KR102241674B1 - Method of coating the steel sheet for the scrubber of the ship - Google Patents

Abstract

A method of coating a steel plate for a scrubber purifying exhaust gas of a ship is provided.
The steel plate coating method of the present invention includes the process of preparing a carbon steel plate; On the surface of the carbon steel sheet, in wt%, Mo: 5-20%, Cr: 5-20%, W: 1-5%, Co: 1-5%, Fe: 1-5%, Ni: 50- A process of forming a thermal spray coating layer having a thickness of 200 to 400 μm and a surface roughness of Sa 2+1/2 or more by thermal spray coating using a wire containing 75%; And a fluorine-based resin having a viscosity of between 7 and 14 seconds with a viscosity of pod cup and a molecular weight of between 10,000 and 20,000 is coated on the formed thermal spray coating layer, and then naturally cured to form a fluorine-based resin layer having a thickness of 150 to 250 μm. The process of doing; includes.

Description

Method of coating the steel sheet for the scrubber of the ship}

The present invention relates to a method for coating a steel plate for a scrubber purifying exhaust gas of a ship.

As the emission regulation of ships has been strengthened from 2020 by IMO regulations, ships currently in operation and newly built ships are applying various technologies to comply with this regulation.

Most of the newly built ships meet the emission gas regulation by applying the LNG combustion engine, but the problem is the ship in operation. Most ships have a lifespan of about 30 years, and for ships with a short lifespan, it is costly to adopt an LNG combustion engine.Therefore, a scrubber to purify the exhaust gas is installed at the rear end of the diesel combustion engine to regulate emissions. The way you want to satisfy is the most common.

A total of two types of marine scrubbers are applied. First, in a close type method, an alkaline solution such as NaOH is stored in a tank and the exhaust gas is passed through the solution to purify it.It is a method widely used in refinery chemistry processes, but after a certain time has passed due to the operating conditions of the ship. Since there is a problem in that an alkali-based solution has to be treated, there are many points that are difficult to apply in practice. The second is a method of diluting and purifying _{the SO x} and NO _x components of the exhaust gas by spraying seawater into the scrubber chamber in a cyclone method. Compared to the first method, the purification capacity is inferior, but it is a method that is most suitable for the operating environment of the ship and is currently adopted in most marine scrubbers.

This marine scrubber is operated by spraying a large amount of seawater, so it is exposed to a very severe corrosive environment. The main chamber is a corrosive environment in which a large amount of seawater and oxygen and a temperature of about 50 degrees are operated, and the lower part of the chamber is an environment in which sulfuric acid and nitric acid are deposited by reacting with the seawater _{by concentrated SO x} and NO _x. It is an exposed environment. Currently, in order to secure the durability in such a severe corrosive environment, a scrubber with 6% Mo stainless steel is being manufactured, but there is a disadvantage in that it takes a huge manufacturing cost due to the very expensive material price and very difficult processing and welding during manufacturing.

As described above, the durability life of the ship is about 30 years, and it is very economical to install a scrubber with such an expensive material on a ship that only has a durability life of less than 10 years, depending on the situation of the ship in operation. In addition, there is a need to develop an economical and durable coating technology that can replace this.

In the shipbuilding industry, various coatings are applied to prevent corrosion of steel materials. Examples include painting, plating, and thermal spray coating. The thermal spray coating has been mainly applied to offshore plants that must ensure high durability, and the most widely used is the aluminum arc thermal spray method, but it has the advantage that various metal materials can be applied as a coating material due to the characteristics of the thermal spraying process. Even in the case of the painting method, there are various material systems, and if the adhesion to the substrate to be coated is secured, the durability life of the designed material system can be realized.

However, in the case of a marine scrubber, it is virtually impossible to secure the durability in the extreme corrosive environment predicted by applying the existing coating alone, and thus the necessity of developing a coating technology that can overcome this is emerging.

Therefore, the present invention was devised to solve the problems of the prior art described above, forming a thermal spray coating layer having high durability in a complex corrosive environment such as seawater and sulfuric acid on a carbon steel sheet, and having excellent adhesion to the coated surface is optimal. It is an object of the present invention to provide a coating method of a steel plate for a ship exhaust gas purification scrubber that can form a composite coating layer of.

In addition, the technical problems to be achieved in 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.

The present invention for achieving the above object,

A process of preparing a carbon steel sheet;

On the surface of the carbon steel sheet, in wt%, Mo: 5-20%, Cr: 5-20%, W: 1-5%, Co: 1-5%, Fe: 1-5%, Ni: 50- A process of forming a thermal spray coating layer having a thickness of 200 to 400 μm and a surface roughness of Sa 2+1/2 or more by thermal spray coating using a wire containing 75%; And

The formed thermal spray coating layer is coated with a fluorine-based resin having a viscosity of between 7 and 14 seconds in terms of pod cup viscosity and a molecular weight between 10,000 and 20,000, and then naturally cured to form a fluorine-based resin layer having a thickness of 150 to 250 μm. It relates to a coating method of a steel plate for a ship exhaust gas purification scrubber including a process.

It is preferable to increase the surface roughness so that 50% of the upper layer is not relatively dense compared to 50% of the lower layer of the formed thermal spray coating layer thickness.

In the process of manufacturing the thermal spray coating layer, it is preferable that the lower layer is formed at an injection pressure of 7 to 8 bar, and the upper layer is formed at an injection pressure of 5 to 6 bar to increase the surface roughness of the surface layer.

The fluorine-based resin may be a PVDF (polyvinylidene fluoride)-based fluorine resin.

The present invention having the configuration as described above improves the durability of the steel sheet by forming a thermal spray coating layer on the surface of the carbon steel sheet in an arc spray method with a Ni base material, and secondary adhesion to the thermal spray coating layer. By forming an excellent fluororesin layer, it is possible to effectively provide a steel plate for a ship exhaust gas purification scrubber that is also excellent in corrosion resistance.

Figure 1 shows in the application of the air pressure among the process conditions of the thermal spray coating, (a) is a spraying pressure of about 7 to 8 bar, after continuously forming the thermal spray coating layer, (b) is up to 50% of the initial thickness. This is a photograph showing the result of the adhesion test result of forming a fluorine-based resin layer after forming a thermal spray coating layer using a spraying pressure of about 7~8bar, and then using a spraying pressure of about 5~6bar at the remaining 50% thickness. .
FIG. 2 is an SEM photograph showing a cross section of the composite coating layer of FIG. 1(a).
3 is an SEM photograph showing a cross section of the composite coating layer of FIG. 1(b).
4 is a photograph showing the results of an accelerated corrosion test in an environment of 5wt% NaCl and 2.5wt% H2SO4 for 60 days by forming an I cut scratch after forming a Ni-based thermal spray layer and a urethane-based coating,
(a) shows a case where a urethane coating layer is formed on the thermal spray coating layer of FIG. 1(a), and (b) shows a case where a urethane coating layer is formed on the thermal spray coating layer of FIG. 1(b).
5 is a photograph showing the result of an accelerated corrosion test under the same conditions as in FIG. 4 after forming a Ni-based sprayed layer and a fluorine-based resin layer,
(a) shows a case where a fluorine-based coating layer is formed on the thermal spray coating layer of FIG. 1(a), and (b) shows a case where a fluorine-based resin layer is formed on the thermal spray coating layer of FIG. 1(b).

Hereinafter, the present invention will be described.

Corrosive environment of the scrubber is NaCl is 3.5 ~ 5wt%, and pH 2.5 to 8.4, the temperature is 0 to 50, SO ⁴ the environment of about 2.4 ~ 2.7g / L, inlet pipe portion of the exhaust gas is corrosive material, but However, it must withstand a temperature of about 200 degrees, and outlet piping contains most of the corrosive substances, but it can be said that it is an environment where the temperature is about 0 to 30 degrees.

Materials that can withstand such corrosive environments include 6% Mo STS, Ti, Inconel, etc. as known to date. However, as described above, since a lot of cost is consumed to manufacture the scrubber, it was attempted to form a Ni-based Inconel material on the upper portion of the general carbon steel by using a thermal spray coating. In addition, in order to overcome the quality deviation of the coating film, a corrosion-resistant coating was added on the top to secure the durability in the scrubber corrosive environment through complex coating, since local pores caused by the characteristics of the scrubber product become a problem for the product's lifespan. .

At this time, the most important part is the part that secures mutual adhesion between the thermal spray coating and the corrosion resistance coating in the layered structure consisting of carbon steel-Inconel thermal spray coating-corrosion resistance coating. In general, since the surface of the thermal spray coating layer is rough, satisfactory adhesion strength is obtained when a coating is formed on the top even if there is no special blasting treatment, but since the corrosion environment is very harsh, the coating on the top must be formed so that the adhesion strength is at least 25 MPa. , As the upper coating layer is a fluorine-based coating material with corrosion/chemical resistance, it is a coating material with relatively low adhesion strength, so more attention should be paid to the improvement of adhesion strength.

Therefore, the present inventors confirmed that high corrosion resistance coating technology applied to a marine scrubber can be secured by optimizing the Inconel-based thermal spray coating layer formation process, the thermal spray coating layer finishing process to secure the surface roughness of Sa 2+1/2 or higher, and the upper fluorine-based coating forming process. And present the present invention.

In consideration of this, the method of coating a steel plate for a scrubber purifying exhaust gas of a ship of the present invention includes a process of preparing a carbon steel plate; On the surface of the carbon steel sheet, in wt%, Mo: 5-20%, Cr: 5-20%, W: 1-5%, Co: 1-5%, Fe: 1-5%, Ni: 50- A process of forming a thermal spray coating layer having a thickness of 200 to 400 μm and a surface roughness of Sa 2+1/2 or more by thermal spray coating using a wire containing 75%; And a fluorine-based resin having a viscosity of between 7 and 14 seconds with a viscosity of pod cup and a molecular weight of between 10,000 and 20,000 is coated on the formed thermal spray coating layer, and then naturally cured to form a fluororesin layer having a thickness of 150 to 250 μm. The process of doing; includes.

That is, the present invention is a technology for manufacturing a scrubber in which a carbon steel sheet-a thermal spray coating layer-a fluorine-based resin layer is laminated, and will be described in detail below.

First, in the present invention, a carbon steel sheet, which is a base material, that can be used in the manufacture of a scrubber for purifying marine exhaust gas, is provided. Such a carbon steel sheet may be used without limitation on a specific steel composition component as long as it has various mechanical properties such as strength that can be used in the manufacture of a ship exhaust gas purifying scrubber, and both cold rolled steel sheets and hot rolled steel sheets may be used.

Preferably, the carbon steel sheet as the base material in the present invention is a composition comprising, by weight, C: 0.25% or less, Si; 0.45% or less, Mn: 1.40% or less, residual Fe and unavoidable impurities.

Then, in the present invention, on the surface of the carbon steel sheet, by weight %, Mo: 5-20%, Cr: 5-20%, W: 1-5%, Co: 1-5%, Fe: 1-5% , Ni: A thermal spray coating layer having a thickness of 200 to 400 μm and a surface roughness of Sa 2+1/2 or more is formed by thermal spray coating using a wire containing 50 to 75%.

In the present invention, it is important to select a coating material suitable for a corrosive environment in which oxygen is supplied smoothly and seawater and sulfuric acid act simultaneously.

In the case of the thermal spray coating of the present invention, an arc spraying process was applied to secure economic efficiency, and Ni base thermal spray coating was performed to secure durability for a certain period in a severe corrosive environment.

Preferably, the Ni-based thermal spraying material is in wt%, Mo: 5-20%, Cr: 5-20%, W: 1-5%, Co: 1-5%, Fe: 1-5%, Ni: It is a thermal spray coating using a wire containing 50-75%.

In addition, it is desirable to manage the optimum coating thickness to be 200 ~ 400㎛ for realizing economy and corrosion resistance. If the thickness is less than 200 μm, durability is deteriorated, whereas if the thickness exceeds 400 μm, delamination may occur or economical efficiency may decrease.

Meanwhile, in the present invention, it is important to maximize the adhesion between the thermal spray coating layer and the fluorine-based resin coating layer described later. In general, it is difficult to chemically bond the thermal spray and paint to each other, and it is necessary to approach it in a way to improve the physical bonding strength. As a method of maximizing such physical bonding force, a method of maximizing Sa 2+1/2 or more while minimizing the effect of coating quality can be used to maximize the surface roughness of the lower surface of the thermal spray coating layer.

In detail, maximizing the adhesion strength between the thermal spray coating layer and the paint layer can be solved through the thermal spray coating process. Specifically, in order to coat the Ni-based thermal spray coating with a 200-400 μm thick film, it is possible to perform a number of passes. In this case, in the present invention, the upper layer 50% of the formed thermal spray coating layer thickness is not relatively dense compared to the lower layer 50%. Therefore, it is desirable to increase the surface roughness. If about 50% of the thickness of the thermal spray coating layer is formed by forming a very dense film and the remaining 50% is formed by maximizing the surface roughness, the physical bonding force with the upper coating layer can be maximized.

The structure of the above-described thermal spray coating layer can be formed by changing the air pressure during the thermal spray coating process conditions. Preferably, the lower layer is formed at a spray pressure of 7 to 8 bar to form a dense coating layer, and the upper layer is formed at a spray pressure of 5 to 6 bar to maximize the surface roughness of the surface layer.

Subsequently, in the present invention, the formed thermal spray coating layer is coated with a fluorine-based resin having a viscosity of between 7 and 14 seconds in terms of pod cup viscosity and a molecular weight between 10,000 and 20,000, and then naturally cured to have a thickness of 150 to 250 μm. A fluorine-based resin layer is formed.

That is, in the present invention, an upper fluorine-based coating layer that serves to repair the pores of the thermal spray coating layer in a buried form is formed to act as a sealer. Since the pore size of the thermal spray coating layer is at the ㎛ level, in order to seal this part well, the molecular weight and flowability of the fluororesin must be used, and this must be properly designed at a level that does not degrade the durability of the entire fluorine coating.

As described above, if the surface roughness is maximized by forming about 50% of the upper thermal spray coating layer at 5 to 6 bar, the adhesion to the fluororesin coating layer is improved, but the thermal spray layer durability decreases due to the formation of a large number of pores in the thermal spray coating layer. Problems can arise. Therefore, in order to solve this problem, the present invention proposes a method of improving the durability of the entire system by controlling the viscosity and molecular weight of the fluorine-based resin to fill the pores of the thermal sprayed layer when coating a fluorine-based resin having corrosion resistance/chemical resistance. That is, since the thermal spray pores are very small pores with a diameter of several µm, in order to smoothly fill these pores, the flowability of the fluorine-based resin must be improved.

To this end, in the present invention, the fluorine-based resin has a viscosity of between 7 and 14 seconds as a pod cup viscosity, and preferably has a molecular weight between 10,000 and 20,000. If the viscosity is lower than this, it is difficult to form a fluorine coating layer, and durability may also decrease.

More preferably, the fluorine-based resin is a PVDF (polyvinylidene fluoride)-based fluorine resin.

In the present invention, in order to provide excellent resistance to seawater corrosion, sulfuric acid corrosion, friction wear corrosion, and high temperature corrosion occurring inside the scrubber, it is preferable to manage the thickness of the fluorine-based resin layer in the range of about 150 to 250 μm. Since the fluorine-based resin coating must be applied after the internal spray coating of the scrubber, it is preferable to apply a fluorine-based coating capable of natural drying for curing.

Hereinafter, the present invention will be described in detail through examples.

(Example 1)

On the surface of the carbon steel sheet, in wt%, Mo: 5-20%, Cr: 5-20%, W: 1-5%, Co: 1-5%, Fe: 1-5%, Ni: 50-75% A thermal spray coating layer having a thickness of 300 μm was formed by thermal spray coating using a wire containing a. At this time, the structure of the thermal spray coating layer was adjusted differently by changing the air pressure among the thermal spray coating process conditions. Specifically, one formed a dense thermal spray coating layer by applying a spray pressure of 7 to 8 bar to the surface of the carbon steel sheet, and the other forms a dense coating layer by forming a thermal spray coating layer with a spray pressure of 7 to 8 bar on the lower layer, The upper layer was formed at an injection pressure of 5 to 6 bar, and the surface roughness of the surface layer was controlled to increase.

In this way, PVDF (polyvinylidene fluoride)-based fluororesin having a molecular weight of 10,000 to 20,000 and having a viscosity of pods and cups of between 7 and 14 seconds, respectively, on the surface of the prepared two thermal spray coating layers, to a thickness of 200 μm. After formation, it was naturally dried and cured.

Figure 1 shows in the application of the air pressure among the process conditions of the thermal spray coating, (a) is a spraying pressure of about 7 to 8 bar, after continuously forming the thermal spray coating layer, (b) is up to 50% of the initial thickness. This is a photograph showing the result of the adhesion test result of forming a fluorine-based resin layer after forming a thermal spray coating layer using a spraying pressure of about 7~8bar, and then using a spraying pressure of about 5~6bar at the remaining 50% thickness. . As shown in Fig. 1, when the composite coating layer of the present invention, which maximizes the surface roughness by varying the spraying pressure in forming the sprayed coating layer, combines the fluorine-based coating layer with the sprayed coating layer formed at a continuous spraying pressure of 7 to 8 bar. It can be seen that the adhesion strength is improved by more than about 30%.

Meanwhile, FIG. 2 is an SEM photograph showing a cross-section of the composite coating layer of FIG. 1(a), and FIG. 3 is an SEM photograph showing a cross-section of the composite coating layer of FIG. 1(b).

(Example 2)

A urethane-based coating having a thickness of 200 μm was formed on the Ni-based thermal spray coating layer prepared in FIGS. 1(a) and 1(b), respectively. Thereafter, the two prepared composite coating layers were subjected to an accelerated corrosion test in an environment of 5wt% NaCl and 2.5wt% H2SO4 for 60 days by forming I cut scratches, and the results are shown in FIG. 4.

In addition, for comparison, PVDF having a viscosity of between 7 and 14 seconds as a pod and cup viscosity on the Ni-based thermal spray coating layer prepared in FIGS. 1 (a) and 1 (b), and a molecular weight of between 10,000 and 20,000 A (polyvinylidene fluoride)-based fluororesin coating film was formed to a thickness of 200 μm. In addition, the two prepared composite coating layers were subjected to an accelerated corrosion test in an environment of 5wt% NaCl and 2.5wt% H2SO4 for 60 days by forming I cut scratches, and the results are shown in FIG. 5.

As shown in Fig. 4-5, after forming the thermal spray coating layer on the carbon steel base material, the case where the fluorine-based resin coating film of Fig. 5 is formed is more excellent than the case where the urethane-based resin coating film of Fig. 4 is formed as an upper coating. Can be seen to show.

In addition, as shown in Fig. 4-5, the corrosion resistance characteristics of Figs. 4(b) and 5(b), which are controlled to increase the surface roughness of the carbon steel base material, are not compared to Figs. 4(a) and 5(a). It can be seen that it is excellent.

In particular, it can be seen that the case of the present invention in which a fluorine-based resin coating layer is formed on the surface of the thermal spray coating layer controlled to increase the surface roughness on the carbon steel base material as shown in FIG. 5(b) has the most excellent anti-fogging properties.

As described above, in the detailed description of the present invention, preferred embodiments of the present invention have been described, but those of ordinary skill in the art to which the present invention pertains, various modifications within the limit not departing from the scope of the present invention. Of course this is possible. Therefore, the scope of the present invention is limited to the described embodiments and should not be determined, and should not be determined by the claims to be described later, as well as those equivalent thereto.

Claims (4)

A process of preparing a carbon steel sheet;
On the surface of the carbon steel sheet, in wt%, Mo: 5-20%, Cr: 5-20%, W: 1-5%, Co: 1-5%, Fe: 1-5%, Ni: 50- A process of forming a thermal spray coating layer having a thickness of 200 to 400 μm and a surface roughness of Sa 2+1/2 or more by thermal spray coating using a wire containing 75%; And
The formed thermal spray coating layer is coated with a fluorine-based resin having a viscosity of between 7 and 14 seconds in terms of pod cup viscosity and a molecular weight between 10,000 and 20,000, and then naturally cured to form a fluorine-based resin layer having a thickness of 150 to 250 μm. Including;
Of the formed thermal spray coating layer thickness, 50% of the upper layer is not relatively dense compared to 50% of the lower layer to increase the surface roughness, and
In the process of manufacturing the thermal spray coating layer, the lower layer is formed at an injection pressure of 7 to 8 bar, and the upper layer is formed at an injection pressure of 5 to 6 bar to increase the surface roughness of the surface layer. Coating method.
delete delete The method of claim 1, wherein the fluorine-based resin is a PVDF (polyvinylidene fluoride)-based fluororesin.

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