A phase change latent heat type anti-natural gas hydrate hydrophilic gel coating

Abstract

The application discloses a phase change latent heat type natural gas hydrate resistant hydrophilic gel coating and belongs to the technical field of protective coating of oil and gas conveying pipelines. The coating is prepared by coating a hydrophilic gel coating containing a phase change calcium chloride hydrate on the inner surface of a pipeline and curing in situ by 365 nm ultraviolet light; the three-dimensional polymer network formed by AM and HEMA copolymerization stably locks the calcium chloride hydrate system and water molecules in the gel network through hydrogen bonds and metal ion coordination, and no leakage, salt precipitation or water loss occurs, and the performance is stable during long-term service; meanwhile, the preparation and curing process is simple, the in-situ curing can be carried out at room temperature by ultraviolet light, the curing time is short, the inner surface coating of the pipeline on site is suitable for rapid construction, the cost of large-scale application is low, the industry pain points of mechanical interlocking and cyclic failure of traditional super-hydrophobic coatings are solved, and the industrial application demand of deep sea oil and gas pipeline hydrate blockage prevention and control is met.

Description

Technical Field

[0001] This invention relates to the field of protective coating technology for oil and gas pipelines, specifically to a phase change latent heat type hydrophilic gel coating resistant to natural gas hydrates. Background Technology

[0002] Currently, during deep-sea oil and gas extraction and long-distance transportation, light hydrocarbon components such as methane, ethane, and propane in natural gas combine with water under high pressure and low temperature (typically 1-15 MPa, 0-10℃) pipeline conditions to form cage-like crystals of natural gas hydrate. This type of hydrate is an ice-like solid; one volume of natural gas hydrate can seal 150-180 times its volume of natural gas under standard conditions. Once it forms and accumulates in a pipeline, it can easily cause a reduction in pipeline diameter or even complete blockage, leading to a sudden increase in pipeline pressure, equipment damage, production stoppage, and in severe cases, safety accidents and huge economic losses.

[0003] Currently, the mainstream control method for hydrate blockage in the oil and gas industry is the chemical inhibitor injection method, which mainly includes three categories: thermodynamic hydrate inhibitors (THI), kinetic hydrate inhibitors (KHI), and anti-polymerization agents (AA). Among them, thermodynamic inhibitors (such as methanol and ethylene glycol) require large injection volumes, usually reaching more than 20% of the aqueous phase mass, resulting in high subsequent separation and processing costs. In addition, some inhibitors are volatile and environmentally toxic, limiting their use in offshore oil and gas development scenarios. Although kinetic inhibitors and anti-polymerization agents require lower injection volumes, they suffer from high synthesis costs, poor biodegradability, and failure under high subcooling conditions, thus preventing large-scale industrial application.

[0004] In recent years, passive hydrate control through coating the inner wall of pipelines with anti-hydrate coatings has been regarded as a green and efficient alternative to chemical inhibitors. Existing anti-hydrate coatings are mainly superhydrophobic coatings, which reduce the contact area between water and the pipe wall by constructing micro / nano rough structures and low surface energy modifications, thus delaying hydrate nucleation and reducing adhesion. For example, CN103189594 B discloses coating at least a portion of the inner surface of the pipeline with a non-metallic surface coating, wherein the non-metallic surface coating is selected from silicon coatings and coatings formed by applying cross-linked polymers selected from siloxanes, fluorosiloxanes, and fluoropolymers. However, this type of coating has fatal flaws: First, under high pressure and low temperature conditions, water droplets easily penetrate into the pores of the micro / nano structure and condense. After hydrate crystallization, it forms a mechanical interlock with the surface structure, leading to a significant increase in adhesion and accelerating hydrate deposition. Second, long-term oil and gas scouring and repeated freeze-thaw cycles within the pipeline can cause damage and detachment of the micro / nano structure, resulting in rapid failure of the coating's anti-hydrate performance, short cycle life, and difficulty in meeting the needs of long-term oil and gas transportation.

[0005] In addition, the inventor's previous work CN 120137504 A provides a phase change type anti-natural gas hydrate coating, which is made by applying a coating containing dimethyl sulfoxide aqueous solution, gelatin and waterborne polyurethane to the inner surface of the pipe and then curing it at a low temperature of 0-5℃. Because the dimethyl sulfoxide aqueous solution releases the latent heat of phase change when the temperature drops, it delays the freezing of hydrates and reduces the adhesion of hydrates. In addition, the gelatin has self-healing properties, which solves the problem of mechanical interlocking between hydrates and the surface structure of the superhydrophobic coating due to excessively low temperature, and the problem of coagulation inside the surface texture. However, it has problems such as high raw material cost, long coating curing time (requiring 48 hours), insufficient latent heat of phase change, and easy leakage of solution. Therefore, it is necessary to further develop a new type of anti-hydrate coating that is low in cost, has a short coating curing time, sufficient latent heat of phase change, and can simultaneously delay hydrate nucleation, reduce hydrate adhesion, have stable mechanical properties, and good cycle durability. Summary of the Invention

[0006] The purpose of this invention is to provide a phase change latent heat resistant hydrophilic gel coating for natural gas hydrates, which solves the problems of high raw material cost, long coating curing time, insufficient phase change latent heat, and easy leakage of solution in the prior art.

[0007] This invention is achieved through the following technical solutions:

[0008] A phase change latent heat resistant hydrophilic gel coating for natural gas hydrates is disclosed. The coating is obtained by applying a hydrophilic gel coating containing phase change hydrated calcium chloride to the inner surface of a pipe and curing it in situ under 365nm ultraviolet light. The raw materials of the coating, by 100% of total mass, include 80-90wt% calcium chloride dihydrate aqueous solution, 10-20wt% hydrophilic comonomer, and 0.1-0.5wt% photoinitiator. The hydrophilic comonomer is a mixture of acrylamide (AM) and hydroxyethyl methacrylate (HEMA).

[0009] Furthermore, the calcium chloride dihydrate aqueous solution is composed of calcium chloride dihydrate and deionized water in a mass ratio of (5-7):(3-5). In this calcium chloride hydrate salt system, the concentration of calcium chloride dihydrate is between 50% and 70%, exhibiting a suitable phase transition temperature and high latent heat of phase transition. Under the low-temperature operating conditions commonly found in oil and gas pipelines, a solid-liquid phase transition can occur, releasing latent heat and suppressing the temperature drop of the pipeline inner wall, thus thermodynamically delaying the nucleation and growth process of natural gas hydrates.

[0010] Furthermore, the mass ratio of acrylamide (AM) to hydroxyethyl methacrylate (HEMA) is 1:(0.8-1.2). The three-dimensional hydrophilic polymer network formed by the copolymerization of AM and HEMA can stably encapsulate the calcium chloride hydrate system in the gel network through hydrogen bonding and coordination, preventing salt solution leakage and water loss. At the same time, a dense hydration layer can be formed on the surface of the hydrophilic gel, avoiding direct contact between the hydrate and the pipe wall, significantly reducing the adhesion of the hydrate after crystallization, and preventing the hydrate from depositing and adhering on the pipe wall.

[0011] Furthermore, the photoinitiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone (photoinitiator I2959), which has high initiation efficiency under 365nm ultraviolet light and good dispersibility in aqueous / high-salt systems, enabling rapid in-situ polymerization at room temperature, and is suitable for on-site construction requirements of the inner surface of pipes.

[0012] Furthermore, the base material of the pipeline is stainless steel such as 304 and 316L, which are commonly used for oil and gas transportation. The coating has excellent interfacial adhesion to the stainless steel substrate and is resistant to long-term erosion by oil and gas fluids.

[0013] Furthermore, the coating method is selected from brushing, dripping, dipping, and spraying, which can be adapted to the coating needs of the inner surface of pipes with different diameters and construction scenarios. It is easy to operate and does not require complicated pretreatment and high-temperature curing equipment.

[0014] Furthermore, the cured coating thickness is 1.0-1.5 mm. This thickness balances excellent phase change temperature control capability with mechanical stability. Too thin a coating will result in insufficient latent heat of phase change and poor temperature control, while too thick a coating will reduce pipe diameter and increase construction costs. The UV curing time is 45-90 minutes, which ensures complete polymerization of monomers and the formation of a structurally stable three-dimensional gel network.

[0015] This invention also provides a method for preparing the above-mentioned hydrophilic gel coating against natural gas hydrates, comprising the following steps: First, preparation of phase change calcium chloride hydrate solution: Weigh calcium chloride dihydrate and deionized water according to the ratio, mix and seal, and sonicate until the solution is completely clear and transparent to obtain an aqueous solution of calcium chloride dihydrate; Second, preparation of prepolymer solution: Add hydrophilic comonomer and photoinitiator to the above-mentioned aqueous solution of calcium chloride dihydrate, seal the container and place it in an oil bath environment at 60-70℃, and stir magnetically in the dark until the solution is clear and uniform, without layering and suspended matter, to obtain a prepolymer solution, which is stored in the dark throughout the process to avoid premature polymerization; Third, coating and curing: Apply the prepolymer solution evenly to the inner surface of the pipe by brushing, dripping or other methods, and then place the coated pipe under 365nm ultraviolet light for 45-90 minutes to cure through in-situ free radical polymerization to form a uniform and complete hydrophilic gel coating.

[0016] This invention also protects the application of the above-mentioned anti-natural gas hydrate hydrophilic gel coating, which is applied to the prevention and control of natural gas hydrate blockage on the inner surface of oil and gas pipelines. The applicable operating conditions are pressure 1~30MPa and temperature -20℃~35℃, covering the conventional operating conditions of deep-sea oil and gas extraction and transportation.

[0017] The beneficial effects of this invention are as follows:

[0018] 1) Phase change temperature control, effectively delaying hydrate nucleation: This invention uses calcium chloride dihydrate hydrate salt as the phase change core. When it undergoes a phase change at low temperature, it can release a large amount of latent heat, effectively suppressing the temperature drop of the inner wall of the pipe, reducing the supercooling of hydrate formation, and significantly extending the hydrate nucleation induction time, thus inhibiting hydrate formation from the thermodynamic source.

[0019] 2) Hydrophilic interface, eliminating mechanical interlocking defects: The present invention adopts a fully hydrophilic gel network structure, abandoning the micro-nano rough structure design of superhydrophobic coating, completely avoiding the mechanical interlocking problem of hydrate-surface caused by water droplets penetrating into pores; at the same time, the hydration layer formed on the hydrophilic surface can significantly reduce the adhesion between hydrate and pipe wall, and even if hydrate is formed, it is easily washed away by fluid and is not easy to form deposit blockage.

[0020] 3) Network locking and excellent long-term stability: The three-dimensional polymer network formed by the copolymerization of AM and HEMA locks the calcium chloride hydrate salt system and water molecules stably in the gel network through hydrogen bonding and metal ion coordination, without leakage, salt precipitation, or water loss, and maintains stable performance during long-term service. At the same time, the gel coating has good flexibility and mechanical strength, strong adhesion to stainless steel substrates, and is resistant to oil and gas erosion and freeze-thaw cycles, with a cycle life far superior to traditional superhydrophobic coatings.

[0021] 4) Simple process and suitable for industrial applications: The raw materials for the coating of this invention are all industrial bulk products, which are readily available and inexpensive, and have no toxic or harmful components, making them green and environmentally friendly; the preparation and curing process is simple, and it can be cured in situ by ultraviolet light at room temperature. The curing time is short, and there is no need for high-temperature sintering, complex surface pretreatment and other processes. It can be adapted to the rapid construction of the inner surface coating of pipelines on site, and the cost of large-scale application is low.

[0022] 5) Strong functional adaptability and wide operating condition coverage: The phase change temperature and mechanical properties of the coating of this invention can be flexibly adjusted by the raw material ratio, which can be adapted to oil and gas transportation conditions of different temperature zones and different pressures, and can achieve protection of various pipeline inner wall environments. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the crosslinking structure and anti-hydrate mechanism of the phase change latent heat type hydrophilic gel coating for resisting natural gas hydrates described in this invention. Detailed Implementation

[0024] The following is a further description of the invention, but not a limitation thereof.

[0025] Example 1:

[0026] A phase change latent heat resistant hydrophilic gel coating for natural gas hydrates, the coating raw materials are: 6g calcium chloride dihydrate, 4g deionized water, 0.6g acrylamide (AM), 0.6g hydroxyethyl methacrylate (HEMA), and 0.02g photoinitiator I2959; that is, the raw materials of the coating, by 100% of total mass percentage, include 89.12wt% calcium chloride dihydrate aqueous solution, 10.6wt% hydrophilic comonomer, and the remainder is photoinitiator. The preparation method is as follows: First, preparation of the phase change salt solution: Accurately weigh 6g of calcium chloride dihydrate and 4g of deionized water using an electronic balance, place them in a 50ml covered glass beaker, seal with plastic wrap to prevent moisture evaporation, and sonicate in an ultrasonic device for 20 minutes until the solution is completely clear and transparent with no solid residue, thus obtaining an aqueous solution of calcium chloride dihydrate; Second, preparation of the prepolymer solution: Add 0.6g AM, 0.6g HEMA, and 0.02g I2959 to the above beaker, seal with plastic wrap and wrap with a black cloth to protect from light, place in a 65℃ oil bath, and turn on magnetic stirring for 20 minutes until the solution is completely clear and transparent with no layering or suspended matter, thus obtaining the prepolymer solution, which should be stored in the dark throughout the process; Third, coating and curing: Take the above prepolymer solution and evenly coat it onto the surface of a 316L stainless steel sheet (a commonly used substrate for oil and gas pipelines), controlling the coating thickness to 1.3mm, then place it under a 365nm ultraviolet lamp and irradiate at room temperature for 60 minutes. In-situ polymerization and curing were completed to obtain a hydrophilic gel coating resistant to natural gas hydrates.

[0027] Example 2:

[0028] Referring to Example 1, the difference lies in the following: the coating raw materials are: 7g calcium chloride dihydrate, 3g deionized water, 0.7g acrylamide (AM), 0.7g hydroxyethyl methacrylate (HEMA), and 0.03g photoinitiator I2959. That is, the raw materials of the coating, based on a 100% total mass percentage, include 87.49wt% calcium chloride dihydrate aqueous solution, 12.25wt% hydrophilic comonomer, and the remainder being photoinitiator. The preparation method is the same as in Example 1, and the coating thickness is controlled at 1.2mm.

[0029] Example 3:

[0030] Referring to Example 1, the difference lies in the following: the coating raw materials are: 5g calcium chloride dihydrate, 5g deionized water, 0.8g acrylamide (AM), 0.8g hydroxyethyl methacrylate (HEMA), and 0.04g photoinitiator I2959. That is, the raw materials of the coating, based on a 100% total mass percentage, include 85.9wt% calcium chloride dihydrate aqueous solution, 13.7wt% hydrophilic comonomer, and the remainder being photoinitiator. The preparation method is the same as in Example 1, and the coating thickness is controlled at 1.5mm.

[0031] Example 4:

[0032] Referring to Example 1, the difference is that the mass ratio of acrylamide (AM) to hydroxyethyl methacrylate (HEMA) is 1:0.8, while the total monomer mass remains unchanged. The preparation method is the same as in Example 1, and the coating thickness is controlled to 1.0 mm.

[0033] Comparative Example 1:

[0034] The blank control group used 316L stainless steel sheets of the same specifications as in Example 1, with no coating on the surface, and was only cleaned and dried with anhydrous ethanol and deionized water.

[0035] Comparative Example 2:

[0036] A pure hydrophilic gel coating without phase change components, referring to Example 1, except that 4g of deionized water is used instead of the calcium chloride dihydrate aqueous solution, and the other raw materials and preparation methods are completely consistent with Example 1.

[0037] Comparative Example 3:

[0038] Referring to Example 1, the difference is that the raw materials calcium chloride dihydrate and deionized water are replaced with dimethyl sulfoxide aqueous solution. The preparation method is as follows: 0.6g AM, 0.6g HEMA and 0.02g I2959 are added to the dimethyl sulfoxide aqueous solution (6g dimethyl sulfoxide dissolved in 4g deionized water). The solution is sealed with plastic wrap and wrapped with black cloth to avoid light. It is placed in an oil bath at 65°C and magnetically stirred for 20 minutes until the solution is completely clear and transparent, without layering or suspended matter, to obtain the prepolymer solution. It is stored in the dark throughout the process. The above prepolymer solution is taken and evenly coated on the surface of 316L stainless steel sheet (a common substrate for oil and gas pipelines). The coating thickness is controlled to be 1.3mm. Then it is placed under a 365nm ultraviolet lamp and irradiated at room temperature for 60 minutes to complete in-situ polymerization and curing, to obtain a hydrophilic gel coating resistant to natural gas hydrates.

[0039] Comparative Example 4:

[0040] Referring to Example 1, the difference is that acrylamide, hydroxyethyl methacrylate, and photoinitiator are replaced with gelatin and waterborne polyurethane.

[0041] The preparation method is as follows: Step 1, preparation of phase change salt solution: Accurately weigh 6g of calcium chloride dihydrate and 4g of deionized water using an electronic balance, place them in a 50ml glass beaker with a lid, seal with plastic wrap to prevent moisture evaporation, and sonicate in an ultrasonic device for 20 minutes until the solution is completely clear and transparent with no solid residue, thus obtaining an aqueous solution of calcium chloride dihydrate; Step 2, preparation of prepolymer solution: Add 0.6g of gelatin to the above beaker, place it in a 65℃ oil bath, turn on magnetic stirring for 20 minutes, then add 0.6g of waterborne polyurethane, and continue stirring to obtain a prepolymer solution; Step 3, coating and curing: Take the above prepolymer solution and evenly coat it on the surface of a 316L stainless steel sheet (a commonly used substrate for oil and gas pipelines), and cure at 5℃ for 48 hours to obtain a hydrophilic gel coating resistant to natural gas hydrates.

[0042] Performance Testing and Results Analysis

[0043] 1. Testing of nucleation induction time for natural gas hydrates

[0044] The hydrate nucleation induction time of samples from Examples 1-4 and Comparative Examples 1-4 was tested using a high-pressure hydrate reactor and a flow loop experimental setup.

[0045] Test conditions: The experimental gas was a mixture (92 vol% methane, 5 vol% ethane, and 3 vol% propane), the experimental temperature was 274.15 K (1 °C), and the experimental pressure was 3 MPa, which are common hydrate formation conditions in oil and gas pipelines. The nucleation of hydrates on the sample surface was observed in real time through a high-pressure viewing window and microscope. The time from when the experimental conditions stabilized to when the first hydrate crystal nucleus appeared on the sample surface was recorded as the induction time. Each experiment was repeated 5 times, and the average value was taken. The results are shown in Table 1.

[0046] Table 1. Test results of nucleation induction time of natural gas hydrate in different samples

[0047] The test results show that the coating of this invention can extend the nucleation induction time of natural gas hydrates by more than 3 times, which is far superior to the blank stainless steel of Comparative Example 1, the pure hydrophilic gel of Comparative Example 2, and also superior to Comparative Examples 3 and 4. Specifically, the formulation in Example 1 can extend the induction time from 12 min to 42 min, demonstrating the superior temperature control and nucleation inhibition effect brought about by the higher latent heat of phase change in the calcium chloride molten hydrate salt system. A comparison between Example 1 and Comparative Example 3 shows that calcium chloride dihydrate has a better nucleation inhibition effect than dimethyl sulfoxide. A comparison between Example 1 and Comparative Example 4 shows that rapid in-situ polymerization of acrylamide, hydroxyethyl methacrylate, and photoinitiator has a better nucleation inhibition effect than gelatin and waterborne polyurethane.

[0048] 2. Hydrate Adhesion Test

[0049] The shear adhesion strength between hydrates and different sample surfaces was tested using a low-temperature, high-pressure material surface adhesion strength testing device. The test temperature was 273.15 K (0 °C) and the pressure was 3 MPa. The results are shown in Table 2.

[0050] Table 2. Hydrate shear adhesion strength on different sample surfaces

[0051] Test results show that the coating of this invention can reduce the adhesion of hydrates by more than two orders of magnitude, far lower than that of a blank stainless steel surface. In contrast, the pure gel system without added calcium chloride dihydrate, lacking the latent heat of phase change functional component, cannot achieve interfacial viscosity reduction through interfacial temperature control and the construction of a non-freezing water layer; the adhesion of hydrates on its surface increases by orders of magnitude compared to the coating of this invention. This fully demonstrates the significant advantages of this invention in reducing hydrate adhesion and preventing deposition and clogging. A comparison of Example 1 and Comparative Example 3 shows that calcium chloride dihydrate, used in this application, has a better effect on reducing hydrate adhesion than dimethyl sulfoxide. A comparison of Example 1 and Comparative Example 4 shows that rapid in-situ polymerization of acrylamide, hydroxyethyl methacrylate, and photoinitiator has a better effect on reducing hydrate adhesion than gelatin and waterborne polyurethane.

[0052] 3. Cyclic stability test

[0053] The coatings of Example 1, Comparative Example 3, and Comparative Example 4 were subjected to repeated freeze-thaw cycle tests (-10℃~25℃, 24h per cycle). The hydrate nucleation induction time after 10, 30, 50, and 100 cycles was tested, and the performance retention rate was calculated. The results are shown in Table 3.

[0054] Table 3 Performance retention of coatings in Example 1, Comparative Examples 3-4 after freeze-thaw cycles

[0055] Test results show that after 100 freeze-thaw cycles, the coating of this invention retains over 80% of its hydrate-induced time performance, with no significant performance degradation, while the performance retention rates of Comparative Examples 3 and 4 both dropped below 45%. This demonstrates the excellent cycle stability and long-term service capability of the material of this invention.

[0056] 4. Moisture retention and leak-proof performance test

[0057] The coating samples of Example 1, Comparative Example 3, and Comparative Example 4 were placed in a dry environment at 25°C and RH=30%, and the mass changes were recorded periodically by weighing. Their water retention performance was tested, and the results are shown in Table 4.

[0058] Table 4 Moisturizing and Leakage Resistance Tests

[0059] The results showed that after 100 days of storage, the mass loss rate of the coating in Example 1 was <3wt%, with no salt precipitation, cracking, or leakage. In contrast, the mass loss rates of Comparative Examples 3 and 4 were between 7% and 11%. Comparative Example 3 showed a small amount of coating cracking, while Comparative Example 4 showed both coating cracking and salt precipitation. A comparison of Example 1 and Comparative Example 3 shows that the calcium chloride dihydrate and deionized water system has better moisturizing and anti-leakage performance than replacing it with dimethyl sulfoxide aqueous solution. This is because in the system of the present invention, the AM-HEMA copolymer skeleton can form strong coordination bonds with calcium ions to build a dense and stable three-dimensional cross-linked network. At the same time, the calcium chloride hydrated salt achieves strong locking of water molecules through hydration. The two work together to achieve stable encapsulation of the system components. In contrast, in Comparative Example 3, DMSO can only form weak hydrogen bonds with polymer chains, and its ability to lock water molecules is much weaker than that of the calcium chloride hydrated salt system. Moreover, DMSO itself is more volatile, and small molecule DMSO and free water are very easy to continuously evaporate and lose from the network, ultimately leading to significant mass loss and drying shrinkage of the coating.

[0060] A comparison of Example 1 and Comparative Example 4 shows that the rapid in-situ polymerization using acrylamide, hydroxyethyl methacrylate, and a photoinitiator exhibits better moisturizing and anti-leakage properties than gelatin and waterborne polyurethane. Comparative Example 4, employing a physical crosslinking network of gelatin and waterborne polyurethane, relies solely on weak hydrogen bonds, resulting in low crosslinking density and high network porosity. This makes it unable to stably lock in calcium chloride hydrate through coordination, nor can it effectively prevent the evaporation of water molecules and the migration and precipitation of salt ions. Therefore, it suffers the highest mass loss and exhibits coating cracking and salt precipitation.

[0061] The above results fully demonstrate that the AM-HEMA copolymer three-dimensional network and calcium chloride hydrated salt water-locking system constructed in this invention can synergistically achieve stable encapsulation of functional components and water molecules within the coating, without leakage, salt precipitation, or cracking. Its long-term storage and service stability is significantly better than that of existing control schemes.

[0062] The above embodiments and test results fully demonstrate that the phase change latent heat type hydrophilic gel coating for resisting natural gas hydrates of the present invention can simultaneously delay hydrate nucleation, significantly reduce hydrate adhesion, and achieve excellent cycle stability and long-term service performance. The preparation process is simple and the raw material cost is low. It is perfectly suited to the hydrate control requirements of deep-sea oil and gas pipelines and has extremely high industrial application value.

Claims

1. A latent heat phase change resistant hydrophilic gel coating for natural gas hydrates, characterized in that, The coating is obtained by applying a hydrophilic gel coating containing phase change hydrated calcium chloride to the inner surface of the pipe and curing it in situ under 365nm ultraviolet light. The raw materials of the coating, by 100% of total mass, include 80-90wt% calcium chloride dihydrate aqueous solution, 10-20wt% hydrophilic comonomer, and 0.1-0.5wt% photoinitiator. The hydrophilic comonomer is a mixture of acrylamide and hydroxyethyl methacrylate.

2. The coating according to claim 1, characterized in that, The calcium chloride dihydrate aqueous solution is composed of calcium chloride dihydrate and deionized water in a mass ratio of (5-7):(3-5).

3. The coating according to claim 1, characterized in that, The mass ratio of acrylamide to hydroxyethyl methacrylate is 1:(0.8-1.2).

4. The coating according to claim 1, characterized in that, The photoinitiator is 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone.

5. The coating according to claim 1, characterized in that, The base material of the pipe is 304 or 316L stainless steel.

6. The coating according to claim 1, characterized in that, The coating method is selected from any one of brushing, dripping, dipping, and spraying.

7. The coating according to claim 1, characterized in that, The cured thickness of the coating is 1.0-1.5 mm.

8. The coating according to claim 1, characterized in that, The UV curing time is 45-90 minutes.

9. The method for preparing the coating according to claim 1, characterized in that, The process includes the following steps: Step 1, preparation of phase change calcium chloride hydrate solution: Weigh calcium chloride dihydrate and deionized water, mix and seal, and sonicate until the solution is completely clear and transparent to obtain calcium chloride dihydrate aqueous solution; Step 2, preparation of prepolymer solution: Add hydrophilic comonomer and photoinitiator to the above calcium chloride dihydrate aqueous solution, seal the container and place it in a 60-70℃ oil bath environment, and stir magnetically in the dark until the solution is clear and homogeneous to obtain prepolymer solution. Store in the dark throughout the process to avoid premature polymerization; Step 3, coating and curing: Apply the prepolymer solution evenly to the inner surface of the pipe by brushing, dripping, etc., and then place the coated pipe under 365nm ultraviolet light for 45-90 minutes to cure, forming a uniform and complete hydrophilic gel coating.

10. The application of the coating according to claim 1, characterized in that, It is used to prevent and control natural gas hydrate blockage on the inner surface of oil and gas pipelines, and is applicable to working conditions of pressure 1~30MPa and temperature -20℃~35℃.

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