WO2018210212A1 - Ductile iron pipe having anti-corrosion inner coating, and production process therefor - Google Patents

Abstract

A ductile iron pipe having an anti-corrosion inner coating, and a production process therefor. An epoxy coating is applied on the inner wall of the ductile iron pipe and the paint of the epoxy coating is a solvent-free phenolic epoxy ceramic paint. The volume solid content of the solvent-free phenolic epoxy ceramic paint is greater than or equal to 98%, preferably greater than or equal to 99%. By applying the epoxy ceramic coating to the inner wall of the ductile iron pipe, the ductile iron pipe is endowed with excellent high temperature resistance, anti-corrosion performance, and abrasive resistance, the surface is smooth, frictional resistance between water and the pipe wall can be reduced, and thus a long service life of the pipe can be ensured.

Description

Ductile iron pipe with anti-corrosion inner coating and production process thereof Technical field

The invention relates to the technical field of ductile iron pipes, in particular to a ductile iron pipe for a high performance epoxy ceramic anticorrosive inner coating applied to a water pipeline.

Background technique

Ductile iron pipe has the advantages of good mechanical properties, high interface reliability, good corrosion resistance and long service life. It is widely used in urban construction water and gas transmission industries. The existing standard internal anti-corrosion coating is cement mortar lining. The inner lining has the advantages of good economy and active anti-corrosion. However, due to the inherent alkaline characteristics of cement mortar, the pH value of water quality will rise in the initial stage of water delivery. In addition, the corrosive soft water is also highly corrosive to this inner coating.

For this reason, the ductile iron pipe industry has also developed other organic internal anti-corrosion coatings, such as polyurethane coatings and epoxy coatings.

For polyurethane coatings, the main problem is that the surface treatment and environmental humidity of the substrate are very high, otherwise it may cause defects such as foaming of the coating. For centrifugal casting, the ductile iron pipe is especially hot-casting. For the caliber ductile iron pipe, the inherent inner surface slag pit and crack are very difficult to meet the surface treatment requirements, so it is particularly likely to cause problems such as foaming and peeling of the polyurethane inner coating.

Epoxy coatings are widely used in the protection of steel, but their performance requirements vary according to their application. For ductile iron pipe, it is mainly used for buried pipelines. As a water supply and drainage in the fields of municipal, water conservancy and seawater desalination, it requires a service life of 100 years, especially soft water such as soft water and municipal sewage. This requires an epoxy anticorrosive lining to have excellent corrosion resistance and wear resistance, and it is difficult to achieve such a requirement in general solvent-based epoxy coatings and solvent-free coatings. Especially for special areas (such as high temperature areas in the Middle East), higher requirements are placed on the high temperature resistance of epoxy anticorrosive linings to ensure coating adhesion and coating performance during stacking in high temperature areas like the Middle East.

However, current epoxy coatings are not able to meet the higher requirements for corrosion resistance and wear resistance. Therefore, the development of a high-performance epoxy ceramic anti-corrosion coating with high temperature resistance and excellent anti-corrosion and wear resistance is the key point and difficulty in the research of anti-corrosion coating for ductile iron pipe for conveying corrosive water in high temperature environment.

Summary of the invention

The technical problem to be solved by the invention is to provide a ductile iron pipe with an anti-corrosion inner coating and a production process thereof, and the epoxy resin coating layer of the invention is coated on the inner wall of the ductile iron pipe to have excellent high temperature resistance and corrosion resistance. Sexual, wear-resistant, smooth surface, can reduce the frictional resistance between water and pipe wall, thus ensuring the long service life of the pipeline.

The technical solution adopted by the invention is: a ductile iron pipe with an anti-corrosion coating, comprising a ductile iron pipe body, the two ends of which are a socket and a socket, and the inner wall of the ductile iron pipe is coated with the epoxy ceramic coating layer of the invention.

The commonly used phenolic epoxy coating layers are both solvent-based and solvent-free. Since the epoxy group of the novolac type epoxy resin is substantially ≥ 2 and has a relatively high viscosity, it is usually prepared as a solvent-based paint, and the solvent-based phenolic epoxy paint has a common disadvantage of a general solvent-based paint, that is, it cannot be thick. Coating, the thickness of a single coating is about ≤200μm, and in the process of solvent evaporation, there will be more channels in the coating. These two disadvantages will seriously affect the corrosion resistance of the coating. Even a century of ductile iron pipes can not achieve the long-term anti-corrosion effect of demand. If a thick coating of heavy anti-corrosion effect is to be achieved, multi-pass coating must be used, and batch production of ductile iron pipes cannot be realized.

There is also a phenolic epoxy coating known as "solvent free". Because of the high viscosity of the general polyfunctional phenolic epoxy resin, a relatively large amount of benzyl alcohol (a non-reactive diluent, which is retained in the coating due to its high boiling point) is usually added to such a coating. But these so-called solvent-free phenolic epoxy coatings are not really solvent-free. Some standards stipulate that a coating that achieves a mass solids content of ≥95% is defined as a solvent-free coating, ie a small amount of benzyl alcohol or a solvent is added. It has been found through experiments that even if a small amount of benzyl alcohol is added, the solvent-free epoxy coating (quality solid content ≥95%) specified in the relevant standards will reduce the mechanical properties, solvent resistance and chemical resistance of the cured product, especially the high temperature resistance. .

The solvent-free phenolic epoxy ceramic coating of the present invention achieves true solvent-free addition, thereby achieving a mass solid content of ≥98%, even reaching a level of ≥99%.

The solventless phenolic epoxy ceramic coating of the present invention is a two component epoxy coating of an epoxy resin component (component A) and an amine curing agent component (component B), wherein the epoxy resin component contains phenolic acid. The epoxy resin, the epoxy equivalent of the novolac epoxy resin used is 160-190, and the content (parts by weight) of the novolac epoxy resin in the epoxy resin component is 20% to 60%. It has been found that the solvent-free phenolic epoxy ceramic coating of the invention can significantly improve the crosslinking density of the coating, improve the Tg of the coating, make the coating have high temperature resistance, and have excellent corrosion resistance, compared with the previous The coating layer improves the corrosion resistance and high temperature resistance of the pipe.

Usually in order to improve the wear resistance of the pipe coating, some ceramic powder is added to the coating. The current common ceramic powder is one or more of titanium dioxide, talc (mainly composed of magnesium silicate), calcium carbonate and silica. These are known fillers used in coatings, of which titanium dioxide is generally used as a pigment; talcum powder The main role is to reduce the stress shrinkage of the coating; while calcium carbonate as a filler has better hiding power, which can reduce the cost of the coating; silica can reduce the internal stress of the coating and prevent cracking. The prior art uses ceramic powder to have no requirement for the purity of the material, and the amount used is in the range of 0.2-30% of the total coating weight, and the amount used is small.

The present invention finds through experiments that although the phenolic epoxy coating without adding ceramic powder has greatly improved the performance of the coating itself, it was found that when the ceramic powder used is quartz powder or / and α-Al ₂ O ₃ , Is the α-Al ₂ O ₃ purity mass percentage ≥98%, the quartz powder SiO ₂ purity mass percentage ≥99%, especially the high-purity aluminum oxide (ie corundum), the coating is extremely high Wear resistance. These ceramic powders are not often used in the coatings industry, although some coatings use aluminum oxide, but they are all made of low-purity bauxite, which has a low content of aluminum oxide and is not wear-resistant like corundum. Sex. And the volume of ceramic powder used is between 20% and 40% of the coating volume (between 40% and 55% of the coating weight). The coating has excellent wear resistance and can also significantly reduce the curing process of solvent-free coatings. Stress contraction. This is because when the amount of ceramic powder is small (<20% coating volume, that is, the weight of ceramic powder is about <40% coating weight), the wear resistance of the coating cannot be guaranteed; when the amount of ceramic powder is large, the coating volume is exceeded. 40% of the base material does not wrap the pigment and filler well, the permeability of the coating increases, and the viscosity of the coating rises sharply. Therefore, although the solventless phenolic epoxy coating of the present invention does not achieve good results even with the coating process equipment of the present invention.

Therefore, through experimental comparison, it is found that the ceramic powder used in the present invention is different from the commonly used pipe coating ceramic powder in that it can improve the pulverization of talc powder; avoid the reaction of calcium carbonate with other substances (such as acidic substances), and is intolerant. The erosion of strong corrosive media can affect the acid resistance and water resistance of the coating in the coating. The coating of the present invention can increase the amount of use to achieve better wear resistance and reduce the internal stress of the coating.

It has further been found to be very beneficial when controlling the coating of the present invention to a certain thickness. Generally, the thickness of the steel pipe coating is about 400 μm. In order to meet the long-term anti-corrosion effect of the buried steel pipe, in addition to the coating of the usual thickness, it is necessary to assist the cathodic protection to achieve the required corrosion protection period, but still hope Anti-corrosion coatings extend the corrosion protection time. At the same time, the use of cathodic protection increases the operating cost of the pipeline.

For the commonly used solvent-based and solvent-free epoxy coating layers, if the thickness is too thick, the internal stress of the coating will be large, which may cause problems such as cracking and peeling of the coating. However, the coating provided by the present invention has excellent wear resistance due to the volume of the ceramic powder used being between 20% and 40% of the coating volume (between 40% and 55% of the coating weight). The stress shrinkage of the solventless coating curing process is remarkably reduced to achieve a coating thickness of ≥ 500 μm, preferably 500 μm to 2000 μm, more preferably 1000 μm to 1500 μm. The thickness of the coating has a close correlation with the anti-corrosion performance of the coating. The thicker the coating, the better the corrosion resistance. Especially for ductile iron pipes, the inherent disadvantages of centrifugal casting are the slag pits, bumps and bumps on the inner wall. Etc., when the internal grinding shot blasting, the surface roughness of the local area is much higher than that of the steel pipe. If the coating thickness of the steel pipe is used, the thickness of the coating is relatively thin at the peak position, which will cause the corrosion resistance of the coating. At the same time, because the ductile iron pipe is a socket-type interface, it is not a large electrical conductor. Cathodic protection is very difficult. Therefore, increasing the thickness of the coating is also one of the solutions to ensure the service life of the pipeline reaches 100 years. According to the ductile iron pipe with anticorrosive coating, the coating used for the high performance epoxy ceramic coating layer is a solventless phenolic epoxy ceramic coating.

Accordingly, the present invention provides a ductile iron pipe having an anticorrosive inner coating layer coated with an epoxy coating layer on the inner wall of the ductile iron pipe, and the coating used is a solventless phenolic epoxy coating, preferably solvent free Phenolic epoxy ceramic coating.

According to the ductile iron pipe having the anticorrosive inner coating, the high-performance epoxy ceramic coating layer has a volume solid content of ≥98%, preferably ≥99%.

According to the ductile iron pipe with anticorrosive inner coating, the coating for the high performance epoxy ceramic coating layer is a solventless phenolic epoxy ceramic coating, wherein the ceramic powder as a filler has a volume of 20%-40 of the coating volume. %, preferably 20% to 30%.

According to the ductile iron pipe having an anticorrosive inner coating layer, the coating for the high performance epoxy ceramic coating layer is a solventless phenolic epoxy ceramic coating, wherein the ceramic powder as a filler is quartz powder or/and α-Al ₂ O ₃ , the α-Al ₂ O ₃ purity mass percentage ≥98%; the quartz powder SiO ₂ purity mass percentage ≥99%. .

According to the ductile iron pipe having an anticorrosive inner coating layer, the solventless phenolic epoxy ceramic coating used in the high performance epoxy ceramic coating layer is a two component coating, wherein one component is an epoxy resin component, one group Divided into an amine curing agent component, and the ratio of the epoxy resin component (A component) to the amine curing agent component (B component) is 1:1 (weight ratio).

According to the ductile iron pipe with anticorrosive inner coating, the solventless phenolic epoxy ceramic coating used in the high performance epoxy ceramic coating layer is a two component epoxy coating, wherein the epoxy resin component contains phenolic epoxy The resin, the epoxy equivalent of the novolac epoxy resin used is 160-190, and the content (parts by weight) of the novolac epoxy resin in the epoxy resin component is 20% to 60%.

According to the ductile iron pipe having an anticorrosive coating, the epoxy resin component (component A) of the high performance phenolic epoxy ceramic coating comprises:

Phenolic epoxy resin: 20-60%;

Liquid bisphenol A epoxy resin: 0-25%;

Reactive diluent: 7-12%;

Auxiliary: 2-3%;

Pigment: 11-14%;

Ceramic powder: 20-34%.

Wherein, the auxiliary agent is a mixture of one or more of a wetting and dispersing agent, an anti-settling agent, and an antifoaming agent.

The phenolic epoxy resin has a phenolic epoxy resin having an epoxy equivalent of 160-190. The phenolic epoxy resin has high functionality, increases the crosslink density of the coating, improves the Tg of the coating, imparts high temperature resistance to the coating, and excellent corrosion resistance, especially acid resistance.

The epoxy equivalent of the bisphenol A epoxy resin is 190 liquid epoxy resin, such as DER 331.

The reactive diluent is a glycidyl ether reactive reactive diluent having an epoxy equivalent of 175-330. The reactive diluent has strong dilution ability to the solventless epoxy resin, can effectively reduce the viscosity of the system, and can increase the system. The flexibility increases the impact resistance of the coating while avoiding the toxicity due to the use of inert diluents. Commonly used commercial products are: polypropylene glycol diglycidyl ether, such as DER 732 of DOW, o-tolyl glycidyl ether, such as HELOXY 62.

The present invention incorporates suitable pigments depending on the particular application. The rutile titanium dioxide R-930 and carbon black which are harmless to the human body are selected, and they may be used alone or in combination according to the color requirements of the coating film.

The ceramic powder is quartz powder or/and α-Al ₂ O ₃ .

According to the ductile iron pipe having an anticorrosive coating, the amine curing agent component (component B) comprises:

Amine curing agent: 22-30%;

Catalyst: 0-2%

Ceramic powder: 65-75%;

Additives: 3-4%;

The amine curing agent is a specially prepared modified amine curing agent, which can be Mannich base or/and modified alicyclic amine, Mannich base has low temperature curability, and has excellent adhesion to wet surfaces, It has good compatibility with the resin; alicyclic amine can increase the Tg of the coating, thereby improving the heat resistance and high temperature adhesion of the coating.

The catalyst is a tertiary amine catalyst such as Ancamine K54.

The auxiliary agent is a mixture of one or more of a wetting and dispersing agent, an anti-settling agent, and an antifoaming agent.

The ceramic powder is quartz powder or/and α-Al ₂ O ₃ .

The solvent-free phenolic epoxy ceramic coating is formulated into two components of A/B, and is mixed at a weight ratio of A:B=1:1 in use.

According to the production process of the ductile iron pipe with the anticorrosive inner coating, the coating procedure of the high performance epoxy coating layer is as follows:

(1) Grinding of ductile iron pipe;

(2) Sandblasting or shot blasting on the inner wall of ductile iron pipe;

(3) preheating, so that the temperature of the ductile iron pipe is between 30 ° C and 70 ° C;

(4) Repair of defects such as slag pits in the inner wall;

(5) The pipe is rotated at a certain speed, and the rotational speed is a linear velocity ≥ 250 m/min;

(6) A and B components need to be preheated to 45-55 ° C;

(7) using a two-component spraying device, respectively conveying the epoxy resin component and the curing agent component to the nozzle, and driving the spray cup to rotate at a high speed by a motor or an air motor to atomize and spray the coating onto the pipe;

(8) After spraying, the tube continues to rotate for 10-40 minutes to fully level the paint;

(9) Curing: The coated ductile iron pipe needs to be heated and accelerated in the drying room. The curing conditions are: curing temperature is 50-90 ° C, curing for more than 1 h; preferred curing conditions are: temperature is 75-85 ° C , curing for 2h; then curing at room temperature for 7d, ready to use.

Compared with the prior art, the outstanding effects of the present invention are:

1) The anti-corrosion coating provided by the invention is a high-performance phenolic epoxy ceramic coating layer sprayed on the inner wall of the ductile iron pipe. The coating has excellent adhesion to the ductile iron pipe, and the tensile strength is tested by ASTM D4541, and the room temperature is tested. Pulling adhesion can reach more than 15Mpa, and high-temperature drawing adhesion (80°C) can reach more than 4Mpa.

2) The high-performance phenolic epoxy ceramic coating provided by the present invention can achieve a film thickness of 2000 μm at one time because it does not contain a solvent.

3) This coating is given by the addition of quartz powder or / and α-Al ₂ O ₃ ceramic powder filler, and its volume content accounts for more than 20% of the total volume of the coating, giving the coating excellent wear resistance according to ASTM D4060 Test, using CS-17 wheel, load 1kg, 1000 rpm, wear amount ≤ 50mg.

4) Also, the high performance phenolic epoxy ceramic inner anticorrosive coated ductile iron pipe provided by the invention has smooth inner wall, can effectively reduce the frictional resistance between the water medium and the pipe wall, and saves transportation energy.

5) The high performance phenolic epoxy ceramic inner anticorrosive coating provided by the invention is based on a phenolic epoxy film-forming material, has a high epoxy content, increases the crosslink density of the coating, and improves the Tg of the coating. The coating has high temperature resistance, and the coating provided by the present invention can be used for long-term transportation of an aqueous medium of 80 °C.

6) The high-performance phenolic epoxy ceramic inner anticorrosive coating provided by the invention also has a phenolic epoxy-based film-forming substance, which increases the cross-linking density of the coating, and is excellent in the coating due to the addition of the ceramic powder. The corrosion resistance ensures the 100-year life of ductile iron pipes.

7) The high performance phenolic epoxy ceramic coating provided by the invention does not contain any organic solvent, is safe, environmentally friendly and hygienic, and is tested by domestic and foreign authorities to meet the safety of GB 17219/T drinking water distribution equipment and protective materials. The evaluation criteria require that it be used for the delivery of drinking water.

The ductile iron pipe with anticorrosive inner coating of the present invention and the production process thereof will be further described below in conjunction with specific embodiments.

detailed description

The ductile iron pipe of the epoxy ceramic coating anticorrosive inner coating applied to the water pipeline is prepared as follows. The preparation method comprises the following steps:

(1) Grinding of ductile iron pipe;

(2) sandblasting or shot blasting on the inner wall of the ductile iron pipe, so that the roughness Rz≥60μm;

(3) preheating, so that the temperature of the ductile iron pipe is between 30 ° C and 70 ° C;

(4) Repair of defects such as slag pits in the inner wall, use high-performance epoxy ceramic coatings, add appropriate amount of ceramic powder, and adjust to appropriate viscosity to repair surface defects;

(5) The pipe is rotated at a certain speed, and the rotational speed is a linear velocity ≥ 250 m/min;

(6) High-performance phenolic epoxy ceramic coatings have high viscosity at room temperature and must be preheated: components A and B must be preheated to 45-55 ° C to reduce viscosity;

(7) Using a two-component spraying equipment, the A component (epoxy resin component) and the B component (curing agent component) are separately delivered to the nozzle, and the spray cup is rotated at a high speed by a motor or an air motor to mix the coating mist. Sprayed onto a rotating tube;

(8) After spraying, the tube continues to rotate for 10-40 minutes, so that the paint is fully leveled, and does not remain hanging after stopping, and enters the curing process;

(9) Curing: After spraying, the ductile iron pipe needs to be heated in the drying room to accelerate the curing. The curing conditions are: curing temperature is 50-90 ° C, curing for more than 1 h, and then curing at room temperature for 7 d; the preferred curing conditions are: temperature is Curing at 75-85 ° C for 2 h, then curing at room temperature for 7 d, ready for use.

The manufacturing process of the high performance phenolic epoxy ceramic coating is as follows:

Component A: epoxy resin component, including novolac epoxy resin, or a mixture of phenolic epoxy resin and liquid bisphenol A epoxy resin, reactive diluent, auxiliary agent, pigment, ceramic powder. Add phenolic epoxy resin, or phenolic epoxy resin and liquid bisphenol A epoxy resin to the dispersion tank, and stir evenly at medium speed; add relevant additives (including wetting and dispersing agent, defoaming agent) under slow stirring. After the mixture is evenly stirred, the desired pigment and filler are added, and the desired fineness is dispersed at a high speed, and then the remaining auxiliary materials and the like are uniformly dispersed in a medium speed, and the filter package is formed into the A component.

Component B: an amine curing agent component, including a Mannich base amine curing agent, a ceramic powder, an auxiliary agent; or a modified alicyclic amine curing agent, a ceramic powder, and an auxiliary agent.

Put the Mannich base/modified alicyclic amine curing agent into the dispersing tank and stir evenly at medium speed; add the dispersant, defoaming agent and other additives under slow stirring, and after adding evenly, add the required The ceramic powder is dispersed at a high speed to the desired fineness, and then the remaining auxiliary materials and the like are uniformly dispersed in a medium speed, and the package is filtered.

The production of the preferred high performance phenolic epoxy ceramic coating examples was carried out by the above method, and coated in the above manner to obtain the anticorrosive coated ductile iron pipe of the present invention and its properties.

Example 1

The coating materials given below were prepared and coated according to the method of the Preparation Examples, and the effects were compared after coating. A coating material different from the coating material given by the present invention is prepared according to a method similar to the present invention according to a conventional technique in the art.

Table 1

Comparative Example 1 is a "solvent-type coating", and Comparative Example 2 is a solventless coating currently conventionally used. It can be seen that the solvent-based coating is inferior to the solvent-free coating material in terms of coating process, acid resistance, distillation resistance, and abrasion resistance and high temperature resistance. The "solvent-free coating" currently used in Comparative Example 2, although improving some properties of the solvent-based coating, still contains an undesired inactive diluent on the one hand, but is resistant to acid and water. Sexual aspects as well as wear resistance and high temperature resistance are still unsatisfactory. The solventless coating of the present invention overcomes the dissatisfaction of the prior coatings and greatly improves the wear resistance, corrosion resistance, and particularly high temperature adhesion.

Example 2

Table 2

Comparative Examples 3 and 4 used a coating which is conventionally used in the prior art for ceramic powder. However, it can be seen that the conventionally used ceramic powder has a large inconvenience in the process of preparation, and the existing ceramic powder calcium carbonate is easily reacted with other substances (for example, an acidic substance), and is not resistant to the corrosion of a highly corrosive medium in the coating. It will affect the acid resistance and water resistance of the coating; the talc powder and calcium carbonate have lower hardness than the high-purity ceramic powder material required by the present invention, and thus are significantly weaker in mechanical properties and chemical resistance than the coating used in the present invention.

Example 3

table 3

Summary: It can be seen through experiments that the coating material of the present invention can meet the current needs of use, and has excellent corrosion resistance, wear resistance and high temperature resistance.

The embodiments described above are only intended to describe the preferred embodiments of the present invention, and are not intended to limit the scope of the present invention, and various embodiments of the present invention may be made by those skilled in the art without departing from the spirit of the invention. Modifications and improvements are intended to fall within the scope of the invention as defined by the appended claims.

Industrial applicability

The ductile iron pipe with anticorrosive inner coating of the invention and the production process thereof have great influence in the field of water transportation and gas transmission. The anti-corrosion coating provided by the invention is a high-performance phenolic epoxy ceramic coating layer sprayed on the inner wall of the ductile iron pipe, the coating has excellent adhesion to the ductile iron pipe, and the tensile strength test is tested by ASTM D4541, and the normal temperature drawing is performed. The adhesion can reach more than 15Mpa, and the high-temperature drawing adhesion (80°C) can reach more than 4Mpa. The ductile iron pipe with anti-corrosion inner coating of the invention and the production process thereof have strong industrial applicability and operability, and are of great significance for pipeline transportation.

Claims (23)

1. A ductile iron pipe with an anticorrosive inner coating, characterized in that: the inner wall of the ductile iron pipe is coated with an epoxy coating layer, and the coating for the epoxy coating layer is a solventless phenolic epoxy coating, preferably a solventless phenolic Epoxy ceramic coating.
2. The ductile iron pipe with an anti-corrosion inner coating according to claim 1, wherein the solvent-free phenolic epoxy ceramic coating has a volume solid content of ≥98%, preferably ≥99%.
3. The ductile iron pipe with anticorrosive inner coating according to claim 1 or 2, wherein the solventless phenolic epoxy ceramic coating is a two component of epoxy resin component A and amine curing agent component B. Epoxy coating, wherein the epoxy resin component contains a phenolic epoxy resin, the epoxy equivalent of the phenolic epoxy resin is 160-190, and the content of the phenolic epoxy resin in the epoxy resin component is 20% -60%.
4. The ductile iron pipe with an anticorrosive inner coating according to any one of claims 1 to 3, wherein the volume of the ceramic powder as a filler in the solventless phenolic epoxy ceramic coating is 20% of the coating volume - 40%, preferably 20%-30%.
5. The ductile iron pipe with an anticorrosive inner coating according to any one of claims 1 to 4, wherein the ceramic powder as a filler in the solventless phenolic epoxy ceramic coating is quartz powder or/and α-Al. ₂ O ₃ , the α-Al ₂ O ₃ purity mass percentage ≥98%; the quartz powder SiO ₂ purity mass percentage ≥99%.
6. The ductile iron pipe with an anticorrosive inner coating according to claim 3, wherein the weight ratio of the epoxy resin component A to the amine curing agent component B is 1:1.
7. The ductile iron pipe with anti-corrosion inner coating according to claim 5, wherein the epoxy resin component A of the solvent-free phenolic epoxy ceramic coating comprises:

   Phenolic epoxy resin: 20-60%;

   Liquid bisphenol A epoxy resin: 0-25%;

   Reactive diluent: 7-12%;

   Auxiliary: 2-3%;

   Pigment: 11-14%;

   Ceramic powder: 20-34%.
8. The ductile iron pipe with anti-corrosion inner coating according to claim 7, characterized in that: the epoxy resin component A of the solvent-free phenolic epoxy ceramic coating, wherein the auxiliary agent is a wetting and dispersing agent a mixture of one or more of an anti-settling agent and an antifoaming agent;

   And/or, the bisphenol A epoxy resin has an epoxy equivalent of 190 liquid epoxy resin;

   And/or, the reactive diluent is a glycidyl ether reactive reactive diluent having an epoxy equivalent of 175-330;

   And/or, the pigment is rutile titanium dioxide and/or carbon black;

   And/or, the ceramic powder is quartz powder or/and α-Al ₂ O ₃ .
9. The ductile iron pipe with an anti-corrosion inner coating according to claim 3, wherein the amine curing agent component B of the solvent-free phenolic epoxy ceramic coating comprises:

   Amine curing agent: 22-30%;

   Catalyst: 0-2%;

   Ceramic powder: 65-75%;

   Additives: 3-4%.
10. The ductile iron pipe with an anticorrosive inner coating according to claim 9, wherein the amine curing agent component B of the solventless novolac epoxy ceramic coating comprises:

    The catalyst is a tertiary amine catalyst;

    And/or the auxiliary agent is a mixture of one or more of a wetting and dispersing agent, an anti-settling agent, and an antifoaming agent.

    And/or, the ceramic powder is quartz powder or/and α-Al ₂ O ₃ .
11. The ductile iron pipe having an anticorrosive inner coating according to claim 1, wherein the epoxy coating layer has a thickness of ≥ 500 μm, preferably 500 μm to 2000 μm, more preferably 1000 μm to 1500 μm.
12. The process for producing a ductile iron pipe having an anticorrosive inner coating according to any one of claims 1 to 11, characterized in that it comprises the following steps:

    (1) Grinding of ductile iron pipe;

    (2) Sandblasting or shot blasting on the inner wall of ductile iron pipe;

    (3) preheating, so that the temperature of the ductile iron pipe is between 30 ° C and 70 ° C;

    (4) Repair of defects such as slag pits in the inner wall;

    (5) The pipe is rotated at a certain speed, and the rotational speed is a linear velocity ≥ 250 m/min;

    (6) A and B components need to be preheated to 45-55 ° C;

    (7) using a two-component spraying device, respectively conveying the epoxy resin component and the curing agent component to the nozzle, and driving the spray cup to rotate at a high speed by a motor or an air motor to atomize and spray the coating onto the pipe;

    (8) After spraying, the tube continues to rotate for 10-40 minutes to fully level the paint;

    (9) Curing: The coated ductile iron pipe needs to be heated and accelerated in the drying room. The curing conditions are: curing temperature is 50-90 ° C, curing for more than 1 h; preferred curing conditions are: temperature is 75-85 ° C , curing for 2h; then curing at room temperature for 7d, ready to use.
13. An epoxy coating layer characterized in that the coating for the epoxy coating layer is a solventless phenolic epoxy coating, preferably a solventless phenolic epoxy ceramic coating.
14. The epoxy coating layer according to claim 13, wherein the solvent-free phenolic epoxy ceramic coating has a volume solid content of ≥98%, preferably ≥99%.
15. The epoxy coating layer according to claim 13 or 14, wherein the solvent-free phenolic epoxy ceramic coating is a two-component epoxy coating of epoxy resin component A and amine curing agent component B, wherein The epoxy resin component contains a novolac epoxy resin, the epoxy equivalent of the novolac epoxy resin is 160-190, and the content of the novolac epoxy resin in the epoxy resin component is 20% to 60%.
16. The epoxy coating layer according to any one of claims 13-15, wherein the volume of the ceramic powder as a filler in the solventless phenolic epoxy ceramic coating is from 20% to 40% by volume of the coating, preferably 20%-30%.
17. The epoxy coating layer according to any one of claims 13-16, wherein the ceramic powder as a filler in the solventless phenolic epoxy ceramic coating is quartz powder or/and α-Al ₂ O ₃ , The α-Al ₂ O ₃ purity mass percentage is ≥98%; the quartz powder SiO ₂ purity mass percentage is ≥99%.
18. The epoxy coating layer according to any one of claims 13 to 16, wherein the weight ratio of the epoxy resin component A to the amine curing agent component B is 1:1.
19. The epoxy coating layer according to claim 18, wherein the epoxy resin component A comprises:

    Phenolic epoxy resin: 20-60%;

    Liquid bisphenol A epoxy resin: 0-25%;

    Reactive diluent: 7-12%;

    Auxiliary: 2-3%;

    Pigment: 11-14%;

    Ceramic powder: 20-34%.
20. The epoxy coating layer according to claim 19, wherein the auxiliary agent is a mixture of one or more of a wetting and dispersing agent, an anti-settling agent, and an antifoaming agent;

    And/or, the bisphenol A epoxy resin has an epoxy equivalent of 190 liquid epoxy resin;

    And/or, the reactive diluent is a glycidyl ether reactive reactive diluent having an epoxy equivalent of 175-330;

    And/or, the pigment is rutile titanium dioxide and/or carbon black;

    And/or, the ceramic powder is quartz powder or/and α-Al ₂ O ₃ .
21. The epoxy coating layer according to claim 20, wherein the amine curing agent component B comprises:

    Amine curing agent: 22-30%;

    Catalyst: 0-2%

    Ceramic powder: 65-75%;

    Additives: 3-4%.
22. The epoxy coating layer according to claim 21, wherein:

    The catalyst is a tertiary amine catalyst;

    And/or the auxiliary agent is a mixture of one or more of a wetting and dispersing agent, an anti-settling agent, and an antifoaming agent.

    And/or, the ceramic powder is quartz powder or/and α-Al ₂ O ₃ .
23. The epoxy coating layer according to claim 13, wherein the epoxy ceramic coating layer has a thickness of ≥ 500 μm, preferably 500 μm to 2000 μm, more preferably 1000 μm to 1500 μm.