use a metal brush to remove oil and rust from the outer wall of the waste oil pipe after preliminary selection; Then, the inner wall of the waste oil pipe after the preliminary selection is sprayed with NaOH hot solution for cleaning, and at the same time, a reamer is used to scrape and a metal brush is used to scrub the inner wall to remove scale and rust; Then place it in a combustion furnace for combustion, sandblast the inner wall of the burned waste oil pipe and brush the outer wall to obtain an oil pipe without oil stains, scaling and corrosion products; The combustion temperature is 360-400°C and the combustion time is 1-2h; The inner wall of the waste oil pipe passes through a double-layer rotating pipe, and is scraped by a reamer, scrubbed with a copper brush, and cleaned with a 360° rotating jet of a hot NaOH solution to remove scale and rust from the inner wall. The outer wall of the waste oil pipe is degreased and derusted by four sets of copper brushes rotating in opposite directions in cooperation with the transmission roller.

Images