System for spraying polyurea anticorrosive paint on outer surface of PCCP (prestressed concrete cylinder pipe)

Abstract

The invention provides a system for spraying polyurea anticorrosive paint on the outer surface of a PCCP (prestressed concrete cylinder pipe). The system consists of epoxy primer, sealing putty and spraying polyurea finish paint, the epoxy primer component A comprises the following components in parts by mass: 60-80 parts of epoxy resin, 0.3-0.5 part of a defoaming agent, 0.3-0.5 part of a base material wetting agent and 20-40 parts of a reactive diluent, and the epoxy primer component B comprises the following components in parts by mass: 18-30 parts of phenolic aldehyde amine; the sealing putty component A comprises the following components in parts by mass: 30-45 parts of an isocyanate prepolymer A, 15-30 parts of an isocyanate prepolymer B and 30-50 parts of a solvent, and the sealing putty component B comprises the following components in parts by mass: 40-50 parts of wood flour; the spraying polyurea finish paint component A is 100 parts by mass of an isocyanate prepolymer A, and the spraying polyurea finish paint component B comprises 18-30 parts by mass of an amine chain extender, 70-80 parts by mass of polyether amine and 0-3 parts by mass of carbon black color paste; the method has the characteristics of easiness in construction, high construction efficiency, attractive construction surface, no defects such as through holes and the like, meanwhile, the coating has excellent adhesive force, and the technical problems that polyurea sprayed on the outer surface of the PCCP is difficult to adhere, dense holes appear and the like are solved.

Description

Technical Field

[0001] This invention relates to the field of special coatings technology, and in particular to a polyurea anti-corrosion coating system for spraying on the outer surface of PCCP pipes, especially for a polyurea anti-corrosion coating system for spraying on the outer surface of PCCP-C pipes. Background Technology

[0002] Prestressed concrete cylinder pipes (PCCPs) are widely used in large-scale water diversion projects such as urban water supply trunk lines due to their high strength, high impermeability, and durability. However, PCCP pipes are subjected to harsh conditions such as complex aquatic environments (e.g., corrosive media containing chloride ions and sulfates), soil stress, and alternating wet and dry conditions. Their steel cylinders and concrete structures are susceptible to chemical corrosion, electrochemical corrosion, and microbial erosion, leading to decreased pipe strength and increased leakage risk. Statistics show that PCCP pipes without effective corrosion protection measures may develop localized corrosion perforation in the steel cylinder within 5-10 years, seriously threatening water supply safety and the project's lifespan. Therefore, developing high-performance anti-corrosion coatings has become crucial for ensuring the long-term stable operation of PCCP pipes.

[0003] In recent years, due to the advantages of high construction efficiency and aesthetic appeal of sprayed polyurea, major pipe manufacturers have gradually begun to test sprayed polyurea coatings on the outer surface of PCCP pipes. The outer surface of PCCP-DE pipes is coated with cement mortar, which has fewer surface pores. Directly applying sprayed polyurea topcoat results in a smoother appearance. A small number of through holes may exist in the coating, which can be repaired later with anti-corrosion putty.

[0004] However, for PCCP-C pipes, the outer surface is a cement-cast surface, which is extremely smooth and contains a large number of pores. If a sprayed polyurea or a "primer + sprayed polyurea" coating system is directly used, dense through holes will appear on the coating surface, which is extremely unsightly. Furthermore, it is time-consuming and laborious to repair the through holes with putty later, and it is difficult to repair them completely. As a result, the coating system is in a state of failure after the coating construction is completed, and it cannot play a role in corrosion protection. Summary of the Invention

[0005] In view of this, the present invention aims to propose a polyurea anti-corrosion coating system for the outer surface of PCCP pipes, so as to solve the problem of dense pores that occur when applying polyurea or "primer + polyurea" to the outer surface of PCCP-C pipes in the prior art.

[0006] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0007] A polyurea anti-corrosion coating system for the outer surface of PCCP pipe consists of epoxy primer, sealing putty, and sprayed polyurea topcoat;

[0008] By weight, component A of the epoxy primer comprises 60-80 parts epoxy resin, 0.3-0.5 parts defoamer, 0.3-0.5 parts substrate wetting agent, and 20-40 parts reactive diluent; component B of the epoxy primer comprises 18-30 parts phenolic amine.

[0009] By mass, component A of the sealing putty includes 30-45 parts of isocyanate prepolymer A, 15-30 parts of isocyanate prepolymer B, and 30-50 parts of solvent, while component B of the sealing putty is 40-50 parts of wood flour.

[0010] By mass, component A of the sprayed polyurea topcoat consists of 100 parts of isocyanate prepolymer A, and component B of the sprayed polyurea topcoat consists of 18-30 parts of amine chain extender, 70-80 parts of polyetheramine, and 0-3 parts of carbon black paste.

[0011] Furthermore, the anti-corrosion coating system is applied to the outer surface of the PCCP pipe in the following order: epoxy primer, sealing putty, and sprayed polyurea topcoat.

[0012] Furthermore, the epoxy primer has a wet film thickness of 200 μm, and the sprayed polyurea topcoat has a wet film thickness of 1500 μm.

[0013] Furthermore, the isocyanate prepolymer A is an MDI-modified isocyanate prepolymer with an NCO content of 15.5-18%; and the isocyanate prepolymer B is an MDI-modified isocyanate prepolymer with an NCO content of 12-15.5%.

[0014] Furthermore, in component A of the epoxy primer, the epoxy resin is E51 with a solid content of 100%; the defoamer is Eucalyptus 272s; the substrate wetting agent is one or a mixture of TEGO Twin4100 or TEGO Wet 280; and the reactive diluent is one or a mixture of D131, EPG-270, GE-24 or GE-21.

[0015] Furthermore, the phenolic amine is one of T-31, NX-2015 or KD-504 or a mixture thereof.

[0016] Furthermore, in component A of the sealing putty, the solvent is a high-boiling-point solvent, including one or a mixture of 100# solvent oil, propylene carbonate, or 200# solvent oil.

[0017] Furthermore, the wood flour is one of 200-mesh wood flour or 400-mesh wood flour, or a mixture thereof.

[0018] Furthermore, in component B of the sprayed polyurea topcoat, the amine chain extender is one or a mixture of diethyltoluene diamine (DETDA), 3,3-dichloro-4,4-diaminodiphenyl (MOCA), or dimethylthiotoluene diamine (DMTDA); the polyether amine is one or a mixture of D230, D400, D2000, T403, or T5000; and the carbon black paste is a solvent-based carbon black paste with a solid content of 36.8%.

[0019] Compared with existing technologies, the polyurea anti-corrosion coating system for the outer surface of PCCP pipes described in this invention has the following advantages:

[0020] The polyurea anti-corrosion coating system for the outer surface of PCCP pipe described in this invention has the advantages of easy construction, high construction efficiency, beautiful surface finish, and absence of defects such as through holes. At the same time, its coating has excellent adhesion, which solves the technical problems of poor adhesion and dense pores in the spraying of polyurea on the outer surface of PCCP-C pipe, improves the application quality of polyurea on PCCP pipe, and helps to promote the widespread application of polyurea in this field. Attached Figure Description

[0021] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0022] Figure 1 The infrared spectrum of isocyanate prepolymer A described in the embodiments of the present invention;

[0023] Figure 2 The infrared spectrum of isocyanate prepolymer B described in the embodiments of the present invention;

[0024] Figure 3 This is a photograph of the initial state of the PCCP-C tube described in an embodiment of the present invention;

[0025] Figure 4 This is a partial photograph of the outer surface of the PCCP-C pipe described in an embodiment of the present invention;

[0026] Figure 5 This is a photograph of the outer surface of the PCCP-C pipe after coating, which is Comparative Example 1 of the present invention.

[0027] Figure 6 This is a partial surface photograph of the outer surface of the PCCP-C pipe after coating, as shown in Comparative Example 1 of the present invention.

[0028] Figure 7 This is a photograph of the outer surface of the PCCP-C pipe after coating, which is Comparative Example 2 of the present invention;

[0029] Figure 8This is a partial surface photograph of the outer surface of the PCCP-C pipe after coating, as shown in Comparative Example 2 of the present invention.

[0030] Figure 9 This is a photograph of the outer surface of the PCCP-C pipe after coating, according to Embodiment 1 of the present invention.

[0031] Figure 10 This is a partial surface photograph of the PCCP-C pipe after coating in Embodiment 1 of the present invention. Detailed Implementation

[0032] The inventive concepts of this application will be described below using terminology commonly used by those skilled in the art to communicate the essence of their work to others skilled in the art. However, these inventive concepts may be embodied in many different forms and should not be construed as limited to the embodiments described herein.

[0033] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. The accompanying drawings are mostly outdoor photographs taken on-site, and are inevitably affected by factors such as the actual shooting environment and angle, and are for reference only. Furthermore, this application primarily targets PCCP-C pipes; all PCCP pipes mentioned in this application can be understood as PCCP-C pipes. However, the coating system of this application is not limited to use on PCCP-C pipes and can also be used on other types of PCCP pipes.

[0034] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] To address the issue of dense pores that occur when applying polyurea or a combination of primer and polyurea to the outer surface of PCCP-C pipes in existing technologies, this embodiment proposes a polyurea anti-corrosion coating system for the outer surface of PCCP pipes, consisting of an epoxy primer, a sealing putty, and a polyurea topcoat.

[0036] By weight, component A of the epoxy primer comprises 60-80 parts epoxy resin, 0.3-0.5 parts defoamer, 0.3-0.5 parts substrate wetting agent, and 20-40 parts reactive diluent; component B of the epoxy primer comprises 18-30 parts phenolic amine.

[0037] By mass, component A of the sealing putty includes 30-45 parts of isocyanate prepolymer A, 15-30 parts of isocyanate prepolymer B, and 30-50 parts of solvent, while component B of the sealing putty is 40-50 parts of wood flour.

[0038] By mass, component A of the sprayed polyurea topcoat consists of 100 parts of isocyanate prepolymer A, and component B of the sprayed polyurea topcoat consists of 18-30 parts of amine chain extender, 70-80 parts of polyetheramine, and 0-3 parts of carbon black paste.

[0039] It should be noted that, for any coating such as epoxy primer, sealing putty, or sprayed polyurea topcoat, this application specifies the amount of each substance in components A and B by mass parts, which can be used to calculate the ratio between components A and B.

[0040] The anti-corrosion coating system is applied to the outer surface of the PCCP pipe in the following order: epoxy primer, sealing putty, and sprayed polyurea topcoat.

[0041] The isocyanate prepolymer A is a commercially available, highly reactive MDI-modified isocyanate prepolymer, and its infrared spectrum is shown below. Figure 1 As shown, its NCO content is 15.5-18%; the isocyanate prepolymer B is a commercially available MDI-modified isocyanate prepolymer with medium to low reactivity, and its infrared spectrum is shown in the figure. Figure 2 As shown, its NCO content is 12-15.5%. To avoid ambiguity, high reactivity and medium-low reactivity can be simply and intuitively understood as the speed of gelation (corresponding to gel time) of the MDI-modified isocyanate prepolymer during the polymerization reaction. For example, high reactivity corresponds to a gel time of less than 15 seconds, while medium-low reactivity corresponds to a gel time of more than 30 seconds. Of course, this is just a simple example for easy understanding of high reactivity and medium-low reactivity. This application recommends combining infrared spectra and NCO content to distinguish between high reactivity and medium-low reactivity.

[0042] For PCCP-C pipes, the outer surface is a smooth concrete surface. When applying conventional primer, the microporous structure of the concrete absorbs the resin base of the primer into the concrete interior, while pigments and fillers are blocked on the outer surface. Once the paint film is surface dry, the pigments and fillers on the outer surface, lacking sufficient base material coating, are easily detached, leading to poor coating adhesion. Furthermore, concrete, being an alkaline material, easily causes hydrolysis of some coating components. In this application, the epoxy primer is a solvent-free epoxy primer with quick-drying properties. Applied to the outer surface of the PCCP pipe as a sealing primer, it not only possesses excellent sealing properties, effectively sealing the micropores of the concrete, but also exhibits alkali resistance and stability with excellent adhesion to concrete, thus providing excellent adhesion for the entire anti-corrosion coating system.

[0043] For PCCP pipes coated with the epoxy primer, although the micropores of the concrete can be sealed, the outer surface of the PCCP-C pipe has dense large and deep pores. Therefore, this application further applies a sealing putty after applying the epoxy primer to repair and seal the large and deep pores. In this application, the sealing putty uses isocyanate prepolymer as component A, and the viscosity of the material is adjusted to between 50 and 100 cps, and wood flour is used as a filler. The lower the viscosity of component A of the sealing putty, the easier the scraping and the higher the worker's construction efficiency. However, low viscosity makes the paint prone to sagging, while wood flour (component B of the sealing putty) can perfectly solve this problem. Due to its high oil absorption, the wood flour absorbs the resin of component A, thereby preventing the resin of component A from flowing. In addition, the low density of wood flour makes the mixture of wood flour and component A lighter, with less gravitational effect. Therefore, the sealing putty of this application has good construction (scraping) performance, can be thickly coated according to actual needs, and is not prone to sagging.

[0044] Furthermore, PCCP-C pipes have numerous pores on their surface. If existing technology (direct spraying of polyurea products) is used, the appearance will have a large number of through-holes, failing to provide adequate protection. This application employs a "primer + putty + topcoat" anti-corrosion coating system. The epoxy primer seals micropores, and the sealing putty seals most large and deep pores. After primer and putty treatment, PCCP-C pipes still have many small pores, placing high demands on the pore-sealing effect of the topcoat. Through extensive field coating tests, the applicant has found that a faster topcoat drying rate results in better pore-sealing and a more complete appearance. Therefore, the sprayed polyurea topcoat in this application is a fast-drying type, achieving a pore-free surface after the entire anti-corrosion coating system is applied.

[0045] For sealing putty, it is mainly used to repair and seal large and deep holes. It needs to be applied manually in appropriate amounts according to the actual hole conditions on the surface of the PCCP pipe. Given that the hole conditions on the surface of each PCCP pipe are different, this application does not impose too many restrictions on its application. For the spraying of epoxy primer and sprayed polyurea topcoat, existing spraying equipment is used for construction. In terms of the corresponding paint film thickness, the wet film thickness of the epoxy primer is preferably 200μm, and the wet film thickness of the sprayed polyurea topcoat is preferably 1500μm.

[0046] In component A of the epoxy primer, the epoxy resin is E51 with a solid content of 100%; the defoamer is Ucar 272s; the substrate wetting agent is one or a mixture of TEGO Twin 4100 or TEGO Wet 280; and the reactive diluent is one or a mixture of D131, EPG-270, GE-24 or GE-21.

[0047] For component B of the epoxy primer, the phenolic amine is one of T-31, NX-2015 or KD-504 or a mixture thereof.

[0048] In the A component of the sealing putty, the isocyanate prepolymer A and isocyanate prepolymer B are the same as described above and will not be repeated. The solvent is a high-boiling-point solvent, including one or a mixture of 100# solvent oil, propylene carbonate, or 200# solvent oil.

[0049] For component B of the sealing putty, the wood flour is either 200-mesh wood flour or 400-mesh wood flour or a mixture thereof; the wood flour can be directly purchased commercially, and its main components are cellulose, hemicellulose and lignin, etc.

[0050] For component A of the sprayed polyurea topcoat, the isocyanate prepolymer A is the same as described above and will not be repeated.

[0051] In component B of the sprayed polyurea topcoat, the amine chain extender is one or a mixture of diethyltoluene diamine (DETDA), 3,3-dichloro-4,4-diaminodiphenyl (MOCA), or dimethylthiotoluene diamine (DMTDA); the polyether amine is one or a mixture of D230, D400, D2000, T403, or T5000; and the carbon black paste is a solvent-based carbon black paste with a solid content of 36.8%. Of course, if it is not necessary to enhance the color of the sprayed polyurea topcoat, the carbon black paste can be omitted.

[0052] It should be noted that all the substances described in this application are commercially available, and some of the names are trade names commonly used in the field.

[0053] The present invention is further illustrated by the following comparative examples and embodiments, but is not limited to the embodiments described.

[0054] The coating system formulations of Comparative Examples 1, 2, and Example 1 are shown in Table 1. Example 1 uses the anti-corrosion coating system components described in this application. Comparative Example 1 has the same components as Example 1, except that component A of the sprayed polyurea topcoat is replaced with isocyanate prepolymer B instead of isocyanate prepolymer A. Comparative Example 2 has the same components as Example 1, except that the sealing putty is omitted.

[0055] Table 1. Coating system formulations for Comparative Examples 1, 2, and Example 1 (all by parts by mass).

[0056]

[0057] The preparation methods for Comparative Examples 1 and 2 and Example 1 are as follows:

[0058] epoxy primer

[0059] According to the formulation in Table 1, epoxy resin E51, defoamer Yuka 272s, substrate wetting agent TEGO Twin 4100, and reactive diluent EGP-270 were added to the mixing tank and dispersed at a stirring speed of 300 r / min for 5 min to obtain epoxy primer component A. According to the formulation in Table 1, phenolic amine T31 was dispensed to obtain epoxy primer component B.

[0060] Sealing putty (no preparation required for comparison ratio 2)

[0061] According to the formula in Table 1, isocyanate prepolymer A, isocyanate prepolymer B, and 100# solvent oil were added to the mixing tank and dispersed at a stirring speed of 300 r / min for 5 min to obtain sealing putty component A. According to the formula in Table 1, 200 mesh wood flour was packaged to obtain sealing putty component B.

[0062] Spraying polyurea topcoat

[0063] According to the formulation in Table 1, isocyanate prepolymer A was packaged to obtain component A of the sprayed polyurea topcoat used in Comparative Example 2 and Example 1; isocyanate prepolymer B was packaged to obtain component A of the sprayed polyurea topcoat used in Comparative Example 1. According to the formulation in Table 1, amine chain extender DETDA, polyetheramine D400, polyetheramine D2000, polyetheramine T5000 and carbon black paste were added to the mixing tank and dispersed at a stirring speed of 300 r / min for 5 min to obtain topcoat component B.

[0064] After the samples of Comparative Examples 1, 2 and Example 1 were prepared, on-site coating tests were conducted.

[0065] Take at least three PCCP-C pipes from the same batch as corresponding samples, all with a size of Φ3400mm. See attached sample photos. Figure 3 , 4 .

[0066] The epoxy primer is applied to the outer surface of the PCCP-C pipe using a conventional airless spraying method; the sealing putty is applied manually by scraping, mainly to repair and seal large and deep holes, with the aim of completely sealing them; the polyurea topcoat is applied using a conventional two-component spraying method; the processes and equipment for airless spraying and two-component spraying can be directly adopted from existing technologies, and will not be elaborated upon in this application.

[0067] The specific on-site coating test process and test results are shown in Table 2. Photos of the coated sample from Comparative Example 1 are attached. Figure 5 , 6 As shown in the attached image, the sample of Comparative Example 2 was photographed after coating. Figure 7 , 8As shown in the attached image, photographs were taken of the sample from Example 1 after coating. Figure 9 , 10 As shown.

[0068] Table 2. Field coating test process and test results for Comparative Examples 1 and 2 and Example 1.

[0069]

[0070] To avoid ambiguity, the number of coating passes in Table 2 refers to one round trip of spraying.

[0071] Combined with Table 2 and Appendix Figure 5-10 It can be seen that:

[0072] Comparative Examples 1, 2, and Example 1 were all coated with the epoxy primer proposed in this application. Based on GB / T 35490-2017 "Corrosion Protection Technology for Prestressed Concrete Cylinder Pipes", the final coating adhesion of the three was 3.5, 3.8, and 4.1 MPa, respectively, which can meet the national standard requirement of ≥2.5 MPa for PCCP pipe adhesion.

[0073] In addition, Comparative Example 2 did not use sealing putty to repair the epoxy primer after it was applied. The surface had dense, large and deep pores. These large pores could not be completely blocked by the fast-drying sprayed polyurea topcoat, resulting in a large number of through holes on the appearance of the pipe, which greatly increased the amount of repair work in the later stage and the coating system had poor protection.

[0074] Compared to Comparative Example 2, Comparative Example 1 used sealing putty for repair, which greatly reduced the number of through holes in the entire pipe. However, a small number of through holes still existed in some areas. This is mainly because sealing putty repair cannot completely block all holes. Small holes that are not easy to detect still exist in some areas. The slow-drying spray polyurea topcoat used in Comparative Example 1 (the material difference is isocyanate prepolymer B) cannot effectively block these small holes because the slow-drying spray polyurea topcoat cannot dry quickly during the coating process, allowing it sufficient time to flow, resulting in paint flowing away from the holes and a weak hole-blocking ability.

[0075] Example 1 has a beautiful and complete surface with almost no through holes. This is mainly because, based on Comparative Example 1, a fast-drying spray polyurea topcoat was used. The fast-drying spray polyurea topcoat dries in about 15 seconds. The paint does not have enough time to flow during the coating process, and there is still enough paint left at the holes. As a result, with multiple sprays, the holes gradually decrease in size until they are completely blocked.

[0076] Referring to the entire implementation process of Example 1, the final coating adhesion of Example 1 is 4.1 MPa, meeting the requirements of GB / T35490-2017. Furthermore, in Example 1, putty application is effortless, with a single person's application time being 1.5 hours. The primer and topcoat can be automatically sprayed using existing technology, with each application taking 5 minutes. Simultaneously, the surface after application in Example 1 is aesthetically pleasing and intact, with almost no through-holes. Therefore, the PCCP pipe external surface anti-corrosion coating system developed in this invention has the characteristics of easy application, high application efficiency, and aesthetically pleasing surface without through-holes. At the same time, its coating has excellent adhesion, solving the technical problems of poor adhesion and dense pore formation when spraying polyurea on the external surface of PCCP-C pipes, improving the application quality of polyurea on PCCP pipes, and contributing to the widespread application of polyurea in this field.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. 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.

Claims

1. A polyurea anti-corrosion coating system for spraying on the outer surface of a PCCP pipe, characterized in that, The anti-corrosion coating system consists of epoxy primer, sealing putty, and sprayed polyurea topcoat; By weight, component A of the epoxy primer comprises 60-80 parts epoxy resin, 0.3-0.5 parts defoamer, 0.3-0.5 parts substrate wetting agent, and 20-40 parts reactive diluent; component B of the epoxy primer comprises 18-30 parts phenolic amine. By mass, component A of the sealing putty includes 30-45 parts of isocyanate prepolymer A, 15-30 parts of isocyanate prepolymer B, and 30-50 parts of solvent, while component B of the sealing putty is 40-50 parts of wood flour. By mass, component A of the sprayed polyurea topcoat consists of 100 parts of isocyanate prepolymer A, and component B of the sprayed polyurea topcoat consists of 18-30 parts of amine chain extender, 70-80 parts of polyetheramine, and 0-3 parts of carbon black paste.

2. The polyurea anti-corrosion coating system for the outer surface of a PCCP pipe according to claim 1, characterized in that, The anti-corrosion coating system is applied to the outer surface of the PCCP pipe in the following order: epoxy primer, sealing putty, and sprayed polyurea topcoat.

3. The polyurea anti-corrosion coating system for the outer surface of a PCCP pipe according to claim 2, characterized in that, The epoxy primer has a wet film thickness of 200 μm, and the sprayed polyurea topcoat has a wet film thickness of 1500 μm.

4. The polyurea anti-corrosion coating system for the outer surface of a PCCP pipe according to claim 1, characterized in that, The isocyanate prepolymer A is an MDI-modified isocyanate prepolymer with an NCO content of 15.5-18%; the isocyanate prepolymer B is an MDI-modified isocyanate prepolymer with an NCO content of 12-15.5%.

5. The polyurea anti-corrosion coating system for the outer surface of a PCCP pipe according to claim 1, characterized in that, In component A of the epoxy primer, the epoxy resin is E51 with a solid content of 100%; the defoamer is Ucar 272s; the substrate wetting agent is one or a mixture of TEGO Twin 4100 or TEGO Wet 280; and the reactive diluent is one or a mixture of D131, EPG-270, GE-24 or GE-21.

6. The polyurea anti-corrosion coating system for the outer surface of a PCCP pipe according to claim 1, characterized in that, The phenolic amine is one of T-31, NX-2015 or KD-504 or a mixture thereof.

7. The polyurea anti-corrosion coating system for the outer surface of a PCCP pipe according to claim 1, characterized in that, In component A of the sealing putty, the solvent is a high-boiling-point solvent, including one or a mixture of 100# solvent oil, propylene carbonate, or 200# solvent oil.

8. The polyurea anti-corrosion coating system for the outer surface of a PCCP pipe according to claim 1, characterized in that, The wood flour is one of 200-mesh wood flour or 400-mesh wood flour, or a mixture thereof.

9. A polyurea anti-corrosion coating system for the outer surface of a PCCP pipe according to claim 1, characterized in that, In component B of the sprayed polyurea topcoat, the amine chain extender is one or a mixture of diethyltoluene diamine (DETDA), 3,3-dichloro-4,4-diaminodiphenyl (MOCA), or dimethylthiotoluene diamine (DMTDA); the polyether amine is one or a mixture of D230, D400, D2000, T403, or T5000; and the carbon black paste is a solvent-based carbon black paste with a solid content of 36.8%.

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