A method of manufacturing a stainless steel cooling tube

Abstract

This invention relates to the field of rolled steel pipe processing, specifically a method for manufacturing a stainless steel cooling pipe. The stainless steel cooling pipe is grade 022Cr17Ni12Mo2, with the following chemical composition by weight percentage: C 0.010~0.020, Si<0.50, Mn<2.00, Cr 16.50~17.50, Ni 10.50~11.50, Mo 2.00~3.00, S<0.015, P<0.030. A typical specification is Φ25×2mm. The manufacturing method includes: (i) billet manufacturing; (ii) hot extrusion; (iii) cold rolling; (iv) heat treatment; (v) straightening; and (vi) surface treatment. The finished tube has a low-temperature elongation of ≥50% (0℃), an inner surface roughness Ra≤0.8μm, an outer surface roughness of 6.3μm>Ra≥3.2μm, a uniform microstructure, a grain size of 5~6 grade, and a thermal conductivity ≥17.6 W(m·K). ‑1 (0℃), carbon dioxide corrosion rate <0.05 mm / a (CO2 partial pressure 0.1MPa).

Description

TECHNICAL FIELD

[0001] The present application relates to the field of rolling steel pipe processing, in particular to a manufacturing method of a stainless steel cooling pipe. BACKGROUND

[0002] The National Speed Skating Hall of the 2022 Beijing Winter Olympics (the "Ice Ribbon") is the first Winter Olympics venue to use "carbon dioxide transcritical direct evaporation refrigeration technology" in history. After a certain high pressure is applied, carbon dioxide will become a critical fluid, which is transported to the ice surface through stainless steel pipes to achieve the purpose of cooling and refrigeration. This technology has a carbon emission value close to zero, high system heat exchange efficiency, and significantly improved ice-making energy efficiency. The ice surface area is about 12,000 square meters, and the total length of the stainless steel cooling pipes in the entire ice rink reaches 120 kilometers.

[0003] As a speed skating venue for the Winter Olympics, there are high requirements for the quality of the ice surface. If the ice surface temperature is uneven, it will affect the performance and results of the players, which requires the cooling pipe to have good low-temperature plasticity, carbon dioxide corrosion resistance, high thermal conductivity, uniform organization, etc. The application of the stainless steel cooling pipe can control the temperature difference of the entire venue ice surface to 0.5 degrees Celsius, which is beneficial to the athletes to create good results, and innovatively explores the application of stainless steel seamless pipes in large industrial refrigeration systems and liquid carbon dioxide medium refrigeration systems.

[0004] The present application produces a stainless steel cooling pipe for the Winter Olympics speed skating venue, which has good low-temperature plasticity, high thermal conductivity, carbon dioxide corrosion resistance, uniform organization, high dimensional accuracy, long service life, etc. SUMMARY

[0005] The purpose of the present application is to solve the above problems, and to provide a manufacturing method of a stainless steel cooling pipe.

[0006] The purpose of the present application is achieved as follows: a manufacturing method of a stainless steel cooling pipe,

[0007] The method comprises the following steps: step one: pipe blank manufacturing: round steel blank is obtained through converter+AOD+LF furnace smelting, mold casting, electroslag remelting and initial rolling and blooming, and the round steel is forged into round steel through a fast forging machine with a forging ratio of 7-10; the round steel is peeled and sawed to become a blank, and a through hole is drilled in the center of the blank with a deep hole drill; the outer diameter of the blank allows deviation of (0, -2) mm, the length allows deviation of (+5, 0) mm, the through hole concentricity is less than 0.5 mm, and the surface roughness of the blank is Ra≤1.6 μm; step two: hot extrusion: the blank is heated through a ring furnace, first induction heating, hole expansion, second induction heating, glass powder lubrication, and then is subjected to hot extrusion through a horizontal extruder to obtain a rough pipe with an outer diameter of (67-89) mm±1.5 mm and a wall thickness of (4.0-8.0)±0.5 mm; the ring furnace heating temperature is 750±20℃, and the heating time is 120-180 min; the first induction heating temperature is 1180±15℃, and the heating time is 4-7 min; the hole expansion cone gauge is Φ50-65 mm, and the expansion coefficient is 1.05-1.10; the second induction heating temperature is 1180±15℃, and the heating time is 4-7 min; the extrusion ratio is 18-25, and the extrusion speed is 25-35%, and the rough pipe is air cooled to 15-25℃ after the extrusion is completed; step three: cold rolling: after the rough pipe is subjected to pickling to remove the oxide skin, the rough pipe is subjected to cold rolling through a two-roller high-speed pilger rolling mill, is cold rolled to a gauge of Φ(38-60)×(2.5-3.5) mm in the first pass, the feed amount is 6-9 mm, and the rolling speed is 80-100 times / min; is cold rolled to a gauge of Φ(15-38)×(1.5-3) mm in the second pass, the feed amount is 5-8 mm, and the rolling speed is 100-120 times / min; and annealing heat treatment is performed in the middle of the two cold rolling processes. The acid liquid used for pickling is HNO3+HF mixed acid (HNO315-18%, HF 3-6%, according to mass fraction). Step four: heat treatment: intermediate annealing heat treatment process: the annealing temperature is 1030-1050℃, the holding time is 4-8 min, and the pipe is discharged and water cooled to 15-25℃; finished product solid solution heat treatment process: the solid solution temperature is 1070-1090℃, the holding time is 4-7 min, and the pipe is discharged and water cooled to 15-25℃; step five: straightening: the finished steel pipe is subjected to straightening treatment after the solid solution heat treatment, and the bending degree is less than or equal to 0.8 mm / m; step six: surface treatment: the finished steel pipe is subjected to surface treatment through inner hole mechanical polishing and outer surface shot blasting, the shot used is 304 or 316 stainless steel round shot, the particle size is Φ0.2-0.5 mm; after the inner and outer surface treatment, the pipe is subjected to sand wheel polishing and cleaning, the inner surface roughness is Ra≤0.8 μm, the outer surface roughness is 6.3 μm> Ra≥3.2 μm, the structure is uniform, the grain size is 5-6 levels, and the thermal conductivity is greater than or equal to 17.6 W(m·K) -1 (0℃), and the carbon dioxide corrosion rate is less than 0.05 mm / a (under a carbon dioxide partial pressure of 0.1 MPa).

[0008] The steel grade of the stainless steel cooling pipe is 022Cr17Ni12Mo2, and the chemical composition percentage by weight is C: 0.010-0.020, Si: <0.50, Mn: <2.00, Cr: 16.50-17.50, Ni: 10.50-11.50, Mo: 2.00-3.00, S: <0.015, and P: <0.030; typical specifications are Φ18*1.5mm, Φ25*2mm, Φ32*3mm and Φ38*3mm, and typical process routes are Φ150mm round steel-hot extrusion Φ67*5.0mm hollow pipe-cold rolling Φ38*2.5mm round pipe-cold rolling Φ18*1.5mm round pipe, Φ150mm round steel-hot extrusion Φ67*5.0mm hollow pipe-cold rolling Φ38*3.0mm round pipe-cold rolling Φ25*2.0mm round pipe, Φ150mm round steel-hot extrusion Φ67*5.0mm hollow pipe-cold rolling Φ32*3.0mm round pipe, and Φ150mm round steel-hot extrusion Φ67*5.0mm hollow pipe-cold rolling Φ38*3.0mm round pipe.

[0009] The application has the advantages that: the application adopts targeted component design, ensures heat transfer coefficient, corrosion resistance and low temperature plasticity, and prolongs service life; the application adopts large forging ratio blanking process and large elongation hot extrusion process to obtain uniform and fine austenite grain structure; the application adopts high temperature solid solution heat treatment and inner surface mechanical polishing / outer surface shot blasting surface treatment process to obtain the effect of smooth inner surface / rough outer surface, improves material thermal conductivity while ensuring coolant flow rate, and ensures heat exchange efficiency of the whole refrigeration system; high precision two-roller pilger high speed rolling mill is adopted to realize two-pass rolling forming; high precision seven-roller straightening machine is adopted to straighten twice to ensure that the bending degree of the finished steel pipe is less than 0.8mm / m. DETAILED DESCRIPTION

[0010] The main innovation of the application is that low C content, low Si content, low Ni content, high Cr content and Mo content are adopted in component design, large forging ratio, large extrusion ratio, two-pass cold rolling deformation process, high temperature solid solution heat treatment and inner surface mechanical polishing / outer surface shot blasting surface treatment process, so that the pipe has good low temperature plasticity, carbon dioxide corrosion resistance, high thermal conductivity, uniform structure, long service life, smooth inner surface and rough outer surface.

[0011] We use raw materials with very low content of harmful elements such as phosphorus and sulfur, and make targeted composition design, use lower silicon content and nickel content to improve the heat transfer coefficient; use higher chromium content and molybdenum content to improve the CO2 corrosion resistance; use lower carbon content to improve the low temperature plasticity at 0℃ and prolong the service life; use large forging ratio blanking process and large elongation hot extrusion process to obtain uniform and fine austenite grain structure; use high temperature solid solution heat treatment and internal surface mechanical polishing / external surface shot blasting surface treatment process to obtain the effect of smooth internal surface / rough external surface, while ensuring the coolant flow rate, improving the thermal conductivity of the material and ensuring the heat exchange efficiency of the entire refrigeration system.

[0012] To improve the dimensional accuracy of the product and ensure the flow and flow rate of the coolant in the pipeline, we use high-precision two-roller pilger high-speed rolling mill to form in two passes; use high-precision seven-roller straightening machine to straighten twice to ensure that the bending degree of the finished steel pipe is less than 0.8 mm / m.

[0013] A manufacturing method of a stainless steel cooling pipe, the steel grade of which is 022Cr17Ni12Mo2, and the chemical composition in weight percentage is C 0.010-0.020, Si <0.50, Mn <2.00, Cr 16.50-17.50, Ni 10.50-11.50, Mo 2.00-3.00, S <0.015, P <0.030. The typical specifications are Φ18×1.5mm, Φ25×2mm, Φ32×3mm, Φ38×3mm, and the typical process route is Φ150mm round steel- hot extrusion Φ67×5.0mm rough pipe- cold rolling Φ38×2.5mm round pipe- cold rolling Φ18×1.5mm round pipe; Φ150mm round steel- hot extrusion Φ67×5.0mm rough pipe- cold rolling Φ38×3.0mm round pipe- cold rolling Φ25×2.0mm round pipe; Φ150mm round steel- hot extrusion Φ67×5.0mm rough pipe- cold rolling Φ32×3.0mm round pipe; Φ150mm round steel- hot extrusion Φ67×5.0mm rough pipe- cold rolling Φ38×3.0mm round pipe.

[0014] The manufacturing method is: (1) pipe blank manufacturing; (2) hot extrusion; (3) cold rolling; (4) heat treatment; (5) straightening; (6) surface treatment. The low temperature elongation of the finished pipe is ≥50% (0℃), the internal surface roughness Ra is ≤0.8μm, the external surface roughness is 6.3μm> Ra ≥3.2μm, the structure is uniform, the grain size is 5-6 grade, the thermal conductivity is ≥17.6 W(m·K) (0℃), and the carbon dioxide corrosion rate is <0.05 mm / a (CO2 partial pressure 0.1MPa). -1 The specific steps are as follows.

[0015] Pipe blank manufacturing

[0016] The diameter 700 mm round billets are obtained by converter + AOD + LF furnace smelting, mold casting, electroslag remelting and initial rolling and blooming, and the diameter 150 mm and length 15 m round steel is obtained by multi-pass forging with a forging ratio of 7-10.

[0017] The round steel is peeled and sawed into a diameter 150 mm and length 500 mm blank, and a diameter 30 mm through hole is drilled in the center of the blank by a deep hole drill. The allowable deviation of the outer diameter of the blank is (0, -2) mm, the allowable deviation of the length is (+5, 0) mm, the through hole concentricity is <0.5 mm, and the surface roughness Ra of the blank is ≤1.6 μm.

[0018] Hot extrusion

[0019] The blank is heated by a ring furnace, first induction heating, hole expanding, second induction heating, glass powder lubrication, and then hot extrusion is carried out in a horizontal extrusion machine to obtain a hollow pipe with an outer diameter of (67-89) mm ± 1.5 mm and a wall thickness of (4-8) ± 0.5 mm.

[0020] The heating temperature of the ring furnace is 750 ± 20 °C, and the heating time is 120-180 min.

[0021] The first induction heating temperature is 1180 ± 15 °C, and the heating time is 4-7 min.

[0022] The hole expanding cone gauge is Φ 50-65 mm, and the expansion coefficient is 1.05-1.10.

[0023] The second induction heating temperature is 1180 ± 15 °C, and the heating time is 4-7 min.

[0024] The extrusion ratio is 18-25, the extrusion speed is 25-35%, and after the extrusion is completed, air cooling is carried out to 15-25 °C.

[0025] Cold rolling

[0026] After the scale is removed from the hollow pipe by pickling, cold rolling is carried out by using a two-roll high-speed pilger mill, the first pass cold rolling is carried out to a gauge Φ (38-60) x (2.5-3.5) mm, the feed amount is 6-9 mm, and the rolling speed is 80-100 times / min; the second pass cold rolling is carried out to a gauge Φ (15-38) x (1.5-3) mm, the feed amount is 5-8 mm, and the rolling speed is 100-120 times / min; annealing heat treatment is carried out between the two cold rollings; the acid used for pickling is HNO3 + HF mixed acid (HNO3 15-18%, HF 3-6%, by mass fraction).

[0027] Heat treatment

[0028] Intermediate annealing heat treatment process: annealing temperature 1030-1050℃, holding time 4-8min, water cooling to 15-25℃ after discharging; finished product solid solution heat treatment process: solid solution temperature 1070-1090℃, holding time 4-7min, water cooling to 15-25℃ after discharging;

[0029] Straightening

[0030] The finished steel pipe is straightened on a five-roller straightening machine after solid solution heat treatment, and the bending degree is less than or equal to 0.8mm / m.

[0031] (Six) Surface treatment

[0032] The finished steel pipe is treated by inner hole mechanical polishing and outer surface shot blasting, and the shot used is 304 or 316 stainless steel round shot with a particle size of Φ0.2-0.5mm.

[0033] After the inner and outer surface treatment, the pipe is treated by cloth wheel polishing and cleaning, and the inner surface roughness is less than or equal to 0.8μm, and the outer surface roughness is greater than or equal to 3.2μm and less than or equal to 6.3μm.

[0034] This method uses raw materials with extremely low content of harmful elements such as phosphorus and sulfur, and is designed for specific composition, uses lower silicon content and nickel content to improve the heat transfer coefficient, uses higher chromium content and molybdenum content to improve the CO2 corrosion resistance, uses lower carbon content to improve the low temperature plasticity at 0℃ and prolong the service life, uses large forging ratio blanking process and large elongation hot extrusion process to obtain uniform and fine austenite grain structure, uses high temperature solid solution heat treatment and inner surface mechanical polishing / outer surface shot blasting surface treatment process to obtain smooth inner surface / rough outer surface effect, which ensures the coolant flow rate while improving the material thermal conductivity and ensuring the heat exchange efficiency of the entire refrigeration system.

[0035] To improve the dimensional accuracy of the product and ensure the flow and flow rate of the coolant in the pipeline, we use high-precision two-roller pilger high-speed rolling mill to form in two passes, and use high-precision seven-roller straightening machine to straighten repeatedly twice to ensure that the bending degree of the finished steel pipe is less than 0.8mm / m. The application of this stainless steel cooling pipe can control the temperature difference of the entire venue ice surface within 0.5℃, which is beneficial to the athletes to create good results, and it is an innovative exploration for the application of stainless steel seamless pipe in large industrial refrigeration systems and liquid carbon dioxide medium refrigeration systems. Example 1

[0036] The steel chemical composition used in this pipe is C: 0.013, Si: 0.46, Mn: 1.00, Cr: 17.35, Ni: 10.50, Mo: 2.35, S: 0.010, P: 0.025, and the balance is Fe and unavoidable impurities.

[0037] The 700 mm diameter round billets are obtained by converter + AOD + LF furnace smelting, mold casting, electroslag remelting and initial rolling and blooming, and the 150 mm diameter and 15 m long round steel is forged by a fast forging machine with a forging ratio of 7.5.

[0038] The round steel is peeled and sawed into a 150 mm diameter and 500 mm long blank, and a 30 mm diameter through hole is drilled in the center of the blank.

[0039] The blank is heated in a ring furnace, first induction heated, hole expanded, second induction heated, and glass powder lubricated, and then is hot extruded in a horizontal extruder to obtain a 67x5.0 mm rough pipe.

[0040] The heating temperature of the ring furnace is 750±20℃, and the heating time is 150 min.

[0041] The first induction heating temperature is 1180±15℃, and the heating time is 5 min.

[0042] The hole expansion cone specification is 60 mm, and the expansion coefficient is 1.10.

[0043] The second induction heating temperature is 1180±15℃, and the heating time is 5 min.

[0044] The extrusion ratio is 21, and the extrusion speed is 33%, and after the extrusion is completed, air cooling is performed to 15-25℃.

[0045] After the rough pipe is pickled to remove the oxide skin, two high-speed pilger rolling mills are used for cold rolling, the first pass is cold rolled to a specification of 38x3.0 mm, the feed amount is 6 mm, and the rolling speed is 90 times / min; the second pass is cold rolled to a specification of 25x2.0 mm, the feed amount is 6 mm, and the rolling speed is 110 times / min. Annealing heat treatment is performed in between the two cold rolling passes.

[0046] The intermediate annealing heat treatment process is: annealing temperature 1030-1050℃, holding for 5 min, and water cooling to 15-25℃ after discharging.

[0047] The finished product solid solution heat treatment process is: solid solution temperature 1070-1090℃, holding for 4 min, and water cooling to 15-25℃ after discharging.

[0048] After the finished steel pipe is subjected to solid solution heat treatment, straightening treatment is performed on a five-roll straightening machine to achieve a bending degree of ≤0.8 mm / m.

[0049] The finished steel pipe is subjected to surface treatment by inner hole mechanical polishing and outer surface shot blasting, and the shot material is 304 stainless steel shot with a particle size of Φ0.3 mm.

[0050] After the inner and outer surface treatment, the grinding and cleaning are carried out by using a cloth grinding wheel, so that the inner surface roughness is Ra≤0.8 μm and the outer surface roughness is 6.3 μm>Ra≥3.2 μm. Example 2

[0051] The smelting and billet-making process of Example 2 is the same as that of Example 1.

[0052] The round steel is peeled and sawed into a billet with a diameter of 150 mm and a length of 500 mm, and a through hole with a diameter of 30 mm is drilled in the center of the billet by using a deep hole drill.

[0053] The billet is heated in a ring furnace, subjected to first induction heating, hole expansion, second induction heating and glass powder lubrication, and then is subjected to hot extrusion in a horizontal extruder to obtain a crude pipe with a specification of 67x5.0 mm.

[0054] The heating temperature of the ring furnace is 750±20℃, and the heating time is 3 hours.

[0055] The first induction heating temperature is 1180±15℃, and the heating time is 6 min.

[0056] The hole expansion cone specification is 60 mm, and the expansion coefficient is 1.10.

[0057] The second induction heating temperature is 1180±15℃, and the heating time is 6 min.

[0058] The extrusion ratio is 21, and the extrusion speed is 33%, and after the extrusion is completed, air cooling is carried out to 15-25℃.

[0059] After the crude pipe is subjected to pickling to remove the oxide skin, cold rolling is carried out by using a two-roller high-speed pilger mill, the first pass cold rolling is carried out to a specification of 38x2.5 mm, the feed-in amount is 5 mm, and the rolling speed is 90 times / min; the second pass cold rolling is carried out to a specification of 18x1.5 mm, the feed-in amount is 6 mm, and the rolling speed is 120 times / min. Annealing heat treatment is carried out in the middle of the two times of cold rolling.

[0060] The annealing heat treatment process in the middle is as follows: the annealing temperature is 1030-1050℃, the holding time is 4 min, and the furnace discharge water cooling is carried out to 15-25℃.

[0061] The solid solution heat treatment process of the finished product is as follows: the solid solution temperature is 1070-1090℃, the holding time is 3 min, and the furnace discharge water cooling is carried out to 15-25℃.

[0062] After the finished steel pipe is subjected to solid solution heat treatment, straightening treatment is carried out on a five-roller straightening machine, and the bending degree is ≤0.8 mm / m.

[0063] The finished steel pipe is subjected to surface treatment by using inner hole mechanical polishing and outer surface shot blasting, the shot material is 316 stainless steel shot, and the particle size is Φ0.2 mm.

[0064] After the inner and outer surface treatment, the grinding and cleaning are carried out by using a cloth grinding wheel, so that the inner surface roughness is Ra≤0.8 μm and the outer surface roughness is 6.3 μm>Ra≥3.2 μm. Example 3

[0065] The smelting and billet-making process of Example 3 is the same as that of Example 1.

[0066] The round steel is peeled and sawed into a billet with a diameter of 150 mm and a length of 500 mm. A through hole with a diameter of 30 mm is drilled in the center of the billet by using a deep hole drill.

[0067] The billet is heated in a ring furnace, subjected to first induction heating, hole expansion, second induction heating and glass powder lubrication, and then is subjected to hot extrusion in a horizontal extruder to obtain a crude pipe with a specification of 67x5.0 mm.

[0068] The heating temperature of the ring furnace is 750±20℃, and the heating time is 130 min.

[0069] The first induction heating temperature is 1180±15℃, and the heating time is 5 min.

[0070] The hole expansion cone specification is 60 mm, and the expansion coefficient is 1.10.

[0071] The second induction heating temperature is 1180±15℃, and the heating time is 4 min.

[0072] The extrusion ratio is 21, and the extrusion speed is 33%. After the extrusion is completed, the pipe is air-cooled to 15-25℃.

[0073] After the crude pipe is subjected to pickling to remove the oxide skin, the pipe is subjected to cold rolling by using a two-roll high-speed pilger rolling mill. The pipe is cold-rolled to a specification of 38x3.0 mm, the feed-in amount is 8 mm, and the rolling speed is 80 times / min.

[0074] The solid solution heat treatment process of the finished product is as follows: the solid solution temperature is 1070-1090℃, the holding time is 5 min, and the pipe is water-cooled to 15-25℃ after being discharged from the furnace.

[0075] After the finished product pipe is subjected to solid solution heat treatment, the pipe is subjected to straightening treatment on a five-roll straightening machine, so that the bending degree is ≤0.8 mm / m.

[0076] The finished product pipe is subjected to surface treatment by using inner hole mechanical polishing and outer surface shot blasting. The shot material is 304 stainless steel shot with a particle size of Φ0.5 mm.

[0077] After the inner and outer surface treatment, the grinding and cleaning are carried out by using a cloth grinding wheel, so that the inner surface roughness is Ra≤0.8 μm and the outer surface roughness is 6.3 μm>Ra≥3.2 μm.

[0078] The above merely describes the specific embodiments of the present application, but the structural features of the scope of protection of the present application are not limited thereto, and any changes or modifications made by those skilled in the art within the scope of the present application are covered by the patent scope of the present application.

Claims

1. A method for manufacturing a stainless steel cooling pipe, characterized in that: Includes the following steps: Step 1: Billet Manufacturing: Round steel billets are obtained by smelting in a converter + AOD + LF furnace, ingot casting, electroslag remelting, and initial rolling. The billets are then forged into round steel using a high-speed forging mill with a forging ratio of 7-10. The round steel is peeled and sawn to become billets. A through hole is drilled in the center of the billet using a deep hole drill. The allowable deviation of the billet's outer diameter is (0, -2) mm, the allowable deviation of the length is (+5, 0) mm, the concentricity of the through hole is <0.5 mm, and the surface roughness of the billet Ra is ≤1.6 μm. Step 2: Hot Extrusion: The billet is heated in a ring furnace, subjected to a first induction heating, pore expansion, a second induction heating, and lubrication with glass powder. It then enters a horizontal extruder for hot extrusion to obtain a rough tube with an outer diameter of (67-89) mm ± 1.5 mm and a wall thickness of (4.0-8.0) ± 0.5 mm. The ring furnace heating temperature is 750 ± 20℃, and the heating time is 120-180 min. The first induction heating temperature is 1180 ± 15℃, and the heating time is 4-7 min. The pore expansion cone specification is Φ50-65 mm, and the expansion coefficient is 1.05-1.

10. The second induction heating temperature is 1180 ± 15℃, and the heating time is 4-7 min. The extrusion ratio is 18-25, and the extrusion speed is 25-35%. After extrusion, the billet is air-cooled to 15-25℃. Step 3: Cold Rolling: After the rough tube is pickled to remove the oxide scale, it is cold rolled using a two-roll high-speed Pilger mill. The first pass is cold rolled to the specification Φ (38-60) × (2.5-3.5) mm, with a feed rate of 6-9 mm and a rolling speed of 80-100 times / min. The second pass is cold rolled to the specification Φ (15-38) × (1.5-3) mm, with a feed rate of 5-8 mm and a rolling speed of 100-120 times / min. Annealing heat treatment is carried out between the two cold rolling processes. The acid used for pickling is a mixed acid of HNO3 and HF, with HNO3 at 15-18% and HF at 3-6% by mass. Step 4: Heat treatment: Intermediate annealing heat treatment process: Annealing temperature 1030-1050℃, holding temperature for 4-8 min, water cooling to 15-25℃ after exiting the furnace; Finished product solution heat treatment process: Solution treatment temperature 1070-1090℃, holding temperature for 4-7 min, water cooling to 15-25℃ after exiting the furnace. Step 5: Straightening: After solution heat treatment, the finished steel pipe is straightened to achieve a curvature of ≤0.8mm / m; Step Six: Surface Treatment: The finished steel pipes undergo surface treatment using internal mechanical polishing and external shot blasting. The shot used is 304 or 316 stainless steel round shot with a particle size of Φ0.2-0.5mm. After internal and external surface treatment, the pipes are polished with a cloth grinding wheel and cleaned to achieve an internal surface roughness Ra≤0.8μm, an external surface roughness 6.3 μm>Ra≥3.2μm, uniform microstructure, grain size grade 5~6, and thermal conductivity ≥17.6 W(m·K). -1 (0℃), under the condition of carbon dioxide partial pressure of 0.1MPa, the carbon dioxide corrosion rate is <0.05 mm / a; The stainless steel cooling pipe has the steel grade 022Cr17Ni12Mo2, and its chemical composition by weight percentage is: C: 0.010~0.020, Si<0.50, Mn<2.00, Cr: 16.50~17.50, Ni: 10.50~11.50, Mo: 2.00~3.00, S<0.015, P<0.

030. Typical specifications are Φ18×1.5mm, Φ25×2mm, Φ32×3mm, and Φ38×3mm. The typical process route is: Φ150mm round steel — hot extrusion of Φ67×5.0mm rough tube — cold rolling of Φ38×2.5mm round tube — cold rolling of Φ18×1.5mm round tube. Φ150mm round steel — hot extruded Φ67×5.0mm rough tube — cold rolled Φ38×3.0mm round tube — cold rolled Φ25×2.0mm round tube; Φ150mm round steel — hot extruded Φ67×5.0mm rough tube — cold rolled Φ32×3.0mm round tube; Φ150mm round steel — hot extruded Φ67×5.0mm rough tube — cold rolled Φ38×3.0mm round tube.