Coal bunker dome and construction method

Abstract

The invention relates to the technical field of coal bunker domes, and discloses a coal bunker dome and a construction method.The coal bunker dome comprises a composite protective coating attached to the outer surface of a dome-shaped steel base body, and the composite protective coating comprises a steel base interface layer, a middle transition layer and a surface sealing layer which are sequentially distributed from inside to outside; the zinc content difference between adjacent layers of the composite protective coating is 1.5 + / -0.2%, and a stepped electrochemical gradient is formed between the layers, so that the corrosion resistance and the stability of the dome protective coating are improved, and the service life is prolonged.

Description

Technical Field

[0001] The present invention relates to the field of coal bunker domes, in particular to a coal bunker dome and a construction method thereof. Background Art

[0002] A hypothesis is proposed to solve the problem that the steel structure of the coal bunker dome in coastal areas of coal-fired power plants is exposed to long-term erosion by sea breeze and salt spray, and the traditional three-layer anti-corrosion coating is prone to local corrosion, coating peeling and other problems, resulting in a short service life.

[0003] The existing traditional anti-corrosion coating has poor anti-corrosion and wear-resistant effects. There are certain variations in the setting of zinc content among the three layers of anti-corrosion coating, and the wear resistance is poor.

[0004] In the coal storage sector, circular bunker domes, as a crucial component of steel structures, face long-term exposure to complex environmental erosion. Especially in coastal areas, salt spray (primarily composed of NaCl) carried by sea breezes can cause severe electrochemical corrosion to the dome's steel structure, making it difficult for traditional anti-corrosion coating systems to meet long-term protection requirements. Existing technologies commonly use a three-layer coating structure (primer + midcoat + topcoat) for coal bunker dome corrosion protection, but this suffers from electrochemical protection failure and insufficient weathering and wear resistance. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is: for the coal bunker dome steel structure in coastal areas of coal-fired power plants, which is exposed to long-term erosion by sea breeze and salt spray, the traditional three-layer anti-corrosion coating has problems such as disordered potential conduction due to improper control of the zinc content difference between adjacent layers, prone to local corrosion, coating peeling and short service life.

[0006] The above technical problems are solved by the following technical solution: The present invention proposes a coal bunker dome, which includes a composite protective coating attached to the outer surface of a dome-shaped steel substrate. The composite protective coating includes a steel-based interface layer, an intermediate transition layer, and a surface sealing layer distributed in sequence from the inside to the outside. The difference in zinc content between adjacent layers of the composite protective coating is 1.5±0.2%, and a stepped electrochemical gradient is formed between the layers.

[0007] In a preferred embodiment of the coal bunker dome and construction method of the present invention, the metal zinc content in the steel-based interface layer is 85±1%, the zinc content in the intermediate transition layer is 83.5±1%, and the zinc content in the surface sealing layer is 82±1%.

[0008] In a preferred embodiment of the coal bunker dome and construction method of the present invention: the steel-based interface layer is coated twice to form two dry film layers, and the total thickness of the two dry film layers is 130±5 μm.

[0009] In a preferred embodiment of the coal bunker dome and construction method of the present invention: the intermediate transition layer has a thickness of 70±3 μm and is solidifiable in an environment of -10°C, wherein the solid content of the intermediate transition layer is 85±1%.

[0010] In a preferred embodiment of the coal bunker dome and construction method of the present invention, the surface sealing layer comprises acrylic polyurethane, with a total dry film thickness of 60±2 μm and a solid content of 78±1%.

[0011] Another object of the present invention is to provide a construction method for a coal bunker dome, which aims to solve the problem that the construction surface is processed without being treated during on-site construction, thereby reducing the corrosion resistance and wear resistance of the dome in the later stage.

[0012] In order to solve the above technical problems, the present invention also provides the following technical solutions: a construction method for a coal bunker dome, which includes performing heavy rust removal treatment on the surface of the dome-shaped steel substrate to achieve a clean state suitable for coating adhesion, and removing surface oil, oxide scale and rust products.

[0013] In a preferred embodiment of the coal bunker dome and construction method of the present invention: an epoxy zinc-rich coating having a zinc content that meets cathodic protection requirements is sprayed to form an electrochemical protective base layer, and the coating is applied using pressure-type spraying equipment to ensure a dense bond with the steel substrate.

[0014] In a preferred embodiment of the coal bunker dome and construction method of the present invention: an epoxy micaceous iron oxide coating having an interlayer adhesion enhancement function is sprayed, and the coating can be cured in a low temperature environment to form an intermediate shielding layer that buffers the electrochemical gradient.

[0015] In a preferred embodiment of the coal bunker dome and construction method of the present invention: in the construction step of the intermediate transition layer, the solid content of the coating meets the shielding performance requirements, and the ambient temperature during construction is not lower than the critical curing temperature of the coating.

[0016] In a preferred embodiment of the coal bunker dome and construction method of the present invention: each layer of coating is cured according to the process requirements to ensure that the total dry film thickness meets the long-term protection requirements and the interlayer bonding strength meets the design standards.

[0017] The beneficial effects of the present invention are: in view of the long-term erosion of the coal bunker dome steel structure in coastal areas by sea breeze and salt spray, the difference in zinc content between adjacent layers is optimized, thereby avoiding the problems of potential conduction disorder, local corrosion, coating peeling and short service life, thereby improving the corrosion resistance and stability of the dome protective layer and extending its service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to make the technical solution of the embodiments of the present application clearer, the drawings of the embodiments of the present application will be briefly introduced below. Obviously, the drawings described in the following description only relate to some embodiments of the present application, but not limit the present application. Among them:

[0019] Figure 1 A partial structure schematic diagram of a composite protective coating in a coal bunker dome is shown. DETAILED DESCRIPTION

[0020] In order to make the technical solution of the embodiments of the present application clearer, the drawings of the embodiments of the present application will be briefly introduced below. Obviously, the drawings described in the following description only relate to some embodiments of the present application, but not limit the present application. Among them:

[0021] The terms used in the present application are those general terms currently widely used in the art in consideration of the functions about the present application, but the terms can be changed according to the intention of the person of ordinary skill in the art, precedent or new technology in the art. In addition, specific terms can be selected by the applicant, and in this case, the detailed meaning thereof will be described in the detailed description of the present application. Therefore, the terms used in the specification should not be understood as mere names, but based on the meaning of the terms and the overall description of the present application.

[0022] Embodiment one

[0023] Referring to Figure 1 , the present embodiment provides a coal bunker dome and a construction method, which comprises a composite protective coating 1 attached to the outer surface of the dome-shaped steel base, the composite protective coating 1 comprises a steel base interface layer 11, an intermediate transition layer 12 and a surface sealing layer 13 distributed in turn from inside to outside, the composite protective coating 1 is a technical solution painted by the staff, wherein the steel base interface layer 11 is coated with a layer by epoxy zinc-rich paint.

[0024] Specifically, the steel base interface layer 11 is composed of epoxy resin, modified polyamide curing agent, ultra-fine zinc powder (average particle size of 3-4 um), additives and solvents, etc. Among them, the epoxy resin is used to provide a three-dimensional cross-linked network, to carry zinc powder particles, to block the penetration of water and oxygen, thereby achieving the effect of reducing the water permeability, which is used to react with the curing agent to form a dense network to wrap the zinc powder.

[0025] Further, the amide curing agent can enhance the toughness of the material itself due to the long-chain fatty acid structure to improve the flexibility of the coating, prevent the phenomenon of fracture, and the material itself is resistant to hydrolysis

[0026] Among them, the ultra-fine zinc powder is through the sacrifice anode reaction:

[0027] Zn→Zn 2+ +2e -

[0028] so as to accelerate the ion exchange reaction:

[0029] O2+2H2O+4e - →4OH -

[0030] Furthermore, the difference in zinc content between adjacent layers of the composite protective coating 1 is 1.5±0.2%, and a step-type electrochemical gradient is formed between the layers.

[0031] The steel-based interface layer 11 uses high zinc, which acts as a sacrificial anode and is corroded first, providing cathodic protection for the steel. The zinc powder forms a Zn-Fe alloy layer with the steel surface, which enhances the adhesion of the coating.

[0032] Furthermore, the intermediate transition layer 12 mainly includes epoxy mica iron oxide and zinc powder, which is usually used to maintain a certain electrochemical protection ability for electrical conduction during operation, make up for the protection gap after the surface shielding fails, maintain the flexibility of the coating, and reduce cracking caused by thermal expansion and contraction. The surface sealing layer 13 is directly in contact with external substances because it is arranged on the outer surface of the composite protective coating 1. It usually includes epoxy-polysiloxane hybrid resin, phosphorus graphene and silane coupling modified zinc powder to ensure the enhanced surface hardness of the coating.

[0033] At the same time, if one of the two adjacent coatings is a high-zinc coating (a coating with a high zinc content) and the other is a zinc-free paint layer (the paint surface is not painted with zinc), the standard electrode potential of zinc (relative to the standard hydrogen electrode) is lower than that of iron due to the presence of an electrolyte solution (such as a conductive film formed by moisture in the air, salt spray, etc.) between the zinc (Zn) in the high-zinc coating and the metal matrix (usually iron Fe) in the paint layer. In a galvanic cell, zinc, as the anode, has a lower potential and is more likely to lose electrons and undergo oxidation reactions; while iron, as the cathode, has a higher potential and attracts electrons to it. This potential difference is the driving force for the generation of current and corrosion reactions. Due to the large difference in electrode potential between zinc and iron, the potential difference between the two poles in the galvanic cell is large. This large potential difference prompts electrons to flow from zinc to iron, forming a current loop in the electrolyte solution, thereby accelerating the dissolution and corrosion of zinc, and gradually increasing the potential difference between the two, resulting in local excessive consumption of the high zinc layer (for example, the corrosion rate at the damaged coating is 3-5 times faster than that in the normal area), forming an electrolytic cell at the interface, and accelerating the peeling of the coating. Through the three-layer zinc content gradient, the potential difference between adjacent layers is controlled to be small, forming a smooth potential conduction curve, avoiding local insufficient protection. In addition, in the salt spray test, the non-gradient coating has obvious rust pits in the area with a large potential difference.

[0034] The steel-based interface layer 11 serves as the main anode layer, and sacrificial anode reaction occurs preferentially. The intermediate transition layer 12 forms a potential difference with the steel-based interface layer 11. The surface sealing layer 13 serves as a buffer layer to provide electrochemical protection. The potential difference between adjacent layers avoids the sudden change in current density of traditional coatings, so that the corrosion current is evenly distributed throughout the composite layer rather than concentrated in a weak area. When the steel-based interface layer 11 is locally worn or corroded, the intermediate transition layer 12 becomes a new anode due to the potential difference and continues to provide protection, forming a mechanism for mutual transmission between the three layers, thereby extending the overall protection period.

[0035] Specifically, traditional coatings produce electrochemical expansion stress due to the large potential difference, which leads to microcracks in the coating. Therefore, the potential difference needs to be reduced. The smooth potential gradient regulates the interfacial electrochemical environment, so that the zinc, iron, and oxygen systems are in the optimal reaction state both thermodynamically and kinetically. The transition layer is mainly composed of spinel structure ZnFe2O4, which has both high bonding strength and excellent corrosion resistance, thus promoting the formation of a nano-scale Zn-Fe-O transition layer. Its standard formation free energy has a tendency to form spontaneously, which promotes the adhesion of traditional coatings to be improved, thereby reducing the risk of coating peeling due to wear.

[0036] An experiment was conducted on the difference in zinc content between adjacent layers of the composite protective coating 1.

[0037] First, an electrochemical workstation was used to measure the potential difference / polarization curve, a salt spray test chamber was used to simulate the corrosion environment, a scanning electron microscope was used to observe the interface structure, an X-ray spectrometer was used to analyze the composition of the Zn-Fe-O transition layer, and a potentiometer with an accuracy of 0.1mV was used to monitor the interlayer potential in real time.

[0038] First we select the standard composite protective coating 1:

[0039] Experimental material 1: The zinc content of the steel-based interface layer 11 is 86%, the zinc content of the intermediate transition layer 12 is 84%, and the zinc content of the surface sealing layer 13 is 83%. The difference in zinc content between adjacent layers is large and unequal;

[0040] Experimental material 2: The zinc content of the steel-based interface layer 11 is 86%, the zinc content of the intermediate transition layer 12 is 84%, and the zinc content of the surface sealing layer 13 is 83.5%. The difference in zinc content between adjacent layers is not equal, but is smaller than that of experimental material 1.

[0041] Experimental material 3: The metal zinc content in the steel-based interface layer 11 is 86%, the zinc content in the intermediate transition layer 12 is 84%, and the zinc content in the surface sealing layer 13 is 82%. The zinc content difference between adjacent layers is equal, but the difference is larger than that in experimental material 2.

[0042] It is noted that during the experiment, due to the long normal measurement period, the salt spray concentration was adjusted using conventional salt spray: 5% NaCl solution to simulate a mild marine environment;

[0043] Accelerated salt spray: It can be increased to 10% NaCl solution, accelerating the corrosion rate by about 1.5 times. However, it should be noted that excessively high chloride ion concentration may change the corrosion mechanism, so conventional salt spray comparison verification should be carried out simultaneously.

[0044] Ring salt spray test, using the "salt spray → dry → wet heat" cycle mode

[0045] The following is the experimental data:

[0046]

[0047]

[0048]

[0049]

[0050] Table 1

[0051] in:

[0052] Salt spray test results are for one week (after the accelerated salt spray process);

[0053] H represents the maximum impact height of the elastic impactor.

[0054] In summary, we can conclude that:

[0055] In experimental material 1, the potential difference between the two layers is extremely large, resulting in a disordered potential conduction path. The potential standard deviation is as high as 18.7 mV, the charge transfer resistance is small, the corrosion current is easily concentrated, and local corrosion is accelerated.

[0056] Experimental material 2 reduces the potential difference between the transition layer and the sealing layer, making the potential conduction relatively stable. The potential standard deviation is reduced to 12.3mV, the charge transfer resistance is increased, and the corrosion current is effectively suppressed.

[0057] Although the potential difference between the two layers of experimental material 3 is equal, the value is too large, resulting in violent potential fluctuations and the highest potential standard deviation. The charge transfer resistance decreases instead, which is not conducive to corrosion prevention.

[0058] In experimental material 1, due to the disordered potential difference, the corrosive medium easily penetrates the coating in a salt spray environment, resulting in a large area of ​​rust, peeling, and white rust, and a fast electrochemical corrosion rate;

[0059] Experimental material 2 effectively blocked the corrosive medium by optimizing the potential difference, and various corrosion indicators were significantly reduced, and the corrosion rate was slowed down;

[0060] Although the potential difference of experimental material 3 is equal, the excessive difference causes stress concentration inside the coating, which accelerates the destruction of the coating and results in the worst corrosion resistance.

[0061] The electrochemical stress caused by the potential difference in experimental material 1 weakened the interlayer bonding force, resulting in low adhesion and average coating hardness;

[0062] The reasonable potential difference design of experimental material 2 reduces the stress effect, and the interlayer adhesion and overall hardness are improved;

[0063] The excessive potential difference of experimental material 3 produces large internal stress, which seriously affects the interlayer adhesion and coating hardness, and has the worst structural stability.

[0064] Based on the experiment, it was concluded that when the difference in zinc content between adjacent layers of the composite protective coating 1 is equal, the best solution is obtained for the existing corrosion degree and the hardness test of the coating as a whole. Therefore, when the difference in zinc content between adjacent layers of the composite protective coating 1 is equal, the effect is best.

[0065] Example 2

[0066] According to the above results, it is necessary to determine the optimal zinc content in the steel-based interface layer 11. The experimental method is the same as above. This experiment provides 15 sets of experimental data, and the experimental data meet the zinc content standard of the composite protective coating 1, as shown in Table 2 below:

[0067]

[0068]

[0069] Table 2

[0070] As can be seen from Table 2, from experimental group 5 (84.0%) to experimental group 4 (83.5%), the corrosion area increased sharply from 0.9% to 1.3%, an increase of 44%; the potential standard deviation increased from 6.8mV to 7.4mV, and the charge transfer resistance increased from 1.2×10 8 Ω·cm 2 reduced to 1.1×10 8 Ω·cm 2 , indicating that when the zinc content is lower than 84%, the electrochemical protection efficiency decreases significantly and the interlayer potential conduction begins to be unstable. This is because the insufficient zinc content leads to the weakening of the sacrificial anode effect and the incomplete growth of the Zn-Fe-O transition layer (SEM shows that the thickness is reduced from 60nm to 45nm), which cannot effectively block the corrosive medium.

[0071] From experimental group 9 (86.0%) to experimental group 8 (85.5%), the corrosion area increased from 1.1% to 0.4%, a decrease of 64%; the potential standard deviation decreased from 7.5mV to 5.1mV, and the charge transfer resistance decreased from 1.2×10□Ω·cm2 Increased to 1.6×10 8 Ω·cm 2 The average interlayer adhesion dropped from 6.6MPa to 7.3MPa, indicating that a zinc content of more than 86% would increase interlayer stress and reduce structural stability. Excessive zinc content leads to zinc powder accumulation, a relatively reduced resin ratio, and increased internal stress in the coating. At the same time, the rapid consumption of zinc reduces the subsequent protective ability and accelerates the corrosion process.

[0072] Experimental groups 6-8 (84.5%-85.5%) performed well in all indicators, with corrosion area <0.5%, potential standard deviation <6.0mV, and charge transfer resistance >1.4×10 8 Ω·cm 2 The interlayer adhesion is greater than 7.1MPa, achieving the best balance among electrochemical protection, potential conduction uniformity and structural stability. This interval forms a dense and stable Zn-Fe-O transition layer (TEM shows that the crystals are complete and have no obvious defects) by precisely controlling the zinc content, so that the coating can still maintain excellent protective performance in complex environments, which has significant technical advantages compared with other intervals.

[0073] Example 3

[0074] The steel-based interface layer 11 is coated twice to form two layers of dry film, and the total thickness of the two layers of dry film is 130±5μm. A layer of epoxy zinc-rich paint is first applied to the surface of the steel substrate, and then a second layer is applied after it dries. This will make the zinc powder denser and the protective layer formed thicker. The thickness of the intermediate transition layer 12 is 70±3μm, and the ambient temperature during construction is at -10℃, which can be cured. Therefore, it is necessary to ensure that the temperature is not lower than the critical curing temperature of the coating -10℃ during construction. The solid content of the intermediate transition layer 12 is 85±1%, and the surface sealing layer 13 includes acrylic polyurethane, with a total dry film thickness of 60±2μm and a solid content of 78±1%.

[0075] Specifically, the epoxy zinc-rich primer consists of epoxy resin (40% by mass), modified polyamide curing agent (15%), ultrafine zinc powder (average particle size 3-4μm, content 85±1%) and additives (5%). After mixing, the viscosity is measured by applying 4 cups at 25°C for 80-100 seconds to ensure good leveling during spraying. The epoxy mica iron oxide intermediate paint consists of epoxy resin (50%), polyamine curing agent (20%), mica iron oxide (25%) and low-temperature accelerator (5%). The composition is 85±1% solid content, and the viscosity is ≤200mPa·s at -10℃ to ensure construction fluidity in low temperature environment. The environmental conditions are in a low temperature environment of -10℃±2℃. Heating spraying equipment is used (the paint is preheated to 20℃), and the pressure of 12MPa is used for spraying. The wet film thickness is controlled at 150±5μm, and the dry film thickness after curing is 70±3μm. The coating surface temperature is monitored in real time by an infrared temperature recorder. After curing for 7 days at -10℃, the coating hardness meets the standard.

[0076] Furthermore, air spraying (pressure 0.4 MPa) was used in two passes, with each pass having a wet film thickness of 80 μm and a total dry film thickness of 60 ± 2 μm. The construction environment temperature was controlled between -5°C and 40°C, with a relative humidity of ≤85%. Performance testing was performed after curing at room temperature for 7 days.

[0077] Furthermore, the three-layer coating forms a smooth potential conduction curve through zinc content gradient design. Combined with double-pass coating and low-temperature curing processes, the thickness of the Zn-Fe-O transition layer reaches 65nm and the crystal structure is complete.

[0078] Furthermore, the surface of the dome-shaped steel substrate is subjected to heavy rust removal treatment, with attention paid to achieving clean coating adhesion, removing surface oil, oxide scale and rust products, and avoiding degradation of coating performance due to construction operations.

[0079] Finally, it should be pointed out that the methods and devices described in detail above are merely embodiments, and those skilled in the art can modify these embodiments in different ways without departing from the scope of the present invention.

Claims

1. A coal bunker dome, characterized by: include, A composite protective coating (1) attached to the outer surface of a dome-shaped steel substrate, the composite protective coating (1) comprising a steel-based interface layer (11), an intermediate transition layer (12), and a surface sealing layer (13) sequentially distributed from the inside to the outside; The difference in zinc content between adjacent layers of the composite protective coating (1) is 1.5±0.2%, and a step-type electrochemical gradient is formed between the layers.

2. The coal bunker dome according to claim 1, characterized in that: The metal zinc content in the steel-based interface layer (11) is 85±1%; The zinc content of the intermediate transition layer (12) is 83.5±1%; The zinc content of the surface sealing layer (13) is 82±1%.

3. The coal bunker dome according to claim 2, characterized in that: The steel-based interface layer (11) is coated twice to form two layers of dry film, and the total thickness of the two layers of dry film is 130±5 μm.

4. The coal bunker dome according to claim 1 or 3, characterized in that: The intermediate transition layer (12) has a thickness of 70±3 μm and is curable in an environment of -10°C, wherein the solid content of the intermediate transition layer (12) is 85±1%.

5. The coal bunker dome according to claim 4, characterized in that: The surface sealing layer (13) comprises acrylic polyurethane, with a total dry film thickness of 60±2 μm and a solid content of 78±1%.

6. A method for constructing a coal bunker dome, characterized in that: Applicable to the coal bunker dome according to any one of claims 1 to 5; and, performing heavy rust removal treatment on the surface of the dome-shaped steel substrate, paying attention to achieving clean adhesion of the coating, and removing surface oil, oxide scale and rust products.

7. The method for constructing a coal bunker dome according to claim 6, characterized in that: An epoxy zinc-rich coating whose zinc content meets the requirements of cathodic protection is sprayed to form an electrochemical protection base layer. The coating is applied through a pressure-type spraying device to ensure a dense bond with the steel substrate.

8. The method for constructing a coal bunker dome according to claim 7, characterized in that: An epoxy micaceous iron oxide coating with interlayer adhesion enhancement function is sprayed and can be cured in a low temperature environment to form an intermediate shielding layer that buffers the electrochemical gradient.

9. The method for constructing a coal bunker dome according to claim 8, characterized in that: During the construction of the intermediate transition layer, the solid content of the coating meets the shielding performance requirements, and the ambient temperature during construction is not lower than the critical curing temperature of the coating.

10. The method for constructing a coal bunker dome according to claim 9, characterized in that: Each layer of coating is cured according to process requirements.

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