Description:FIELD OF THE INVENTION
The present invention relates to the field of anti-corrosion composition. Particularly, the present invention relates to an anti-corrosive coating composition for refineries and a method of coating/ applying the same.
BACKGROUND OF THE INVENTION
Petroleum refineries are equipped with various components, including offshore structures and storage tanks, which are constantly exposed to salty environments, leading to corrosion. This corrosion can result in the deterioration of critical assets like valves and gauges, causing downtime for repairs and replacements.
Formerly/Earlier, phosphate and chromate-based conversion coatings were commonly used to protect these components from corrosion, but due to environmental and health concerns, there has been a move away from these coatings. As an alternative, epoxy-based coatings have been used to protect metallic surfaces from corrosive environments by creating a barrier effect. However, relying solely on epoxy coating may not always be sufficient to protect the underlying metal, as prolonged exposure to harsh conditions can cause the epoxy coating to fail due to cathodic disbondment.
US 2011/0294918 A1 discloses a method for producing anticorrosive paints and coatings containing nano particles made of inorganic aluminum-silicate in a platelet shape. In this invention, the platelets are chemically treated to align parallel to the substrate, increasing the pathways for corrosive ions. The amount of these nanoparticles is less than 2% by weight of the total formulation.

WO 2013/091686 A1 discloses a method for producing a highly structured composite material to coat equipment used in oil and gas drilling, storage, and transportation, such as pressure vessels, tools, pipes, and tubes. The composite coating enhances barrier properties and protects metal surfaces from corrosive substances like hydrogen sulfide, carbon dioxide, and sea water. The composite coating contains hydrophilic flakes which enlarges the pathways for corrosive ions.

CN1667040A1 discloses the production of anti-corrosive coatings using modified carbon nanotubes (CNTs). The CNTs are dispersed in epoxy resin using high-speed agitation and ultra-sonication in the presence of a dispersing agent selected from polypriopionate and modified polyurethane. The resulting CNT/epoxy composites exhibit good corrosion resistance, heat resistance, solvent resistance, and improved adhesion.

WO2007055498A1 discloses an organoclay containing anticorrosive coating composition, comprising a curable monomer or polymer, such as epoxy, which is dissolved in an organic solvent, a curing agent, having two or more amine groups, and organoclay, which is uniformly mixed and dispersed in either or both of the monomer or polymer and the curing agent or in the mixture of the two components using ultrasonic waves. The coating composition is a coating agent having corrosion resistance for preventing the corrosion of the surface of metal.

The corrosion protection of pure polymers/epoxies can be significantly improved by incorporating organic polymers mixed with reinforcing fillers in composite coatings. These fillers include ceramic nanoparticles, metals, clays, and glasses. The common nanoparticle fillers used are 2D nanoclays, graphene, 1D carbon nanotubes, and 3D metal oxide nanoparticles such as zinc oxide (ZnO), titanium dioxide (TiO2), and zirconia (ZrO2). The shape and size of the fillers play a crucial role in determining the properties of the composite coatings. Additionally, the interaction between the filler and the host matrix also affects the overall properties of the composites. Inadequate dispersion and interaction can lead to the formation of voids, pinholes, and cracks within the matrix, which in turn create pathways for corrosive ions.
Inventors of the invention described herein have developed an anticorrosive nanocomposite coating composition, which overcome the limitations of related compositions known in the art. The anticorrosive nanocomposite coating composition described herein overcome the drawbacks of related compositions known in the art by improving the barrier properties of epoxy coatings by incorporating impermeable entities with 3D spherical and 2D plate-like structures.
SUMMARY OF THE INVENTION
This summary is provided to introduce a selection of concepts in a simplified format that are further described in the detailed description of the invention.
The present invention relates to an anticorrosive nanocomposite coating composition having (a) 3 D nanofillers (b) 2-D nanofiller (c) reinforcing filler (d) epoxy resin (e) iron oxide-based pigment; and (f) polyamide-based hardener.
The present invention also relates to a method for applying an anticorrosive nanocomposite coating composition on pre-primed steel surface, the method includes preparing the anti-corrosive coating composition, preparing the surface substrate for applying a layer of anti-corrosive coating composition, and applying a layer of coating composition to the surface substrate.

These and other features, aspects, and advantages of the present subject matter will be better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

OBJECTIVES OF THE PRESENT INVENTION
It is the primary objective of the present invention to provide an anticorrosive coating composition.
It is further objective of the present invention to provide an anticorrosive nanocomposite coating composition to be applied at substrate in salty environment.
It is further objective of the present invention to provide a method for applying the coating composition on the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1: Illustrates the schematic representation of anti-corrosion coating composed of three layers out of which the proposed coating is for the middle layer.
Figure 2: Illustrates the mechanism of path blocking for corrosive ions with the introduction of 3D-2D nanofillers in epoxy.
Figure 3. Illustrates the coating preparation process involving mixing of constituent elements.
Figure 4. Illustrates the SEM micrograph of alumina nanofiller.
Figure 5. Illustrates the SEM micrograph of TiO2 nanofiller.
Figure 6. Illustrates the SEM micrograph of glass flakes.
Figure 7. Illustrates the impedance measurement of neat epoxy.
Figure 8. Illustrates the impedance plot of nanocomposite coating.
Figure 9. Illustrates the salt spray pictures of proposed coating till 1000 h (42 days).

DETAILED DESCRIPTION OF THE INVENTION
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments in the specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated composition, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The composition, methods, and examples provided herein are illustrative only and not intended to be limiting.
The articles “a”, “an” and “the” are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.
The terms “comprise” and “comprising” are used in the inclusive, open sense, meaning that additional elements may be included. It is not intended to be construed as “consists of only”.
Throughout this specification, unless the context requires otherwise the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated element or step or group of element or steps but not the exclusion of any other element or step or group of element or steps.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the disclosure, the preferred methods and materials are now described. All publications mentioned herein are incorporated herein by reference.
The terminology and structure employed herein is for describing, teaching, and illuminating some embodiments and their specific features and elements and does not limit, restrict, or reduce the spirit and scope of the invention.
The term “optionally,” as used in the present disclosure, means that a feature or element described as ‘optional’ within the context of the invention is not required for the invention to function as claimed. It indicates that the presence or absence of the described feature or element does not alter the fundamental operation or scope of the invention, and its inclusion or exclusion may be determined based on the specific requirements or preferences of a practitioner skilled in the art or the particular application in question.

As used herein, the term “nanocomposite” refers to a material that consists of a matrix (such as epoxy) reinforced with nanoparticle.

As used herein, the term “nanofillers” refers to a nanoscale-sized material that is added to another substance, such as an epoxy, to enhance its properties.

As used herein, the term “hardener” refers to a substance added to a material, such as epoxy or paint, to promote or control the curing or hardening process. When mixed with the base material, the hardener initiates a chemical reaction that leads to the formation of a hardened or cured product with improved strength, durability, and other desirable properties.

As used herein, the term “impedance” refers to the resistance that a material presents to the penetration or interaction of corrosive ions, which can cause corrosion.

As used herein, the term “primer” refers to the initial coat of paint or sealant applied to a surface before the topcoat. Its purpose is to enhance adhesion, provide a uniform base for the topcoat, and improve the overall durability and appearance of the painted surface.

The present invention discloses a nanocomposite coating composition, which is corrosion resistant for refinery applications in salty environment for such extended duration.

In an embodiment, the present invention provides an anti-corrosive nanocomposite coating composition comprising: 3-D nanofillers; 2-D nanofiller; reinforcing filler; and epoxy resin.

In yet another embodiment, the present invention provides an anti-corrosive nanocomposite coating composition comprising optional compound, iron oxide-based pigment; and polyamide-based hardener mixed prior to final use of coating composition.

In still another embodiment, the present invention provides an anti-corrosive nanocomposite coating composition comprising of 3 D nanofillers are selected from the group consisting of Al2O3 and TiO2 and combination thereof, wherein Al2O3 in an amount of 18 to 33 weight % , preferably, Al2O3 is added in an amount ranging from 17 to 20 weight % of the total weight of epoxy resin and TiO2 in an amount of 3 to 4 weight % , of the total weight of epoxy resin.

2D nanofillers is glass flakes in an amount of 3% to 5 weight % of the total weight% of the total weight of epoxy resin, the reinforcing filler is fumed SiO2 in amount ranging from 3% to 5 weight % of the total weight of the of the total weight of epoxy resin, the iron oxide-based pigment in an amount ranging from 3% to 5 weight % of the total weight of the of the total weight of epoxy resin, the epoxy resin, and the epoxy resin to hardener ratio is 3:1, wherein the 3D nanofiller Al2O3 having size ranging from 50-100 nm (0.05 -0.10 µm) TiO2, having size ranging from 50 nm to 200 nm (0.05 -0.2 µm) and 2D nanofillers having size ranging from 50-285 µm.

In still another embodiment, the present invention provides a method for applying an anti-corrosive nanocomposite coating on the steel substrate, wherein the method includes the following steps: a) preparing the surface substrate for applying a layer of anti-corrosive coating composition; b) preparing the anti-corrosive coating composition for substrate application by mixing with a hardener; and c) applying a layer of coating composition as prepared in step b) to the surface substrate as prepared in step a). Wherein the substrate is not limited to carbon steel, stainless steel, tiles etc.

The surface of the substrate is prepared by a copper slag blasting technique, where the technique creates a micro-nano roughness over the substrate to enhance the bonding strength between the substrate and the coating.

The copper slag, a fine and coarse particle, is used to clean the metal surfaces. During the blasting process, the copper slag is propelled at high velocity onto the surface to be treated using compressed air or another medium to remove dirt, rust, and other impurities. This process is commonly used in cleaning and preparing metal surfaces before the application of protective coatings or paint.

The coating composition is applied on the surface of the substrate. By defining, the application is to spray the coating composition on the substrate.
In still another embodiment, the present invention provides a method for preparing an anti-corrosive nanocomposite coating, said method comprising following steps:
a) adding of Al2O3 to epoxy resin;
b) mixing the Al2O3 and epoxy resin at a speed from 500 rpm to 2000 rpm, most preferably at 1700 rpm to 2000 rpm to obtain a mixture with homogenous dispersion of agglomerated particles;
c) adding TiO2 to the mixture obtained in preceding step b), followed by addition of glass flakes;
d) mixing at a speed in the range of 1800 rpm to 2000 rpm to obtain a mixture with homogenous dispersion of agglomerated particles;
e) adding fumed SiO2 to the mixture obtained in preceding step followed by mixing;
f) adding an iron oxide-based pigment optionally to the mixture obtained in preceding step e) followed by mixing.
The present invention provides a method for preparing an anti-corrosive nanocomposite composition, wherein epoxy resin is bisphenol-A based epoxy, used as a base layer on the carbon steel substrate. 3D filler is mixed to the epoxy to improve the barrier properties of the neat epoxy and minimizing the pin holes and cracks and increases the corrosive ions pathway.

The present invention provides an anti-corrosive nanocomposite composition, where the epoxy mixture contains 3D filler alumina, which is blended using mechanical mixing. However, the higher surface area of the filler causes smaller particles to clump together in the liquid epoxy. To achieve even dispersion of the agglomerated particles having size from 80nm to 300 nm in the liquid epoxy, the mixing speed ranged from 500 rpm to 2000 rpm, with the most preferable range being 1700 rpm to 2000 rpm. The high shearing forces during mixing broke down the clumped filler particles into smaller ones. These de-agglomerated particles offer increased surface area, enhancing particle compatibility with the host matrix and blocking pinholes to expand the diffusion pathways for corrosive ions.

The present invention provides an anti-corrosive nanocomposite composition, where TiO2, ranging in size from 50-200 nm, enhances the corrosion resistance and reduces the absorption of UV radiation in the epoxy, thereby safeguarding the coating from deterioration. The UV resistance attribute of TiO2 effectively eliminates the need for polyurethane, which is typically employed as the third or topmost layer in traditional coatings to prevent UV-induced degradation. The percentage of filler in the host matrix ranges between 3-4 %.

The present invention provides an anti-corrosive nanocomposite composition, where 2-D glass flakes having size from 50-285 µm, is added to improve corrosion resistance and epoxy anchoring. The sheet-like structure of glass flakes prevents corrosive ions from reaching the base substrate, thereby resisting corrosion. The filler percentage in the host matrix typically ranges from 1-5%, with the preferred range being 3-5%. A homogenous dispersion is achieved by mixing at a speed of 1000-2000 rpm, preferably at 1800 – 2000 rpm.

Corrosive ions encounter the glass flakes first and must travel a longer path to reach the voids. Upon reaching the voids, they further encounter the fine alumina and TiO2 nanofiller particles trapped inside the network. The combination of 3D-2D materials reduces voids and enlarges the diffusion path in a more effective way compared to previous methods, resulting in enhanced corrosion resistance.

The present invention provides an anti-corrosive nanocomposite composition, where the fumed silica improves the mechanical properties of the coating and provides thixotropic behaviour, ensuring consistent application and effective protection against UV radiation. The iron oxide-based pigment maintains the coating's color stability over time and offers some protection against UV radiation.
The present invention provides an anti-corrosive nanocomposite composition, where the hardener is incorporated into the epoxy coating composition mix to achieve a sprayable viscosity ranging from 90000 cP to 100000 cP.

The present invention provides an anti-corrosive nanocomposite composition, where the epoxy coating composition can be stored for a period maximum of 2 years, but it is crucial to apply the coating within 30 min to 45 min after the incorporation of hardener.

From fig 1, the middle layer (epoxy-based coating) is mainly responsible for corrosion protection by minimizing the penetration of corrosive ions to base substrate. However, epoxy resins have an inherent drawback, i.e., during the curing process there is formation of micro-nano pores, which significantly weakens the barrier ability of the neat epoxy coating to the corrosive media, such as Cl-, O2 and H2O. The corrosive liquid medium quickly permeates through the micro-nano pores and start corroding the protected substrate.
To improve the barrier properties of epoxy coatings, impermeable entities with 3D spherical and 2D plate-like structures are incorporated. By orienting these layered plates perpendicular to the direction of permeation, the pathway for corrosive ions is increased, reducing, or inhibiting their permeation and providing effective corrosion resistance to the base substrate.
In neat epoxy, micro-pores allow corrosive ions to penetrate the base substrate within a short time of 12 hours, leading to a significant decrease in impedance. The addition of the nanofillers increases impedance to approximately 1010 ? and sustains it for around 1000 hours during the salt spray test. Over a period of 7 to 42 days in a salty environment with 3.5 wt.% NaCl solution, there are no visible signs of corrosion on the coating surface in the scratch areas.

The present disclosure, with reference to the accompanying examples, describes the present disclosure. However, those of skill in the art should, considering the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. It is understood that the examples are provided for the purpose of illustrating the invention only and are not intended to limit the scope of the invention in any way.
The present invention is further explained by way of non-limiting examples.
EXAMPLES
Example 1: Different premix composition:

The different anti-corrosive coating composition premixes are prepared as per the below given table.

S. No Composition premix 1 Composition premix 2 Composition premix 3 Composition premix 4
Al2O3 17 % of epoxy resin 18 % of epoxy resin 19% of epoxy resin 20 % of epoxy resin
TiO2 3% of epoxy resin 3% of epoxy resin 4% of epoxy resin 4% of epoxy resin
glass flakes 3% of epoxy resin 4% of epoxy resin 4.5% of epoxy resin 5% of epoxy resin
fumed SiO2 3% of epoxy resin 4% of epoxy resin 4.5% of epoxy resin 5% of epoxy resin
iron oxide-based pigment 0.3% of epoxy resin 0.4% of epoxy resin 0.4% of epoxy resin 0.5% of epoxy resin
Bisphenol A - based epoxy 50 gm 50 gm 50 gm 50 gm

Example 2: Evaluation of Corrosion Performance:

To assess the corrosion resistance of the coating, Electrochemical Impedance Spectroscopy (ASTM G 106) was conducted on the In-house nanocomposite coating formulations and compared with the conventionally used refinery coating. The method entailed immersing the coated sample in a 3.5 wt% NaCl solution, chosen for its similarity to seawater and its ability to create an accelerated corrosive environment. The coated samples were immersed using a flat bottom cell. The electrochemical impedance spectra were measured across frequencies ranging from 10-2 to 105 Hz with a 10 mV sine perturbation.
The EIS results for the nanocomposite coating is presented in Figure 8. The impedance values at lower frequencies indicate corrosion resistance, while those at higher frequencies point to solution resistance. The measured impedance values are mentioned in Table 1.

Table 1: Impedance value of nanocomposite coatings.

Composition Impedance (?) at 10-2 HZ
Refinery coating 1010
Nanocomposite coating 2.18 ×1010

As seen from these values, the in-house formulations are showing improved performance as per EIS spectroscopy.
Example 3: Corrosion performance with salt spray test:
The reliability of coatings in corrosive environments was assessed using the Salt Spray Test method. In this method, coated metals were subjected to a salt fog environment for an extended period. A scratch was deliberately made in the coating to expose the underlying metal to corrosion. The test lasted for 1000 hours (42 days). The in-house nanocomposite coating exhibited no corrosion throughout the entire 1000 hours and beyond. Conversely, the commercially used refinery coating showed signs of corrosion after just 7 days of exposure. These observations lead to the conclusion that the nanocomposite coating outperforms the commercial coating. Therefore, it is proposed to switch to a bi-layer coating instead of the current three-layer system based on these findings.
Example 4: Evaluation of bond strength between substrate and coating
To evaluate the bond strength between the substrate and the coating composition, peel off test was carried out. The peel-off test for coatings is a method used to evaluate the adhesion strength of a coating to a substrate. In this test, a specialized adhesive (i.e., small metal dolly is bonded to the coated surface using an adhesive) is applied to the coated surface, and then it is pulled off at a controlled rate. The force required to remove adhesive (dolly) determine the adhesion strength of the coating. The results revealed that the peel off strength was 10.47 MPa, which implies high bond strength between the coating composition and the substrate.

Example 5: Evaluation of particle size of the nano fillers.
The SEM provides detailed information about the morphology and particle size at a very high magnification. In the SEM image of alumina, agglomerated particles ranging from 50-150 nm in size are visible, along with some larger particles. The SEM image of TiO2 reveals that the particles are agglomerated and nearly spherical, with a size of 50-100 nm (0.05 – 0.1 µm). Additionally, the SEM image of 2-D glass flakes illustrates the sheet-like structure of the glass flakes, which acts as a barrier, preventing corrosive ions from reaching the base substrate and thereby enhancing corrosion resistance. The sheet sizes range from 50-285 µm.
, Claims:1. An anticorrosive nanocomposite coating composition premix comprising:
a) a Al2O3 in 18 to 33 weight % of the total weight of epoxy resin;
b) a TiO2 in an amount of 3 to 4 weight % of the total weight of epoxy resin;
c) a 2-D nanofiller in an amount of 3 to 5 weight % of the total weight of epoxy resin;
d) a reinforcing filler in an amount of 3 to 5 weight % of the total weight of epoxy resin;
e) an epoxy resin; and
f) optionally an iron oxide-based pigment.
2. The coating composition premix as claimed in claim 1, wherein Al2O3 is in an amount of 17 to 20 weight % of the of the total weight of epoxy resin and having a particles size in the range 0.05 -0.10 µm.
3. The coating composition premix as claimed in claim 1, wherein TiO2 is in an amount of 3 to 4 weight % of the of the total weight of epoxy resin and having a particles size in the range 0.05 -0.20 µm.
4. The coating composition premix as claimed in claim 1, wherein the 2D nanofillers is glass flakes in an amount of 3 to 5 weight % of the of the total weight of epoxy resin and having a particles size in the range 50-285 µm.
5. The coating composition premix as claimed in claim 1, wherein the reinforcing filler is fumed SiO2 in amount ranging from 3 to 5 weight % of the total weight of the epoxy resin.
6. The coating composition premix as claimed in claim 1, wherein the iron oxide-based pigment is in an amount in the range of 0.3% to 0.5 weight % of the total weight of the epoxy resin.
7. The coating composition premix as claimed in claim 1, wherein the epoxy resin is a Bisphenol A - based epoxy.
8. The coating composition premix as claimed in claim 1, wherein the coating composition is provided with a hardener compound to be added prior to application in a ratio sufficient to obtain a ready to use sprayable coating composition having a viscosity in a range of 90000 to 100000 cP.
9. The coating composition premix as claimed in claim 8, wherein the hardener is a polyamide-based hardener in a ratio of 1:3 to coating composition premix.
10. A method for preparation of coating composition premix as defined in claims 1 to 7, said method comprising steps:
a) adding of Al2O3 to epoxy resin;
b) mixing the Al2O3 and epoxy resin at a speed from 500 rpm to 2000 rpm, to obtain a mixture with homogenous dispersion of agglomerated particles;
c) adding TiO2 to the mixture obtained in preceding step b), followed by addition of glass flakes;
d) mixing at a speed in the range of 1000 rpm to 2000 rpm to obtain a mixture with homogenous dispersion of agglomerated particles;
e) adding fumed SiO2 to the mixture obtained in preceding step followed by mixing;
f) adding an iron oxide-based pigment optionally to the mixture obtained in preceding step e) followed by mixing.
11. The method for preparation of coating composition premix as claimed in claim 10, wherein mixing in step b) is carried out at 1700 rpm to 2000 rpm.
12. The method for preparation of coating composition premix as claimed in claim 10, wherein mixing in step d) is carried out at 1800 rpm to 2000 rpm.
13. A method for applying an anticorrosive nanocomposite coating composition as defined in claim 8 - 9 on substrate surface, the method comprising:
a) preparing the substrate surface for applying an anti-corrosive coating composition;
b) preparing an anti-corrosive coating composition for substrate application by mixing a coating composition premix as defined in claims 1 - 7 with a hardener; and
c) applying a layer of coating composition as prepared in step b) to the substrate surface as prepared in step a).
14. The method as claimed in claim 13, wherein preparing the substrate surface comprises copper slag blasting.
15. The method as claimed in claim 13, wherein the layer of coating composition is applied by methods selected from spraying, rolling, brush application.