Preparation method of corrosion-resistant coating of carbon steel pipe

Abstract

The invention discloses a preparation method of a corrosion-resistant coating of a carbon steel pipe, which adopts a sodium metaaluminate (NaAlO2), sodium dihydrogen phosphate (NaH2PO4), sodium carbonate (NaCO2) and sodium tetraborate (Na2B4O7) aqueous solution electrolyte system to perform surface modification. The method has the remarkable advantages of high environmental protection property, no generation of harmful waste liquid and reduction of pollutant emission. The nanosecond pulse laser is used for replacing a traditional high-voltage discharge technology (such as 400-800 V high voltage in MAO), energy consumption can be remarkably reduced, meanwhile, the machining efficiency is improved, and energy is saved. According to the method, a compact, uniform and stable Al2O3 oxide layer is generated on the surface of the carbon steel, the corrosion resistance and mechanical strength of the surface are remarkably improved, and especially in a high-chlorine environment, the excellent corrosion resistance effect is shown.

Description

Technical Field

[0001] The invention relates to the field of material surface modification, and in particular to a method for preparing a corrosion-resistant coating of a carbon steel pipe. Background Art

[0002] In the actual application process, especially when in contact with chloride ion media (such as seawater), carbon steel is very easy to rust and produce serious corrosion problems, which damages the structural integrity and brings great safety risks. Specifically, in a humid environment, a water film is easily generated on the surface of carbon steel to form a primary cell. The dissolved oxygen and the surface iron elements will generate hydroxide ions and ferrous ions. The two combine to form iron hydroxide and further generate rust (the main components are Fe2O3·nH2O or FeO·Fe2O3·nH2O). This layer of rust is loose and porous. Instead of protecting the inside of the metal, it will become a channel for corrosive media and accelerate corrosion. In a high-chlorine environment, chloride ions accelerate electrochemical reactions as electrolytes on the one hand, and on the other hand, they will work together with water inside the steel to cause hydrogen embrittlement, resulting in brittle fracture of the steel. In addition, the presence of chloride ions significantly reduces the pitting potential of carbon steel, greatly promotes the induction and initial development of pitting, and easily forms perforations on the pipe wall, resulting in pipe rupture failure and instrument failure. As corrosion progresses, the mechanical properties of carbon steel pipes will also be affected. Humid and high-chloride environments will cause embrittlement and reduced strength of the material, ultimately leading to premature failure of carbon steel pipes.

[0003] The prior art of manufacturing corrosion-resistant coatings for carbon steel pipes requires a large amount of energy input and expensive reinforcing materials. The corrosion-resistant coatings for carbon steel pipes provide insufficient corrosion resistance in chlorine-rich environments. The surfaces of the corrosion-resistant coatings for carbon steel pipes often lack strength and durability, thereby limiting their anti-corrosion capabilities.

[0004] Therefore, there is an urgent need to develop a method for preparing a corrosion-resistant coating for carbon steel pipes. Summary of the invention

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A method for preparing a corrosion-resistant coating for a carbon steel pipe comprises the following steps:

[0007] (1) Use 180 mesh, 500 mesh, 800 mesh and 1200 mesh metallographic sandpaper to polish the carbon steel pipe to be coated;

[0008] (2) Using an electronic balance, weigh 14-16 g of sodium aluminate powder, 3-5 g of sodium dihydrogen phosphate particles, 3-5 g of sodium carbonate powder, and 3-5 g of sodium tetraborate powder, and dissolve them in deionized water; then place the carbon steel pipe in a flat-bottomed container, and pour the prepared solution into it until the liquid level is 2-4 mm above the upper surface of the carbon steel;

[0009] (3) Adjust the parameters of the pulse laser beam modulation equipment: power is 80-90W, pulse width is 200-220ns, frequency is 500-510kHz, moving speed is 100-110mm / min, adjust the distance between the laser output device and the carbon steel pipe to the optimal focal length and scan back and forth 10-15 times;

[0010] (4) After the laser treatment, cool in the prepared solution for 1-2 hours. After cooling, take out from the solution and dry at room temperature for 24-30 hours.

[0011] Preferably, in step (2), the concentration of sodium aluminate in the prepared solution is 15 g / L.

[0012] Preferably, in step (2), the concentration of sodium dihydrogen phosphate in the prepared solution is 3 g / L.

[0013] Preferably, in step (2), the concentration of sodium carbonate in the prepared solution is 3 g / L.

[0014] Preferably, in step (2), the concentration of sodium tetraborate in the prepared solution is 3 g / L.

[0015] Preferably, the solution prepared in step (2) covers the upper surface of the carbon steel pipe by 2 mm.

[0016] Furthermore, the optimal focal length of the laser output device is 26 cm.

[0017] Furthermore, in step (3), the parameters of the pulse laser beam modulation equipment were adjusted: power was 80 W, pulse width was 220 ns, frequency was 500 kHz, moving speed was 100 mm / min, the distance between the laser output device and the carbon steel pipe was adjusted to the optimal focal length and scanned back and forth 10 times.

[0018] Furthermore, in step (4), after the laser treatment is completed, the mixture is cooled in the prepared solution for 1 hour, and after cooling, it is taken out of the solution and dried at room temperature for 24 hours.

[0019] Due to the adoption of the above technical solution, the present invention has the following technical advances compared with the prior art:

[0020] 1. The present invention adopts a weak alkaline electrolyte system (NaAlO2, NaH2PO4, NaCO2, Na2B4O7) for surface modification. Compared with the acidic or strong alkaline electrolyte systems commonly used in the prior art, it has the significant advantages of high environmental protection, no generation of harmful waste liquid, and reduced pollutant emissions.

[0021] 2. The present invention replaces the traditional high-voltage discharge technology (such as 400-800V high voltage in MAO) with nanosecond pulse laser, which can significantly reduce energy consumption, improve processing efficiency and save energy.

[0022] 3. The Al2O3 oxide layer generated by the present invention is dense, uniform and stable, which significantly improves the corrosion resistance and mechanical strength of the carbon steel surface, especially in a high-chlorine environment, showing excellent corrosion resistance.

[0023] 4. The present invention can be implemented under normal pressure or low pressure conditions, without the need for high-voltage discharge equipment or additional cooling systems, thereby significantly reducing equipment costs and overall process costs.

[0024] 5. The present invention realizes the grain refinement and mechanical strength optimization of the carbon steel surface through laser processing, improves the corrosion resistance and hardness of the surface, and enhances the density and uniformity of the coating.

[0025] 6. The process of the present invention is simple and applicable to a variety of carbon steel materials, especially the modification effect on carbon steel substrates is particularly significant, and can be widely used in industrial fields such as ships, construction, and automobiles.

[0026] 7. The electrolyte raw materials NaAlO2, NaH2PO4, NaCO2, and Na2B4O7 used in the present invention are cheap and easily available, and the process flow is simple, which significantly reduces the production cost and has the potential for large-scale industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0028] Figure 1 This is a comparison group of polarization curves obtained by electrochemical linear sweep voltammetry of the samples prepared in Example 1 and Comparative Examples 1-2.

[0029] Figure 2 The SEM comparison images of the samples obtained in Example 1 and Comparative Examples 1-2 are shown in Figures ac and ac are the surface morphology comparisons before and after electrochemical linear sweep voltammetry. DETAILED DESCRIPTION

[0030] The following embodiments may help those skilled in the art to more fully understand the present invention, but shall not limit the present invention in any way.

[0031] Example

[0032] A method for preparing a corrosion-resistant coating for a carbon steel pipe comprises the following steps:

[0033] (1) Use 180 mesh, 500 mesh, 800 mesh and 1200 mesh metallographic sandpaper to polish the carbon steel pipe to be coated;

[0034] (2) Using an electronic balance, weigh 14-16 g of sodium aluminate powder, 3-5 g of sodium dihydrogen phosphate particles, 3-5 g of sodium carbonate powder, and 3-5 g of sodium tetraborate powder, and dissolve them in deionized water; then place the carbon steel pipe in a flat-bottomed container, and pour the prepared solution into it until the liquid level is 2-4 mm above the upper surface of the carbon steel;

[0035] (3) Adjust the parameters of the pulse laser beam modulation equipment: power is 80-90W, pulse width is 200-220ns, frequency is 500-510kHz, moving speed is 100-110mm / min, adjust the distance between the laser output device and the carbon steel pipe to the optimal focal length and scan back and forth 10-15 times;

[0036] (4) After the laser treatment, cool in the prepared solution for 1-2 hours. After cooling, take out from the solution and dry at room temperature for 24-30 hours.

[0037] In one embodiment of the present invention, in step (2), the concentration of sodium aluminate in the prepared solution is 15 g / L.

[0038] In one embodiment of the present invention, in step (2), the concentration of sodium dihydrogen phosphate in the prepared solution is 3 g / L.

[0039] In one embodiment of the present invention, in step (2), the concentration of sodium carbonate in the prepared solution is 3 g / L.

[0040] In one embodiment of the present invention, in step (2), the concentration of sodium tetraborate in the prepared solution is 3 g / L.

[0041] NaAlO2 is the aluminum source of aluminum oxide on the surface of carbon steel; NaH2PO4 inhibits the formation of iron oxide and promotes the formation of aluminum oxide; Na2CO3 promotes the growth of Al2O3 crystals, and the addition of Na2B4O7 significantly inhibits the formation of FePO4 in the coating, which is more conducive to the growth of Al2O3 crystals.

[0042] In one embodiment of the present invention, the solution prepared in step (2) covers the upper surface of the carbon steel pipe by 2 mm.

[0043] Furthermore, the optimal focal length of the laser output device is 26 cm.

[0044] In one embodiment of the present invention, the model of the pulse laser beam modulation device is HGTECH LSF200C.

[0045] Furthermore, in step (3), the parameters of the pulse laser beam modulation equipment were adjusted: power was 80 W, pulse width was 220 ns, frequency was 500 kHz, moving speed was 100 mm / min, the distance between the laser output device and the carbon steel pipe was adjusted to the optimal focal length and scanned back and forth 10 times.

[0046] Furthermore, in step (4), after the laser treatment is completed, the mixture is cooled in the prepared solution for 1 hour, and after cooling, it is taken out of the solution and dried at room temperature for 24 hours.

[0047] Example 1

[0048] (1) Wire EDM processing: Place the carbon steel pipe on the fixed table of the wire EDM machine, and then set the wire EDM machine parameters to pulse width 60, pulse interval c, power amplifier c, and cut to 22×15×10cm at a speed of 250 steps per minute. 3 Then use 180 mesh, 500 mesh, 800 mesh and 1200 mesh metallographic sandpaper to grind the cut carbon steel pipe.

[0049] (2) Solution preparation: 7.5 g of sodium aluminate powder, 1.5 g of sodium dihydrogen phosphate granules, 1.5 g of sodium carbonate powder and 1.5 g of sodium tetraborate powder were weighed on an electronic balance and dissolved in 500 mL of deionized water. The mixture was magnetically stirred at 500 rpm for 30 min at room temperature. Then, a carbon steel pipe was placed in a flat-bottomed glass container and the prepared solution was poured in until the liquid level was 2 mm above the upper surface of the carbon steel pipe.

[0050] (3) Adjust the parameters of the pulse laser beam modulation equipment: power is 80 W, pulse width is 220 ns, frequency is 500 kHz, moving speed is 100 mm / min, adjust the distance between the laser output device and the carbon steel pipe to the optimal focal length and control the programmable logic controller to scan back and forth 10 times.

[0051] (4) Cooling, waiting and drying: After the laser treatment, the carbon steel pipe is cooled in the prepared solution for 1 hour. After cooling, it is taken out of the solution and dried at room temperature for 24 hours.

[0052] Comparative Example 1

[0053] (1) Wire EDM processing: Place the carbon steel pipe or carbon steel block on the fixed table of the wire EDM machine, and then set the wire EDM machine parameters to pulse width 60, pulse interval c, power amplifier c, and cut to 22×15×10cm at a speed of 250 steps per minute. 3 Then, the cut carbon steel pipe was polished with 180 mesh, 500 mesh, 800 mesh and 1200 mesh metallographic sandpaper in turn.

[0054] Comparative Example 2

[0055] (1) Wire EDM processing: Place the carbon steel pipe or carbon steel block on the fixed table of the wire EDM machine, and then set the wire EDM machine parameters to pulse width 60, pulse interval c, power amplifier c, and cut to 22×15×10cm at a speed of 250 steps per minute. 3 Then, the cut carbon steel pipe was polished with 180 mesh, 500 mesh, 800 mesh and 1200 mesh metallographic sandpaper in turn.

[0056] (2) Adjust the parameters of the pulse laser beam modulation equipment: power is 80 W, pulse width is 220 ns, frequency is 500 KHz, moving speed is 100 mm / min, adjust the distance between the laser output device and the carbon steel pipe to the optimal focal length and control the programmable logic controller to scan back and forth 10 times.

[0057] Electrochemical corrosion testing

[0058] To evaluate the corrosion resistance of the oxide layer of each sample, a potentiodynamic polarization test was performed using an electrochemical workstation. Before the test, all samples were cleaned with ethanol and acetone in sequence and dried thoroughly. The test used a three-electrode system, in which the sample was used as the working electrode, the saturated calomel electrode (SCE) was used as the reference electrode, and the platinum electrode was used as the counter electrode.

[0059] During the experiment, the sample was first immersed in a 3.5wt.% NaCl solution, left to stand for 40 minutes to ensure the stability of the open circuit potential (OCP), and then the electrochemical test was performed. The potentiodynamic polarization curve was scanned at a rate of 0.33mV / s, a sampling frequency of 1Hz, and a potential range of -0.25V to 0.5V. The data analysis was fitted using the Taaffe extrapolation method. In order to ensure the reliability of the results, each sample was tested three times and the average value was taken as the final result. The table after data collation is as follows:

[0060] Table 1 Polarization curve data and Nyquist data table of each sample

[0061] Sample corrosion potential (V) Corrosion current density (Acm -2 )

[0062] Example 1-0.703 2.708×10 -10

[0063] Comparative Example 1-0.891 6.599×10 -6

[0064] Comparative Example 2 - 0.567 1.627 × 10 -5

[0065] When the corrosion potential is more positive and the corrosion current density is lower, it often indicates that it is easier to form an effective protective layer or passivation film on the coating surface, thereby improving its corrosion resistance. By combining these two parameters, the corrosion resistance of the coating can be evaluated as a whole. Table 1 lists the Tafel fitting results of the potentiodynamic polarization curves of the three samples. Among them, the corrosion potential of Example 1 is -0.703V, and the corrosion current density is only 2.708×10 -10 A cm -2 ,and Figure 1 The polarization curves shown are consistent. As can be seen from Table 1, Example 1 has a lower corrosion current density and a higher corrosion potential than Comparative Example 1, indicating that the aluminum oxide film formed on the carbon steel by the method described in the example can effectively block the entry of corrosive media, thereby giving the coating more excellent corrosion resistance. Compared with the comparative example, the corrosion current density of Example 1 is nearly 4 orders of magnitude lower than that of Comparative Example 1 and 5 orders of magnitude lower than that of Comparative Example 2, highlighting its excellent corrosion resistance.

[0066] Surface morphology

[0067] Scanning electron microscopy was used to analyze the surface morphology of each sample coating. Figure 2 (ac) show the microstructures of Example 1, Comparative Example 1 and Comparative Example 2 before and after corrosion in the above electrochemical corrosion experiment (magnification is 500 times). The results show that the surface of Example 1 has a porous structure with different pore sizes and significant metal remelting and alumina cluster accumulation characteristics. After corrosion, no obvious corrosion pits appear on the surface. In contrast, both Comparative Example 1 and Comparative Example 2 have obvious corrosion, and the surface has different degrees of damage.

[0068] The above generally describes the present invention in detail, but it is obvious to a person skilled in the art that some modifications or improvements can be made to the present invention. Therefore, modifications or improvements that do not depart from the spirit of the present invention are within the scope of protection of the present invention.

Claims

1. A method for preparing a corrosion-resistant coating for a carbon steel pipe, characterized in that: The following steps are involved: (1) Use 180 mesh, 500 mesh, 800 mesh and 1200 mesh metallographic sandpaper to polish the carbon steel pipe to be coated; (2) Using an electronic balance, weigh 14-16 g of sodium aluminate powder, 3-5 g of sodium dihydrogen phosphate particles, 3-5 g of sodium carbonate powder, and 3-5 g of sodium tetraborate powder, and dissolve them in deionized water; then place the carbon steel pipe in a flat-bottomed container, and pour the prepared solution into it until the liquid level is 2-4 mm above the upper surface of the carbon steel; (3) Adjust the parameters of the pulse laser beam modulation equipment: power is 80-90W, pulse width is 200-220ns, frequency is 500-510kHz, moving speed is 100-110mm / min, adjust the distance between the laser output device and the carbon steel pipe to the optimal focal length and scan back and forth 10-15 times; (4) After the laser treatment, cool in the prepared solution for 1-2 hours. After cooling, take out from the solution and dry at room temperature for 24-30 hours.

2. The method for preparing a corrosion-resistant coating for a carbon steel pipe according to claim 1, characterized in that: In step (2), the concentrations of the components in the prepared solution are 15 g / L sodium aluminate, 3 g / L sodium dihydrogen phosphate, 3 g / L sodium carbonate and 3 g / L sodium tetraborate.

3. The method for preparing the corrosion-resistant coating of carbon steel pipe according to claim 1, characterized in that: Step (2) The solution is prepared to cover the upper surface of the carbon steel pipe by 2 mm.

4. The method for preparing a corrosion-resistant coating for a carbon steel pipe according to claim 1, characterized in that: In step (3), the parameters of the pulse laser beam modulation equipment are adjusted: the power is 80 W, the pulse width is 220 ns, the frequency is 500 kHz, the moving speed is 100 mm / min, the distance between the laser output device and the carbon steel pipe is adjusted to the optimal focal length and scan back and forth 10 times.

5. The method for preparing the corrosion-resistant coating of carbon steel pipe according to claim 4, characterized in that: In step (4), after the laser treatment is completed, the sample is cooled in the prepared solution for 1 hour. After cooling, the sample is taken out of the solution and dried at room temperature for 24 hours.

Images