KR102258373B1 - Method for manufacturing high-durability coated steel pipe using heterogeneous epoxy coating agents and coated steel pipe with improved durability manufactured thereby - Google Patents

Abstract

The present invention relates to a method for manufacturing a high-durability coated steel pipe with excellent adhesion while preventing the deposition of scale or contaminants and preventing corrosion for a long time by using different types of epoxy coating agents having different compositions. The method for manufacturing a coated steel pipe according to the present invention includes the steps of: (a) coating an inner surface of a steel pipe with a first epoxy coating agent to a thickness of 50 to 500 μm to form an undercoat layer; and (b) coating a second epoxy coating agent to a thickness of 150 to 1,000 μm on the inner surface of the steel pipe on which the undercoat layer is formed to form an inner surface coating layer having a double-layer structure including an undercoat layer and a topcoat layer.

Description

{Method for manufacturing high-durability coated steel pipe using heterogeneous epoxy coating agents and coated steel pipe with improved durability manufactured thereby}

The present invention relates to a method of manufacturing a highly durable coated steel pipe having excellent adhesion while preventing the deposition of scales or contaminants by using different types of epoxy coating agents having different compositions, and not causing corrosion for a long time.

In addition, the present invention relates to a method of manufacturing a coated steel pipe with improved durability through surface treatment using plasma.

In general, piping is a structure having a shape such as a pipe, tube, or tube, and is used for transporting gas, liquid, powder, three-dimensional substances, etc., and is used for transporting iron pipes, steel pipes, stainless steel pipes, copper pipes, brass pipes, lead pipes, etc. Inorganic material pipes such as metal pipes, reinforced concrete pipes, asbestos cement pipes, ceramic pipes, concrete pipes, and synthetic resin pipes such as hard vinyl chloride pipes and polyethylene pipes are being used.

The material, diameter, and thickness of the pipe are determined according to the specificity of the field of use, such as the chemical properties of the transport fluid, flow rate, flow rate, and pressure, and are installed in consideration of durability, reactivity with transport fluid, and circulation. , Steel pipes made of metal materials have superior durability compared to plastic pipes made using polymer resins and are therefore used for a wide range of applications.

However, when a steel pipe is used for a long period of time, contaminants are deposited on the surface and contaminate the fluid, and the inner surface is easily corroded, resulting in a short lifespan.In the case of a steel pipe buried underground, it is very cumbersome to replace once buried. As there is a secondary problem of contamination of the fluid flowing through the steel pipe, an epoxy resin paint is applied to the inner surface of the steel pipe to coat it, or a coated steel pipe coated with a polyethylene film is introduced and used on the outer surface. Recently, the durability of the steel pipe has been improved. In order to improve it, ceramics such as zeolite are introduced into the epoxy resin paint to improve the physical properties of the coating layer, or a heterogeneous polymer resin paint such as polyethylene resin is coated instead of the epoxy resin paint.

On the other hand, the flame plasma improves the surface energy of the adherend by completely burning a heat source gas such as LPG or LNG under atmospheric pressure by a thermal fusion method to form a plasma zone of a certain size. It is widely used because it can improve adhesion.

However, in the past, research on a technology for improving the durability of a steel pipe by forming a coating layer having a low surface roughness on the inner surface of a steel pipe is insufficient, and thus a study on a method to supplement this is required.

Korean Patent Registration No. 10-1737408 (Announcement date: 2017.05.19) Korean Patent Registration No. 10-1184344 (Announcement date: 2012.09.20) Korean Patent Registration No. 10-1772004 (announcement date: 2017.09.05) Korean Patent Registration No. 10-1921894 (Announcement date: 2018.11.26)

The present invention was conceived to solve the problems of the prior art as described above, and the present invention uses different types of epoxy coatings having different compositions and viscosity, and sequentially coats a bottom coat layer and a top coat layer on the inner surface of a steel pipe. It is intended to provide technical details on a method of manufacturing a coated steel pipe that can prevent scale deposition for a long time and effectively prevent steel pipe corrosion by forming an inner coating layer having a low surface roughness through the method.

In addition, the present invention is to provide a technical content of a method for manufacturing a coated steel pipe having excellent durability by cleaning the surface of a steel pipe by pretreating the surface of a steel pipe with plasma, and activating the surface.

In addition, the present invention is to provide a technical content of a method for manufacturing a coated steel pipe that can more effectively prevent scale deposition and corrosion of a steel pipe through plasma treatment.

The technical problems to be solved by the present invention are not limited to the technical problems mentioned above, and other technical problems that are not mentioned are clearly understood by those of ordinary skill in the technical field to which the present invention belongs from the following description. It will be possible.

In order to achieve the above-described technical problem, the present invention provides a method for manufacturing a coated steel pipe by forming a coating layer on the inner surface, (a) coating the first epoxy coating agent on the inner surface of the steel pipe to a thickness of 50 to 500 µm. Forming a primer coating layer; And (b) coating a second epoxy coating agent to a thickness of 150 to 1,000 µm on the inner surface of the steel pipe on which the undercoat layer is formed to form a double-layered inner coating layer including a undercoat layer and a top coat layer; including, The first epoxy coating agent includes a first base material and a curing agent, and the first base material is a polymer of 4,4'-(1-methylethylidene) bisphenol and (chloromethyl) oxirane (4,4' -(1-methylethylidene)bisphenol polymer with (chloromethyl)oxirane) 20 to 50 parts by weight, quartz (SiO ₂ ) 10 to 40 parts by weight, cashew nut shell oil and polymer of epichlorohydrin (Cashew, nutshell liq. , polymer with epichlorohydrin, OHS53097) 5 to 30 parts by weight, trimethoxy-[3-(oxiranylmethoxy)propyl]silane (Silane, trimethoxy[3-(oxiranylmethoxy)propyl]-) 1 to 20 parts by weight, dioxide Titanium (TiO ₂ ) 1 to 20 parts by weight, formaldehyde, (chloromethyl) oxirane and polymer of phenol (formaldehyde polymer with (chloromethyl) oxirane and phenol) 1 to 20 parts by weight and 1 to 20 parts by weight of an anti-rust pigment, and , The curing agent, cashew nutshell liq. polymer with ethylenediamine and formaldehyde 40 to 70 parts by weight, benzyl alcohol 5 to 30 parts by weight, quartz 5 to 30 Parts by weight, 3-Aminomethyl-3,5,5-trimethylcyclohexylamine (Isophorone diamine) 1 to 20 parts by weight, 3-aminopropyltriethoxysilane ( 3-Aminopropyltriethoxysilane) 1 to 20 And 1 to 10 parts by weight of ethylenediamine, and the second epoxy coating agent includes a second main material and the hardener, and the second main material is 4,4'-(1-methylethylidene) bisphenol And (chloromethyl) oxirane polymer (4,4'-(1-methylethylidene) bisphenol polymer with (chloromethyl)oxirane) 20 to 50 parts by weight, quartz (quartz, SiO ₂ ) 10 to 40 parts by weight, cashew nut shell Oil and epichlorohydrin polymer (Cashew, nutshell liq., polymer with epichlorohydrin, OHS53097) 5 to 30 parts by weight, trimethoxy-[3-(oxiranylmethoxy)propyl]silane (Silane, trimethoxy[3- (oxiranylmethoxy)propyl]-) 1 to 20 parts by weight, titanium dioxide (TiO ₂ ) 1 to 20 parts by weight, formaldehyde, (chloromethyl) oxirane and phenol polymer (formaldehyde polymer with (chloromethyl)oxirane and phenol) 1 It provides a method of manufacturing a coated steel pipe, characterized in that it comprises to 20 parts by weight and 1 to 10 parts by weight of a silicone additive.

According to a preferred embodiment of the present invention, the steel pipe of step (a) may be a steel pipe in which the inner surface is pretreated at a processing speed of 5 to 25 m/min using flame plasma.

According to a preferred embodiment of the present invention, the first epoxy coating agent may have a viscosity of 20,000 to 100,000 cps, and the second epoxy coating agent may have a viscosity of 3,000 to 50,000 cps.

According to a preferred embodiment of the present invention, in the step (b), a second epoxy coating agent is coated on the inner surface of the steel pipe on which the undercoat layer is formed, and then the inner surface of the steel pipe on which the inner surface coating layer is formed is 10 to 10 by using flame plasma. It may further include a finish treatment step of surface treatment at a treatment speed of 30 m / min.

In addition, the present invention provides a coated steel pipe comprising an inner coating layer having a double-layer structure including a primer coating layer and a top coating layer, manufactured by the method for manufacturing a coated steel pipe described above.

The method of manufacturing a coated steel pipe according to the present invention can form an inner coating layer having low surface roughness and excellent adhesion by sequentially coating a base coat layer and a top coat layer using different types of epoxy coating agents having different compositions and viscosity on the inner surface of the steel pipe. It is possible to manufacture a coated steel pipe that can prevent scale deposition and contamination for a long time and effectively prevent corrosion.

In addition, the method of manufacturing a coated steel pipe according to the present invention can easily remove contaminants from the inner surface of the steel pipe in a short time by pretreatment with plasma, and the surface smoothness is improved through flame plasma treatment to effectively prevent scale deposition. In addition, it is possible to manufacture a coated steel pipe with a highly durable inner coating layer that is not easily separated by improving the adhesion between the undercoat layer and the upper coat layer.

Therefore, when the coated steel pipe manufactured by the method for manufacturing the coated steel pipe according to the present invention is used for installation as a water supply pipeline, scale deposition and contamination can be prevented for a long time, thereby reducing the pipe diameter or decreasing the water flow capacity due to an increase in the roughness coefficient for a long time. It can be prevented, and it is possible to supply high quality raw water by reducing the occurrence of contaminated water such as poor water supply or rust.

1 is a flow chart showing a method of manufacturing a coated steel pipe according to the present invention.
2 is a conceptual diagram showing a coated steel pipe manufactured by the method of manufacturing a coated steel pipe according to the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present invention. However, since the description of the present invention is merely an embodiment for structural or functional description, the scope of the present invention should not be construed as being limited by the embodiments described in the text. That is, since the embodiments can be variously changed and have various forms, the scope of the present invention should be understood to include equivalents capable of realizing the technical idea. In addition, since the object or effect presented in the present invention does not mean that a specific embodiment should include all or only such effects, the scope of the present invention should not be understood as being limited thereto.

The meaning of the terms described in the present invention should be understood as follows.

Terms such as "first" and "second" are used to distinguish one component from other components, and the scope of rights is not limited by these terms. For example, a first component may be referred to as a second component, and similarly, a second component may be referred to as a first component. When a component is referred to as being "connected" to another component, it should be understood that although it may be directly connected to the other component, another component may exist in the middle. On the other hand, when a component is referred to as being "directly connected" to another component, it should be understood that there is no other component in the middle. On the other hand, other expressions describing the relationship between components, that is, "between" and "just between" or "neighboring to" and "directly neighboring to" should be interpreted as well.

Singular expressions are to be understood as including plural expressions unless the context clearly indicates otherwise, and terms such as "comprises" or "have" refer to the specified features, numbers, steps, actions, components, parts, or these. It is to be understood that it is intended to designate that a combination exists and does not preclude the presence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

All terms used herein have the same meaning as commonly understood by one of ordinary skill in the field to which the present invention belongs, unless otherwise defined. Terms defined in commonly used dictionaries should be interpreted as having meanings in the context of related technologies, and cannot be interpreted as having an ideal or excessively formal meaning unless explicitly defined in the present invention.

Hereinafter, the present invention will be described in detail.

1 is a process chart showing a method of manufacturing a coated steel pipe according to the present invention.

Referring to FIG. 1, a method of manufacturing a coated steel pipe according to the present invention includes the steps of: (a) forming a primer coating layer by coating a first epoxy coating agent on the inner surface of the steel pipe; And (b) coating a second epoxy coating agent on the inner surface of the steel pipe on which the undercoating layer is formed to form an inner coating layer having a double-layer structure including a undercoating layer and a top coating layer. The formed coated steel pipe can be manufactured.

The method for manufacturing a coated steel pipe according to the present invention is to first form a primer coating layer on the inner surface of the steel pipe through two coating processes in which a first epoxy coating agent and a second epoxy coating agent having different compositions are applied as described above, and then A top coat layer is formed on the top surface to form a double-layered inner coat layer including a bottom coat layer and a top coat layer.

Looking at the process for the manufacturing method of the coated steel pipe in detail, step (a) is a step of forming a primer coating layer on the inner surface of the steel pipe using a first epoxy coating agent, which has excellent adhesion to the inner surface of the steel pipe and has rust prevention properties. Therefore, a primer coating layer can be formed by coating the first epoxy coating agent that can prevent corrosion of the steel pipe for a long time.

To this end, the first epoxy coating agent may use a mixture comprising a first main agent and a curing agent.

Specifically, the first subject is a polymer of 4,4'-(1-methylethylidene)bisphenol and (chloromethyl)oxirane (4,4'-(1-methylethylidene)bisphenol polymer with (chloromethyl)oxirane), Quartz (SiO ₂ ), Cashew nutshell liq., polymer with epichlorohydrin, OHS53097, trimethoxy-[3-(oxiranylmethoxy)propyl]silane (Silane) , trimethoxy[3-(oxiranylmethoxy)propyl]), titanium dioxide (TiO ₂ ), formaldehyde, (chloromethyl) oxirane and phenol polymer (formaldehyde polymer with (chloromethyl)oxirane and phenol) and a mixture containing a rust preventive pigment Can be used.

Looking at the constituents of the first subject in detail, the polymer of 4,4'-(1-methylethylidene) bisphenol and (chloromethyl) oxirane is cured as a type of epoxy resin to form an inner coating layer. And, it may be mixed in a ratio of 20 to 50 parts by weight based on 100 parts by weight of the first subject.

If the polymer content of 4,4'-(1-methylethylidene) bisphenol and (chloromethyl) oxirane is less than 20 parts by weight, there is a problem that properties such as mechanical properties and chemical resistance of the coating film are deteriorated, and 50 parts by weight If it exceeds part, there is a fear that the viscosity increases and the workability decreases.

Quartz contains silica or silicon dioxide as a main component, and serves as a filler that can improve the heat resistance, durability, abrasion resistance, thixotropic properties, strength, etc. of the inner coating layer, and can adjust the viscosity and workability of the first subject. , It may be mixed in a ratio of 10 to 40 parts by weight.

If the content of quartz is less than 10 parts by weight, it is difficult to expect improvement in physical properties, and if it exceeds 40 parts by weight, there is a concern that the durability of the underlying coating layer coating film is deteriorated.

The polymer of cashew nut shell oil and epichlorohydrin is prepared by reacting epichlorohydrin with a cashew nut shell oil containing a phenol derivative, that is, cardanol, which is an unsaturated hydrocarbon. It is bonded with a hydrocarbon compound to have multiple functional groups, and it includes at least one double bond in the chain to impart a functional group for crosslinking to improve crosslinking properties, and has excellent mechanical properties, flexibility, hydrolysis resistance, heat resistance, and bending resistance. A coating layer can be formed.

The polymer of cashew nut shell oil and epichlorohydrin can be mixed in a ratio of 5 to 30 parts by weight, and if it is included in a ratio of less than 5 parts by weight, crosslinking properties are poor and it is difficult to expect improvement in physical properties, and if it exceeds 30 parts by weight There is a risk of deteriorating mechanical properties.

Trimethoxy-[3-(oxiranylmethoxy)propyl]silane is a silane-containing compound that improves the adhesion of the first epoxy coating agent to the inner surface of the steel pipe, and improves the water resistance and long-term durability of the coating film. It may be mixed in a proportion of 20 parts by weight.

When the content of trimethoxy-[3-(oxiranylmethoxy)propyl]silane is less than 1 part by weight, it is difficult to expect improved adhesion of the undercoat layer, and when it exceeds 20 parts by weight, it is difficult to expect additional physical property improvement.

Titanium dioxide is a white powder that improves chemical resistance and UV resistance of the first subject matter, serves to form a white coating film as a white pigment, and may be included in a ratio of 1 to 20 parts by weight relative to 100 parts by weight of the first subject. . As the titanium dioxide, a rutile type, an anatase type, or titanium dioxide powder including a mixture thereof may be introduced, and preferably, rutile titanium dioxide may be used.

When the content of titanium dioxide is less than 1 part by weight, it is difficult to impart color, and when it exceeds 20 parts by weight, the elasticity and adhesion of the first epoxy coating agent may be deteriorated.

Polymers of formaldehyde, (chloromethyl) oxirane and phenol are epoxide-based organic compounds containing an oxirane ring and a phenol group capable of ring-opening polymerization, and contain an epoxy group to promote reactivity with the first main agent and a curing agent. It enhances the adhesion of water and lowers the transmittance of water vapor and oxygen to impart corrosion resistance, thereby forming a coating film with excellent long-term durability.

The polymer of formaldehyde, (chloromethyl) oxirane and phenol may be mixed in a ratio of 1 to 20 parts by weight, and if it is contained less than 1 part by weight, a problem of lowering reactivity and adhesion may occur, and exceeding 20 parts by weight. In this case, it is difficult to expect additional physical property improvement.

Anti-rust pigments improve the corrosion resistance of steel pipes by imparting anti-corrosion properties to the underlying coating layer, and phosphate solutions such as zinc phosphate, zinc oxide, calcium phosphate, mica-type iron oxide, aluminum, manganese, zinc, molybdenum fluorine, etc. An aqueous phosphoric acid solution of ammonium hepta molybdate hydrate, an aqueous phosphate solution of soda, or a mixture thereof may be used.

The rust preventive pigment as described above may be included in a ratio of 1 to 20 parts by weight, and if the content of the rust preventive pigment is less than 1 part by weight, it is difficult to expect sufficient anti-rust performance, and if it exceeds 20 parts by weight, the durability of the underlying coating layer may be deteriorated. There is.

In addition, the first subject may be configured to further include an additive in order to improve the physical properties of the coating film, and the additives include adhesion, dispersibility, water resistance, defoaming resistance, weather resistance, UV resistance, durability, rust prevention, plasticity, It is added to control workability and the like, and a surfactant, an antioxidant, an anti-settling agent, a water reducing agent, a retarder, a flame retardant, an antifoaming agent, a binder, a plasticizer, a pigment, or a mixture thereof may be introduced.

The additive may be added in a range that does not adversely affect the physical properties of the first subject, and may be included in a ratio of 1 to 10 parts by weight.

On the other hand, the curing agent included in the first epoxy coating agent, cashew nut shell oil, polymer of ethylenediamine and formaldehyde (Cashew nutshell liq. polymer with ethylenediamine and formaldehyde), benzyl alcohol (Benzyl alcohol), quartz, 3-aminomethyl- A mixture containing 3,5,5-trimethylcyclohexylamine (Isophorone diamine), 3-Aminopropyltriethoxysilane and ethylenediamine can be used. I can.

Specifically, the polymer of cashew nut shell oil, ethylenediamine and formaldehyde is a polymer containing cashew nut shell oil, which is a cardanol derivative, ethylenediamine which is a polyamine, and formaldehyde containing an aldehyde group. As a base curing agent), it exhibits low-temperature fast curing properties that can accelerate curing at low temperatures compared to conventional curing agents, and thus energy consumption required for curing can be reduced.

The polymer of cashew nut shell oil, ethylenediamine and formaldehyde may be included in a ratio of 40 to 70 parts by weight, and if the content is less than 40 parts by weight, there is a problem that the curing time increases, and if it exceeds 70 parts by weight, the appearance of the coating film And there is a concern that mechanical properties may be deteriorated.

Benzyl alcohol is a non-reactive diluent and serves to increase the fluidity of the epoxy coating agent, adjust the viscosity and workability, and can control the storage stability of the curing agent.

Benzyl alcohol may be included in a ratio of 5 to 30 parts by weight, and if the content is less than 5 parts by weight, the viscosity is high and there is a concern that workability may be deteriorated. It is difficult to form a coating film, and there is a fear that the storage stability is deteriorated.

Quartz contains silica or silicon dioxide as a main component, and serves as a filler that can improve the heat resistance, durability, abrasion resistance, thixotropic properties, strength, etc. of the inner coating layer, and it can control the viscosity and workability of the epoxy coating agent and the curing agent. And, it may be mixed in a ratio of 5 to 30 parts by weight.

3-Aminomethyl-3,5,5-trimethylcyclohexylamine is a modified alicyclic amine and serves to accelerate the curing of the epoxy coating agent, and can improve the mechanical properties and chemical resistance of the coating film.

3-Aminomethyl-3,5,5-trimethylcyclohexylamine can be mixed in a ratio of 1 to 20 parts by weight, and when its content is less than 1 part by weight, it is difficult to accelerate the curing rate, and when it exceeds 20 parts by weight Although the strength of the coating film increases, there is a fear that the surface roughness of the coating film increases and the smoothness decreases.

3-Aminopropyltriethoxysilane is a trifunctional silane coupling agent having a hydrolyzable trialkyl group, which accelerates the curing of the main material and forms a coating film having excellent barrier properties and corrosion resistance. In addition, the first epoxy coating agent and By improving the adhesion between the coating layers formed by the second epoxy coating agent, an inner coating layer having excellent adhesion may be formed.

3-Aminopropyltriethoxysilane may be included in a ratio of 1 to 20 parts by weight, and if its content is less than 1 part by weight, it is difficult to expect improvement in physical properties, and if it exceeds 20 parts by weight, there is a concern that the smoothness of the coating film may be lowered. .

Ethylenediamine is an aliphatic amine, and is a non-aromatic curing agent capable of accelerating the curing of the main material including a reactive amine group, and may be mixed in a ratio of 1 to 10 parts by weight.

The first epoxy coating agent including the first main material and the curing agent as described above has excellent adhesion to the inner surface of the steel pipe and has rust prevention properties, so that it is possible to form an undercoat layer capable of preventing corrosion of the steel pipe for a long time.

In this step, the first epoxy coating agent may be coated on the inner surface of the steel pipe to form an undercoat layer having a thickness of 50 to 500 μm, and may be coated by various conventional coating methods such as spray coating.

If the thickness of the underlying coating layer is less than 50 µm, there is a problem that it is difficult to impart sufficient rust prevention performance to the inner surface of the steel pipe, and if it exceeds 500 µm, it is difficult to expect additional physical properties improvement, and a coating film of uneven thickness is formed when the first epoxy coating is coated. There is a risk of becoming.

The first epoxy coating agent as described above may be used a mixture comprising a first main agent and a curing agent in a volume ratio of 5:1 to 1:1, respectively, and preferably, a first main agent and a curing agent of 3:1 to 3: A mixture containing in a ratio of 2 may be used, thereby forming a primer coating layer having excellent physical properties such as rust prevention, bending resistance, adhesion, and chemical resistance.

In addition, the first epoxy coating agent may have a viscosity of 20,000 to 100,000 cps, and when the viscosity of the first epoxy coating agent is less than 20,000 cps, the curing time is lengthened, and there is a concern that a coating film of uneven thickness may be formed due to the flow of the coating film during coating. In addition, when it exceeds 100,000 cps, it is difficult to sufficiently adhere to the inner surface of the steel pipe due to high viscosity, and there is a concern that cracks may occur in the underlying coating layer or workability may be deteriorated.

According to a preferred embodiment of the present invention, the steel pipe may be a pretreated steel pipe in which the inner surface is pretreated using flame plasma.

Flame plasma can uniformly treat the surface of steel pipes in a short time, polish and remove surface debris with high efficiency, processing speed is very fast, no special equipment is required, so economical and easy to use, as well as excellent surface cleaning It exhibits performance and anti-lubrication performance, and can improve the adhesion of the epoxy coating agent by increasing the surface energy, thereby making it possible to manufacture a highly durable coated steel pipe.

Preferably, the steel pipe may be a steel pipe in which the inner surface is pretreated at a processing speed of 5 to 25 m/min using flame plasma, and is performed by adjusting the feed rate at which the burner discharging the flame plasma is transferred, that is, the treatment time, and , If the processing speed is less than 5 m/min, there is a problem that the manufacturing cost increases due to a long processing time, and if the processing time exceeds 25 m/min, the processing time is short and there is a fear that cleaning may be insufficient, and the surface energy of the steel pipe is greatly increased. Because it is difficult to improve the adhesion of the epoxy coating agent, the effect of the flame plasma treatment is insignificant.

On the other hand, the step (b) is a step of forming a double-layered inner coating layer including a bottom coating layer and a top coating layer by coating a second epoxy coating agent on the inner surface of the steel pipe on which the bottom coating layer is formed, and has excellent adhesion to the bottom coating layer. , When applied to the upper surface of the undercoat layer, it exhibits excellent slip properties so that it can have a uniform thickness, and it has excellent surface smoothness to prevent scale deposition for a long time, so that water stains are not easily pinched and thus corrosion is effectively prevented. Can be formed.

To this end, the second epoxy coating agent may use a mixture including a second main agent and a curing agent.

Specifically, the second subject is a polymer of 4,4'-(1-methylethylidene) bisphenol and (chloromethyl) oxirane, a polymer of quartz, cashew nut shell oil and epichlorohydrin, trimethoxy- A mixture containing a polymer of [3-(oxiranylmethoxy)propyl]silane, titanium dioxide, formaldehyde, (chloromethyl)oxirane and phenol, and a silicone additive can be used.

Specifically, the silicone-based additive included in the second subject may lower the surface tension of the coating film, prevent adhesion of contaminants, and improve the blocking resistance and scratch resistance of the coating film.

In addition, the silicone additive contains a siloxane-binding component, so it has excellent adhesion to the undercoat layer, and improves the slip property of the second epoxy coating agent to easily fill the surface of the irregular undercoat layer to form a topcoat layer with excellent smoothness due to its low surface roughness. I can.

The silicone additive may include a polyether siloxane copolymer, an organic modified polysiloxane, a polyether modified dimethylpolysiloxane, or a mixture thereof, and may be included in a ratio of 1 to 10 parts by weight in the second subject.

When the content of the silicone additive is less than 1 part by weight, it is difficult to expect sufficient improvement in physical properties, and when it exceeds 10 parts by weight, the workability of the coating film may be deteriorated, and physical properties such as abrasion resistance, water repellency, and scratch resistance may be deteriorated.

Preferably, the silicone additive may be a polyether-modified dimethylpolysiloxane, and the polyether-modified dimethylpolysiloxane contains a lot of methyl groups in the structure, and the methyl group lowers the surface tension of the coating film, thereby further improving the slip property.

Polyether-modified dimethylpolysiloxane is BYK's BYK-333 (brand name), BYK-306 (brand name), BYK-341 (brand name), BYK-344 (brand name), BYK-377 (brand name), BYK-322 (brand name) , BYK-340 (brand name), etc. are representative examples.

In addition, the second subject may be configured to further include an additive, and the additive may be used to control adhesion, dispersibility, water resistance, defoaming, weather resistance, UV resistance, durability, rust prevention, plasticity, workability, etc. In addition, surfactants, antioxidants, anti-settling agents, water reducing agents, retarders, flame retardants, antifoaming agents, binders, plasticizers, pigments, or mixtures thereof may be introduced.

The additive may be added in a range that does not adversely affect the physical properties of the second subject, and may be included in a ratio of 1 to 10 parts by weight.

In addition, the curing agent may be the same as the curing agent contained in the first epoxy coating agent described above.

The second epoxy coating agent including the second main material and the curing agent as described above has excellent adhesion to the undercoat layer, and has a low surface roughness to form a top coat layer with excellent smoothness, and the top coat layer has slip properties so that contaminants are not prevented. Since it is not easily deposited, it is possible to form an inner coating layer that can prevent corrosion of the steel pipe for a long time.

In particular, the second epoxy coating agent may be used a mixture containing a second main agent and a curing agent in a volume ratio of 2:1 to 1:1, respectively, and preferably, a second main agent and a curing agent are 3:2 to 1:1 A mixture containing in the ratio of may be used, whereby a top coat layer having excellent physical properties such as durability, adhesiveness, chemical resistance, and surface smoothness can be formed.

In this step, the second epoxy coating agent may be coated on the upper surface of the undercoat layer to form a top coat layer having a thickness of 150 to 1000 μm, and may be coated by various conventional coating methods such as spray coating.

When the thickness of the top coat layer is less than 150 µm, it is difficult to provide sufficient hiding power, and when the thickness of the top coat layer exceeds 1000 µm, it is difficult for the top coat layer to sufficiently adhere to the base coat layer during coating, and the fluidity of the coating layer increases, causing the coating layer to flow down. There is a problem in that it is difficult to form a top coat layer having a uniform thickness.

In addition, the second epoxy coating agent may have a viscosity of 3,000 to 50,000 cps, and when the viscosity of the second epoxy coating agent is less than 3,000 cps, the curing time is prolonged, and there is a concern that a coating film of an uneven thickness may be formed due to the coating film being pushed during coating. If it exceeds 50,000 cps, it is difficult to sufficiently adhere to the inner surface of the steel pipe due to high viscosity, and it is difficult to expect improvement of surface smoothness due to high viscosity.

As described above, the method of manufacturing a coated steel pipe according to the present invention uses a heterogeneous epoxy coating agent of the first epoxy coating agent having excellent rust prevention performance and high viscosity and the second epoxy coating agent having excellent slip property and low viscosity. The inner coating layer of the double layer structure of the coating layer is formed, and when the inner coating layer of the double layer structure is formed in this way, the inner coating layer exhibits excellent adhesion to the surface of the steel pipe, while the surface smoothness is improved, resulting in an inner coating layer having a low surface roughness. It can be formed, so that scale deposition can be prevented for a long time, so that a coated steel pipe can be manufactured in which corrosion does not occur for a long time.

In addition, the first epoxy coating agent and the second epoxy coating agent may be adjusted to have different viscosity, and when the viscosity of the second epoxy coating agent forming the top coat layer is lower than that of the first epoxy coating agent, the surface smoothness may be further improved. have.

In particular, the first epoxy coating agent and the second epoxy coating agent are solvent-free and are non-polluting coatings with a low content of organic solvents that are harmful to the human body. Since dirt or the like is not easily pinched, an inner coating layer that can effectively prevent corrosion can be formed, so that the durability of the coated steel pipe can be greatly improved.

In addition, the method of manufacturing a coated steel pipe according to the present invention may be configured to further include a step of surface treatment using plasma on the coating layer in the process of forming a primer coating layer and a top coating layer on the steel pipe, respectively.

Specifically, the method of manufacturing a coated steel pipe according to the present invention may be configured to further include a plasma surface step of coating the first epoxy coating agent in step (a) and then surface-treating the surface using flame plasma.

The flame plasma surface treatment as described above can be performed for the purpose of removing contaminants and static electricity on the surface of the underlying coating layer, and improving the bonding strength between the underlying coating layer and the top coating layer to form an inner surface coating layer having excellent physical properties.

To this end, the plasma surface treatment step may be performed at a processing speed of 10 to 30 m/min on the inner surface of the steel pipe using flame plasma, and when flame plasma is treated on the upper surface of the underlying coating layer as described above, the surface of the underlying coating layer This modification improves the adhesion between the second epoxy coating agent and the undercoat layer, so that separation of the undercoat layer and the upper coat layer does not easily occur, so that an inner surface coating layer having improved durability can be formed.

If the treatment time is less than 10 m/min, it is difficult to expect improved cleaning and adhesion due to insufficient surface modification by flame plasma, and if it exceeds 30 m/min, the underlying coating layer may be carbonized and physical properties may be deteriorated. Preferably, plasma surface treatment can be performed at a speed of 12 to 24 m/min.

In addition, the method of manufacturing a coated steel pipe according to the present invention may be configured to further include a plasma surface treatment step of coating a second epoxy coating agent in step (b) and then finishing using flame plasma.

When the steel pipe on which the inner coating layer including the undercoat layer and the top coat layer is formed as described above is finished with flame plasma, the protrusions and depressions formed on the top coat layer are removed, thereby lowering the surface roughness of the top coat layer and further improving the surface smoothness. I can.

To this end, the plasma surface treatment step may be performed at a treatment speed of 10 to 30 m/min on the inner surface of the steel pipe on which the inner coating layer is formed using flame plasma, and when the treatment time is less than 10 m/min, the inner surface by flame plasma There is a problem that physical properties may be deteriorated due to carbonization of the coating layer, and if it exceeds 30 m/min, it is difficult to expect the effect of improving the surface smoothness due to a high treatment speed, and preferably, at a speed of 12 to 24 m/min. Plasma surface treatment is possible.

For reference, if you look at the flame plasma technology in detail, flame plasma completely burns hydrocarbon-based fuels such as pulverized coal, LPG, LNG, or a mixture thereof under atmospheric pressure by a thermal fusion method to form a plasma zone of a certain size. In addition, by exposing the surface of the steel pipe to the formed flame plasma, contaminants on the surface of the steel pipe are removed, and the surface energy of the steel pipe is increased to increase the bonding strength between the epoxy coating layer and the surface of the steel pipe. The flame plasma treatment apparatus may perform flame plasma treatment using a variety of conventional devices that generate flame plasma.

Flame plasma can uniformly treat the surface of steel pipes in a short time, and can polish and remove surface debris with high efficiency, processing speed is very fast, no special equipment is required, economical and simple to use, excellent surface cleaning performance, It exhibits anti-lubrication performance, and can improve the adhesion of the epoxy coating agent by increasing the surface energy, thereby making it possible to manufacture a highly durable coated steel pipe.

In addition, when flame plasma is treated on the upper surface of the inner coating layer, it is possible to further improve the surface smoothness of the inner coating layer, thereby preventing scale deposition and contamination for a long time, thereby producing a highly durable coated steel pipe that can effectively prevent steel pipe corrosion. .

On the other hand, Figure 2 is a conceptual diagram showing the coated steel pipes (1, 1') manufactured by the method of manufacturing a coated steel pipe according to the present invention.

Referring to Fig. 2, a detailed look at the structure of the coated steel pipes 1, 1'manufactured by the manufacturing method of the coated steel pipes 1, 1'according to the present invention will be described in detail. ) Has a structure in which a coating layer is formed on the inner and outer surfaces, respectively, an outer epoxy coating layer formed on the outer surface of a steel pipe, an adhesive layer formed on the upper surface of the epoxy coating layer, and the adhesive layer. PE coating having a structure in which a three-layered outer coating layer including a polyethylene film layer formed on the upper surface is formed, and a double-layered inner epoxy coating layer is formed on the inner surface of the steel pipe. It may be a steel pipe 1 (see Fig. 2(a)).

In addition, the coated steel pipe 1 ′ according to a preferred embodiment of the present invention includes an adhesive layer formed on the outer surface of a steel pipe, a polyethylene resin coating layer formed on the upper surface of the adhesive layer, and the It may include a three-layered outer coating layer including a polyethylene film layer (PE flim layer) formed on the upper surface of the polyethylene resin coating layer, and a double-layered inner epoxy coating layer is formed on the inner surface of the steel pipe. It may be a PE coated steel pipe (1 ′) having (see Fig. 2(b)).

The coated steel pipes 1 and 1 ′ having the above structure may be manufactured using a steel pipe having a structure in which both sides are open and including a hollow formed through which fluid flows therein, The steel pipe may be a metal pipe manufactured using a variety of conventional metals exhibiting corrosive properties, such as a carbon steel pipe, a stainless steel pipe, a galvanized steel pipe, a cast iron pipe, and the like, and preferably, may be a carbon steel pipe. It can be used for purposes such as oil pipelines, conduit pipes, and gas transfer pipes.

In addition, the steel pipe used in the manufacturing method of the coated steel pipe according to the present invention uses a pre-treated steel pipe to have a constant surface roughness of 10 to 100 µm on the surface by polishing the surface through a surface treatment method such as shot blasting or sand blasting. It can be used for the purpose of manufacturing a coated steel pipe by pre-treating the steel pipe to have a surface roughness as described above and then pre-treating the inner surface of the steel pipe with flame plasma.

In addition, as the steel pipe, a steel pipe pretreated by degreasing, washing, pickling, chemical conversion coating treatment, etc. may be used, but is not limited thereto.

The method of manufacturing a coated steel pipe according to the present invention as described above can form an inner coating layer having low surface roughness and excellent adhesion by sequentially coating a base coat layer and a top coat layer using a different type of epoxy coating agent on the inner surface of the steel pipe. It is possible to manufacture a coated steel pipe that can prevent deposition and contamination for a long time and effectively prevent corrosion.

In addition, the method of manufacturing a coated steel pipe according to the present invention can effectively prevent scale deposition by improving surface smoothness through flame plasma treatment, and a highly durable inner coating layer that is not easily separated by improving adhesion between the undercoat layer and the upper coat layer. The formed coated steel pipe can be manufactured.

Therefore, when the coated steel pipe manufactured by the method for manufacturing the coated steel pipe according to the present invention is used for installation as a water supply pipeline, scale deposition and contamination can be prevented for a long time, thereby reducing the pipe diameter or decreasing the water flow capacity due to an increase in the roughness coefficient for a long time. It can be prevented, and it is possible to supply high quality raw water by reducing the occurrence of contaminated water such as poor water supply or rust.

Hereinafter, the present invention will be described in more detail by way of examples.

The examples presented are only specific examples of the present invention, and are not intended to limit the scope of the present invention.

<Production Example>

The surface of the steel pipe was shot blasted to prepare a steel pipe having a surface roughness of 30 to 35 µm.

<Example 1>

Coating the first epoxy coating agent to a thickness of 200 μm on the inner surface of the steel pipe subjected to shot blasting to form a primer coating layer, and then coating the second epoxy coating agent to a thickness of 200 μm on the upper surface of the underlying coating layer and curing to form a top coat layer. Thus, an inner coating layer having a double-layer structure including a primer coating layer and a top coating layer was formed.

As the first epoxy coating agent, a mixture containing a first main agent and a curing agent in a volume ratio of 2:1 was used, and a viscosity adjusted to 50,000 cps was used.

The first subject is, 20 to 50 parts by weight of a polymer of 4,4'-(1-methylethylidene) bisphenol and (chloromethyl) oxirane, 10 to 40 parts by weight of quartz, cashew nut shell oil and epichlorohydrin 5 to 30 parts by weight of a polymer, 1 to 20 parts by weight of trimethoxy-[3-(oxiranylmethoxy)propyl]silane, 1 to 20 parts by weight of titanium dioxide (TiO ₂ ), formaldehyde, (chloromethyl)oxy A mixture containing 1 to 20 parts by weight of a polymer of lan and phenol and 1 to 20 parts by weight of a rust preventive pigment was used.

The curing agent is a cashew nut shell oil, 40 to 70 parts by weight of a polymer of ethylenediamine and formaldehyde, 5 to 30 parts by weight of benzyl alcohol, 5 to 30 parts by weight of quartz, 3-aminomethyl-3,5,5-trimethylcyclo A mixture containing 1 to 20 parts by weight of hexylamine, 1 to 20 parts by weight of 3-aminopropyltriethoxysilane, and 1 to 10 parts by weight of ethylenediamine was used.

In addition, as the second epoxy coating agent, a mixture including a second main agent and a curing agent in a volume ratio of 5.3:4.7 was used, and the viscosity of the second epoxy coating agent was adjusted to 20,000 cps.

The second subject is, 20 to 50 parts by weight of a polymer of 4,4'-(1-methylethylidene) bisphenol and (chloromethyl) oxirane, 10 to 40 parts by weight of quartz, cashew nut shell oil and epichlorohydrin Of 5 to 30 parts by weight of the polymer, 1 to 20 parts by weight of trimethoxy-[3-(oxiranylmethoxy)propyl]silane, 1 to 20 parts by weight of titanium dioxide, formaldehyde, (chloromethyl) oxirane and phenol A mixture containing 1 to 20 parts by weight of a polymer and 1 to 10 parts by weight of a silicone additive was used.

<Example 2>

After forming a bottom coat layer and a top coat layer in the same manner as in Example 1, the inner surface of the steel pipe on which the top coat layer is formed is finished with flame plasma at the processing speed shown in Table 1 and completely cured to obtain a steel pipe with an inner coat layer. Was prepared.

The finishing treatment using flame plasma was performed in a state that the distance between the flame plasma burner and the inner surface of the steel pipe was adjusted to be 80 to 100 mm, and the flame plasma was performed using AETP flame plasma burner products using LNG as a heat source gas. .

<Example 3>

A first epoxy coating agent and a second epoxy coating agent each having a viscosity (unit: cps based on 25° C.) as shown in Table 2 were prepared, and the prepared first epoxy coating agent and the second epoxy coating agent were used in the same manner as in Example 1. Each was coated to a thickness of 250 μm to form a double-layered inner coating layer including a bottom coat layer and a top coat layer.

<Example 4>

The inner surface of the steel pipe subjected to the shot blasting treatment was pretreated by transferring the flame plasma head at the speed shown in Table 3 below to prepare a steel pipe pretreated with flame plasma.The first epoxy coating agent was applied to the inner surface of the pretreated steel pipe in the same manner as in Example 1. After coating to a thickness of 200 μm to form a undercoat layer, a second epoxy coating agent was coated on the upper surface of the undercoat layer to a thickness of 200 μm to form a top coat layer and then cured, 2 including the undercoat layer and the top coat layer. A layered inner coating layer was formed.

<Example 5>

Pre-treat the inner surface of the steel pipe in the same manner as in Example 4-3, use the first epoxy coating agent and the second epoxy coating agent, finish treatment using flame plasma in the same manner as in Example 2-3, and completely cure the inner surface coating layer. This formed steel pipe was manufactured.

<Comparative Example 1>

A first epoxy coating agent was coated on the inner surface of the pretreated steel pipe to a thickness of 400 μm, and cured to prepare a steel pipe having an inner surface coating layer formed thereon.

<Comparative Example 2>

A second epoxy coating agent was coated on the inner surface of the pretreated steel pipe to a thickness of 400 µm and cured to prepare a steel pipe having an inner surface coating layer formed thereon.

<Comparative Example 3>

In the same manner as in Example 1, except that the first epoxy coating agent and the second epoxy coating agent having the viscosity as shown in Table 2 were used, an inner coating layer having a double-layer structure including a primer coating layer and a top coating layer was formed.

<Experimental Example 1> Evaluation of surface smoothness

(1) Evaluation of surface smoothness

The surface roughness (unit: µm) of the inner coating layer of the steel pipe specimen manufactured by the method according to the Examples and Comparative Examples was measured, and the results are shown in Table 4 below.

As shown in Table 4, when the inner coating layer is formed through two coatings of the first epoxy coating layer and the second epoxy coating layer as in Example 1, the inner coating layer has a low surface roughness and a coating layer having high surface smoothness can be formed. I was able to confirm the fact.

In particular, it was confirmed that the surface smoothness of the inner coating layer can be further improved through flame plasma surface treatment and finishing treatment as in Examples 2 and 3.

In addition, the flame plasma surface treatment as described above is affected by the treatment speed, and if the treatment speed is too high, it is difficult to achieve sufficient surface activation by the flame plasma treatment, making it difficult to improve physical properties, and if the treatment speed is too low, It was confirmed that the surface roughness may rather increase due to reasons such as carbonization in the inner coating layer due to heat.

Through the above results, it was confirmed that the surface smoothness can be improved when the two-layer structure of the base coat layer and the top coat layer is formed, and the surface smoothness can be improved even through flame plasma treatment. It was judged that it could be possible to manufacture a coated steel pipe that can effectively prevent the occurrence of pollution and odor caused by.

(2) Analysis of influence by viscosity

In order to analyze the effect of viscosity on the surface smoothness in the double coating, a double layer structure formed on the inner surface of a steel pipe using the first epoxy coating agent and the second epoxy coating agent prepared by the method according to Example 3 and Comparative Example 3 The smoothness was evaluated by measuring the surface roughness (unit: µm) of the inner coating layer, and the results are shown in Table 5 below.

As shown in Table 5, it was confirmed that the viscosity of the first epoxy coating agent and the second epoxy coating agent has a great influence on the surface smoothness, and when the viscosity of the first epoxy coating agent and the second epoxy coating agent is the same, the effect of improving the surface smoothness is It can be seen that the surface smoothness is not improved when the viscosity of the first epoxy coating agent is lower than that of the second epoxy coating agent.

In addition, as in Comparative Example 3-6, when the viscosity of the epoxy coating agent is low, when a coating film having a certain thickness or more is formed, the surface smoothness may be greatly reduced due to the spillage of the epoxy coating agent.By adjusting the viscosity of the epoxy coating agent, It was determined that a thick coating layer could be formed.

In addition, it was also confirmed that the surface smoothness can be further improved through flame plasma finishing treatment.

<Experimental Example 3> Evaluation of physical properties of coating film

The physical properties of the coated steel pipe specimens manufactured by the methods according to Examples and Comparative Examples were evaluated, and the results are shown in Tables 6 and 7 below. The physical property evaluation was performed according to the test method according to KS D 8502: 2010, and the appearance, bending test, impact test (direct, indirect), adhesion, low temperature high speed repeat test, salt spray test, and resistance to products with excellent surface smoothness. Physical properties such as moisture were evaluated.

As shown in Table 6, it was judged that the coated steel pipe manufactured by the method according to the Example would have excellent durability due to the excellent physical properties of the inner coating layer coating film.

On the other hand, in the case of the steel pipe specimen manufactured by the method of Comparative Examples 1 and 2, a thick coating layer was coated on the surface of the steel pipe that was not surface-treated with flame plasma in a short time, and in the case of Comparative Example 1, fine wrinkles were generated in the coating layer. It was confirmed that, in the case of Example 2, it was confirmed that cratering or the like occurred and fine wrinkles were formed on the surface, thereby forming a coating layer having a slightly poor appearance quality.

In addition, as a result of evaluating the appearance and flexibility of the inner surface of the steel pipe manufactured by the method according to Example 3, Example 4, Example 5, and Comparative Example 3, when using an epoxy coating agent of the same viscosity as in Comparative Example 3-1, flexibility It was also confirmed that fine cracks may occur due to this decrease, and that when a second epoxy coating agent having a low viscosity, as in Example 3-6, is used, the coating agent flows down during the curing process, resulting in fine cracks in the top coat layer.

<Experimental Example 3> Dissolution test

It was evaluated whether or not harmful components generated in the inner coating layer of the coated steel pipe specimen prepared by the method according to the Examples and Comparative Examples were detected, and the results are shown in Table 8 below.

The dissolution test was evaluated by the method based on the hygiene and safety standard process test (Ministry of Environment Notification No. 2009-59) and the water quality process test standard (2010) of water materials and products, and turbidity, Cd, Se, Cr, CN, nitrate nitrogen. And nitrite nitrogen, F, carbon tetrachloride, 1,2-dichloroethane, 1,1-dichloroethylene, 1,1,2-trichloroethane, trichloroethylene, benzene, Zn, Fe, Cu, phenol, benzene, dichloro Items such as methane (DCM), Hg, residual chlorine, As, Pd, xylene, and toluene were evaluated.

As shown in Table 8, it was determined that the coated steel pipe manufactured by the method according to the Example could be used for water supply because there was little elution of harmful components.

Therefore, the coated steel pipe manufactured by the manufacturing method of the present invention not only had no abnormality in adhesion, durability, and appearance, but also the detection of harmful components such as phenols could be minimized, and the stability was high because there was no risk of elution of environmental hormones, and plasma treatment was performed. Also, it was confirmed that the risk of dissolution of harmful ingredients did not increase.

Detailed description of the preferred embodiments of the present invention disclosed as described above has been provided to enable those skilled in the art to implement and practice the present invention. Although the above has been described with reference to preferred embodiments of the present invention, those skilled in the art will understand that various modifications and changes can be made to the present invention without departing from the scope of the present invention. For example, a person skilled in the art may use the configurations described in the above-described embodiments in a manner that combines them with each other. Accordingly, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

The present invention may be embodied in other specific forms without departing from the spirit and essential features of the present invention. Therefore, the detailed description above should not be construed as restrictive in all respects and should be considered as illustrative. The scope of the present invention should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent scope of the present invention are included in the scope of the present invention. The invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. In addition, the embodiments may be configured by combining claims that do not have an explicit citation relationship in the claims, or may be included as new claims by amendment after filing.

Claims (5)

In the method of manufacturing a coated steel pipe by forming a coating layer on the inner surface,
(a) forming a primer coating layer by coating a first epoxy coating agent to a thickness of 50 to 500 µm on the inner surface of the steel pipe; And
(b) coating a second epoxy coating agent to a thickness of 150 to 1,000 µm on the inner surface of the steel pipe on which the undercoat layer is formed to form a double-layered inner coating layer including a undercoat layer and a top coat layer; Including,
The first epoxy coating agent,
Including a first subject and a curing agent,
The first topic is,
4,4'-(1-methylethylidene)bisphenol polymer with (chloromethyl)oxirane) 20 to 50 parts by weight, quartz ( quartz, SiO ₂ ) 10 to 40 parts by weight, cashew nutshell liq., polymer with epichlorohydrin, OHS53097 5 to 30 parts by weight, trimethoxy-[3-(oxirane Ilmethoxy) propyl] silane (Silane, trimethoxy[3-(oxiranylmethoxy)propyl]-) 1 to 20 parts by weight, titanium dioxide (TiO ₂ ) 1 to 20 parts by weight, formaldehyde, (chloromethyl) oxirane and phenol Including 1 to 20 parts by weight of a polymer (formaldehyde polymer with (chloromethyl)oxirane and phenol) and 1 to 20 parts by weight of an anti-rust pigment,
The curing agent,
Cashew nutshell liq. polymer with ethylenediamine and formaldehyde 40 to 70 parts by weight, benzyl alcohol 5 to 30 parts by weight, quartz 5 to 30 parts by weight, 3- Aminomethyl-3,5,5-trimethylcyclohexylamine (3-Aminomethyl-3,5,5-trimethylcyclohexylamine; Isophorone diamine) 1 to 20 parts by weight, 3-Aminopropyltriethoxysilane 1 To 20 parts by weight and 1 to 10 parts by weight of ethylenediamine,
The second epoxy coating agent,
Including a second subject and the curing agent,
The second subject is,
Polymer of 4,4'-(1-methylethylidene) bisphenol and (chloromethyl) oxirane (4,4'-(1-methylethylidene) bisphenol polymer with (chloromethyl)oxirane) 20 to 50 parts by weight, quartz ( quartz, SiO ₂ ) 10 to 40 parts by weight, cashew nutshell liq., polymer with epichlorohydrin, OHS53097 5 to 30 parts by weight, trimethoxy-[3-(oxirane Ilmethoxy) propyl] silane (Silane, trimethoxy[3-(oxiranylmethoxy)propyl]-) 1 to 20 parts by weight, titanium dioxide (TiO ₂ ) 1 to 20 parts by weight, formaldehyde, (chloromethyl) oxirane and phenol Polymer (formaldehyde polymer with (chloromethyl)oxirane and phenol) 1 to 20 parts by weight and 1 to 10 parts by weight of a silicone additive, characterized in that it comprises a coated steel pipe manufacturing method. The method of claim 1,
The steel pipe of the step (a) is a method of manufacturing a coated steel pipe, characterized in that the inner surface is pretreated using flame plasma at a processing speed of 5 to 25 m/min. The method of claim 1,
The first epoxy coating agent has a viscosity of 20,000 to 100,000 cps, and the second epoxy coating agent has a viscosity of 3,000 to 50,000 cps. The method of claim 1,
In step (b),
After coating a second epoxy coating agent on the inner surface of the steel pipe on which the undercoat layer is formed, a finishing treatment step of surface-treating the inner surface of the steel pipe on which the inner surface coating layer is formed at a treatment speed of 10 to 30 m/min using flame plasma; A method of manufacturing a coated steel pipe, comprising: A coated steel pipe comprising an inner coating layer having a double-layer structure comprising a base coat layer and a top coat layer, manufactured by the method for producing a coated steel pipe according to any one of claims 1 to 4.

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