A rolling heat treatment process for precision drawn tubes for petrochemical industry

Abstract

The present invention relates to a rolling heat treatment process for a precision drawn tube for petrochemical industry, which is characterized by comprising the following steps: a heating step: heating and heat-insulating the tube step by step; a perforation step: a mandrel penetrates the tube to form a perforation; rollers are arranged obliquely around the tube; the rollers rotate and roll the outer circumference of the tube; a rolling step: rollers are arranged at intervals along the moving direction of the tube; the diameter of the tube gradually decreases as the rollers roll; a pre-treatment step: heating the tube and then rapidly cooling it out of the furnace; pickling the inner and outer surfaces of the tube; a precision drawing step: cold drawing the tube at room temperature to form a precision drawn tube; a post-treatment step: cutting and trimming the precision drawn tube; heating and cooling the precision drawn tube; and flaw detection of the precision drawn tube. The present invention solves the problem in existing solutions that precision drawn tubes need to be fastened and assembled when used as oil pipelines and need to withstand the high pressure during oil transportation, which requires high dimensional accuracy and high impact resistance.

Description

Technical Field

[0001] The invention relates to the field of precision drawn tubes, and in particular to a rolling heat treatment process for precision drawn tubes used in petrochemical industry. Background Art

[0002] As petroleum, chemical, and process pipelines, their operating environment is quite harsh, with high temperature, high pressure, and severe corrosion being common phenomena. Precision drawn pipes are a vital component in the development of modern industry, and their usage varies depending on their shape and cross-section. Oil well pipes are the application scope of precision drawn pipes, and are generally used in oil extraction. Precision drawn pipes are a type of pipe with a hollow cross-section and seamless edges. They are important pipe fittings widely used in pipeline projects in the petroleum, chemical, electric power, metallurgy and other industries. They are widely used to transport various fluids such as oil, natural gas, coal gas, water, and certain solid materials. As transmission pipelines, precision drawn pipes usually have high operating temperatures and must withstand certain pressures. Depending on the application, different mechanical or physical and chemical performance requirements are required. When used as oil pipelines, precision drawn pipes need to be tightened and assembled while also needing to withstand the greater pressure during oil transportation. This requires high dimensional accuracy for precision drawn pipes, as well as high impact resistance for precision drawn pipes. How to solve the above problems becomes crucial. Summary of the Invention

[0003] In view of the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a rolling heat treatment process for precision drawn tubes for petrochemical use, so as to solve the problems in the prior art that precision drawn tubes need to be tightened and assembled when used as oil pipelines and need to withstand the high pressure during oil transportation, which requires high dimensional accuracy of the precision drawn tubes and high impact resistance of the precision drawn tubes.

[0004] To achieve the above object, the technical solution of the present invention is as follows:

[0005] A rolling heat treatment process for precision drawn tubes for petrochemical industry;

[0006] The following steps are involved:

[0007] Heating steps: Heat the pipeline steps step by step and keep them warm;

[0008] Piercing steps: a mandrel penetrates the pipe to form a perforation; rollers are arranged obliquely around the pipe; the rollers rotate and press the outer circumference of the pipe;

[0009] Rolling steps: rollers are arranged at intervals along the moving direction of the pipe; the diameter of the pipe rolled by the rollers gradually decreases;

[0010] Pre-treatment steps: heat the pipe and then take it out of the furnace for rapid cooling; pickling the inner and outer surfaces of the pipe;

[0011] Fine drawing steps: the pipe is cold drawn at room temperature to form a fine drawn pipe;

[0012] Post-processing steps: cutting and trimming the precision drawn tube; heating and then cooling the precision drawn tube; flaw detection of the precision drawn tube.

[0013] A further technical solution is: the heating step includes three heating processes:

[0014] First heating process: heat the pipe to 600-630℃; holding time: 0.5h;

[0015] Second heating process: heat the pipe to 940-960℃; holding time: 0.5-1h;

[0016] The third heating process: heat the pipeline to 1170-1200℃; insulation time: 1.5-2h.

[0017] A further technical solution is: the pre-treatment step includes the following processing processes:

[0018] First treatment process: heat the pipe to 840-860℃; heating time: 3-4 hours; holding time: 1.5-2 hours; the pipe is quickly cooled to 700℃ after being taken out of the furnace; quick cooling time: 10-12 minutes;

[0019] Second treatment process: heat the pipe to 770-790℃; heating time: 15-25 minutes; holding time: 1.5-2 hours; the pipe is removed from the furnace and air-cooled to room temperature;

[0020] The third treatment process: the pipe is placed in the pickling chamber; the pickling time is 15 to 20 minutes; the pickling temperature is 75 to 85°C.

[0021] A further technical solution is: in the third treatment process, the mass ratio of the pickling solution is: potassium dichromate: 10-12%; hydrofluoric acid: 5-6%; hydrochloric acid: 5-6%; sulfuric acid: 5-6%; thiourea: 0.45-0.55%; potassium thiocyanate: 0.65-0.85%; additive: 0.75%; the balance is pure water.

[0022] A further technical solution is that in the post-processing step, the precision drawn tube undergoes two heating processes:

[0023] First heating process: heat the drawn tube and then cool it with water; heating time: 3.5-4h; heating temperature: 920-930℃;

[0024] The second heating process: heat the precision drawn tube and then water cool it; heating time: 1.5 to 2 hours; heating temperature: 675 to 675°C.

[0025] A further technical solution is that in the post-processing step, the precision drawing tube cutting and trimming process is processed through three steps:

[0026] The first processing step: squeeze and shrink the ends of the precision-drawn tube; the squeezed and shrunk diameters of the ends of the precision-drawn tube are smaller than the diameter of the precision-drawn tube;

[0027] Second processing step: cutting off and removing the ends of the precision drawn tube; sawing around the ends of the precision drawn tube;

[0028] The third processing step: grinding the end faces of the precision drawn tube at both ends; trimming the edges of the end faces of the precision drawn tube; cleaning impurities from the precision drawn tube.

[0029] A further technical solution is that the cold drawing of the pipe in the fine drawing step includes three cold drawing processes:

[0030] First cold drawing process: The pipe is cold drawn into the first prefabricated pipe at room temperature; the cold drawing speed is alternately increased and decreased gradually;

[0031] Second cold drawing process: cold drawing the first preformed tube into the second preformed tube at room temperature; the cold drawing speed is alternately increased and decreased gradually; the positions of the cold drawing speed alternatingly increased and decreased in the first cold drawing process and the positions of the cold drawing speed alternatingly increased and decreased in the second cold drawing process are staggered;

[0032] The third cold drawing process: the second preformed tube is cold drawn into a precision drawn tube at room temperature; with the middle position of the second preformed tube as the dividing line, the cold drawing speed is switched from gradually decreasing to gradually increasing.

[0033] A further technical solution is: after the first cold drawing process, the first prefabricated tube is left to stand for 12 to 14 hours; after the second cold drawing process, the second prefabricated tube is left to stand for 12 to 14 hours; after the third cold drawing process, the third prefabricated tube is left to stand for 24 to 26 hours.

[0034] Compared with the prior art, the beneficial technical effects of the present invention are as follows: (1) the holding time of the first heating process is gradually increased through the three heating processes, which shortens the holding time of the first heating process. The time of the subsequent holding processes can make up for the holding time of the first heating process, thereby shortening the time of the entire heating step; (2) as the pipeline heating temperature is approached, the temperature increase amplitude of the three heating processes in the heating step is gradually reduced, and the pipeline heating temperature is accurately controlled; (3) the pipeline is sizing rolled through the rolling step, and the diameter of the pipeline rolled by the roller gradually decreases until it reaches the specified diameter size. The rolling is completed by multiple rollers, and the pipeline passes through multiple sizing rolling processes and finally reaches the specified diameter size, reducing the time of each sizing rolling. The deformation of the secondary sizing rolling is reduced to avoid the rolling deformation of the pipeline and reduce the internal stress of the pipeline; (4) In the first treatment process, the pipeline is heated to 840-860℃ through a slow heating process, and is kept warm, and then quickly cooled so that the pipeline obtains an equilibrium structure. The hardness of the pipeline is reduced through the first treatment process and the second treatment process, the cutting performance is improved, the residual stress is eliminated, and the surface cracks of the pipeline are reduced; (5) In the first treatment process, the pipeline is slowly heated to 840-860℃. During the heating process, the transformation of pearlite, proeutectoid ferrite, and cementite to austenite occurs, and the first phase transformation recrystallization occurs. The pipeline is quickly cooled to 700℃ after being taken out of the furnace, and the rapid cooling time is limited to 10-12 minutes. During this process, a second phase transformation and recrystallization occurs, forming a stable metallographic structure of pearlite, proeutectoid ferrite and cementite with finer grains, thicker layers, uniform structure and no internal stress, which reduces the strength of the pipe and improves the plasticity of the pipe, making it easier for the subsequent steps to perform fine drawing on the pipe; (6) In the second treatment process, the rapidly cooled pipe is heated again. During the second treatment process, there is no structural transformation of the pipe, which eliminates the residual stress of the pipe, reduces the cracks on the surface of the pipe, and facilitates the subsequent steps to perform fine drawing on the pipe. At the same time, it improves the surface quality of the pipe after fine drawing and avoids corrosion of the internal structure of the pipe during pickling; (7) Sodium nitrite, hydrofluoric acid, hydrochloric acid and The corrosion of the pipeline by sulfuric acid shortens the pickling time in the third treatment process. At the same time, the higher pickling temperature accelerates the corrosion reaction of sodium nitrite, hydrofluoric acid, hydrochloric acid and sulfuric acid. Sodium nitrite forms a continuous and dense passivation film on the surface of the pipeline. The passivation film has high chemical stability, thereby hindering the oxidation of the pipeline by air; (8) The cold drawing speeds in the first cold drawing process and the second cold drawing process are alternately increased and decreased at positions that are staggered to avoid overlapping of the cold drawing speeds in the first cold drawing process and the second cold drawing process. Through the two cold drawing processes, different degrees of extrusion of the outer and inner circumferences of the pipeline are completed, and the degree of extrusion is evenly distributed, thereby reducing the internal stress generated during the cold drawing process;(9) When the second preformed tube starts to be cold drawn during the third cold drawing process, the cold drawing position of the second preformed tube transitions from one end face to the middle position, and the cold drawing speed gradually decreases. When the cold drawing position of the second preformed tube transitions from the middle position to the other end face, the cold drawing speed gradually increases, thereby ensuring the surface quality of the outer and inner peripheries of the precision drawn tube; (10) By squeezing and shrinking the ends of the precision drawn tube, the diameters of the ends of the precision drawn tube are controlled, so that the diameter data of any position of the precision drawn tube remain consistent. Since the ends of the precision drawn tube will expand to a certain extent after being squeezed and shrunk due to toughness, it is necessary to make the squeezed and shrunk diameters of the ends of the precision drawn tube smaller than the diameter of the precision drawn tube, leaving a margin for the expansion of the ends of the precision drawn tube; (11) In the pre-treatment step, the hardness of the pipe is reduced, the cutting performance is improved, the residual stress is eliminated, and the cold drawing of the pipe is facilitated. The precision drawn tube is cut off, After trimming the tail and trimming the edges, a precision drawn tube is obtained. However, the precision drawn tube is not a finished product and cannot meet the hardness requirements for use. The stress in the precision drawn tube is released during the first heating process, thereby improving the hardness of the precision drawn tube. (12) During the second heating process, the martensite of the precision drawn tube is completely decomposed by a higher heating temperature, which results in a limited improvement in the tensile strength of the precision drawn tube, but greatly improves the impact energy of the precision drawn tube. (13) By reducing the stress generated in the perforation step during the rolling step, and by heat-treating the pipe in the pre-treatment step, the stress of the pipe is eliminated, which facilitates the cold drawing of the pipe in the precision drawing step and improves the cold drawing quality. At the same time, the cold drawing speed of the pipe is alternately increased and decreased during the precision drawing step, further reducing the stress generated in the pipe in the precision drawing step. The stress of the precision drawn tube is eliminated through the post-treatment step, while improving the hardness of the precision drawn tube and its ability to absorb plastic deformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The flowchart of the rolling heat treatment process of the precision drawn tube for petrochemical industry according to the embodiment of the present invention is shown. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention clearer, the device proposed in the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the drawings are in a very simplified form and use non-precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, please refer to the drawings. It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no technical substantive significance. Any structural modification, change in proportional relationship or adjustment of size, without affecting the efficacy and purpose that can be achieved by the present invention, should still fall within the scope of the technical content disclosed by the present invention.

[0037] Figure 1 The flowchart of the rolling heat treatment process of the precision drawn tube for petrochemical industry according to the embodiment of the present invention is shown. Figure 1 As shown, the present invention discloses a rolling heat treatment process for precision drawn tubes for petrochemical industry.

[0038] The rolling heat treatment process of the precision drawn tube for petrochemical industry includes the following steps:

[0039] Heating steps: Heat the pipeline steps step by step and keep them warm;

[0040] Piercing steps: a mandrel penetrates the pipe to form a perforation; rollers are arranged obliquely around the pipe; the rollers rotate and press the outer circumference of the pipe;

[0041] Rolling steps: rollers are arranged at intervals along the moving direction of the pipe; the diameter of the pipe rolled by the rollers gradually decreases;

[0042] Pre-treatment steps: heat the pipe and then take it out of the furnace for rapid cooling; pickling the inner and outer surfaces of the pipe;

[0043] Fine drawing steps: the pipe is cold drawn at room temperature to form a fine drawn pipe;

[0044] Post-processing steps: cutting and trimming the precision drawn tube; heating and then cooling the precision drawn tube; flaw detection of the precision drawn tube.

[0045] The heating step includes three heating processes:

[0046] First heating process: heat the pipe to 600-630℃; holding time: 0.5h;

[0047] Second heating process: heat the pipe to 940-960℃; holding time: 0.5-1h;

[0048] The third heating process: heat the pipeline to 1170-1200℃; insulation time: 1.5-2h.

[0049] The pipe needs to be heated before the perforation step. During the perforation step, the core rod needs to penetrate the pipe to form the perforation, and the temperature difference between the inside and outside of the pipe needs to be consistent. The heating step is carried out three times, which reduces the temperature difference between the inside and outside of the pipe.

[0050] The holding time is gradually increased through the three heating processes, which shortens the holding time of the first heating process. The time of the subsequent holding processes can make up for the holding time of the first heating process, thereby shortening the time of the entire heating step.

[0051] As the temperature approaches the pipeline heating temperature, the temperature increase amplitude of the three heating processes in the heating step gradually decreases, thereby achieving accurate control of the pipeline heating temperature.

[0052] During the perforation step, a gap is formed between adjacent rollers. When a perforation is required, a mandrel is inserted through the pipe. This pushes the pipe outward, causing the pipe's outer circumference to transition into the gap between the rollers. The rollers then rotate and press the pipe's outer circumference, flattening it toward the transition point between the rollers and creating a circular shape.

[0053] The outer surface of the roller contacts the outer circumference of the pipe, and the outer circumference of the pipe is kept circular by rotating and rolling the outer circumference of the pipe. However, the outer circumference of the pipe has many depressions and protrusions.

[0054] The pipe is sizing-rolled through a series of rolling steps. The rollers gradually reduce the pipe diameter until it reaches the specified diameter. Rolling is completed through multiple roller passes, and the pipe undergoes multiple sizing steps until it reaches the specified diameter. This reduces the amount of deformation during each sizing step, preventing pipe deformation and reducing internal stress in the pipe.

[0055] The pre-processing steps include the following processes:

[0056] First treatment process: heat the pipe to 840-860℃; heating time: 3-4 hours; holding time: 1.5-2 hours; pipe is quickly cooled to 700℃ after being taken out of the furnace; quick cooling time: 10-12 minutes;

[0057] Second treatment process: heat the pipe to 770-790℃; heating time: 15-25 minutes; holding time: 1.5-2 hours; the pipe is removed from the furnace and air-cooled to room temperature;

[0058] The third treatment process: the pipe is placed in the pickling chamber; the pickling time is 15 to 20 minutes; the pickling temperature is 75 to 85°C.

[0059] In the third treatment process, the mass ratio of the pickling solution is: potassium dichromate: 10-12%; hydrofluoric acid: 5-6%; hydrochloric acid: 5-6%; sulfuric acid: 5-6%; thiourea: 0.45-0.55%; potassium thiocyanate: 0.65-0.85%; additive: 0.75%; the balance is pure water.

[0060] During the first treatment, the pipe is slowly heated to 840-860°C, held at that temperature, and then rapidly cooled to achieve an equilibrium microstructure. The first and second treatments reduce the pipe's hardness, improve machinability, eliminate residual stress, and reduce surface cracks.

[0061] During the first treatment, the pipe is slowly heated to 840-860°C. During this heating process, pearlite, proeutectoid ferrite, and cementite transform into austenite, and a primary phase transformation and recrystallization occur. After exiting the furnace, the pipe is rapidly cooled to 700°C for a limited cooling time of 10-12 minutes. During this process, a secondary phase transformation and recrystallization occurs, resulting in a stable metallographic structure of pearlite, proeutectoid ferrite, and cementite with finer grains, thicker lamellae, and a uniform structure free of internal stress. This reduces the pipe's strength and improves its plasticity, facilitating subsequent fine drawing.

[0062] The second treatment process reheats the rapidly cooled pipe. This process eliminates residual stress and reduces surface cracking, facilitating subsequent fine drawing of the pipe. This improves the surface quality after drawing and prevents corrosion of the pipe's internal structure during pickling.

[0063] During the third treatment, sodium nitrite ionizes to produce nitrate ions, which react with the pipe surface and remove impurities remaining from the first and second treatments. Sodium nitrite, hydrofluoric acid, hydrochloric acid, and sulfuric acid are all corrosive, and thiourea and potassium thiocyanate inhibit their corrosion. This shortens the pickling time during the third treatment, while the higher pickling temperature accelerates the corrosive reactions of sodium nitrite, hydrofluoric acid, hydrochloric acid, and sulfuric acid.

[0064] Sodium nitrite forms a continuous and dense passivation film on the surface of the pipe. The passivation film has high chemical stability, which hinders the oxidation of the pipe by air.

[0065] The cold drawing of the pipe in the fine drawing step includes three cold drawing processes:

[0066] First cold drawing process: The pipe is cold drawn into the first prefabricated pipe at room temperature; the cold drawing speed is alternately increased and decreased gradually;

[0067] Second cold drawing process: cold drawing the first preformed tube into the second preformed tube at room temperature; the cold drawing speed is alternately increased and decreased gradually; the positions of the cold drawing speed alternatingly increased and decreased in the first cold drawing process and the positions of the cold drawing speed alternatingly increased and decreased in the second cold drawing process are staggered;

[0068] The third cold drawing process: the second preformed tube is cold drawn into a precision drawn tube at room temperature; with the middle position of the second preformed tube as the dividing line, the cold drawing speed is switched from gradually decreasing to gradually increasing.

[0069] After the first cold drawing process, the first preform tube is left to rest for 12-14 hours; after the second cold drawing process, the second preform tube is left to rest for 12-14 hours; and after the third cold drawing process, the third preform tube is left to rest for 24-26 hours. Through these three cold drawing processes, the pipe's dimensions gradually approach those specified in the drawing, ultimately forming a precision-drawn tube. The pipe is cold-drawn into the first preform tube during the first cold drawing process. During this process, the cold drawing speed alternates between increasing and decreasing, with a smooth transition between these two stages. By continuously adjusting the cold drawing speed during the first cold drawing process, varying degrees of compression are achieved on the outer and inner circumferences of the pipe.

[0070] The first preformed tube is cold-drawn into the second preformed tube during the second cold-drawing process. During this second cold-drawing process, the cold-drawing speed alternates between increasing and decreasing, with a smooth transition between the two. The alternating speed increases and decreases during the first and second cold-drawing processes are staggered to avoid overlap. These two cold-drawing processes achieve varying degrees of compression on the outer and inner circumferences of the tube, with evenly distributed compression, reducing internal stress generated during the cold-drawing process.

[0071] During the third cold drawing process, the second preform tube is cold-drawn to its final dimensions. The second preform tube is relatively long, and when cold-drawn to the middle of the second preform tube, its structure is weak, which can easily cause damage to the second preform tube, resulting in cracks in the middle of the second preform tube.

[0072] During the third cold drawing process, as the second preform tube begins cold drawing, the drawing position transitions from one end surface to the middle, and the cold drawing speed gradually decreases. As the drawing position transitions from the middle to the other end surface, the cold drawing speed gradually increases, ensuring the surface quality of both the outer and inner circumferences of the precision-drawn tube.

[0073] After the first cold drawing process, the first preformed tube is still hot. This is done by leaving it to cool for 12-14 hours. After the second cold drawing process, the second preformed tube is still hot. This is done by leaving it to cool for 12-14 hours. After the third cold drawing process, the precision-drawn tube is still hot. This is done by leaving it to cool for 24-26 hours.

[0074] In the post-processing step, the precision drawing tube cutting process goes through three processing steps:

[0075] The first processing step: squeeze and shrink the ends of the precision-drawn tube; the squeezed and shrunk diameters of the ends of the precision-drawn tube are smaller than the diameter of the precision-drawn tube;

[0076] The second processing step: cutting off and removing the ends of the precision drawn tube; sawing around the ends of the precision drawn tube;

[0077] The third processing step: grinding the end faces of the precision drawn tube at both ends; trimming the edges of the end faces of the precision drawn tube; cleaning impurities from the precision drawn tube.

[0078] In the post-processing step, the precision drawn tube undergoes two heating processes:

[0079] First heating process: heat the drawn tube and then cool it with water; heating time: 3.5-4h; heating temperature: 920-930℃;

[0080] The second heating process: heat the precision drawn tube and then water cool it; heating time: 1.5 to 2 hours; heating temperature: 675 to 675°C.

[0081] During the cold drawing process, precision-drawn tubing deforms at both ends. During the cold drawing process, one end of the tube is clamped and drawn through the die. This causes one end to deform due to the clamping force, and the edge flares outward to a certain extent. Simultaneously, the other end of the tube, squeezed by the die, causes deformation that is concentrated at the other end.

[0082] By squeezing and shrinking the ends of the precision-drawn tube, the diameter of the ends is controlled, so that the diameter data of the precision-drawn tube at any position remains consistent. Since the ends of the precision-drawn tube will expand to a certain extent due to toughness after squeezing and shrinking, the squeezing and shrinking diameter of the ends of the precision-drawn tube needs to be smaller than the diameter of the precision-drawn tube to leave room for expansion at the ends.

[0083] After the ends of the precision drawn tube are cut off, the end surface of the precision drawn tube is relatively rough. The burrs are removed by grinding and trimming the end surfaces of the precision drawn tube to ensure the size and surface accuracy of the precision drawn tube.

[0084] The pretreatment step reduces the pipe's hardness, improves machinability, eliminates residual stress, and facilitates cold drawing. The precision-drawn tube undergoes a shearing process, trimming the head, tail, and edges. However, the finished tube at this point is not yet a finished product and cannot meet the required hardness for use. The initial heating process releases internal stress in the tube, increasing its hardness.

[0085] The second heating process improved the yield strength, tensile strength, and elongation of the drawn tube, but the improvements were not significant. Impact energy was significantly increased. The drawn tube is used in the petrochemical industry and meets the technical requirements for precision-drawn tubes. The second heating process, which raises the temperature to a higher range of 675-675°C, results in a significant loss of dislocations in the drawn tube. The softening effect outweighs the dispersion strengthening effect, resulting in a decrease in yield strength and ultimately a negligible increase in the yield strength of the drawn tube.

[0086] During the second heating process, the higher heating temperature causes the martensite of the precision drawn tube to decompose completely, which results in a limited improvement in the tensile strength of the precision drawn tube, but greatly improves the impact energy of the precision drawn tube.

[0087] Use metal flaw detector to inspect the precision drawn tubes to check whether there are any internal defects such as cracks, scratches, spots, etc.

[0088] The stress generated during the piercing step is reduced during the rolling step, and the pipe is heat treated during the pre-treatment step to eliminate stress. This facilitates cold drawing of the pipe during the finishing step, improving the cold drawing quality. Alternating the cold drawing speed during the finishing step further reduces stress generated during the finishing step. Post-treatment eliminates stress in the finished drawn pipe, improving its hardness and ability to absorb plastic deformation.

[0089] The process of the present invention is explained below by two embodiments:

[0090] First embodiment:

[0091] The rolling heat treatment process of the precision drawn tube for petrochemical industry includes the following steps:

[0092] Heating steps: Heat the pipeline steps step by step and keep them warm;

[0093] The heating step includes three heating processes:

[0094] First heating process: heat the pipe to 600℃; holding time: 0.5h;

[0095] Second heating process: heat the pipe to 940℃; holding time: 0.5h;

[0096] The third heating process: heat the pipeline to 1170℃; insulation time: 1.5h.

[0097] Piercing steps: a mandrel penetrates the pipe to form a perforation; rollers are arranged obliquely around the pipe; the rollers rotate and press the outer circumference of the pipe;

[0098] Rolling steps: rollers are arranged at intervals along the moving direction of the pipe; the diameter of the pipe rolled by the rollers gradually decreases;

[0099] Pre-treatment steps: heat the pipe and then take it out of the furnace for rapid cooling; pickling the inner and outer surfaces of the pipe;

[0100] The pre-processing steps include the following processes:

[0101] First treatment process: heat the pipe to 840℃; heating time: 3h; holding time: 1.5h; the pipe is quickly cooled to 700℃ after being taken out of the furnace; quick cooling time: 10min;

[0102] Second treatment process: heat the pipe to 770℃; heating time: 15 minutes; holding time: 1.5 hours; the pipe is removed from the furnace and air-cooled to room temperature;

[0103] The third treatment process: the pipe is placed in the pickling chamber; the pickling time is 15 minutes; the pickling temperature is 75°C.

[0104] The mass ratio of the pickling solution in the third treatment process is: potassium dichromate: 10%; hydrofluoric acid: 5%; hydrochloric acid: 5%; sulfuric acid: 5%; thiourea: 0.45%; potassium thiocyanate: 0.65%; additives: 0.75%; and the balance is pure water.

[0105] Fine drawing steps: the pipe is cold drawn at room temperature to form a fine drawn pipe;

[0106] The cold drawing of the pipe in the fine drawing step includes three cold drawing processes:

[0107] First cold drawing process: The pipe is cold drawn into the first prefabricated pipe at room temperature; the cold drawing speed is alternately increased and decreased gradually;

[0108] Second cold drawing process: cold drawing the first preformed tube into the second preformed tube at room temperature; the cold drawing speed is alternately increased and decreased gradually; the positions of the cold drawing speed alternatingly increased and decreased in the first cold drawing process and the positions of the cold drawing speed alternatingly increased and decreased in the second cold drawing process are staggered;

[0109] The third cold drawing process: the second preformed tube is cold drawn into a precision drawn tube at room temperature; with the middle position of the second preformed tube as the dividing line, the cold drawing speed is switched from gradually decreasing to gradually increasing.

[0110] After the first cold drawing process, the first prefabricated tube is left to stand for 12 hours; after the second cold drawing process, the second prefabricated tube is left to stand for 12 hours; after the third cold drawing process, the third prefabricated tube is left to stand for 24 hours.

[0111] Post-processing steps: cutting and trimming the precision drawn tube; heating and then cooling the precision drawn tube; flaw detection of the precision drawn tube.

[0112] In the post-processing step, the precision drawn tube cutting and trimming process goes through three processing steps:

[0113] The first processing step: squeeze and shrink the ends of the precision-drawn tube; the squeezed and shrunk diameters of the ends of the precision-drawn tube are smaller than the diameter of the precision-drawn tube;

[0114] Second processing step: cutting off and removing the ends of the precision drawn tube; sawing around the ends of the precision drawn tube;

[0115] The third processing step: grinding the end faces of the precision drawn tube at both ends; trimming the edges of the end faces of the precision drawn tube; cleaning impurities from the precision drawn tube.

[0116] In the post-processing step, the precision drawn tube undergoes two heating processes:

[0117] First heating process: heat the drawn tube and then cool it with water; heating time: 3.5h; heating temperature: 920℃;

[0118] The second heating process: heat the precision drawn tube and then water cool it; heating time: 1.5h; heating temperature: 675℃.

[0119] Second embodiment:

[0120] like Figure 1 As shown, the rolling heat treatment process of the precision drawn tube for petrochemical industry in this embodiment includes the following steps:

[0121] Heating steps: Heat the pipeline steps step by step and keep them warm;

[0122] The heating step includes three heating processes:

[0123] First heating process: heat the pipe to 630℃; holding time: 0.5h;

[0124] Second heating process: heat the pipe to 960℃; holding time: 1h;

[0125] The third heating process: heat the pipeline to 1200℃; insulation time: 2h.

[0126] Piercing steps: a mandrel penetrates the pipe to form a perforation; rollers are arranged obliquely around the pipe; the rollers rotate and press the outer circumference of the pipe;

[0127] Rolling steps: rollers are arranged at intervals along the moving direction of the pipe; the diameter of the pipe rolled by the rollers gradually decreases;

[0128] Pre-treatment steps: heat the pipe and then take it out of the furnace for rapid cooling; pickling the inner and outer surfaces of the pipe;

[0129] The pre-processing steps include the following processes:

[0130] First treatment process: heat the pipe to 860℃; heating time: 4h; holding time: 2h; pipe is quickly cooled to 700℃ after being taken out of the furnace; quick cooling time: 12min;

[0131] Second treatment process: heat the pipe to 790℃; heating time: 25 minutes; holding time: 2 hours; the pipe is removed from the furnace and air-cooled to room temperature;

[0132] The third treatment process: the pipe is placed in the pickling chamber; the pickling time is 20 minutes; the pickling temperature is 85°C.

[0133] In the third treatment process, the mass ratio of the pickling solution is: potassium dichromate: 12%; hydrofluoric acid: 6%; hydrochloric acid: 6%; sulfuric acid: 6%; thiourea: 0.55%; potassium thiocyanate: 0.85%; additives: 0.75%; and the balance is pure water.

[0134] Fine drawing steps: the pipe is cold drawn at room temperature to form a fine drawn pipe;

[0135] The cold drawing of the pipe in the fine drawing step includes three cold drawing processes:

[0136] First cold drawing process: The pipe is cold drawn into the first prefabricated pipe at room temperature; the cold drawing speed is alternately increased and decreased gradually;

[0137] Second cold drawing process: cold drawing the first preformed tube into the second preformed tube at room temperature; the cold drawing speed is alternately increased and decreased gradually; the positions of the cold drawing speed alternatingly increased and decreased in the first cold drawing process and the positions of the cold drawing speed alternatingly increased and decreased in the second cold drawing process are staggered;

[0138] The third cold drawing process: the second preformed tube is cold drawn into a precision drawn tube at room temperature; with the middle position of the second preformed tube as the dividing line, the cold drawing speed is switched from gradually decreasing to gradually increasing.

[0139] After the first cold drawing process, the first prefabricated tube was left to stand for 14 hours; after the second cold drawing process, the second prefabricated tube was left to stand for 14 hours; after the third cold drawing process, the third prefabricated tube was left to stand for 26 hours.

[0140] Post-processing steps: cutting and trimming the precision drawn tube; heating and then cooling the precision drawn tube; flaw detection of the precision drawn tube.

[0141] In the post-processing step, the precision drawn tube cutting and trimming process goes through three processing steps:

[0142] The first processing step: squeeze and shrink the ends of the precision-drawn tube; the squeezed and shrunk diameters of the ends of the precision-drawn tube are smaller than the diameter of the precision-drawn tube;

[0143] Second processing step: cutting off and removing the ends of the precision drawn tube; sawing around the ends of the precision drawn tube;

[0144] The third processing step: grinding the end faces of the precision drawn tube at both ends; trimming the edges of the end faces of the precision drawn tube; cleaning impurities from the precision drawn tube.

[0145] In the post-processing step, the precision drawn tube undergoes two heating processes:

[0146] First heating process: heat the drawn tube and then cool it with water; heating time: 4h; heating temperature: 930℃;

[0147] The second heating process: heat the precision drawn tube and then water cool it; heating time: 2h; heating temperature: 675℃.

[0148] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0149] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A rolling heat treatment process for precision drawn tubes for petrochemical industry, characterized by: The following steps are involved: Heating steps: Heat the pipeline steps step by step and keep them warm; Piercing steps: a mandrel penetrates the pipe to form a perforation; rollers are arranged obliquely around the pipe; the rollers rotate and press the outer circumference of the pipe; Rolling steps: rollers are arranged at intervals along the moving direction of the pipe; the diameter of the pipe rolled by the rollers gradually decreases; Pre-treatment steps: heat the pipe and then take it out of the furnace for rapid cooling; pickling the inner and outer surfaces of the pipe; Fine drawing steps: the pipe is cold drawn at room temperature to form a fine drawn pipe; Post-processing steps: cutting and trimming the precision drawn tube; heating and cooling the precision drawn tube; flaw detection of the precision drawn tube; In the post-processing step, the precision drawn tube cutting and trimming process goes through three processing steps: The first processing step: squeeze and shrink the ends of the precision-drawn tube; the squeezed and shrunk diameters of the ends of the precision-drawn tube are smaller than the diameter of the precision-drawn tube; The second processing step: cutting off and removing the ends of the precision drawn tube; sawing around the ends of the precision drawn tube; The third processing step: grinding the end faces of the precision drawn tube at both ends; trimming the edges of the end faces of the precision drawn tube; cleaning the impurities of the precision drawn tube; The cold drawing of the pipe in the fine drawing step includes three cold drawing processes: First cold drawing process: The pipe is cold drawn into the first prefabricated pipe at room temperature; the cold drawing speed is alternately increased and decreased gradually; Second cold drawing process: cold drawing the first preformed tube into the second preformed tube at room temperature; the cold drawing speed is alternately increased and decreased gradually; the positions of the cold drawing speed alternatingly increased and decreased in the first cold drawing process and the positions of the cold drawing speed alternatingly increased and decreased in the second cold drawing process are staggered; The third cold drawing process: the second preformed tube is cold drawn into a precision drawn tube at room temperature; with the middle position of the second preformed tube as the dividing line, the cold drawing speed is switched from gradually decreasing to gradually increasing.

2. The rolling heat treatment process for the precision drawn tube for petrochemical industry according to claim 1, characterized in that: The heating step includes three heating processes: First heating process: heat the pipe to 600-630℃; holding time: 0.5h; Second heating process: heat the pipe to 940-960℃; holding time: 0.5-1h; The third heating process: heat the pipeline to 1170-1200℃; insulation time: 1.5-2h.

3. The rolling heat treatment process for the precision drawn tube for petrochemical industry according to claim 1, characterized in that: The pre-processing steps include the following processes: First treatment process: heat the pipe to 840-860℃; heating time: 3-4 hours; holding time: 1.5-2 hours; the pipe is quickly cooled to 700℃ after being taken out of the furnace; quick cooling time: 10-12 minutes; Second treatment process: heat the pipe to 770-790℃; heating time: 15-25 minutes; holding time: 1.5-2 hours; the pipe is removed from the furnace and air-cooled to room temperature; The third treatment process: the pipe is placed in the pickling chamber; the pickling time is 15 to 20 minutes; the pickling temperature is 75 to 85°C.

4. The rolling heat treatment process for the precision drawn tube for petrochemical industry according to claim 3, characterized in that: The mass ratio of the pickling solution in the third treatment process is: potassium dichromate: 10-12%; hydrofluoric acid: 5-6%; Hydrochloric acid: 5-6%; Sulfuric acid: 5-6%; Thiourea: 0.45-0.55%; Potassium thiocyanate: 0.65-0.85%; Additive: 0.75%; the balance is pure water.

5. The rolling heat treatment process for the precision drawn tube for petrochemical industry according to claim 1, characterized in that: In the post-processing step, the precision drawn tube undergoes two heating processes: First heating process: heat the drawn tube and then cool it with water; heating time: 3.5-4h; heating temperature: 920-930℃; The second heating process: heat the precision drawn tube and then water cool it; heating time: 1.5 to 2 hours; heating temperature: 675 to 675°C.

6. The rolling heat treatment process for the precision drawn tube for petrochemical industry according to claim 1, characterized in that: After the first cold drawing process, the first prefabricated tube is left to stand for 12 to 14 hours; after the second cold drawing process, the second prefabricated tube is left to stand for 12 to 14 hours; after the third cold drawing process, the third prefabricated tube is left to stand for 24 to 26 hours.

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