A rapid passivation method for the inner surface of BFe30-1-1 copper-nickel alloy heat exchange pipe

Abstract

A rapid passivation method for the inner surface of BFe30-1-1 copper-nickel alloy heat exchanger tubes is disclosed. This method solves the severe corrosion problem caused by local defects in the protective film on the inner surface of the tubes in existing technologies. The method includes: whole-machine sandblasting, degreasing, water washing, and seawater film formation, simultaneously with film formation on a sample tube. Key parameters include sandblasting pressure of 0.6~0.8MPa, sand material of F24 mesh brown corundum, seawater flow velocity of 1.5~1.7m / s, and film formation period ≥30 days. The passivation film formed by this invention has a strong corrosion inhibition effect, exhibiting excellent corrosion resistance and stability. It achieves comprehensive and long-term protection for the inner surface of the heat exchanger tube, eliminates the "large cathode-small anode" galvanic corrosion cell caused by local defects in the film layer, effectively suppresses local corrosion tendency and pitting sensitivity, and ultimately significantly improves the corrosion resistance of the heat exchanger tube, extends its service life, and ensures the long-term operational safety and reliability of the entire heat exchanger.

Description

Technical Field

[0001] This invention specifically relates to a rapid passivation method for the inner surface of a BFe30-1-1 copper-nickel alloy heat exchanger tube. Background Technology

[0002] The corrosion resistance of BFe30-1-1 copper-nickel alloy in seawater environments directly depends on the formation kinetics, structural integrity, and self-healing ability of its protective passivation film. Initially, before the passivation film is fully established, the alloy is in an activated state, exhibiting a relatively negative self-corrosion potential, a high instantaneous corrosion rate, and a significant anodic dissolution current density. However, once a dense and complete passivation film is successfully constructed, it acts as an effective physical barrier, significantly inhibiting the dissolution and mass transfer of metal ions from the alloy matrix into the electrolyte (seawater). Simultaneously, the diffusion of corrosive media (such as dissolved oxygen) from seawater to the matrix surface must also pass through this film layer, thus being greatly hindered. This synergistic effect increases the resistance to charge transfer and mass transport, ultimately resulting in a sharp decrease in the corrosion electrochemical reaction rate, a positive shift in the self-corrosion potential, and a significant reduction in both the instantaneous corrosion rate and the anodic polarization current density.

[0003] However, the integrity of the protective film is crucial. Localized defects or damage to the protective film significantly increase the susceptibility of BFe30-1-1 copper-nickel alloy to localized corrosion (such as pitting), leading to a substantial reduction in its pitting resistance. The mechanism of this phenomenon lies in the formation of a typical galvanic corrosion cell in the defect area: a large area of ​​intact passivation film acts as the cathode, while the exposed micro-defects act as the active anode. This extreme cathode / anode area ratio results in a significant amplification of the corrosion current density in the anodic region, thereby accelerating the dissolution of localized metal and ultimately initiating and exacerbating localized corrosion.

[0004] Given the dynamic characteristics of the protective film formation process of BFe30-1-1 copper-nickel alloy in seawater, BFe30-1-1 copper-nickel alloy tubes, which are currently widely used in heat exchange equipment, are highly susceptible to significant corrosion during the initial service phase or before the protective film has stabilized. This initial corrosion not only leads to rapid thinning of the heat exchanger tubes, severely shortening their designed service life, but may also cause a series of problems such as decreased heat transfer efficiency, media leakage, and even equipment failure, posing a significant threat to the operational reliability and safety of the heat exchange system.

[0005] It is evident that the key deficiency of existing technology lies in its inability to ensure the high quality and integrity of the protective film on the inner surface of BFe30-1-1 copper-nickel alloy tubes. Localized film defects can create a severe corrosion galvanic couple of "large cathode - small anode," causing corrosion to concentrate at the defect points and significantly increasing the risk of localized corrosion (especially pitting corrosion). This microscopic failure mechanism manifests macroscopically as a decrease in the corrosion resistance of the heat exchange tubes, a shortened service life, and ultimately jeopardizes the operational safety of the entire heat exchange system. Summary of the Invention

[0006] The purpose of this invention is to solve the serious corrosion problem caused by local defects in the protective film on the inner surface of the tube in the prior art, and to provide a rapid passivation method for the inner surface of BFe30-1-1 copper-nickel alloy heat exchange tubes.

[0007] A rapid passivation method for the inner surface of a BFe30-1-1 copper-nickel alloy heat exchanger tube, which is implemented according to the following steps:

[0008] 1. Sandblasting: The inner surface of the BFe30-1-1 copper-nickel alloy heat exchange tube to be treated is sandblasted, and then compressed air is used for blowing. After inspection and meeting the standards, the sandblasted BFe30-1-1 copper-nickel alloy heat exchange tube is obtained.

[0009] II. Degreasing:

[0010] After sandblasting, the inner surface of the BFe30-1-1 copper-nickel alloy heat exchange tube is rinsed with water. Within 2 hours after the water rinsing is completed, the inner surface is degreased to obtain the degreased BFe30-1-1 copper-nickel alloy heat exchange tube.

[0011] III. Water washing and seawater film formation:

[0012] The inner surface of the BFe30-1-1 copper-nickel alloy heat exchanger tube after degreasing was subjected to two water washes, followed by seawater film formation. ICP spectroscopy analysis was used to determine that the copper ion concentration at the inlet and outlet of the BFe30-1-1 copper-nickel alloy heat exchanger tube was <0.5ppm. The seawater film formation was then completed, and a uniform yellowish-brown / grayish-brown passivation film was obtained. After inspection and confirmation that the film met the standards, the rapid passivation of the inner surface of the BFe30-1-1 copper-nickel alloy heat exchanger tube was completed.

[0013] Furthermore, the whole-machine sandblasting treatment described in step one is as follows:

[0014] Sand material: F24 mesh brown corundum, meeting GB / T 2478 standard. 20 kg of sand material is used to treat 20 BFe30-1-1 copper-nickel alloy heat exchange tubes before replacement.

[0015] Parameters: Sandblasting pressure 0.6~0.8 MPa, single-tube sandblasting time 600~610s;

[0016] Environment: Temperature 10~40℃, humidity ≤65%, compressed air meets GB / T13277 Class I standard.

[0017] Furthermore, the inspection described in step one meets the standard, as detailed below:

[0018] Appearance: uniform silver-white sandblasted surface, free from defects such as pores, cracks, and rust spots;

[0019] The wall thickness reduction is ≤0.1 mm, and the roughness is ≥6.4 μm, meeting the GB / T 1031 standard;

[0020] Cleanliness: The amount of residual grease meets the Class I standard of JB / T 6896.

[0021] Furthermore, the degreasing process described in step two is as follows;

[0022] Degreasing is performed using an alkaline degreasing solution; the concentration of the alkaline degreasing solution is 30~50g / L.

[0023] Temperature control: 25℃~50℃; Flow rate: 500~700 L / h; Oil removal time: 60min;

[0024] Replace the tubes after treating no more than 500 BFe30-1-1 copper-nickel alloy heat exchangers with every 1000L of alkaline degreasing solution.

[0025] Furthermore, the washing solution mentioned in step three: the water quality meets the requirements of Grade III water in Section 4.3 of GB / T 6682 "Specifications and Test Methods for Water Used in Analytical Laboratories".

[0026] Furthermore, in step three, the two-stage water washing process involves a water washing solution flow rate of 500–700 L / h and a water washing time of 240–360 min. A sample is taken from the outlet to test the pH value of the pure water. When the pH value of the pure water is below 8, the water washing process ends, and the water washing solution used for rinsing is discharged and recycled.

[0027] Furthermore, in step three, the two water washes are performed, wherein each 1000 L of water wash solution treats no more than 150 degreased BFe30-1-1 copper-nickel alloy heat exchange tubes before replacement.

[0028] Furthermore, the seawater film formation described in step three is as follows:

[0029] Water quality: Clean seawater that is not Class 2 or 3. Temperature, reducing bacteria, oxygen content and sediment content are monitored every 7 days. The temperature meets the requirements of 15.5℃~26.0℃, and the reducing bacteria, oxygen content and sediment content meet the requirements of GB / T14643, GB / T11913 and GB / T11901℃ respectively: <1cfc / 10ml, <2mg / L and <2.5mg / L.

[0030] Seawater flow velocity: 1.5~1.7m / s, film formation cycle ≥30 days, and verified by accompanying sample tubes.

[0031] Furthermore, the accompanying sample tube verification is as follows:

[0032] Sample selection: 20 accompanying sample tubes of the same material and process as the BFe30-1-1 copper-nickel alloy heat exchange tube to be treated, covering the entire batch;

[0033] Testing: Two samples were taken every 5 days for endoscopy to observe the film morphology; the corrosion depth was measured to be ≤10% of the nominal wall thickness using a laser confocal microscope.

[0034] Furthermore, the inspection described in step three meets the standard, as detailed below:

[0035] Endoscopic observation: Check the uniformity of the film and corrosion defects. Surface cracking is permissible, but substrate exposure is prohibited.

[0036] Electrochemical detection: impedance ≥10 5 Ω·cm 2 Corrosion current density ≤0.1μA / cm 2 It conforms to ASTM G106 standards;

[0037] Microscopic analysis: FIB-SEM analysis showed that the film thickness was 0.5~3.0μm and the composition was Cu / Ni / Fe oxide.

[0038] The principle of this invention:

[0039] This invention targets the material characteristics of BFe30-1-1 copper-nickel alloy, and achieves in-situ, uniform, and stable growth of passivation films through the synergistic effect of pretreatment surface modification and hydrodynamic regulation of seawater film formation. The core film formation principle consists of the following two stages:

[0040] 1. Pretreatment Surface Modification Stage: F24-mesh brown corundum sandblasting at 0.6~0.8 MPa pressure is used to form a uniform rough surface of ≥6.4 μm on the inner surface of the heat exchange tube. On the one hand, it removes film-forming obstacles such as oxide scale, oil stains, and impurities from the surface, and on the other hand, it increases the surface specific surface area, providing a large number of active sites for passivation film nucleation. Subsequent alkaline degreasing and three-stage water washing further purify the surface, eliminate residual pollutants, ensure the adhesion between the film layer and the substrate, and avoid film defects caused by surface impurities.

[0041] 2. In-situ film formation stage in seawater: By precisely controlling the seawater flow rate to 1.5~1.7 m / s, a stable hydrodynamic environment is formed, which ensures that dissolved oxygen, electrolytes and other substances in the seawater can uniformly contact all surfaces of the inner wall of the tube, while avoiding excessive flow rate from eroding and damaging the primary film layer; During the film formation cycle of ≥30 days, Cu, Ni and Fe ions in BFe30-1-1 alloy undergo selective oxidation on the surface and electrochemically react with oxygen, hydroxyl groups and other substances in the seawater to gradually generate a layered passivation film with Cu / Ni / Fe oxides as the main components.

[0042] In the above process, the uniform rough surface ensures a consistent distribution of film nucleation sites, and the controllable seawater flow rate guarantees that the oxidation reaction proceeds synchronously and slowly throughout the inner wall of the tube, ultimately forming a uniform and dense passivation film with a thickness of 0.5~3.0μm. This film acts as a physical barrier, not only inhibiting the dissolution of alloy matrix metal ions into seawater, but also hindering the diffusion of corrosive media from seawater into the matrix, significantly increasing the resistance to charge transfer and mass transport, and causing a sharp decrease in the rate of corrosion electrochemical reaction. At the same time, the film without local defects eliminates the galvanic corrosion conditions of "large cathode-small anode", fundamentally inhibiting the occurrence of local corrosion and pitting corrosion, and ultimately achieving a significant improvement in the corrosion resistance of the heat exchange tube.

[0043] Advantages of this invention:

[0044] This invention proposes a rapid passivation method for the inner surface of BFe30-1-1 copper-nickel alloy heat exchange tubes. The method first pre-treats the inner surface of the BFe30-1-1 copper-nickel alloy heat exchange tubes with a combination of sandblasting roughening and chemical cleaning. Then, by precisely controlling the flow rate and velocity of seawater, a controlled scouring process is applied to the inner wall of the tube for a specific duration. Finally, utilizing this hydrodynamic process, a uniform, stable, dense, and strongly adherent protective passivation film is grown in situ on the inner surface of the tube. This method, by actively controlling the film formation conditions, achieves rapid and complete formation of the protective film, fundamentally eliminating the "large cathode-small anode" galvanic corrosion cell caused by local defects in the film layer. This effectively suppresses the localized corrosion tendency and pitting sensitivity of the BFe30-1-1 copper-nickel alloy, ultimately significantly improving the corrosion resistance of the heat exchange tubes, extending their service life, and ensuring the long-term operational safety and reliability of the entire heat exchanger.

[0045] This invention aims to rapidly passivate and form a passivation film on the inner surface of a BFe30-1-1 copper-nickel alloy heat exchanger tube. This film exhibits a strong corrosion inhibition effect: after 30 days of film formation, the impedance is (1.45~1.76)×10⁻⁶. 5 Ω·cm 2 Corrosion current density: 0.013~0.074 μA / cm 2 It exhibits excellent corrosion resistance and stability, achieving comprehensive and long-term protection for the inner surface of the heat exchange tubes. It also demonstrates excellent process controllability; through verification with accompanying sample tubes, real-time monitoring was conducted to ensure a high degree of consistency in the film quality on the inner surface of the heat exchange tubes throughout the entire system.

[0046] This invention is applicable to the rapid passivation film formation on the inner surface of BFe30-1-1 copper-nickel alloy heat exchange tubes. Attached Figure Description

[0047] Figure 1 This is a comparison of the electrochemical performance of the BFe30-1-1 copper-nickel alloy heat exchanger tube before and after the formation of the passivation film.

[0048] Figure 2 This is a microscopic morphology diagram of the passivation film on the inner surface of the BFe30-1-1 copper-nickel alloy heat exchange tube in the embodiment.

[0049] Figure 3 The graph shows the change in the amount of copper ions dissolved during the film formation process on the inner surface of the BFe30-1-1 copper-nickel alloy heat exchanger tube in the example. Detailed Implementation

[0050] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0051] Specific Implementation Method 1: This implementation method provides a rapid passivation method for the inner surface of a BFe30-1-1 copper-nickel alloy heat exchanger tube, which is achieved through the following steps:

[0052] 1. Sandblasting: The inner surface of the BFe30-1-1 copper-nickel alloy heat exchange tube to be treated is sandblasted, and then compressed air is used for blowing. After inspection and meeting the standards, the sandblasted BFe30-1-1 copper-nickel alloy heat exchange tube is obtained.

[0053] II. Degreasing:

[0054] After sandblasting, the inner surface of the BFe30-1-1 copper-nickel alloy heat exchange tube is rinsed with water. Within 2 hours after the water rinsing is completed, the inner surface is degreased to obtain the degreased BFe30-1-1 copper-nickel alloy heat exchange tube.

[0055] III. Water washing and seawater film formation:

[0056] The inner surface of the BFe30-1-1 copper-nickel alloy heat exchanger tube after degreasing was subjected to two water washes, followed by seawater film formation. ICP spectroscopy analysis was used to determine that the copper ion concentration at the inlet and outlet of the BFe30-1-1 copper-nickel alloy heat exchanger tube was <0.5ppm. The seawater film formation was then completed, and a uniform yellowish-brown / grayish-brown passivation film was obtained. After inspection and confirmation that the film met the standards, the rapid passivation of the inner surface of the BFe30-1-1 copper-nickel alloy heat exchanger tube was completed.

[0057] The whole machine sandblasting treatment described in step one of this embodiment is to use multi-channel seawater to flush the condenser component, which is composed of multiple heat exchange tubes assembled together, so as to achieve the purpose of forming a film on all the heat exchange tubes of the component.

[0058] The purpose of using compressed air to purge in step one of this embodiment is to remove a small amount of residual sand particles.

[0059] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the whole-machine sandblasting treatment described in step one is as follows:

[0060] Sand material: F24 mesh brown corundum, meeting GB / T 2478 standard. 20 kg of sand material is used to treat 20 BFe30-1-1 copper-nickel alloy heat exchange tubes before replacement.

[0061] Parameters: Sandblasting pressure 0.6~0.8 MPa, single-tube sandblasting time 600~610s;

[0062] Environment: Temperature 10~40℃, humidity ≤65%, compressed air meets GB / T13277 Class I standard. Other steps and parameters are the same as in Specific Implementation Method 1.

[0063] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One in that the verification in step one conforms to the standard, as detailed below:

[0064] Appearance: uniform silver-white sandblasted surface, free from defects such as pores, cracks, and rust spots;

[0065] The wall thickness reduction is ≤0.1mm, and the roughness is ≥6.4μm, meeting the GB / T 1031 standard;

[0066] Cleanliness: The amount of residual grease meets the Class I standard of JB / T 6896. Other steps and parameters are the same as in Specific Implementation Method 1.

[0067] Specific Implementation Method Four: This implementation method differs from Specific Implementation Method One in that the degreasing process described in step two is as follows;

[0068] Degreasing is performed using an alkaline degreasing solution; the concentration of the alkaline degreasing solution is 30~50g / L.

[0069] Temperature control: 25℃~50℃; Flow rate: 500~700L / h; Oil removal time: 60min;

[0070] Replace the tubes after treating no more than 500 BFe30-1-1 copper-nickel alloy heat exchangers with 1000L of alkaline degreasing solution. Other steps and parameters are the same as in Specific Implementation Method 1.

[0071] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method One in that the washing solution mentioned in step three meets the requirements for Grade III water in Section 4.3 of GB / T 6682 "Specifications and Test Methods for Water Used in Analytical Laboratories". Other steps and parameters are the same as in Specific Implementation Method One.

[0072] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method One in that, in step three, the two-stage water washing process involves a water washing solution flow rate of 500–700 L / h and a washing time of 240–360 min. A sample is taken from the outlet to test the pH value of the pure water. The washing process ends when the pH value of the pure water is below 8, and the used washing solution is discharged and recycled. Other steps and parameters are the same as in Specific Implementation Method One.

[0073] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method One in that, in step three, the two water washes are performed, and in each water wash, no more than 150 degreased BFe30-1-1 copper-nickel alloy heat exchange tubes are treated with every 1000 L of water before replacement. Other steps and parameters are the same as in Specific Implementation Method One.

[0074] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method One in that the seawater film formation in step three is as follows:

[0075] Water quality: Clean seawater that is not Class 2 or 3. Temperature, reducing bacteria, oxygen content and sediment content are monitored every 7 days. The temperature meets the requirements of 15.5℃~26.0℃, and the reducing bacteria, oxygen content and sediment content meet the requirements of GB / T14643, GB / T11913 and GB / T11901℃ respectively: <1cfc / 10ml, <2mg / L and <2.5mg / L.

[0076] Seawater flow velocity: 1.5~1.7 m / s, film formation period ≥30 days, verified by accompanying sample tubes. Other steps and parameters are the same as in Specific Implementation Method 1.

[0077] In this embodiment, real-time monitoring was conducted through accompanying sample tube verification to ensure a high degree of consistency in the film quality on the inner surface of the heat exchange tubes throughout the machine.

[0078] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Eight in that the accompanying sample tube verification is as follows:

[0079] Sample selection: 20 accompanying sample tubes of the same material and process as the BFe30-1-1 copper-nickel alloy heat exchange tube to be treated, covering the entire batch;

[0080] Testing: Two samples are taken every 5 days, and the film morphology is observed endoscopically; the corrosion depth is measured to be ≤10% of the nominal wall thickness using a laser confocal microscope. Other steps and parameters are the same as in Specific Implementation Method Eight.

[0081] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method One in that the verification in step three conforms to the standard, as detailed below:

[0082] Endoscopic observation: Check the uniformity of the film and corrosion defects. Surface cracking is permissible, but substrate exposure is prohibited.

[0083] Electrochemical detection: impedance ≥10 5 Ω·cm 2 Corrosion current density ≤0.1μA / cm 2 It conforms to ASTM G106 standards;

[0084] Microscopic analysis: FIB-SEM analysis showed the film thickness to be 0.5–3.0 μm, and the composition to be Cu / Ni / Fe oxide. Other steps and parameters were the same as in Specific Implementation Method 1.

[0085] The beneficial effects of the present invention are verified through the following embodiments:

[0086] The following description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0087] Example:

[0088] A rapid passivation method for the inner surface of a BFe30-1-1 copper-nickel alloy heat exchanger tube, which is implemented according to the following steps:

[0089] 1. Sandblasting: The inner surface of the BFe30-1-1 copper-nickel alloy heat exchange tube to be treated is sandblasted, and then compressed air is used for blowing. After inspection and meeting the standards, the sandblasted BFe30-1-1 copper-nickel alloy heat exchange tube is obtained.

[0090] II. Degreasing:

[0091] After sandblasting, the inner surface of the BFe30-1-1 copper-nickel alloy heat exchange tube is rinsed with water. Within 2 hours after the water rinsing is completed, the inner surface is degreased to obtain the degreased BFe30-1-1 copper-nickel alloy heat exchange tube.

[0092] III. Water washing and seawater film formation:

[0093] The inner surface of the BFe30-1-1 copper-nickel alloy heat exchange tube after degreasing was subjected to two water washes, followed by seawater film formation. ICP spectroscopy analysis was used to determine that the copper ion concentration at the inlet and outlet of the BFe30-1-1 copper-nickel alloy heat exchange tube was <0.5ppm. The seawater film formation was then completed, and a uniform yellowish-brown / grayish-brown passivation film was obtained. After inspection and confirmation that the film met the standards, the rapid passivation of the inner surface of the BFe30-1-1 copper-nickel alloy heat exchange tube was completed.

[0094] The whole-machine sandblasting treatment described in step one of this embodiment is as follows:

[0095] Sand material: F24 mesh brown corundum, meeting GB / T 2478 standard. 20 kg of sand material is used to treat 20 BFe30-1-1 copper-nickel alloy heat exchange tubes before replacement.

[0096] Parameters: Sandblasting pressure 0.67 MPa, single-tube sandblasting time 600s;

[0097] Environment: Temperature 10~40℃, humidity ≤65%, compressed air meets GB / T13277 Class I standard.

[0098] The inspection described in step one of this embodiment meets the standard, as detailed below:

[0099] Appearance: uniform silver-white sandblasted surface, free from defects such as pores, cracks, and rust spots;

[0100] The wall thickness reduction is ≤0.1 mm, and the roughness is ≥6.4 μm, meeting the GB / T 1031 standard;

[0101] Cleanliness: The amount of residual grease meets the Class I standard of JB / T 6896.

[0102] The degreasing process described in step two of this embodiment is as follows;

[0103] Degreasing is performed using an alkaline degreasing solution; the concentration of the alkaline degreasing solution is 40 g / L.

[0104] Temperature control: 25℃~50℃; Flow rate: 600 L / h; Oil removal time: 60 min;

[0105] Replace the tubes after treating no more than 500 BFe30-1-1 copper-nickel alloy heat exchangers with every 1000L of alkaline degreasing solution.

[0106] The washing solution described in step three of this embodiment meets the requirements of Class III water in Section 4.3 of GB / T 6682 "Specifications and Test Methods for Water Used in Analytical Laboratories".

[0107] In step three of this embodiment, the two-stage water washing process is as follows: the water washing liquid flow rate is 600L / h, the water washing time is 300min, and the pH value of the pure water is sampled from the outlet. When the pH value of the pure water is lower than 8, the water washing ends, the water washing liquid used for rinsing is discharged and recycled.

[0108] In step three of this embodiment, the two water washes are performed, and each 1000 L of water wash solution is used to treat no more than 150 degreased BFe30-1-1 copper-nickel alloy heat exchange tubes before replacement.

[0109] The seawater film formation in step three of this embodiment is as follows:

[0110] Water quality: Clean seawater that is not Class 2 or 3. Temperature, reducing bacteria, oxygen content and sediment content are monitored every 7 days. The temperature meets the requirements of 15.5℃~26.0℃, and the reducing bacteria, oxygen content and sediment content meet the requirements of GB / T14643, GB / T11913 and GB / T11901℃ respectively: <1cfc / 10ml, <2mg / L and <2.5mg / L.

[0111] Seawater flow rate: 1.6 m / s, film formation period: 30 days, and verified by accompanying sample tubes.

[0112] The accompanying sample tube verification described in this embodiment is as follows:

[0113] Sample selection: 20 accompanying sample tubes of the same material and process as the BFe30-1-1 copper-nickel alloy heat exchange tube to be treated, covering the entire batch;

[0114] Testing: Two samples were taken every 5 days for endoscopy to observe the film morphology; the corrosion depth was measured to be ≤10% of the nominal wall thickness using a laser confocal microscope.

[0115] The inspection described in step three of this embodiment meets the standard, as detailed below:

[0116] Endoscopic observation: Check the uniformity of the film and corrosion defects. Surface cracking is permissible, but substrate exposure is prohibited.

[0117] Electrochemical detection: impedance ≥10 5 Ω·cm 2 Corrosion current density ≤0.1μA / cm 2 It conforms to ASTM G106 standards;

[0118] Microscopic analysis: FIB-SEM analysis showed that the film thickness was 0.5~3.0μm and the composition was Cu / Ni / Fe oxide.

[0119] In this embodiment, after 30 days of seawater rinsing, a uniform and dense passivation film was successfully formed on the inner surface of the BFe30-1-1 copper-nickel alloy heat exchange tube, significantly improving its corrosion resistance and exhibiting a strong corrosion inhibition effect. The test results are shown in Table 1. After 30 days of film formation, the impedance was (1.45~1.76)×10⁵ Ω·cm. 2 Corrosion current density: 0.013~0.074 μA / cm 2 It exhibits excellent corrosion resistance and stability. It also demonstrates superior process controllability; through verification with accompanying sample tubes, real-time monitoring was conducted to ensure a high degree of consistency in the film quality on the inner surface of the heat exchange tubes throughout the entire unit.

[0120] Table 1

[0121]

[0122] from Figure 1 The comparison of electrochemical performance before and after the formation of a passivation film on the inner surface of the BFe30-1-1 copper-nickel alloy heat exchange tube in this embodiment shows the changes in electrochemical impedance and corrosion current density before and after the formation of the passivation film on the inner surface of the BFe30-1-1 copper-nickel alloy heat exchange tube (bright tube). The impedance of the defective scratched tube and the tube with dark spots is slightly lower than that of the bright, defect-free tube, while the corrosion current is slightly higher. This indicates that the two types of defective tubes can form a passivation film to protect the substrate, but the condition is slightly less than ideal. Where Rp is the electrochemical impedance (Ω·cm). 2 Icorr is the corrosion current density (μA / cm). 2 As shown in the figure, the surface impedance of the inner surface of the bright tube before film formation is much lower than 10. 5 Ω·cm 2 The corrosion current density is much greater than 0.1 μA / cm. 2 After 30 days of treatment using the process of this invention, its impedance value increases to 1.45~1.76×10⁻⁶. 5 Ω·cm 2 The corrosion current density decreased to 0.013~0.074 μA / cm. 2 This indicates that this embodiment can significantly improve the electrochemical corrosion resistance of the heat exchange tube and greatly reduce the corrosion rate.

[0123] from Figure 2As can be seen from the microscopic morphology image of the passivation film on the inner surface of the BFe30-1-1 copper-nickel alloy heat exchange tube, the passivation film formed by the process in this embodiment has a uniform and dense layered structure with a film thickness between 0.5 and 3.0 μm. There are no obvious defects such as pores or cracks, and it is tightly bonded to the alloy substrate. Compared with the film formed by existing processes, there are no problems such as uneven thickness or exposed substrate. This shows that the passivation film prepared by the present invention is uniform, dense, and has strong adhesion, eliminating the structural defects of local corrosion from the root.

[0124] from Figure 3 The graph showing the change in copper ion dissolution during the film formation process on the inner surface of the BFe30-1-1 copper-nickel alloy heat exchanger tube reveals the variation in copper ion concentration at the seawater inlet and outlet of the heat exchanger tube during the film formation period (0-30 days). In the initial stage of film formation, trace amounts of copper ions dissolve, but the dissolution rate decreases rapidly with increasing film formation time. After 30 days of film formation, the copper ion concentration falls below the detection limit (<0.5 ppm). This demonstrates the advantages of controllable film formation in this embodiment, enabling stable in-situ growth of the passivation film, effectively inhibiting metal ion dissolution, and exhibiting excellent film integrity and stability.

Claims

1. A rapid passivation method for the inner surface of a BFe30-1-1 copper-nickel alloy heat exchanger tube, characterized in that, It is implemented in the following steps:

1. Sandblasting: The inner surface of the BFe30-1-1 copper-nickel alloy heat exchange tube to be treated is sandblasted, and then compressed air is used for blowing. After inspection and meeting the standards, the sandblasted BFe30-1-1 copper-nickel alloy heat exchange tube is obtained. II. Degreasing: After sandblasting, the inner surface of the BFe30-1-1 copper-nickel alloy heat exchange tube is rinsed with water. Within 2 hours after the water rinsing is completed, the inner surface is degreased to obtain the degreased BFe30-1-1 copper-nickel alloy heat exchange tube. III. Water washing and seawater film formation: The inner surface of the BFe30-1-1 copper-nickel alloy heat exchanger tube after degreasing was subjected to two water washes, followed by seawater film formation. ICP spectroscopy analysis was used to determine that the copper ion concentration at the inlet and outlet of the BFe30-1-1 copper-nickel alloy heat exchanger tube was <0.5ppm. The seawater film formation was then completed, and a uniform yellowish-brown / grayish-brown passivation film was obtained. After inspection and confirmation that the film met the standards, the rapid passivation of the inner surface of the BFe30-1-1 copper-nickel alloy heat exchanger tube was completed.

2. The rapid passivation method for the inner surface of a BFe30-1-1 copper-nickel alloy heat exchanger tube according to claim 1, characterized in that, The whole machine sandblasting treatment described in step one is as follows: Sand material: F24 mesh brown corundum, meeting GB / T 2478 standard. 20kg of sand material is used to treat 20 BFe30-1-1 copper-nickel alloy heat exchange tubes before replacement. Parameters: Sandblasting pressure 0.6~0.8MPa, single-tube sandblasting time 600~610s; Environment: Temperature 10~40℃, humidity ≤65%, compressed air meets GB / T13277 Class I standard.

3. The rapid passivation method for the inner surface of a BFe30-1-1 copper-nickel alloy heat exchanger tube according to claim 1, characterized in that, The inspection described in step one meets the standards, as detailed below: Appearance: uniform silver-white sandblasted surface, free from defects such as pores, cracks, and rust spots; The wall thickness reduction is ≤0.1mm, and the roughness is ≥6.4μm, meeting the GB / T 1031 standard; Cleanliness: The amount of residual grease meets the Class I standard of JB / T 6896.

4. The rapid passivation method for the inner surface of a BFe30-1-1 copper-nickel alloy heat exchanger tube according to claim 1, characterized in that, The degreasing process described in step two is as follows; Degreasing is performed using an alkaline degreasing solution; the concentration of the alkaline degreasing solution is 30~50g / L. Temperature control: 25℃~50℃; Flow rate: 500~700L / h; Oil removal time: 60min; Replace the tubes after treating no more than 500 BFe30-1-1 copper-nickel alloy heat exchangers with every 1000L of alkaline degreasing solution.

5. The rapid passivation method for the inner surface of a BFe30-1-1 copper-nickel alloy heat exchanger tube according to claim 1, characterized in that, The washing solution mentioned in step three: the water quality meets the requirements of Grade III water in Section 4.3 of GB / T 6682 "Specifications and Test Methods for Water Used in Analytical Laboratories".

6. The rapid passivation method for the inner surface of a BFe30-1-1 copper-nickel alloy heat exchanger tube according to claim 1, characterized in that, The two-stage water washing process described in step three involves a water washing solution flow rate of 500–700 L / h and a water washing time of 240–360 min. A sample is taken from the outlet to test the pH value of the pure water. When the pH value of the pure water is below 8, the water washing process ends, and the water washing solution used for rinsing is discharged and recycled.

7. The rapid passivation method for the inner surface of a BFe30-1-1 copper-nickel alloy heat exchanger tube according to claim 1, characterized in that, In step three, the two water washes are performed, and each 1000 L of water wash solution is used to treat no more than 150 degreased BFe30-1-1 copper-nickel alloy heat exchange tubes before replacement.

8. The rapid passivation method for the inner surface of a BFe30-1-1 copper-nickel alloy heat exchanger tube according to claim 1, characterized in that, The seawater film formation described in step three is as follows: Water quality: Clean seawater that is not Class 2 or 3. Temperature, reducing bacteria, oxygen content and sediment content are monitored every 7 days. The temperature meets the requirements of 15.5℃~26.0℃, and the reducing bacteria, oxygen content and sediment content meet the requirements of GB / T14643, GB / T11913 and GB / T11901℃ respectively: <1cfc / 10ml, <2mg / L and <2.5mg / L. Seawater flow velocity: 1.5~1.7m / s, film formation cycle ≥30 days, and verified by accompanying sample tubes.

9. A rapid passivation method for the inner surface of a BFe30-1-1 copper-nickel alloy heat exchanger tube according to claim 8, characterized in that, The accompanying sample tube verification is as follows: Sample selection: 20 accompanying sample tubes of the same material and process as the BFe30-1-1 copper-nickel alloy heat exchange tube to be treated were selected to cover the entire batch; Testing: Two samples were taken every 5 days for endoscopy to observe the film morphology; the corrosion depth was measured to be ≤10% of the nominal wall thickness using a laser confocal microscope.

10. The rapid passivation method for the inner surface of a BFe30-1-1 copper-nickel alloy heat exchanger tube according to claim 1, characterized in that, The inspection described in step three meets the standards, as detailed below: Endoscopic observation: Check the uniformity of the film and corrosion defects. Surface cracking is permissible, but substrate exposure is prohibited. Electrochemical detection: impedance ≥10 5 Ω·cm 2 Corrosion current density ≤0.1μA / cm 2 It conforms to ASTM G106 standards; Microscopic analysis: FIB-SEM analysis showed that the film thickness was 0.5~3.0μm and the composition was Cu / Ni / Fe oxide.

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