100% solid polyurethane anti-corrosion coating

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The quality of construction for long-distance oil and gas transmission pipelines using 100% solid polyurethane anti-corrosion coatings is directly determined by the quality of the materials used for pipeline anti-corrosion. This article details the characteristics of various common anti-corrosion materials, including how to select them, as well as what their scope of use and applicable conditions are. I. Properties of 100% solid content polyurethane anti-corrosion coatings: 100% solid content polyurethane coatings are formed by a chemical reaction between a polyisocyanate solution and a polyol solution, resulting in a polyurethane coating on the surface to be protected; this is a rapid, exothermic chemical polymerization process. The so-called 100% solid content means that no solvents are used to dissolve, carry away, or reduce any of the coating resin; in other words, the resin remains in a liquid state under normal conditions, and 100% of it converts into a solid coating after application. The 100% solid content polyurethane coating technology is widely used in underground fuel storage tanks, drinking water and industrial wastewater systems, oil and gas industry systems, port and terminal facilities, power industry facilities, ships and warships, etc. The 100% solid-content polyurethane anti-corrosion coating exhibits outstanding performance, which is mainly reflected in the following aspects: 1. Good adhesion. The adhesion of the coating to the substrate is a crucial indicator for evaluating its corrosion resistance. The stronger the adhesion, the better the corrosion resistance and the more durable the coating. The 100% solid-content polyurethane anti-corrosion coating exhibits excellent adhesion to various materials such as steel, cement, and cast iron. 2. Wear resistance: High wear resistance is one of the characteristics that sets the 100% solid-content polyurethane anti-corrosion coating apart from other anti-corrosion coatings. Its excellent wear resistance makes it suitable for use in difficult construction areas such as areas with loose stones or reeds. 3. The bendability of anti-bending coatings can be used to evaluate the coating’s resistance to cracking or other mechanical damage when the coated steel pipe is bent during processing. Good bend resistance is also an important characteristic that sets the 100% solid-content polyurethane anti-corrosion coating apart from other anti-corrosion coatings. 4. Resistance to cathodic disbondment: Cathodic disbondment is an important parameter for evaluating a coating’s resistance to shear stress corrosion. Experience in the oil and gas pipeline industry has shown that coatings with good resistance to cathodic disbondment also exhibit superior corrosion resistance and durability. Coatings that provide effective protection for the steel substrate also have strong resistance to cathodic disbondment. If the coating adheres well to the steel substrate, it tends to resist shear stress corrosion damage, and its service life will be longer. 5. The impermeability: The 100% solid polyurethane anti-corrosion coating is extremely dense and free of pinholes; therefore, it exhibits excellent impermeability. Its water vapor transmission rate is 4.08 mg/cm²·24h, which is better than that of ordinary anti-corrosion coatings. 6. Chemically stable: The 100% solid-content polyurethane anti-corrosion coating is a polymer with a high degree of cross-linking; therefore, its chemical properties are extremely stable. There is no change after 1,000 hours of salt spray testing; there is also no change after immersion in 10% NaOH, 10% HCl, 3.5% NaCl, and diesel fuel for 30 days. The above data come from the Quality Supervision and Inspection Center for Anti-corrosion and Insulation Products of China National Petroleum Corporation. 7. Impact resistance: Impact resistance refers to the ability of a coating to withstand damage resulting from direct collision with another object. In situations where high impact resistance is required, the impact resistance parameters of pipeline coatings are determined through experimental testing, which are then used to evaluate and predict the coating’s resistance to damage. 8. Resistance to temperature fluctuations: The 100% solid-content polyurethane anti-corrosion coating showed no changes after undergoing 30 freeze-thaw cycles (-40 to -70°C). 9. Resistance to ultraviolet radiation: The polyurethane anti-corrosion coating with 100% solid content exhibits improved resistance to ultraviolet radiation after being coated with Acrylathane aliphatic polyurethane anti-corrosion paint. After 500 hours of exposure to strong ultraviolet light, the coating does not change color nor become dusty, outperforming the epoxy powder, liquid epoxy resin coatings, and other ultraviolet-resistant coatings that are currently widely used. II. Advantages of 100% solid-content polyurethane anti-corrosion coatings
Apart from possessing the basic properties of ordinary anti-corrosion coatings, 100% solid-content polyurethane coatings have the following notable advantages compared to other industrial anti-corrosion materials:
1. Rapid curing speed, easy application, and high spraying efficiency
Under the same ambient temperature (20°C) and application conditions, for a solvent-free epoxy resin coating with a dry film thickness of 0.5 mm, the one-component high-pressure airless spraying process requires 8–10 layers to be applied, with an interval of 8 hours between each layer (the drying time for each layer is 6–8 hours). Thus, it takes a total of 8 × 8 = 64 hours to complete the entire coating process. In contrast, for a 100% solid-content polyurethane anti-corrosion coating with a dry film thickness of 0.5 mm, the two-component high-pressure airless thermal spraying process allows the required thickness to be achieved by applying multiple passes in a single layer. Given that the surface-drying time of this coating is just 1 minute and its full drying time ranges from 2 to 3 minutes, applying 8 passes at intervals of 3 minutes each suffices to reach the desired thickness. Consequently, the total time required to complete the coating process is 8 × 3 / 60 = 0.4 hours. In cases where construction is carried out in cold weather or when a greater anti-corrosion thickness is required, the improvement in construction efficiency becomes even more pronounced. 2. Strong temperature adaptability: Polyurethane anti-corrosion coatings with a 100% solid content have excellent temperature adaptability; they can cure rapidly even at low temperatures of -40°C, allowing for the completion of coating applications. This effectively solves the problem of being unable to use anti-corrosion coatings during the cold seasons in northern China. 3. The coating contains no organic volatiles, no harmful substances such as amines, coal tar, or isocyanate monomers, and contains no flammable materials. During the construction process, safety can be ensured, and there is no environmental pollution whatsoever, which aligns with the development trend of safety, environmental protection, and green practices in the coatings industry. 4. Long service life: In foreign countries, there is a record of polyurethane anti-corrosion coatings with 100% solid content being used for 30 years; to this day, the anti-corrosion layer remains intact. III. Construction Procedures
1. Surface Treatment
1) Remove oil and dirt from the surface of the pipelines to be coated ； 2) Sand blasting for rust removal; the rust removal level reaches Sa2.5 as specified in GB/T 8932, with a surface anchor pattern depth of 40–70 μm ； 3) Keep the surface clean and dry, and apply the anti-corrosion coating within 4 hours. ⒉Application process: 1) The 100% solid-content polyurethane anti-corrosion coating is applied using a high-pressure airless thermal spraying equipment. The raw material is heated to 50°C, and the spraying process is as shown in the figure below. 2) The coating must be thoroughly mixed and allowed to mature in accordance with the instructions provided ； 3) Mix components A and B in a ratio of 1:1 or 2:1, heat the mixture, and then apply it using high-pressure airless spray equipment ； 4) Spraying operations can be carried out only when the substrate temperature is at least 3°C above the dew point ； 5) The second coating can be applied only after the first coating has passed the inspection; any defective coating can be removed using acetone or other solvents that do not react with the product ； 6) Freezing protection measures should be taken for the storage of coatings. ⒊Quality inspection includes rust removal level inspection, anchor pattern depth inspection, surface quality inspection, anti-corrosion coating thickness inspection, on-site adhesion inspection, and inspection of the continuous integrity of the coating surface. IV. Application Example: A polyurethane anti-corrosion coating with 100% solid content was used in the renovation project of the Gangcang gas pipeline in the Dagang Oil Field. The applied coating had a smooth and even surface, was continuous and intact, and exhibited good adhesion, resulting in significant economic and social benefits.