A method for manufacturing UNS N06690 alloy seamless heat exchange tube

Abstract

The invention discloses a manufacturing method of a UNS N06690 alloy seamless heat exchange tube, belonging to the field of material processing technology, comprising: (1) peeling, PT inspection, shearing, centering, grinding, heating, perforating, water cooling and inspection of round steel material; (2) pickling the hot perforated blank, and then inspecting the incoming material and grinding the inner and outer surfaces; (3) cold rolling the intermediate product in two passes, and after the cold rolling, the intermediate product needs to be degreased, heat treated, straightened, cut, pickled, ground and inspected; (4) cold rolling the finished product; (5) degreasing the finished product; (6) heat treated the finished product; (7) straightening the finished product; (8) ultrasonic eddy current, water pressure and cutting the finished product, and sampling for physical and chemical testing during the cutting process; (9) surface inspection, dimension inspection, cleaning, spray marking and finishing the obtained steel pipe, and finally packaging and warehousing. The products produced by the method have a high one-time inspection pass rate and a high yield rate.

Description

Technical Field

[0001] The invention relates to a method for manufacturing a heat exchange tube, in particular to a method for manufacturing a UNS N06690 alloy seamless heat exchange tube, and belongs to the technical field of material processing. Background Art

[0002] N06690 is a high-temperature, corrosion-resistant alloy primarily composed of nickel, chromium, and iron. It exhibits excellent resistance to stress corrosion cracking, good metallurgical stability, and excellent processing properties, making it an ideal material for heat transfer tubes in pressurized water reactor steam generators in nuclear power plants. Thin-walled tubes made from this alloy are commonly formed domestically and internationally using a combination of hot extrusion / hot piercing and cold rolling. Currently, domestically produced seamless N06690 alloy heat exchange tubes suffer from low first-pass inspection rates, low yield rates, poor dimensional accuracy, and poor internal and external surface quality.

[0003] Patent CN115921573B discloses a method for manufacturing a UNS N10276 Hastelloy seamless heat exchange tube, which discloses the following steps: (1) subjecting the UNS N10276 hot extruded billet to incoming material inspection and grinding and repairing the inner and outer surfaces of the billet, specifically: subjecting the hot extruded billet to initial inspection + grinding and repairing + re-inspection, and subjecting a random inspection to PT during the re-inspection; (2) subjecting the billet obtained in step (1) to three passes of intermediate cold rolling, wherein each pass of cold rolling requires intermediate degreasing, intermediate heat treatment, intermediate straightening, intermediate pipe cutting, pickling, intermediate inspection and grinding and repairing; (3) subjecting the third pass of the steel pipe obtained in step (2) to finished product cold rolling; (4) subjecting the steel pipe obtained in step (3) to finished product degreasing; (5) subjecting the steel pipe obtained in step (4) to finished product heat treatment; (6) subjecting the steel pipe obtained in step (5) to finished product straightening; (7) subjecting the steel pipe obtained in step (6) to finished product ultrasonic eddy current and water pressure treatment. , cutting the pipe, taking samples for physical and chemical tests when cutting the pipe; (viii) subjecting the steel pipe obtained in step (vii) to finished product surface inspection, cleaning, spray marking and finishing processes, and finally packaging and warehousing; the products produced by this method have a high one-time inspection pass rate, a high yield rate, high dimensional accuracy, good internal and external surface quality, stable organizational performance, strong practicality, and are conducive to batch production; however, the intermediate product inspection and grinding in this patent are only simple grinding, the treatment is uneven, and it is easy to produce rough polishing marks, resulting in slight polishing marks on the surface of the finished product after cold rolling. The metallographic structure is not checked during the entire process, and the mechanical properties such as flaring and flattening and the intergranular corrosion performance cannot be guaranteed. In addition, one-time degreasing is used when degreasing the finished product, which leads to incomplete degreasing and the risk of nitriding.

[0004] Based on this, developing a manufacturing method for N06690 alloy seamless heat exchange tubes that can overcome the above-mentioned difficulties, and developing N06690 alloy seamless heat exchange tubes with a high first-time inspection pass rate, high yield rate, high dimensional accuracy, good internal and external surface quality, and physical and chemical properties that meet standard technical requirements has become a technical problem that needs to be urgently solved by technical personnel in this field. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of the above-mentioned existing technologies and propose a manufacturing method for UNSN06690 alloy seamless heat exchange tubes. The products manufactured by this manufacturing method have a high first-time inspection pass rate, a high yield rate, high dimensional accuracy, good internal and external surface quality, stable microstructure and performance, strong practicality, and are conducive to mass production.

[0006] The technical solution of the present invention to solve the above technical problems is:

[0007] A method for manufacturing a UNS N06690 alloy seamless heat exchange tube specifically comprises the following steps:

[0008] (1) UNS N06690 round steel is peeled, PT tested, sheared, centered, ground, heated, pierced, water-cooled, and tested. The piercing temperature is 1120-1130°C, the heating time is 180 minutes, and the holding time is 20 minutes.

[0009] (2) The UNS N06690 hot-pierced billet is pickled, and the pickled billet is subjected to incoming material inspection and internal and external surface grinding and repair. Specifically, the hot-pierced billet is subjected to initial inspection + grinding and repair + re-inspection. During the re-inspection, each endoscope is used and PT is randomly inspected;

[0010] (3) The tube blank obtained in step (2) is subjected to intermediate product cold rolling, and after cold rolling, the intermediate product needs to be degreased, heat treated, straightened, cut, pickled, ground and inspected, wherein:

[0011] When the intermediate product is cold rolled, the cold rolling deformation is controlled at 55%-65%, the rolling speed is controlled at ≤60 times / min, the feed amount is ≤3mm / time, the Q value is ≥1.10, the outer diameter deviation after rolling is controlled at ±0.5%Dmm, and the wall thickness deviation is controlled at ±5%Smm. The value is an integer multiple of 0.05, where D represents the outer diameter and S represents the wall thickness.

[0012] The specific process of degreasing intermediate products is: degreasing in an alkali tank → rinsing → soaking in a hot water tank → degreasing in an acid tank → rinsing → inspection;

[0013] The intermediate product heat treatment is carried out in a roller hearth furnace with a slightly oxidizing atmosphere, a heat treatment temperature of 1070±10℃, and a holding time ≥ wall thickness × 2min;

[0014] (4) cold rolling the steel pipe obtained in step (3);

[0015] When rolling finished products, the cold rolling deformation is 60%-70%, the rolling speed is controlled at ≤120 times / min, the feed amount is ≤2mm / time, and the Q value is ≥0.75;

[0016] When the finished product is cold rolled, the outer diameter deviation after rolling is controlled within ±0.05mm, and the wall thickness deviation is controlled within ±0.05mm;

[0017] (5) degreasing the steel pipe obtained in step (4);

[0018] The degreasing steps for finished pipes are as follows: soak in alkali tank → soak in hot water tank → wipe the outer surface → hit the inner wall with wool felt balls → inspect → soak in aerospace kerosene tank for 24 hours → soak in alkali tank → soak in hot water tank → wipe the outer surface → hit the inner wall with wool felt balls → inspect;

[0019] (6) subjecting the steel pipe obtained in step (5) to finished product heat treatment;

[0020] The heat treatment of finished products is carried out in a bright furnace with a pure hydrogen atmosphere;

[0021] When heat treating finished products, the heat treatment temperature is controlled at 1070±10℃, and the holding time is ≥ wall thickness × 2.5min;

[0022] (7) straightening the steel pipe obtained in step (6);

[0023] (8) subjecting the steel pipe obtained in step (7) to finished product ultrasonic eddy current, water pressure, and pipe cutting, and taking samples for physical and chemical testing during pipe cutting;

[0024] (9) The steel pipe obtained in step (8) is subjected to finished product surface inspection, dimension inspection, cleaning, label spraying and finishing processes, and finally packaged and stored.

[0025] The technical solution further defined in the present invention is:

[0026] Furthermore, in the aforementioned method for manufacturing UNS N06690 alloy seamless heat exchange tubes, in step (iii) of degreasing the intermediate product, the components of the solution in the alkali tank are controlled to be, by mass, degreasing agent (alkali powder): water = 1:7, the alkali tank temperature is 70-80°C, and the alkali tank immersion time is 40-60 minutes;

[0027] When degreasing the acid cylinder, the components of the solution in the acid cylinder are controlled in percentage by mass as follows: HF: 1%, HNO3: 10-15%, and the balance is tap water. The sum of the above components is 100%. The acid cylinder temperature is 60°C and the pickling time is 40-60 minutes.

[0028] In the aforementioned method for manufacturing UNS N06690 alloy seamless heat exchange tubes, during the straightening of the intermediate product in step (3), the straightening speed is controlled to be ≤8 m / min, the curvature after straightening is ≤1.0 mm / m, and the outer diameter deviation after straightening is ±0.02 mm.

[0029] Technical effect: The present invention stipulates the requirements for straightening speed, straightness and outer diameter deviation range after straightening, which ensures the curvature while avoiding the risks of iron rod straightening scratches and marks, thereby ensuring the straightening quality. Strictly stipulating the outer diameter deviation range after straightening can effectively avoid the risk of outer diameter deviation caused by straightening, thereby improving dimensional accuracy.

[0030] In the aforementioned method for manufacturing UNS N06690 alloy seamless heat exchange tubes, during the pickling of the intermediate product in step (3), the solution in the pickling vat comprises, by weight, 5-8% HF, 10-15% HNO3, and the balance tap water, the sum of which is 100%. The temperature of the pickling vat is controlled at 60°C, and the pickling time is 5-8 hours. After 5 hours of pickling, the vat is opened and inspected every 30 minutes for the inner and outer surfaces. Pickling is stopped when the inner and outer surfaces exhibit a uniform, lightly scaled appearance to avoid over-picking, which could affect subsequent work.

[0031] The present invention provides a method for pickling intermediate products in the first and second passes, including strict control of the acid tank ratio, temperature, and time to ensure pickling quality. Conventional N06690 pickling, in order to avoid over-acidification, often results in severe under-acidification, resulting in excessively thick oxide scale, low internal and external polishing efficiency, and a low pass rate for a single endoscopic inspection after polishing, requiring multiple rework and repairs. However, the N06690 intermediate product tubes washed using this method have only slightly uniform oxide scale on the inner and outer walls, no tendency towards over-acidification, high internal and external polishing efficiency, and a high pass rate for a single endoscopic inspection. This method significantly reduces manual polishing costs, improves production efficiency, and shortens the entire intermediate product production cycle.

[0032] In the manufacturing method of the aforementioned UNS N06690 alloy seamless heat exchange tube, during the first cold rolling and inspection of the intermediate product in step (iii), the grinding and inspection adopts the method of internal and external polishing followed by local spot grinding, the external polishing adopts a thousand-blade wheel for external polishing, the internal polishing adopts an automatic internal polishing machine with a cross polishing head made of sandpaper, the local spot grinding adopts a polishing machine equipped with a patterned impeller, and the inspection adopts visual inspection + endoscope for each. During the second intermediate product grinding and inspection, the grinding and inspection adopts the method of internal and external polishing followed by local spot grinding, the external polishing adopts a belt polishing machine for external polishing, the internal polishing adopts artificial sandpaper for internal polishing, the local spot grinding adopts a polishing machine equipped with a soft-edged patterned impeller, and the inspection adopts visual inspection + endoscope for each. After the internal and external grinding and inspection, the qualified pipes are randomly inspected for metallographic structure according to the frame number to ensure that there is no metallographic precipitation and then arranged for circulation. The aforementioned UNS In the manufacturing method of N06690 alloy seamless heat exchange tube, when the finished tube is degreased once in step (5), the solution in the alkali tank is calculated by mass ratio of degreasing agent: water = 1:6.5, the alkali tank temperature is: 40-60℃, the alkali tank immersion time is: 30-60min, the hot water tank temperature is: 70-80℃, the hot water tank immersion time is: 10-20min, after the hot water tank is taken out of the tank, the outer surface is wiped with a cotton cloth soaked in acetone, and the inner wall is cleaned with wool felt, and the number of times is 3- 5 times; after the first degreasing, transfer to the aerospace kerosene tank and soak for 24 hours before secondary degreasing. The mass ratio of the solution in the secondary degreasing alkali tank is degreaser: water = 1:6.5, alkali tank temperature: 40-60℃, alkali tank soaking time: 20-40min, hot water tank temperature: 70-80℃, hot water tank soaking time: 5-10min. After the hot water tank is taken out of the tank, wipe the outer surface with cotton cloth soaked in acetone, and beat the inner wall with wool felt until it is clean. The number of times is 2-4 times.

[0033] Technical effect: The present invention can improve the final degreasing quality of the finished product by performing a process of degreasing once, soaking in a kerosene cylinder, and then degreasing twice for high value-added nickel-based products, especially small-diameter heat exchange tubes with crystal corrosion requirements. The difficult-to-remove oil molecules remaining after soaking in a kerosene cylinder and cold rolling are similarly dissolved for 24 hours and then degreasing twice, which can greatly improve the degreasing quality of the finished product and avoid the phenomenon of some residual oil, oil spots, oil film, etc. due to unclean degreasing, which leads to the risk of nitriding in the heat treatment of the finished product, and ultimately leads to the risk of unqualified metallographic structure, mechanical properties and crystal corrosion performance of the finished product. The secondary degreasing process and the finished product heat treatment are combined in a pure hydrogen atmosphere, which helps to improve the final physical and chemical properties of the high value-added nickel-based alloy small-diameter heat exchange tube.

[0034] In the aforementioned method for manufacturing UNS N06690 alloy seamless heat exchange tubes, a plastic roller straightener is used for straightening the finished tube in step (seven), the straightener speed is controlled to be ≤10m / min, the curvature after straightening is ≤0.5mm / m, and the outer diameter deviation after straightening is ±0.01mm.

[0035] The present invention provides technical benefits by specifying the straightening machine model, straightening speed, straightness, and the deviation range of the outer diameter after straightening. The straightening of finished products requires the use of a plastic roller straightener at a straightening speed of ≤10 m / min. This ensures curvature while avoiding the risk of iron rod straightening scratches and marks, thus guaranteeing the quality of the finished product. Strictly specifying the deviation range of the outer diameter of the finished product after straightening effectively avoids the risk of outer diameter deviation caused by straightening, thereby improving dimensional accuracy.

[0036] In the aforementioned method for manufacturing the UNS N06690 alloy seamless heat exchange tube, the first ultrasonic qualified rate in step (eight) is ≥96%, and the first eddy current qualified rate is 100%.

[0037] In the aforementioned method for manufacturing UNS N06690 alloy seamless heat exchange tubes, the surface inspection in step (9) includes visual and dimensional inspections, with a pass rate of ≥95%. The dimensional accuracy of the finished tube is controlled to: outer diameter ±0.05 mm, wall thickness ±0.05 mm, and the inner and outer surfaces of the finished tube are smooth, with an inner and outer wall roughness Ra ≤0.8.

[0038] In the aforementioned method for manufacturing the UNS N06690 alloy seamless heat exchange tube, the finished tube obtained by room temperature tensile test has the following results: yield strength of 280-320 MPa, tensile strength of 640-680 MPa, and elongation after fracture ≥55%.

[0039] The beneficial effects of the present invention are:

[0040] The present invention adopts three cold rolling passes, wherein the first and second passes are intermediate product cold rolling, and the cold rolling deformation is controlled at 55%-65%, and the third pass is finished product cold rolling, and the cold rolling deformation is controlled at 60%-70%. Multiple rolling passes can fully crush the grains, and a finer grain size can be obtained after heat treatment. The first and second intermediate product cold rolling passes ensure surface quality by strictly controlling the feed amount ≤3mm / time, and by controlling the Q value ≥1.10, the deformation is made more uniform, thereby improving dimensional accuracy; similarly, the finished product cold rolling ensures surface quality and dimensional accuracy by strictly controlling the feed amount ≤2mm / time and controlling the Q value ≥0.75.

[0041] The present invention provides methods for degreasing intermediate products in steps 1 and 2, including strict control of the solution ratio, temperature, and time in the alkali and acid tanks to ensure degreasing quality and avoid the risk of carburization during heat treatment. A method for degreasing finished products in steps 3 is also provided, including degreasing in an alkali tank, soaking in a clean water tank, wiping the outer surface with acetone, and cleaning the inner wall with an acetone-soaked cloth. Strict control of the alkali tank ratio, temperature, and time, as well as the inner and outer wall cleaning methods, ensures degreasing quality of the finished pipe and ensures that there is no risk of nitriding during the bright heat treatment of the finished product.

[0042] The present invention stipulates that the solution heat treatment of the intermediate products of the 1st and 2nd passes is carried out in a roller hearth furnace, the atmosphere in the furnace is slightly oxidizing, the heat treatment temperature is 1070±10°C, the cold rolling work hardening is eliminated, the seamless pipe has good plasticity, and the subsequent cold rolling forming is convenient; the holding time of the intermediate products of the 1st and 2nd passes is ≥ wall thickness × 2min, generally the nearest integer is taken, the holding time is slightly longer, the oxide scale is more uniform and loose, and the oxide scale is easy to be removed by pickling; the solution heat treatment of the finished product of the 3rd pass is carried out in a bright furnace, the atmosphere in the furnace is pure hydrogen, the heat treatment temperature is 1070±10°C, and the holding time of the finished product is ≥ wall thickness × 2.5min, the purpose is to obtain good organization and comprehensive mechanical properties while ensuring the brightness of the surface color of the heat exchange tube and the consistency of the overall color.

[0043] This invention specifies methods for grinding and repairing hot-pierced billets and intermediate steel pipes. Re-inspection and random PT (PT) of hot-pierced billets ensures that no cracks remain on the outer surface. Endoscopic examination of each hot-pierced billet allows for more precise and efficient treatment of inner wall defects, preventing them from being transferred to the next cold rolling process and causing them to extend. Endoscopic examination of each intermediate product during grinding and repair ensures the inner wall quality of the finished cold-rolled product, reducing the risk of endoscopic failure due to ultrasonic internal damage and inner wall defects, thereby improving the final ultrasonic pass rate, surface inspection pass rate, and final yield rate.

[0044] Compared with the prior art, the present invention adds equipment and methods for grinding intermediate products. Belt polishing is used in the previous pass of the finished product, which is more uniform than the external polishing with a flap wheel, and will not produce rough polishing marks, which will lead to slight polishing marks on the surface of the finished product after cold rolling. Metallographic inspection is performed on the incoming intermediate product before the cold rolling of the finished product, and in order to ensure the degreasing quality of the finished product, the finished product is degreased once and then soaked in a kerosene tank for 24 hours before undergoing a second degreasing. This is to ensure that there is no risk of nitriding after the finished product is heat treated, and to ensure the metallographic structure while also ensuring mechanical properties such as flaring and flattening and intergranular corrosion resistance.

[0045] The method of the present invention solves the problems of low first-time inspection pass rate, low material yield rate, low dimensional accuracy and poor internal and external surface quality by strictly limiting the process optimization of UNS N06690 alloy seamless heat exchange tubes. The products produced by the method have a high first-time inspection pass rate, a high material yield rate, high dimensional accuracy, good internal and external surface quality, stable mechanical properties, strong practicality, and are conducive to mass production.

[0046] The N06690 alloy seamless heat exchange tube prepared by the method of the present invention has a first ultrasonic qualified rate of ≥96%, a first eddy current qualified rate of 100%, a first surface inspection (visual inspection + dimension inspection) qualified rate ≥95%, and a comprehensive first inspection qualified rate (ultrasonic qualified rate×eddy current qualified rate×surface inspection qualified rate) ≥91%.

[0047] The yield rate of the N06690 alloy seamless heat exchange tube prepared by the method of the present invention (round steel → finished tube) is ≥78%. The prepared N06690 alloy seamless heat exchange tube can meet the following dimensional accuracy: outer diameter ±0.05 mm, wall thickness ±0.05 mm. The inner and outer surfaces of the prepared seamless heat exchange tube are smooth and have consistent color, and the inner and outer wall roughness Ra is ≤0.8. The room temperature tensile test shows: the yield strength is 280-320 MPa, the tensile strength is 640-680 MPa, and the elongation after fracture is ≥55%. DETAILED DESCRIPTION

[0048] The present invention will be described clearly and completely below with reference to specific embodiments. It should be understood that the embodiments described are merely some, and not all, of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0049] Example 1

[0050] This embodiment provides a method for manufacturing a UNS N06690 alloy seamless heat exchange tube. The finished product has specifications of φ25×3×7864 mm and technical requirements that meet both ASME SB163-2021 and NB / T47019.9-2021 standards. The method specifically includes the following steps:

[0051] (1) UNS N06690 Yongxing round steel is peeled, PT tested, sheared, centered, ground, heated, pierced, water-cooled, and tested. The piercing temperature is 1120-1130°C, the piercing size is φ95×12mm, the heating time is 180 minutes, and the holding time is 20 minutes.

[0052] (2) The UNS N06690 hot-pierced billets are pickled, and the pickled billets are subjected to incoming material inspection and internal and external surface grinding and repair. The hot-pierced billets are subjected to initial inspection + grinding and repair + re-inspection. During the re-inspection, endoscopes are used for each billet, and PT is performed on random inspections. Specifically, the defects of the billet and its grinding and repair method are preliminarily characterized. For the outer surface hot-piercing defects of the billet, spot grinding + external polishing are performed on it. For some billets with inner burrs and transverse cracks, internal polishing is performed on them. After the billet is ground, it is re-inspected. During the re-inspection, random inspections are performed on it. Only those that pass the re-inspection can be circulated. Unqualified products are subjected to secondary grinding;

[0053] (3) The tube obtained in step (2) is subjected to two passes of intermediate cold rolling. After each pass of cold rolling, the intermediate product is required to be degreased, heat treated, straightened, cut, pickled, ground (local spot grinding after internal and external polishing) and inspected (endoscope for each product), wherein:

[0054] When cold rolling intermediate products, the cold rolling deformation is controlled at 55%-65%, the rolling speed is controlled at ≤60 times / min, the feed amount is ≤3mm / time, the Q value is ≥1.10, the outer diameter deviation after rolling is controlled at ±0.5%Dmm, and the wall thickness deviation is controlled at ±5%Smm. The value is an integer multiple of 0.05, where D represents the outer diameter and S represents the wall thickness.

[0055] The specific process of degreasing intermediate products is: degreasing in an alkali tank → rinsing → soaking in a hot water tank → degreasing in an acid tank → rinsing → inspection;

[0056] The intermediate product heat treatment is carried out in a roller hearth furnace with a slightly oxidizing atmosphere, a heat treatment temperature of 1070±10℃, and a holding time ≥ wall thickness × 2 min (rounded to the nearest integer).

[0057] (4) cold rolling the steel pipe obtained in step (3);

[0058] When rolling finished products, the cold rolling deformation is 60%-70%, the rolling speed is controlled at ≤120 times / min, the feed amount is ≤2mm / time, and the Q value is ≥0.75;

[0059] When the finished product is cold rolled, the outer diameter deviation after rolling is controlled within ±0.05mm, and the wall thickness deviation is controlled within ±0.05mm;

[0060] (5) degreasing the steel pipe obtained in step (4);

[0061] The steps for degreasing finished pipes are as follows: soaking in an alkali tank → soaking in a clean water tank → wiping the outer surface → taping the inner wall with cloth → inspection;

[0062] (6) subjecting the steel pipe obtained in step (5) to finished product heat treatment;

[0063] The heat treatment of finished products is carried out in a bright furnace with a pure hydrogen atmosphere;

[0064] When heat treating finished products, the heat treatment temperature is controlled at 1070±10℃, and the holding time is ≥ wall thickness × 2.5min (rounded up);

[0065] (7) straightening the steel pipe obtained in step (6);

[0066] (8) subjecting the steel pipe obtained in step (7) to finished product ultrasonic eddy current, water pressure, and pipe cutting, and taking samples for physical and chemical testing during pipe cutting;

[0067] (9) The steel pipe obtained in step (8) is subjected to finished product surface inspection, dimension inspection, cleaning, label spraying and finishing processes, and finally packaged and stored.

[0068] In this embodiment, the cold rolling process for UNS N06690 seamless heat exchange tubes strictly controls the cold rolling deformation of intermediate and finished products. A reasonable rolling speed and relatively small feed rate are selected to ensure the quality of the internal and external surfaces. The Q value is controlled to ensure structural uniformity in the wall thickness direction, thereby improving dimensional accuracy and inner wall quality. Specific cold rolling parameters are shown in Table 1 below, and the technical requirements and actual dimensions are shown in Table 2. As can be seen from Table 2, the dimensional accuracy of the intermediate and finished tubes at each pass meets internal control requirements, and the dimensional accuracy of the finished tubes is much higher than the standard requirements for Class I heat exchange tubes in ASME SB163-2021 and NB / T47019.1-2021.

[0069] Table 1 UNS N06690 cold rolling parameters

[0070]

[0071] Table 2 UNS N06690 technical requirements dimensional accuracy and actual measured dimensions

[0072]

[0073] The specific degreasing process for the intermediate product of UNS N06690 alloy seamless heat exchange tube in this embodiment is as follows: degreasing in an alkali tank → rinsing → soaking in a hot water tank → degreasing in an acid tank → rinsing → inspection. The main control requirements for degreasing the intermediate product are shown in Table 3. The specific degreasing steps for the finished tube are as follows: soaking in an alkali tank → soaking in a hot water tank → wiping the outer surface → applying wool felt balls to the inner wall → inspection → soaking in an aerospace kerosene tank for 24 hours →

[0074] Soak in alkali tank → Soak in hot water tank → Wipe outer surface → Beat inner wall with wool felt ball → Inspection. The main control requirements for degreasing finished pipes are shown in Table 4. The inner and outer surfaces of the pipes obtained by degreasing according to the above method are clean and free of oil stains, and there is no risk of nitriding during heat treatment.

[0075] Table 3 Main control requirements for UNS N06690 intermediate product degreasing process

[0076]

[0077] Table 4 Main control requirements for degreasing process of UNS N06690 finished pipes

[0078]

[0079] Table 4 shows that after primary degreasing, finished pipes were transferred to a cylinder of aerospace kerosene for 24 hours before undergoing secondary degreasing. After secondary degreasing, technicians confirmed the quality of the degreasing on both the inner and outer surfaces before proceeding to heat treatment. The outer surface was wiped with a white cloth to ensure no blackening, and the inner surface was inspected with an endoscopic lens to confirm the absence of oil stains, oil spots, or oil film. In this example, intermediate heat treatment of UNS N06690 alloy seamless heat exchange tubes was performed in a roller-hearth furnace with an oxidizing atmosphere; the finished product was heat treated in a bright furnace with a pure hydrogen atmosphere. The heat treatment schedule is shown in Table 5.

[0080] 5UNS N06690 heat treatment system

[0081]

[0082] It can be seen from Table 5 that the solution heat treatment of the intermediate product is carried out in a roller hearth furnace with a slightly oxidizing atmosphere. The furnace has 6 temperature zones, the first three temperature zones T01-T03 are heating zones, and the last three temperature zones T04-T06 are holding zones. The heat treatment temperature is 1070°C, and the holding time is 14min and 9min respectively. The cooling method is water cooling. The finished product heat treatment is bright heat treatment. The furnace atmosphere is pure hydrogen. The furnace has 5 temperature zones, T01-T02 are heating zones, T03-T05 are holding zones, the heat treatment temperature is 1070°C, the holding time is 8min, and the cooling method is water jacket cooling.

[0083] Table 6 shows the straightening parameters for intermediate and finished UNS N06690 seamless heat exchange tubes in this example. By specifying the straightening machine model, straightening speed, straightness, and the outer diameter deviation range after straightening, and specifically specifying the use of a plastic roller straightener and a straightening speed of ≤10 m / min for finished product straightening, the curvature is guaranteed while avoiding the risks of iron rod straightening scratches and marks, thereby ensuring the quality of the finished product. Strictly specifying the outer diameter deviation range after straightening, especially for finished product straightening, effectively avoids the risk of outer diameter deviation caused by straightening, thereby improving dimensional accuracy.

[0084] Table 6 UNS N06690 straightening parameters

[0085]

[0086] In Example 1, the requirements for cutting the intermediate and finished UNS N06690 alloy seamless heat exchange tubes are shown in Table 7. By strictly controlling the amount of flattened ends and adhering to the intermediate cutting method, the intermediate position must be manually measured and marked before cutting the tube, and visual inspection is not allowed. This can reduce the risk of the intermediate and finished tubes being underlength, and improve the final product inspection pass rate and final yield rate.

[0087] Table 7 UNS N06690 pipe cutting requirements

[0088]

[0089] In Example 1, the key control requirements for pickling intermediate products of UNS N06690 alloy seamless heat exchange tubes are shown in Table 8 below. These include strict control of the acid bath ratio, temperature, and time to ensure pickling quality. Conventional N06690 pickling, to avoid over-acidification, often results in severe under-acidification, leading to excessively thick scales, inefficient internal and external polishing, and a low pass rate for a single endoscopic inspection after polishing, necessitating multiple rework and repairs. However, this method produces N06690 intermediate product tubes with only a slight, uniform scale on both the inner and outer surfaces, with no tendency towards over-acidification. This method also improves internal and external polishing efficiency and a high pass rate for a single endoscopic inspection, significantly reducing manual polishing costs, improving production efficiency, and shortening the entire intermediate product production cycle.

[0090] Table 8 Main control requirements for the pickling process of UNS N06690 intermediate products

[0091]

[0092] In Example 1, the inspection and grinding requirements for UNS N06690 seamless heat exchange tube perforated billets and intermediate product tubes are shown in Table 9. Re-inspection and random PT checks of hot perforated billets ensure that no cracks remain on the outer surface. Endoscopic examination of each hot perforated billet allows for more accurate and efficient treatment of inner wall defects, preventing them from transferring to the next cold rolling process and causing them to extend. Endoscopic examination of each billet during the first and second intermediate product grinding passes ensures the inner wall quality of the finished cold-rolled product, reducing the risk of endoscopic failures due to ultrasonic internal damage and inner wall defects, thereby improving the final ultrasonic pass rate, surface inspection pass rate, and final yield rate.

[0093] Table 9 UNS N06690 grinding and repairing operation requirements

[0094]

[0095] When grinding and inspecting the intermediate products after the first cold rolling in Table 9 above, the grinding is carried out by polishing the inside and outside and then spot grinding. The external polishing is carried out by a flap wheel, and the internal polishing is carried out by an automatic internal polishing machine with a cross polishing head made of sandpaper. The local spot grinding is carried out by a polishing machine with a patterned impeller. The inspection is carried out by visual inspection and endoscope one by one.

[0096] During the second round of intermediate product grinding and inspection, the grinding is carried out by internal and external polishing followed by local spot grinding. The external polishing is carried out with a belt polishing machine, the internal polishing is carried out with artificial sandpaper, and the local spot grinding is carried out with a grinder equipped with a soft-edged impeller. The inspection is carried out visually + through an endoscope one by one. After the internal and external grinding and inspection are completed, the metallographic structure of the pipes that have passed the inspection is randomly inspected according to the frame number to ensure that there is no metallographic precipitation before arrangement for circulation.

[0097] In this Example 1, the ultrasonic, eddy current, water pressure, visual, and dimensional inspection results of the finished UNS N06690 alloy seamless heat exchange tubes are shown in Table 10. As can be seen from Table 10, the ultrasonic pass rate of the N06690 alloy seamless heat exchange tubes produced by this production method is as high as 96.71%, the eddy current and water pressure pass rates are both 100.00%, and the dimensional inspection pass rate is also 100.00%. The dimensional accuracy is much higher than the dimensional accuracy specified in the ASME SB163-2021 and NB / T47019.9-2021 standards. The visual inspection pass rate is as high as 95.97%, and the primary inspection pass rate is as high as 93.55%.

[0098] Table 10: Ultrasonic, eddy current, water pressure, visual and dimensional inspection results for UNS N06690 finished pipes

[0099]

[0100] In Example 1, the yield rate of UNS N06690 alloy seamless heat exchange tubes is shown in Table 11. 83.92 tons of round steel were collected for hot-piercing billets, and 5,150 finished products with a diameter of 25×2.1×7864 mm were put into storage, weighing 66.82 tons, with a yield rate of up to 79.62%.

[0101] Table 11 UNS N06690 yield rate

[0102]

[0103] The room temperature tensile properties of finished tubes were tested using ASTM E8, with the test results shown in Table 12. Table 12 shows that the N06690 alloy seamless heat exchange tubes manufactured using this method exhibit excellent mechanical properties. The yield strength across 39 heat batches ranged from 282 to 318 MPa, exceeding the ASME SB163-2021 standard requirement of ≥240 MPa. The tensile strength remained stable at 641 to 678 MPa, exceeding the standard requirement of ≥586 MPa. The elongation after fracture was ≥55%, significantly exceeding the standard requirement of ≥30%.

[0104] Table 12 UNS N06690 finished pipe room temperature tensile properties

[0105]

[0106] Flaring tests conducted according to GB / T 242-2007 revealed no cracks in all 39 batches of N06690 alloy tubes. Flattening tests conducted according to GB / T 246-2017 revealed no cracks in all 39 batches of N06690 alloy tubes.

[0107] According to the requirements of the technical agreement, all batches of N06690φ25×3 steel pipes were subjected to crystal corrosion tests according to the GB / T 15260-2016B method. The crystal corrosion test results are shown in Table 2.15 below.

[0108] Table 13 UNS N06690 crystal corrosion test results

[0109] Crystal rot test Test solution Test cycle Test results GB / T 15260-2016 Method B <![CDATA[Cu-CuSO4-16%H2SO4]]> 24 hours No cracks in flattening test

[0110] The present invention solves the problems of low first-time inspection pass rate, low yield rate, low dimensional accuracy, and poor internal and external surface quality by strictly limiting the process optimization of UNS N06690 alloy seamless heat exchange tubes. As shown in Tables 10-13, the products produced by this method have a high first-time inspection pass rate, a high yield rate, high dimensional accuracy, good internal and external surface quality, stable mechanical properties, strong practicality, and are conducive to mass production.

[0111] In addition to the above embodiments, the present invention may also have other implementations. Any technical solution formed by equivalent replacement or equivalent transformation falls within the scope of protection required by the present invention.

Claims

1. A method for manufacturing a UNS N06690 alloy seamless heat exchange tube, characterized in that: The specific steps include: (1) UNS N06690 round steel is peeled, PT tested, sheared, centered, ground, heated, pierced, water-cooled, and tested. The piercing temperature is 1120-1130°C, the heating time is 180 minutes, and the holding time is 20 minutes. (2) The UNS N06690 hot-pierced billet is pickled, and the pickled billet is subjected to incoming material inspection and internal and external surface grinding and repair. Specifically, the hot-pierced billet is subjected to initial inspection + grinding and repair + re-inspection. During the re-inspection, each endoscope is used and PT is randomly inspected; (3) The tube blank obtained in step (2) is subjected to two passes of intermediate cold rolling. After each pass of cold rolling, the intermediate product is required to be degreased, heat treated, straightened, cut, pickled, ground and inspected, wherein: When the intermediate product is cold rolled, the cold rolling deformation is controlled at 55%-65%, the rolling speed is controlled at ≤60 times / min, the feed amount is ≤3mm / time, the Q value is ≥1.10, the outer diameter deviation after rolling is controlled at ±0.5%Dmm, and the wall thickness deviation is controlled at ±5%Smm; The specific process of degreasing the intermediate product is: degreasing in an alkali tank → rinsing → soaking in a hot water tank → degreasing in an acid tank → rinsing → inspection; The intermediate product is heat treated in a roller hearth furnace with a slightly oxidizing atmosphere at a temperature of 1070±10°C and a holding time of ≥ wall thickness × 2 min. When grinding and inspecting the intermediate products after the first cold rolling, the grinding is carried out by polishing the inside and outside and then spot grinding. The external polishing is done by a flap wheel, and the internal polishing is done by an automatic internal polishing machine with a cross polishing head made of sandpaper. The local spot grinding is done by a polishing machine equipped with a patterned impeller. The inspection is done by visual inspection and endoscope one by one. During the second pass of intermediate product grinding and inspection, the grinding is carried out by internal and external polishing followed by local spot grinding. The external polishing is carried out by a belt polishing machine, the internal polishing is carried out by artificial sandpaper, and the local spot grinding is carried out by a polishing machine equipped with a soft-edge impeller. Inspection is carried out by visual inspection + endoscope one by one. After the internal and external grinding and inspection, the metallographic structure of the pipes that have passed the inspection is randomly inspected according to the frame number to ensure that there is no metallographic precipitation before they are arranged for circulation; (4) cold rolling the steel pipe obtained in step (3); When rolling finished products, the cold rolling deformation is 60%-70%, the rolling speed is controlled at ≤120 times / min, the feed amount is ≤2mm / time, and the Q value is ≥0.75; When the finished product is cold rolled, the outer diameter deviation after rolling is controlled within ±0.05mm, and the wall thickness deviation is controlled within ±0.05mm; (5) degreasing the steel pipe obtained in step (4); The degreasing steps for finished pipes are as follows: soak in alkali tank → soak in hot water tank → wipe the outer surface → hit the inner wall with wool felt balls → inspect → soak in aerospace kerosene tank for 24 hours → soak in alkali tank → soak in hot water tank → wipe the outer surface → hit the inner wall with wool felt balls → inspect; When the finished pipe is degreased for the first time, the mass ratio of the solution in the alkali cylinder is, degreasing agent: water = 1:6.5, the temperature of the alkali cylinder is 40-60℃, the soaking time in the alkali cylinder is 30-60min, the temperature of the hot water cylinder is 70-80℃, the soaking time in the hot water cylinder is 10-20min, after the hot water cylinder is taken out of the cylinder, the outer surface is wiped with a cotton cloth soaked in acetone, and the inner wall is cleaned with wool felt, the number of times is 3-5 times, after the first degreasing, it is transferred to the aerospace kerosene cylinder and soaked for 24h before the second degreasing, the mass ratio of the solution in the second degreasing alkali cylinder is, degreasing agent: water = 1:6.5, the temperature of the alkali cylinder is 40-60℃, the soaking time in the alkali cylinder is 20-40min, the temperature of the hot water cylinder is 70-80℃, the soaking time in the hot water cylinder is 5-10min, after the hot water cylinder is taken out of the cylinder, the outer surface is wiped with a cotton cloth soaked in acetone, and the inner wall is cleaned with wool felt, the number of times is 2-4 times; (6) subjecting the steel pipe obtained in step (5) to finished product heat treatment; The heat treatment of finished products is carried out in a bright furnace with a pure hydrogen atmosphere; When heat treating finished products, the heat treatment temperature is controlled at 1070±10℃, and the holding time is ≥ wall thickness × 2.5min; (7) straightening the steel pipe obtained in step (6); (8) subjecting the steel pipe obtained in step (7) to finished product ultrasonic eddy current, water pressure, and pipe cutting, and taking samples for physical and chemical testing during pipe cutting; (9) The steel pipes obtained in step (8) are subjected to finished product surface inspection, dimension inspection, cleaning, labeling and finishing processes, and finally packaged and stored.

2. The method for manufacturing a UNS N06690 alloy seamless heat exchange tube according to claim 1, characterized in that: In the step (iii) of degreasing the intermediate product, when degreasing the alkali tank, the components of the solution in the alkali tank are controlled to be in the following mass ratio: degreasing agent: water = 1:7, the alkali tank temperature is 70-80°C, and the alkali tank soaking time is 40-60 minutes; When degreasing the acid cylinder, the components of the solution in the acid cylinder are controlled in percentage by mass as follows: HF: 1%, HNO3: 10-15%, and the remainder is tap water. The sum of the above components is 100%. The acid cylinder temperature is 60°C and the pickling time is 40-60 minutes.

3. The method for manufacturing a UNS N06690 alloy seamless heat exchange tube according to claim 1, characterized in that: When straightening the intermediate product in step (3), the straightening control speed is ≤8m / min, the curvature after straightening is ≤1.0mm / m, and the outer diameter deviation after straightening is ±0.02mm.

4. The method for manufacturing a UNS N06690 alloy seamless heat exchange tube according to claim 1, characterized in that: During the pickling of the intermediate product in step (iii), the components of the solution in the acid tank are calculated by mass ratio as follows: HF: 5-8%, HNO3: 10-15%, and the balance is tap water. The sum of the above components is 100%. The temperature of the acid tank is controlled at 60°C, and the pickling time is 5-8 hours.

5. The method for manufacturing a UNS N06690 alloy seamless heat exchange tube according to claim 1, characterized in that: In the step (seven), when straightening the finished pipe, the straightening machine is controlled to have a speed of ≤10 m / min, a curvature after straightening of ≤0.5 mm / m, and an outer diameter deviation after straightening of ±0.01 mm.

6. The method for manufacturing a UNS N06690 alloy seamless heat exchange tube according to claim 1, characterized in that: In the step (eight), the first ultrasonic qualified rate is ≥96%, and the first eddy current qualified rate is 100%.

7. The method for manufacturing a UNS N06690 alloy seamless heat exchange tube according to claim 1, characterized in that: The room temperature tensile test of the manufactured finished pipe shows: yield strength 280-320 MPa, tensile strength 640-680 MPa, and elongation after fracture ≥55%.

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