Experimental study on the selection of corrosion-resistant materials for acidic water tanks in petrochemical acidic water stripping units

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This post was last edited by Wang Wei2 on 2020-6-7 at 10:51. Research on the selection of corrosion-resistant materials for the acidic water tanks in petrochemical acid water stripping units. 1. Selection of corrosion-resistant materials: By analyzing the corrosion situation on metal surfaces, it is necessary to determine which type of corrosion-resistant coating can function effectively under those conditions in order to address the issue of metal surface corrosion. Out of caution, to avoid taking detours, and adhering to the principle of getting it right the first time. Coating coupons are used to select corrosion-resistant coatings suitable for such conditions. A total of 4 types of coating coupons were used for the tests; the coupons were suspended in water for a period of 127 days. The specific details are shown in Table 1. It can be seen from the table that the metal nano-polymer coating performs well in terms of adhesion to test specimens, while the furan-modified coating also shows satisfactory adhesion, but there are still some issues. Other materials have significant issues and are not suitable for use in such environments. Table 1 Results of the coating hanging test on acidic water tanks. Sequence Number, Surface material of the hanging piece, Placement method, Immersion time (days), Surface changes: 1. Furan-modified coating – submerged in the upper part of water; 127 days – small bubbles appeared on the surface, with liquid seeping out from these bubbles. The surface coating was not damaged, but the surface layer became softer and its strength decreased. 2. When the epoxy phenolic coating was immersed in water, bubbling occurred on the upper 127% of the surface; the coating swelled and delaminated, rendering it unusable. 3. With the metal nano-polymer coating, no changes were observed on the upper 123% of the surface, which retained its original gloss. A scratch test using a specialized tool showed that the surface coating maintained its original strength and adhesion. 4. For the metal nano-polymer coating, again no changes were seen on the upper 105% of the surface; it retained its original gloss, and the scratch test indicated good strength. 5. In the case of the WHJ anti-corrosion coating, extensive swelling of the coating occurred on the upper 90% of the surface, with local fractures appearing as well; it was therefore unusable. 6. The WHJ anti-corrosion coating also showed extensive swelling on the upper 63% of the surface, along with local fractures, making it unusable. 7. The Nuko polyurea coating became soft and flaky after being immersed in water, with a significant decrease in strength; it broke when pierced with a wire, rendering it unusable. 2. Reasons for choosing the metal nano-polymer coating: Based on the results of several testing experiments conducted on acidic water tanks in refineries, it was found that the metal nano-polymer coating is a better choice. Metal nanopolymer coatings involve ultra-fining titanium to the nanoscale, thereby **increasing its surface activity**. At the same time, the double bonds in the organic compounds are broken to form free bonds, and these combine with each other through chemical adsorption and chemical bonding to produce high-molecular-weight nanopolymers. Its coating is a two-component coating composed of titanium nanopolymers, resin, curing agent, additives, and a small amount of solvent. It has the following characteristics: 2.1 Strong resistance to penetration. Tiny metal nanopolymer and nanoparticle particles fill the molecular voids; since water, oxygen, and other ions cannot pass through these metal nanopolymer particles themselves, they must find alternative paths to penetrate, thereby lengthening the path of penetration and creating a maze-like effect. 2.2 It has high corrosion resistance and good impermeability, which prevents the passage of water, oxygen, and ions, thereby endowing the coating with shielding capabilities. Metal nanopolymer coatings have very low stress; there are no microcracks within the coating, and they exhibit strong resistance to cracking and peeling. Chemical bonding and chemical adsorption create stable structures that prevent water, oxygen, and other corrosive agents from taking their place, thereby reducing the likelihood of corrosion reactions and enhancing the resistance to chemical corrosion damage. 2.3 Good anti-scaling property: The metal nano-polymer nanocomposite coating has a very high surface smoothness due to the filling effect of tiny nanoparticles. 2.4 Good water resistance: The hydrophilic groups such as hydroxyl, ether, and amino groups in metal nano-polymer coatings form chemical bonds or undergo chemical adsorption with titanium nanopolymers, which significantly reduces their polarity. Additionally, the titanium nanopolymers involved in these bonds are hydrophobic, thereby enhancing the overall water resistance of the coating. Furthermore, the increase in the glass transition temperature after curing, along with the excellent impermeability of the coating, endows it with outstanding water resistance. 3. Performance: After several years of using the metal nano-polymer coating in acidic water tanks, the anti-corrosion purpose was achieved. Among them, when the medium temperature is between 65–70°C, it can be used for over 3 years ； It can be used for over 5 years when the medium temperature is below 50°C. It is possible to achieve an intact anti-corrosion coating, with a glossy surface free from phenomena such as peeling, bubbling, cracking, or flaking. There are no rust products attached to the surface of the anti-corrosion coating. Therefore, this anti-corrosion coating is used in water containing various substances such as H2S, NH3, CO2, CN－, and phenols. It solves the problem of poor corrosion resistance associated with conventional special anti-corrosion coatings. A new method has been found for the corrosion and stress corrosion prevention of the acidic water tank in desulfurization units. It is a type of coating belonging to a high-performance system.