Manufacturing method of Hastelloy UNS N06022 seamless heat exchange tube

Abstract

The invention discloses a manufacturing method of a Hastelloy UNS N06022 seamless heat exchange tube, which belongs to the technical field of material processing, and comprises the following steps: (1) carrying out supplied material acceptance inspection, inner and outer surface grinding repair and reinspection on a hot extrusion blank; (2) carrying out multi-pass intermediate product cold rolling, and after cold rolling, carrying out intermediate product deoiling, intermediate product heat treatment, intermediate product straightening, intermediate product pipe cutting, acid pickling, intermediate product grinding and repairing and intermediate product inspection; (3) performing cold rolling on a finished product, and performing pre-degreasing after cold rolling of the finished product; (4) deoiling a finished product; (5) performing heat treatment on a finished product; (6) straightening a finished product; (7) performing finished product ultrasonic eddy current, water pressure and pipe cutting, sampling during pipe cutting, and performing physical and chemical tests; and (8) the obtained steel pipe is subjected to the procedures of finished product surface inspection, size inspection, cleaning, mark spraying and finishing and finally packaged and warehoused, and the product produced through the method is high in one-time inspection qualification rate and high in yield.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a seamless heat exchange tube, specifically a method for manufacturing a Hastelloy UNS N06022 seamless heat exchange tube, belonging to the field of materials processing technology. Background Technology

[0002] UNS N06022 alloy is a nickel-based Ni-Cr-Mo-Wu alloy renowned for its excellent corrosion resistance and high-temperature strength, particularly excelling in highly oxidizing media and environments containing chloride-containing organic compounds. Chemical and petrochemical production processes often involve high temperatures, high pressures, and corrosive media, thus placing higher demands on the corrosion resistance and high-temperature performance of materials. As a versatile corrosion-resistant alloy, N06022 alloy can adapt to various harsh working environments and possesses excellent resistance to oxidizing aqueous media and reducing and oxidizing environments encountered during processes. Therefore, the research and development and production of UNS N06022 alloy seamless tubes have significant practical importance and market demand, providing a more reliable and efficient material solution for industrial production. Currently, domestically produced small-diameter UNS N06022 alloy seamless heat exchange tubes suffer from problems such as low first-pass yield, low production yield, low dimensional accuracy, and poor internal and external surface quality.

[0003] Currently, patent CN115921573B discloses a manufacturing method for a seamless heat exchanger tube of UNS N10276 Hastelloy alloy. The method involves: (i) inspecting the incoming material and grinding the inner and outer surfaces of the UNS N10276 hot-extruded billet; (ii) performing three intermediate cold rolling passes on the obtained billet, with each pass requiring degreasing, heat treatment, straightening, and cutting, pickling, inspection, and grinding; (iii) cold rolling the obtained third-pass steel tube; (iv) degreasing, heat treatment, straightening, ultrasonic eddy current treatment, hydrostatic testing, and cutting, with samples taken for physicochemical testing during cutting; and (v) inspecting, cleaning, marking, and finishing the obtained steel tube, finally packaging and warehousing it. Patent CN117696621B also discloses a method for manufacturing a seamless heat exchanger tube of UNS N10276 Hastelloy alloy. The manufacturing method of N08810 alloy seamless heat exchange tubes includes the following steps: (i) inspecting the incoming steel material and grinding the inner and outer surfaces; (ii) performing a single-pass intermediate cold rolling, followed by intermediate degreasing, intermediate heat treatment, intermediate straightening, intermediate tube cutting, pickling, intermediate grinding, and intermediate inspection; (iii) performing finished product cold rolling; (iv) performing finished product degreasing; (v) performing finished product heat treatment; (vi) performing finished product straightening; (vii) performing finished product ultrasonic eddy current, hydrostatic, and tube cutting, with samples taken for physicochemical testing during tube cutting; and (viii) performing finished product surface inspection, dimensional inspection, cleaning, marking, and finishing processes on the obtained steel tubes, and finally packaging and warehousing. Both patents use simple degreasing steps in the intermediate and finished product degreasing processes, which to some extent complete the degreasing procedure. However, this direct degreasing method results in a large amount of surface oil, a long degreasing time, prolonged soaking time, reduced production efficiency, a large required degreasing dosage, and increased costs. This approach fails to meet the requirements of future clean production trends. Furthermore, the intermediate inspection and grinding of the patented product is merely a simple grinding process, resulting in uneven processing and the formation of coarse polishing marks, which can lead to slight polishing marks on the surface of the finished product after cold rolling. Patent CN119406965A discloses a manufacturing method for UNS N06690 alloy seamless heat exchange tubes, which employs a method of first-stage alkali tank immersion, aerospace kerosene tank immersion, and second-stage alkali tank immersion for degreasing. However, this degreasing method is only suitable for small-scale or pilot-scale production due to the high cost of aerospace kerosene, and is not suitable for mass production. In contrast, this application achieves the same effect through finished product cold rolling pre-degreasing, specified cold rolling and degreasing process flow time, and cold internal polishing for unqualified FB degreasing.

[0004] Based on this, developing a manufacturing method for Hastelloy UNS N06022 seamless heat exchange tubes that can overcome the above-mentioned difficulties, and producing Hastelloy UNS N06022 seamless heat exchange tubes with high first-pass yield, high yield, high dimensional accuracy, good internal and external surface quality, and physical and chemical properties that meet the standard technical requirements has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology by proposing a manufacturing method for Hastelloy UNS N06022 seamless heat exchange tubes. The products manufactured by this method have a high first-pass yield, high yield, high dimensional accuracy, good internal and external surface quality, stable microstructure and properties, strong practicality, and are conducive to mass production.

[0006] The technical solution of this invention to solve the above technical problems is: A method for manufacturing a Hastelloy UNS N06022 seamless heat exchanger tube specifically includes the following steps: (a) The UNS N06022 hot extrusion billet undergoes incoming material inspection and internal and external surface grinding, specifically: the billet undergoes initial inspection + grinding + re-inspection, and during the re-inspection, each endoscope is randomly selected for PT (partial pressure measurement). (II) The tube blank obtained in step (I) is subjected to multiple passes of intermediate cold rolling. After each pass of cold rolling, the intermediate product must undergo degreasing, heat treatment, straightening, tube cutting, pickling, grinding, and inspection. During the cold rolling of intermediate products, the cold rolling deformation is controlled between 45% and 65%, and the rolling speed and feed rate are controlled as follows: The rolling mill model is LG60 or LG110, the rolling speed is ≤80 times / min, and the feed rate is ≤3mm / time; For intermediate cold-rolled products, the Q value is controlled to be ≥0.95, and the deviations in outer diameter and wall thickness after rolling are controlled as follows: The rolling mill model is LG60 or LG110, with the outer diameter deviation controlled within ±0.5%Dmm (generally taken as a multiple of 0.05 greater than or equal to the calculated value), and the wall thickness deviation controlled within ±5%Smm (generally taken as a multiple of 0.05 greater than or equal to the calculated value). The specific process for removing oil from intermediate products is as follows: oil is scraped off using an oil scraper → oil is removed in an alkaline tank → rinsing → soaking in a hot water tank → oil is removed in an acid tank → rinsing → inspection; The intermediate product heat treatment is carried out in a roller hearth furnace with a slightly oxidizing gas atmosphere. The heat treatment temperature is 1150±10℃ and the holding time is 2.5 times the wall thickness. (iii) The steel pipe obtained in step (ii) is subjected to finished product cold rolling; During finished product rolling, the cold rolling deformation is 50%-65%, the rolling speed is controlled at ≤120 times / min, the feed rate is ≤2mm / time, and the Q value is ≥0.9; During the cold rolling of finished products, the outer diameter deviation after rolling is controlled within ±0.10mm, and the wall thickness deviation is controlled within ±0.10mm; Pre-degreasing is carried out simultaneously during the cold rolling of the finished product. Pre-degreasing involves wiping the outer surface of the finished tube after cold rolling with a cotton cloth soaked in acetone, and then punching the inner hole of the finished tube after cold rolling with a wool felt ball 2-3 times. (iv) The steel pipe obtained in step (iii) is degreased; The specific steps for degreasing the finished tubes are as follows: Step (3) Within 6 hours after pre-degreasing, scrape oil with an oil scraper → Within 6 hours after scraping oil, soak in an alkaline tank → Soak in a hot water tank → Wipe the outer surface → Apply wool felt balls to the inner wall → Check the degreasing quality of the inner hole for each FB tube. If there is a small amount of oil or oil film in the inner hole, clean the inner hole after cold internal polishing. (v) Perform finished product heat treatment on the steel pipe obtained in step (iv); The heat treatment of the finished products is carried out in a bright furnace with a pure hydrogen atmosphere. During the heat treatment of the finished product, the heat treatment temperature is controlled at 1150±10℃, and the holding time is 2.5 times the wall thickness (generally, the larger integer value is taken). (vi) Straighten the steel pipe obtained in step (v); (vii) The steel pipe obtained in step (vi) is subjected to finished ultrasonic eddy current test, water pressure test and pipe cutting. Samples are taken during pipe cutting for physical and chemical tests. (viii) The steel pipes obtained in step (vii) are subjected to finished product surface inspection, dimensional inspection, cleaning, marking and finishing processes, and finally packaged and put into storage.

[0007] The technical solution further defined in this invention is: Furthermore, in the aforementioned method for manufacturing Hastelloy UNS N06022 seamless heat exchange tubes, during the degreasing of intermediate products in step (II) in the alkaline tank, the composition of the solution in the alkaline tank is controlled by mass ratio as follows: degreasing agent: water = 1:20, alkaline tank temperature: 50-60℃, and alkaline tank soaking time: 50-60min. When degreasing in the acid tank, the composition of the solution in the acid tank should be controlled by mass percentage as follows: HF: 1%, HNO3: 10-15%, and the remainder is tap water. The sum of the above components should be 100%. The acid tank temperature should be 55-60℃, and the acid washing time should be 20-35min.

[0008] In the aforementioned method for manufacturing Hastelloy UNS N06022 seamless heat exchange tubes, the straightening parameters are controlled as follows during step (ii) intermediate product straightening: If the outer diameter of the intermediate steel pipe is >57mm, the straightening control speed is ≤6m / min, the curvature after straightening is ≤1.5mm / m, and the deviation of the outer diameter after straightening is ±0.05%Dmm; If the outer diameter of the intermediate steel pipe is ≤57mm, the straightening control speed is ≤8m / min, the curvature after straightening is ≤1mm / m, and the deviation of the outer diameter after straightening is ±0.05%Dmm.

[0009] Technical effects: By specifying the requirements for straightening speed, straightness, and the range of outer diameter deviation after straightening, this invention ensures the curvature while avoiding the risk of straightening damage and marks caused by iron rod straightening, thus guaranteeing straightening quality. Strictly specifying the range of outer diameter deviation after straightening can effectively avoid the risk of outer diameter deviation caused by straightening, thereby improving dimensional accuracy.

[0010] In the aforementioned method for manufacturing Hastelloy UNS N06022 seamless heat exchange tubes, during the intermediate pickling process in step (ii), the solution components in the acid tank are as follows by mass ratio: HF: 5-8%, HNO3: 10-15%, with the remainder being tap water. The sum of all the above components is 100%. The temperature of the acid tank is controlled at 50-55℃, and the pickling time is 20-30 minutes. Preferably, after 20 minutes of pickling, the tank needs to be opened every minute to observe the condition of the inner and outer surfaces. Pickling is stopped when the inner and outer surfaces show a slight and uniform oxide scale.

[0011] Technical effect: The present invention specifies a method for pickling intermediate products, including strict control of the ratio, temperature and time of the acid tank to ensure pickling quality. The N06022 intermediate product tubes washed by this method have a slightly uniform oxide scale on the inner and outer walls. Under the premise of ensuring that no acid is passed through, the amount of oxide scale passed through the internal polishing is minimized, thus saving the labor cost of internal polishing.

[0012] In the aforementioned manufacturing method of Hastelloy UNS N06022 seamless heat exchange tubes, during the intermediate product grinding and inspection in step (ii), the grinding adopts the method of overall external polishing + local spot grinding. External polishing is carried out using a flap wheel, and local spot grinding is carried out using a polishing machine equipped with a flower-shaped flap wheel. Inspection is conducted by visual inspection and one endoscope at a time. Endoscopes with excessive visual inspection marks are re-polished externally. Internal polishing is performed using an automatic internal polishing machine with a cross-shaped polishing head made of sandpaper. After internal polishing, each endoscope is polished individually. Endoscopes that fail to meet the standards are re-polished internally at designated points.

[0013] In the aforementioned manufacturing method of Hastelloy UNS N06022 seamless heat exchange tubes, step (iv) involves degreasing the finished tubes. This is achieved by first removing some of the rolling oil through cold rolling pre-degreasing to prevent the oil from condensing and adsorbing onto the inner wall of the tube. Then, the flow rate of the cold rolling and degreasing processes is accelerated. It is stipulated that oil is scraped off within 6 hours after cold rolling pre-degreasing, and then immersed in an alkali bath within 6 hours after scraping. This greatly improves the degreasing quality of the finished tubes. The alkali bath solution is specified to have a mass ratio of degreasing agent to water of 1:6.5, an alkali bath temperature of 40-60℃, and an alkali bath immersion time of 15-25 minutes. A hot water bath is also specified. Temperature: 70-80℃; Soaking time in hot water tank: 10-20 minutes; After removing from the hot water tank, wipe the outer surface with a cotton cloth soaked in acetone, and clean the inner wall with a wool felt until clean, repeating 3-5 times. After degreasing, quality personnel and technicians should conduct a FB inspection on the inner hole. If the inner hole is basically free of oil stains, oil spots, or oil films, heat treatment can proceed only after the quality personnel or technicians sign off. If a few inner holes have oil films or oil spots during the FB inspection, they should be cold-polished and cleaned, then returned to the original frame and FB should be performed again. Heat treatment can proceed after the FB inspection is qualified.

[0014] Technically, this invention improves the final degreasing quality of high-value-added nickel-based products, especially small-diameter heat exchange tubes with requirements for crystal corrosion. It employs a degreasing process involving pre-degreasing during cold rolling, a specified cold rolling and degreasing cycle time, and cold internal polishing to address issues with incomplete degreasing. This process avoids residual oil, oil spots, and oil films, which can lead to nitriding risks during heat treatment and ultimately result in substandard metallographic structure, mechanical properties, and crystal corrosion resistance. The combination of this degreasing process and heat treatment in a pure hydrogen atmosphere further enhances the final physicochemical properties of high-value-added nickel-based alloy small-diameter heat exchange tubes.

[0015] In the aforementioned method for manufacturing Hastelloy UNS N06022 seamless heat exchange tubes, in step (vi), the straightening machine speed is controlled to be ≤10m / min during the straightening of the finished tube, the curvature after straightening is ≤0.5mm / m, and the outer diameter deviation after straightening is ±0.01mm.

[0016] In terms of technical effectiveness, this invention specifies the requirements for the straightening machine model, straightening speed, straightness, and the range of outer diameter deviation after straightening. It stipulates the use of a plastic roller straightening machine for finished product straightening, with a straightening speed ≤10m / min. This ensures the straightening of the product while avoiding the risks of straightening damage and marks caused by iron rollers, thus guaranteeing the quality of the straightened product. Strictly specifying the range of outer diameter deviation after straightening effectively avoids the risk of outer diameter deviation caused by straightening, thereby improving dimensional accuracy.

[0017] In the aforementioned method for manufacturing Hastelloy UNS N06022 seamless heat exchange tubes, the first ultrasonic pass rate in step (vii) is ≥95%, and the first eddy current pass rate is 100%.

[0018] In the aforementioned method for manufacturing Hastelloy UNS N06022 seamless heat exchange tubes, step (viii) involves surface inspection to ensure that the inner and outer surfaces of the finished tubes are smooth and that the roughness Ra of the inner and outer walls is ≤0.8.

[0019] In the aforementioned manufacturing method of Hastelloy UNS N06022 seamless heat exchange tube, the finished tubes produced have the following characteristics: room temperature tensile test: yield strength ≥330 MPa, tensile strength ≥750 MPa, elongation after fracture ≥60%; and 250℃ high temperature tensile test: yield strength ≥245 MPa, tensile strength ≥655 MPa.

[0020] The beneficial effects of this invention are: This invention employs multi-pass cold rolling, controlling the deformation of intermediate products at 45%-65% and finished products at 50%-65%. The multi-pass rolling process ensures thorough grain breakage, leading to finer grains after heat treatment. For intermediate products, strict control of feed rate and rolling speed (using an LG60 or LG110 mill, with a rolling speed ≤60 times / min and a feed rate ≤3mm / pass) guarantees surface quality. Furthermore, controlling the Q value ≥1 ensures more uniform deformation, thereby improving dimensional accuracy. Similarly, for finished products, strict control of feed rate ≤2mm / pass and Q value ≥0.95 ensures both surface quality and dimensional accuracy.

[0021] This invention specifies a method for degreasing intermediate products, including pre-scraping with an oil scraper followed by degreasing, strictly controlling the ratio of solutions in the alkali and acid tanks, and ensuring degreasing quality by controlling temperature and time to avoid the risk of carburization during heat treatment. The invention also specifies a method for degreasing finished products. For finished pipes, pre-degreasing during cold rolling removes some rolling oil to prevent it from condensing and adsorbing onto the inner wall of the pipe. Then, the flow rate of the cold rolling and degreasing processes is accelerated. The method specifies that oil scraping is performed within 6 hours after pre-degreasing, followed by immersion in the alkali tank within 6 hours. This significantly improves the degreasing quality of the finished pipes. The alkali tank solution has the following mass ratio: degreasing agent: water = 1:6.5; alkali tank temperature: 40-60℃; alkali tank immersion time: 15-25 min; hot water tank temperature: 70-80℃. At 0℃, soaking time in the hot water tank is 10-20 minutes. After removing the tank from the hot water tank, wipe the outer surface with a cotton cloth soaked in acetone and clean the inner wall with a wool felt. Repeat this process 3-5 times. After degreasing, quality personnel and technicians should conduct a FB inspection on the inner hole. If the inner hole is basically free of oil stains, oil spots, or oil films, heat treatment can proceed only after the quality personnel or technicians sign off on it. If a few inner holes have oil films or oil spots during the FB inspection, they should be cold-polished and cleaned, then returned to the original frame and FB should be performed again. Heat treatment can proceed only after the FB inspection is passed.

[0022] This invention specifies that the intermediate product solution heat treatment is carried out in a roller hearth furnace with a slightly oxidizing atmosphere and a heat treatment temperature of 1150±10℃. This eliminates cold rolling work hardening, ensures good plasticity of the seamless tube, and facilitates subsequent cold rolling forming. The holding time for the intermediate product is 2.5 times the wall thickness, generally taking a larger integer value. A slightly longer holding time results in a more uniform and porous oxide scale, which is easier to remove by pickling. The finished product solution heat treatment is carried out in a bright furnace with a pure hydrogen atmosphere and a heat treatment temperature of 1150±10℃. The holding time for the finished product is 2.5 times the wall thickness. The purpose is to obtain good microstructure and comprehensive mechanical properties while ensuring the surface color of the heat exchange tube is bright and the overall color consistency is good.

[0023] This invention specifies methods for grinding and finishing hot-extruded billets and intermediate steel pipes. The PT (Pre-Test) inspection of hot-extruded billets is to ensure the outer surface is free of residual hot-extruded defects. The endoscopy of each hot-extruded billet is performed for more precise and efficient treatment of internal wall defects, preventing these defects from propagating to the next cold rolling process. The endoscopy of each intermediate pipe during grinding ensures the quality of the internal wall in each cold rolling pass, reduces the risk of batch alarms for internal damage in the final finished pipe via ultrasonic testing, and improves the first-pass yield of the endoscopic inspection of the final finished pipe, thereby increasing the final ultrasonic pass rate, surface inspection pass rate, and final yield.

[0024] This invention solves the problems of low first-pass yield, low yield, low dimensional accuracy, and poor internal and external surface quality by strictly optimizing the process of Hastelloy UNS N06022 seamless heat exchange tubes. The products produced by this method have a high first-pass yield, high yield, high dimensional accuracy, good internal and external surface quality, stable mechanical properties, and strong practicality, which is conducive to mass production.

[0025] The Hastelloy UNS N06022 seamless heat exchange tubes prepared using the method of this invention have a first ultrasonic pass rate of ≥95%, a first eddy current pass rate of 100%, a first surface inspection (visual inspection + dimensional inspection) pass rate of ≥95%, and a comprehensive first inspection pass rate (ultrasonic pass rate × eddy current pass rate × surface inspection pass rate) of ≥90%.

[0026] The yield (hot extruded billet → finished tube) of Hastelloy UNS N06022 seamless heat exchange tube prepared by the method of this invention is ≥76%; the prepared N06022 alloy seamless heat exchange tube can meet the following dimensional accuracy: outer diameter ±0.10mm, wall thickness ±0.10mm; the prepared N06022 alloy seamless heat exchange tube has smooth inner and outer surfaces and consistent color, and the inner and outer wall roughness Ra≤0.8; the finished tube has a room temperature tensile test: yield strength ≥330MPa, tensile strength ≥750MPa, elongation after fracture ≥60%; the finished tube has a 250℃ high temperature tensile test: yield strength ≥245MPa, tensile strength ≥655MPa. Detailed Implementation

[0027] The present invention will now be clearly and completely described with reference to specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] This embodiment provides a method for manufacturing a Hastelloy UNS N06022 seamless heat exchange tube, with finished product specifications of φ28×2×5000mm. The technical requirements must meet ASTM B163-2022, NB / T 47019.1-2021, NB / T47019.9-2021 standards, and the requirements of the other party's technical agreement. The specific steps include: (a) The UNS N06022 hot extrusion billet undergoes incoming material inspection and internal and external surface grinding, specifically: the billet undergoes initial inspection + grinding + re-inspection, and during the re-inspection, each endoscope is randomly selected for PT (partial pressure measurement). (II) The tube blank obtained in step (I) is subjected to multiple passes of intermediate cold rolling. After each pass of cold rolling, the intermediate product must undergo degreasing, heat treatment, straightening, tube cutting, pickling, grinding, and inspection. During the cold rolling of intermediate products, the cold rolling deformation is controlled between 45% and 65%, and the rolling speed and feed rate are controlled as follows: The rolling mill model is LG60 or LG110, the rolling speed is ≤80 times / min, and the feed rate is ≤3mm / time; For intermediate cold-rolled products, the Q value is controlled to be ≥0.95, and the deviations in outer diameter and wall thickness after rolling are controlled as follows: The rolling mill model is LG60 or LG110, with the outer diameter deviation controlled within ±0.5%Dmm (generally taken as a multiple of 0.05 greater than or equal to the calculated value), and the wall thickness deviation controlled within ±5%Smm (generally taken as a multiple of 0.05 greater than or equal to the calculated value). The specific process for removing oil from intermediate products is as follows: oil is scraped off using an oil scraper → oil is removed in an alkaline tank → rinsing → soaking in a hot water tank → oil is removed in an acid tank → rinsing → inspection; The intermediate product heat treatment is carried out in a roller hearth furnace with a slightly oxidizing gas atmosphere. The heat treatment temperature is 1150±10℃ and the holding time is 2.5 times the wall thickness. (iii) The steel pipe obtained in step (ii) is subjected to finished product cold rolling; During finished product rolling, the cold rolling deformation is 50%-65%, the rolling speed is controlled at ≤120 times / min, the feed rate is ≤2mm / time, and the Q value is ≥0.9; During the cold rolling of finished products, the outer diameter deviation after rolling is controlled within ±0.10mm, and the wall thickness deviation is controlled within ±0.10mm; Pre-degreasing is carried out simultaneously during the cold rolling of the finished product. Pre-degreasing involves wiping the outer surface of the finished tube after cold rolling with a cotton cloth soaked in acetone, and punching the inner hole of the finished tube after cold rolling with a wool felt ball 2-3 times. Pre-degreasing during cold rolling removes some of the rolling oil to prevent the rolling oil from condensing and adsorbing on the inner wall of the tube, and then speeds up the flow of the cold rolling and degreasing processes. (iv) The steel pipe obtained in step (iii) is degreased; The specific steps for degreasing the finished tubes are as follows: Step (3) Within 6 hours after pre-degreasing, scrape oil with an oil scraper → Within 6 hours after scraping oil, soak in an alkaline tank → Soak in a hot water tank → Wipe the outer surface → Apply wool felt balls to the inner wall → Check the degreasing quality of the inner hole for each FB tube. If there is a small amount of oil or oil film in the inner hole, clean the inner hole after cold internal polishing. (v) Perform finished product heat treatment on the steel pipe obtained in step (iv); The heat treatment of the finished products is carried out in a bright furnace with a pure hydrogen atmosphere. During the heat treatment of the finished product, the heat treatment temperature is controlled at 1150±10℃, and the holding time is 2.5 times the wall thickness (generally, the larger integer value is taken). (vi) Straighten the steel pipe obtained in step (v); (vii) The steel pipe obtained in step (vi) is subjected to finished ultrasonic eddy current test, water pressure test and pipe cutting. Samples are taken during pipe cutting for physical and chemical tests. (viii) The steel pipes obtained in step (vii) are subjected to finished product surface inspection, dimensional inspection, cleaning, marking and finishing processes, and finally packaged and put into storage.

[0030] In this embodiment, the cold rolling process of UNS N06022 alloy seamless heat exchange tube strictly controls the cold rolling deformation of intermediate and finished products. A reasonable rolling speed and a relatively small feed amount are selected to ensure the quality of its inner and outer surfaces. The uniformity of the microstructure in the wall thickness direction is ensured by controlling the Q value, thereby improving dimensional accuracy and inner wall quality. Specific cold rolling parameters are shown in Table 1 below, and the technical requirements for dimensional accuracy and actual dimensions are shown in Table 2. Table 1 Cold Rolling Parameters of UNS N06022

[0031] Table 2. UNS N06022 Technical Requirements: Dimensional Accuracy and Actual Measured Dimensions

[0032] As can be seen from Table 2, the dimensional accuracy of intermediate and finished tubes in each pass meets the internal control requirements, and the dimensional accuracy of finished tubes is higher than that of ASME SB729-2023 and NB / T 47019.1-2021 standards.

[0033] The specific process for degreasing intermediate UNS N06022 alloy seamless heat exchange tubes is as follows: oil scraping with an oil scraper → degreasing in an alkaline tank → rinsing → soaking in a hot water tank → degreasing in an acid tank → rinsing → inspection. The main control requirements for degreasing intermediate tubes are shown in Table 3. The specific steps for degreasing finished tubes are as follows: oil scraping with an oil scraper within 6 hours after cold rolling pre-degreasing → soaking in an alkaline tank within 6 hours after oil scraping → soaking in a hot water tank → wiping the outer surface → applying wool felt balls to the inner wall → inspection. The main control requirements for degreasing finished tubes are shown in Table 4. The tubes obtained by degreasing according to the above method have clean inner and outer surfaces without oil stains, and there is no risk of nitriding during heat treatment.

[0034] Table 3 Key Control Requirements for the Degreasing Process of Intermediate Products in UNS N06022

[0035] Table 4. Key Control Requirements for the Oil Removal Process of UNS N06022 Finished Pipes

[0036] Table 4 above shows the main control requirements for the degreasing process of the finished UNS N06022 alloy heat exchange tube. After degreasing, the quality personnel and technicians shall conduct a FB inspection on the inner hole. If the inner hole is basically free of oil stains, oil spots, oil films, etc., the heat treatment can be carried out only after the quality personnel or technicians sign it. If a few inner holes have oil films, oil spots, etc. during the FB inspection, they shall be cold-polished and cleaned, then put back into the original frame and FB shall be carried out again. After the FB is qualified, the heat treatment shall be carried out. The degreasing agent alkali powder in Tables 3 and 4 includes the following components by mass percentage: disodium silicate: 20-30%, sodium carbonate: 20-30%, tetrasodium ethylenediaminetetraacetate: 3-10%, ethoxycocoylamine: 1-2.5%, and the balance is sodium hydroxide. The sum of the above components is 100%, and it is made using existing conventional degreasing agent processes.

[0037] The oil scraping equipment used for degreasing intermediate and finished pipes in this invention is the commercially available KH-60 fully automatic oil scraping and cutting machine. The oil scraping parameters are: oil scraping machine speed is 15m / min, and oil scraping machine time = (average length of each pipe × number of pipes per frame) / oil scraping machine speed.

[0038] The finished product degreasing process of the present invention is compared with the simple degreasing process without adding an oil skimmer and pre-degreasing as follows: The simple degreasing process involves soaking in an alkaline tank → soaking in a hot water tank → wiping the outer surface → applying wool felt balls to the inner wall → inspection. The degreasing time is 1 hour, the degreasing effect is poor, the roughness is Ra1.0-1.6, the crystal corrosion pass rate is 90%, the first-time inspection pass rate is 95%, white spots are present, and the economy is poor. The degreasing process of this invention involves scraping oil with an oil scraper within 6 hours after cold rolling pre-degreasing → immersing in an alkaline tank within 6 hours after oil scraping → immersing in a hot water tank → wiping the outer surface → applying wool felt balls to the inner wall → inspection. The degreasing time includes 20 minutes of immersion in the alkaline tank and 10 minutes of immersion in the hot water tank, with the total time controlled within 30 minutes. The degreasing effect is good, with a roughness Ra of 0.3-0.8, a 100% crystal corrosion pass rate, a 99% first-time inspection pass rate, and no white spot phenomenon. It is economical and saves on rolling degreasing costs.

[0039] In this embodiment, the heat treatment of intermediate UNS N06022 alloy seamless heat exchange tubes was carried out in a roller hearth furnace with an oxidizing atmosphere; the heat treatment of finished tubes was carried out in a bright furnace with a pure hydrogen atmosphere. The heat treatment process is shown in Table 5 below.

[0040] Table 5 Heat Treatment Regime for UNS N06022

[0041] As shown in Table 5, the intermediate product solution heat treatment was carried out in a roller hearth furnace with a slightly oxidizing atmosphere. The furnace had six temperature zones: zones T01-T03 were heating zones, and zones T04-T06 were holding zones. The heat treatment temperature was 1150℃, and the holding times were 24, 15, and 9 minutes, respectively. The cooling method was water cooling. The finished product heat treatment was a bright heat treatment with a pure hydrogen atmosphere. The furnace had five temperature zones: zones T01-T02 were heating zones, and zones T03-T05 were holding zones. The heat treatment temperature was 1150℃, and the holding time was 6 minutes. The cooling method was water jacket cooling.

[0042] Table 6 shows the straightening parameters for intermediate and finished UNS N06022 alloy seamless heat exchange tubes in this embodiment. By specifying the straightening machine model, straightening speed, straightness, and the range of outer diameter deviation after straightening, especially for finished product straightening, a plastic roller straightening machine is specified. The specified straightening speed ensures the correct curvature while avoiding the risks of straightening damage and marks caused by iron rollers, thus guaranteeing the quality of the straightened product. Strictly specifying the straightening process, especially the range of outer diameter deviation after finished product straightening, effectively avoids the risk of outer diameter deviation caused by straightening, thereby improving dimensional accuracy.

[0043] Table 6 Straightening Parameters for UNS N06022

[0044] The requirements for cutting intermediate and finished UNS N06022 alloy seamless heat exchange tubes in this embodiment are shown in Table 7. By strictly controlling the amount of flattened ends and strictly adhering to the center cutting method, the center position must be manually measured and marked before cutting the tube. Visual inspection is not allowed. This can reduce the risk of the intermediate and finished tubes being under-length and improve the final product inspection pass rate and final yield.

[0045] Table 7 UNS N06022 Pipe Cutting Requirements

[0046] The main control requirements for pickling the intermediate UNS N06022 alloy seamless heat exchange tubes in this embodiment are shown in Table 8 below. These include strictly controlling the acid tank ratio, temperature, and time to ensure pickling quality. The N06022 intermediate tubes washed using this method exhibit a slightly uniform oxide scale on both the inner and outer walls. While ensuring no excessive acid is applied, the amount of internal polishing of the oxide scale is minimized to save on internal polishing labor costs.

[0047] Table 8 Main Control Requirements for the Pickling Process of UNS N06022 Intermediate Product

[0048] The inspection and grinding requirements for UNS N06022 alloy hot-extruded billets and intermediate tubes in this embodiment are shown in Table 9 below. The PT (Pre-Test) re-inspection of hot-extruded billets is to ensure the outer surface is free of defects. The endoscopy of each hot-extruded billet is performed to more accurately and efficiently address internal wall defects, preventing them from spreading to the next cold rolling process and causing further defects. The endoscopy of each intermediate tube during grinding ensures the quality of the inner wall of the finished cold-rolled product, reducing the risk of ultrasonic damage and internal wall defects leading to unqualified endoscopes, thereby improving the final ultrasonic pass rate, surface inspection pass rate, and final yield.

[0049] Table 9 UNS N06022 Grinding Operation Requirements

[0050] In Table 9 above, during the grinding and inspection of intermediate products, the grinding process employs a combination of overall internal and external polishing and local spot polishing. External polishing utilizes a flap wheel, while internal polishing uses an automatic internal polishing machine with a cross-head made of abrasive. Local spot polishing is performed using a polishing machine equipped with a decorative impeller. Products with extensive local spot polishing require re-external polishing. Inspection is conducted visually and through individual endoscopes. Endoscopes that fail inspection require re-internal spot polishing.

[0051] Table 10 shows the ultrasonic, eddy current, hydrostatic, visual, and dimensional inspection results of the finished UNS N06022 alloy seamless heat exchange tubes produced in this embodiment. As can be seen from Table 10, the ultrasonic quality of the N06022 alloy seamless heat exchange tubes produced by this production method is as high as 96.28%, the eddy current and hydrostatic pass rates are both 100.00%, and the dimensional inspection pass rate is also 100.00%. The dimensional accuracy is far higher than the dimensional accuracy specified in ASTM B163-2022 and NB / T 47019.1-2021 standards. The visual inspection pass rate is as high as 96.49%, and the first-pass inspection pass rate is as high as 92.90%.

[0052] Table 10. Ultrasonic, eddy current, hydrostatic, visual, and dimensional inspection results of UNS N06022 finished pipes.

[0053] Table 11 shows the yield statistics of UNS N06022 alloy seamless heat exchange tubes in this embodiment. A total of 7.208 tons of φ139×18 hot extrusion billets were issued, and 825 pieces of φ28×2×5000mm finished products were put into storage, with an actual weight of 5.731 tons, and a yield rate as high as 79.51%.

[0054] Table 11. Yield of UNS N06022

[0055] The room temperature tensile properties test method for finished tubes is ASTM E8-2024, and the test results are shown in Table 12 below. Table 12 shows that the UNS N06022 seamless heat exchange tubes manufactured using this method exhibit excellent mechanical properties. The yield strength across four batches is 337-347 MPa, exceeding the requirement by ≥310 MPa; the tensile strength is consistently between 755-786 MPa, exceeding the requirement by ≥690 MPa; and the elongation after fracture is 63.5-65.5%, significantly exceeding the requirement by ≥45%.

[0056] Table 12 Room Temperature Tensile Properties of UNS N06022 Finished Tubes

[0057] High-temperature tensile tests were conducted as required. The test method for the high-temperature tensile properties of the finished tubes was ASTM E21-2020, with a test temperature of 250℃. The test results are shown in Table 13 below. Table 13 shows that the UNS N06022 seamless heat exchange tubes manufactured using this method exhibit excellent mechanical properties. The high-temperature tensile yield strength across four batches ranged from 245 to 262 MPa, exceeding the requirement by ≥224 MPa. The tensile strength remained stable at 655-670 MPa, exceeding the requirement by ≥643 MPa.

[0058] Table 13 Tensile properties of UNS N06022 finished tubes at 250℃

[0059] The non-metallic inclusions were inspected as required, using the test method ASTM E45-18a Method A. The test results are shown in Table 14 below.

[0060] Table 14 Test Results of Non-metallic Inclusions in Finished Pipes (UNS N06022)

[0061] Grain size analysis was performed as required. The test method was the ASTM E112-13 comparative method. The corrosion method was acid pickling with potassium permanganate solution. The test results are shown in Table 15 below.

[0062] Table 15 Grain Size of UNS N06022 Finished Tube

[0063] As required, under non-sensitized conditions, crystal corrosion tests were conducted on all four batches of N06022 finished pipes according to ASTM G28-2022 B method. The test duration was 24 hours, and the results of the crystal corrosion tests are shown in Table 16 below.

[0064] Table 16 Results of Crystallization Corrosion Test on Finished Tubes of UNS N06022

[0065] This invention solves the problems of low first-pass yield, low yield, low dimensional accuracy, and poor internal and external surface quality by strictly optimizing the process of UNS N06022 alloy seamless heat exchange tubes. As shown in Tables 10-16, the products produced by this method have a high first-pass yield, high yield, high dimensional accuracy, good internal and external surface quality, stable physical and chemical properties, and strong practicality, which is conducive to mass production.

[0066] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A method for manufacturing a Hastelloy UNS N06022 seamless heat exchanger tube, characterized in that, Specifically, the following steps are included: (a) The UNS N06022 hot extrusion billet undergoes incoming material inspection and internal and external surface grinding, specifically: the billet undergoes initial inspection + grinding + re-inspection, and during the re-inspection, each endoscope is randomly selected for PT (partial pressure measurement). (II) The tube blank obtained in step (I) is subjected to multiple passes of intermediate cold rolling. After each pass of cold rolling, the intermediate product must undergo degreasing, heat treatment, straightening, tube cutting, pickling, grinding, and inspection. During the cold rolling of the intermediate product, the cold rolling deformation is controlled between 45% and 65%, and the rolling speed and feed rate are controlled as follows: The rolling mill model is LG60 or LG110, the rolling speed is ≤80 times / min, and the feed rate is ≤3mm / time; For intermediate cold-rolled products, the Q value is controlled to be ≥0.95, and the deviations in outer diameter and wall thickness after rolling are controlled as follows: The rolling mill model is LG60 or LG110, with the outer diameter deviation controlled within ±0.5%Dmm and the wall thickness deviation controlled within ±5%Smm; The specific process for removing oil from the intermediate product is as follows: oil scraping with an oil scraper → oil removal in an alkaline tank → rinsing → soaking in a hot water tank → oil removal in an acid tank → rinsing → inspection; The intermediate product heat treatment is carried out in a roller hearth furnace with a slightly oxidizing gas atmosphere, a heat treatment temperature of 1150±10℃, and a holding time of 2.5 times the wall thickness. During the straightening of the intermediate product, the straightening parameters are controlled as follows: If the outer diameter of the intermediate steel pipe is >57mm, the straightening control speed is ≤6m / min, the curvature after straightening is ≤1.5mm / m, and the deviation of the outer diameter after straightening is ±0.05%Dmm; If the outer diameter of the intermediate steel pipe is ≤57mm, the straightening control speed is ≤8m / min, the curvature after straightening is ≤1mm / m, and the deviation of the outer diameter after straightening is ±0.05%Dmm; (iii) The steel pipe obtained in step (ii) is subjected to finished product cold rolling; During finished product rolling, the cold rolling deformation is 50%-65%, the rolling speed is controlled at ≤120 times / min, the feed rate is ≤2mm / time, and the Q value is ≥0.9; During the cold rolling of finished products, the outer diameter deviation after rolling is controlled within ±0.10mm, and the wall thickness deviation is controlled within ±0.10mm; Pre-degreasing is carried out simultaneously during the cold rolling of the finished product. Pre-degreasing involves wiping the outer surface of the finished tube after cold rolling with a cotton cloth soaked in acetone, and then punching the inner hole of the finished tube after cold rolling with a wool felt ball 2-3 times. (iv) The steel pipe obtained in step (iii) is degreased; The specific steps for degreasing the finished tubes are as follows: Step (3) Within 6 hours after pre-degreasing, scrape oil with an oil scraper → Within 6 hours after scraping oil, soak in an alkaline tank → Soak in a hot water tank → Wipe the outer surface → Apply wool felt balls to the inner wall → Check the degreasing quality of the inner hole for each FB tube. If there is a small amount of oil or oil film in the inner hole, clean the inner hole after cold internal polishing. (v) Perform finished product heat treatment on the steel pipe obtained in step (iv); The heat treatment of the finished products is carried out in a bright furnace with a pure hydrogen atmosphere. The heat treatment temperature of the finished product is controlled at 1150±10℃, and the holding time is 2.5 times the wall thickness. (vi) Straighten the steel pipe obtained in step (v); (vii) The steel pipe obtained in step (vi) is subjected to finished ultrasonic eddy current test, water pressure test and pipe cutting. Samples are taken during pipe cutting for physical and chemical tests. (viii) The steel pipes obtained in step (vii) are subjected to finished product surface inspection, dimensional inspection, cleaning, marking and finishing processes, and finally packaged and put into storage.

2. The method for manufacturing the Hastelloy UNS N06022 seamless heat exchange tube according to claim 1, characterized in that: In step (II), during the degreasing of the intermediate product in the alkaline tank, the composition of the solution in the alkaline tank is controlled by mass ratio as follows: degreasing agent: water = 1:20, alkaline tank temperature: 50-60℃, alkaline tank soaking time: 50-60min; When degreasing in the acid tank, the composition of the solution in the acid tank should be controlled by mass percentage as follows: HF: 1%, HNO3: 10-15%, and the remainder is tap water. The sum of the above components should be 100%. The acid tank temperature should be 55-60℃, and the acid washing time should be 20-35min.

3. The method for manufacturing the Hastelloy UNS N06022 seamless heat exchange tube according to claim 1, characterized in that: In step (ii) of pickling the intermediate product, the solution components in the acid tank are as follows by mass ratio: HF: 5-8%, HNO3: 10-15%, and the remainder is tap water. The sum of the above components is 100%. The temperature of the acid tank is controlled at 50-55℃, and the pickling time is 20-30 minutes.

4. The method for manufacturing the Hastelloy UNS N06022 seamless heat exchange tube according to claim 1, characterized in that: When grinding and inspecting intermediate products in step (II), the grinding process adopts the method of overall external polishing + local spot grinding. External polishing is carried out using a flap wheel, and local spot grinding is carried out using a polishing machine equipped with a flower-shaped flap wheel. Inspection is conducted by visual inspection and one endoscope at a time. Endoscopes with excessive visual inspection marks are re-polished externally. Internal polishing is performed using an automatic internal polishing machine with a cross-shaped polishing head made of sandpaper. After internal polishing, each endoscope is polished individually. Endoscopes that fail to meet the standards are re-polished internally at designated points.

5. The method for manufacturing the Hastelloy UNS N06022 seamless heat exchange tube according to claim 1, characterized in that: In step (iv), when degreasing the finished tube, the solution in the alkali tank is specified to be in the following mass ratio: degreasing agent: water = 1:6.

5. The alkali tank temperature is 40-60℃, and the alkali tank soaking time is 15-25 minutes. The hot water tank temperature is 70-80℃, and the hot water tank soaking time is 10-20 minutes. After the hot water tank is removed, the outer surface is wiped with a cotton cloth soaked in acetone, and the inner wall is wiped clean with a wool felt. This is repeated 3-5 times. After degreasing, the inner hole is manually inspected by FB. If there is no oil stain, oil spot, or oil film in the inner hole, heat treatment is performed. If there is an oil film or oil spot in the inner hole, it is cold-polished and cleaned, then put back into the original frame and FB is performed again. After FB is qualified, heat treatment is performed.

6. The method for manufacturing the Hastelloy UNS N06022 seamless heat exchange tube according to claim 1, characterized in that: In step (vi), the straightening machine speed is controlled to be ≤10m / min during the straightening of the finished tube, the curvature after straightening is ≤0.5mm / m, and the outer diameter deviation after straightening is ±0.01mm.

7. The method for manufacturing the Hastelloy UNS N06022 seamless heat exchange tube according to claim 1, characterized in that: In step (vii), the pass rate for a single ultrasound test is ≥95%, and the pass rate for a single eddy current test is 100%.

8. The method for manufacturing the Hastelloy UNS N06022 seamless heat exchange tube according to claim 1, characterized in that: In step (viii), the surface inspection of the finished tube shows that the inner and outer surfaces are smooth and the roughness Ra of the inner and outer walls is ≤0.

8.

9. The method for manufacturing the Hastelloy UNS N06022 seamless heat exchange tube according to claim 1, characterized in that: The finished pipe produced has the following tensile test results at room temperature: yield strength ≥330 MPa, tensile strength ≥750 MPa, and elongation after fracture ≥60%; and tensile test results at 250℃: yield strength ≥245 MPa, tensile strength ≥655 MPa.

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