Repair of cracked enamel and flake damage on enamel tanks

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Repair of cracked enamel on enamel tanks I. Common problems and analysis of enamel container equipment: 1. Cracking of the enamel on enamel tanks – Due to the complexity of the production processes involved in manufacturing enamel equipment, certain defects are inevitable during this process. Ceramic cracking is one such defect; below is an explanation of the phenomenon of ceramic cracking in equipment. Ceramic cracking refers to the shedding of the enamel layer on enamel-coated equipment, and it can essentially be regarded as a phenomenon resulting from mechanical forces. It has a significant and direct relationship with mechanical impact forces, internal stresses, the structural shape of the product, and the gases present during the product’s manufacturing process. It appears as patches or areas of tissue that fall off the embryo, in varying sizes. Through analysis, if the top glaze on enamel equipment peels off from the bottom glaze (or the bottom glaze is not visible at the areas where cracking occurs), it is likely due to an inappropriate firing temperature. If the firing time for the top glaze layer is too short or the firing temperature is too low, the bottom glaze does not soften sufficiently, resulting in poor bonding between the bottom glaze and the top glaze as well as between layers of glaze itself. Additionally, bubbles formed between the ceramic layers fail to be released during the melting of the glaze, all of which can lead to such cracking phenomena. This porcelain cracking phenomenon can occur in areas with a small radius of curvature of the work in progress, at locations subjected to mechanical stress, as well as in areas where stress is concentrated and the porcelain layer is thick. 　 2. During the firing of enamel-coated pot scaling removal enamel-coating equipment, reactions occur at the interface between the enamel layer and the steel plate, such as between water and iron or between water and cementite. The hydrogen produced as a result penetrates into the enamel layer on one hand, and diffuses into the steel plate on the other hand. During the subsequent cooling process, the enamel layer solidifies. The enamel layer is primarily composed of a continuous network formed by mixed polyhedra; the regularity of this enamel layer network lies between that of crystals and amorphous materials, representing a sub-regular continuous network structure. It is precisely because of this special structure that hydrogen finds it difficult to diffuse outward through the enamel layer. As the temperature drops, the solubility of hydrogen in the steel substrate of the enamel-lined reaction kettle equipment decreases, reaching a supersaturated state, which causes hydrogen to accumulate in the form of gas between the steel plate and the enamel layer. When the pressure of hydrogen builds up to a sufficient level, it will break through the enamel layer of the enamel-coated equipment, causing spalling. In some cases of enamel flaking, only the top glaze is knocked off, revealing the underlying glaze; in other cases, both the underlying glaze and the top glaze are removed, exposing the white metal surface. This is the reason for the enamel flaking phenomenon that occurs in the enamel-lined reaction vessels that we come into contact with. 3. Damage and chipping of enamel tanks (1) Mechanical damage: Enamel has very poor impact resistance; any impact from metal or hard objects will cause the enamel to be damaged. Therefore, during the use of enamel reactors, it is essential to prevent any metal or hard objects from falling into the reactor ； If there is a blockage, it can be cleared using a plastic rod ； Proper protection measures must be taken during maintenance to prevent weld slag from melting the porcelain surface and causing small pits or cracks in it. (2) Damage caused by slag scalding: In the current equipment installation processes, a construction method of connecting pipelines first and then welding is generally used. A lack of awareness regarding equipment protection during welding or improper welding practices can lead to slag scalding of the enamel coating on the tanks, thereby creating potential safety hazards. II. Precautions for using glass-lined reaction tanks: 1. It is strictly prohibited to include metals or foreign substances in the materials fed into the reaction tank; it is also forbidden to add large, hard pieces of material directly into the tank ； 2. During normal operation, it is essential to prevent hard objects such as metal from falling into the container and damaging the enamel surface ； 3. Pay attention to the temperature differences between the equipment and the materials; reduce the temperature difference between the materials and the walls of the reactor. When adding materials, avoid adding them to a cold reactor or to a hot reactor, as large temperature differences can generate internal stresses that affect the service life of the equipment. 4. Precautions to be taken when heating or cooling the equipment and materials is necessary due to the temperature requirements for the reaction of materials in a glass-lined reactor: When heating a glass-lined reactor, the temperature should be increased gradually, with the pressure increase rate in the jacket controlled at 0.1 MPa/min ； When cooling the reaction vessel, avoid rapid cooling to prevent stress-induced ceramic cracking. 5. Precautions for discharging material from the reactor: If the discharge valve or pipes of the reactor are blocked, non-metallic tools such as rubber rods or plastic rods must be used to clear them; forceful hitting is not allowed. Regarding the requirements for the jacket of the equipment, it is strictly prohibited for acids to enter the jacket, in order to prevent a hydrogen absorption reaction by the metal layer of the enamel coating, which could lead to flaking of the enamel layer and cause severe damage to the equipment. III. Application measures to address porcelain cracking, flaking, and peeling in enamel tanks 1. Secondary enameling: This repair method is commonly used when the area of damage is large. When enameling equipment is available, the repair is carried out using the standard enamel application process; in the absence of such equipment, back-side heating with a flame can be used to apply the enamel. 2. Patch repair: For repairing holes that occur as a result of localized enamel loss in enamel-lined tanks, the exposed metal area is punctured, and then the defect is repaired using enamel along with T-nails and PTFE gaskets ； Alternatively, corrosion-resistant metals such as stainless steel and ferrosilicon, along with PTFE gaskets, can be used; the corroded areas of the enamel-lined reactor are covered with sheets of these corrosion-resistant metals, which are then secured in place using screws made from the same metal. 　3. Sorey Industrial carbon nanocoating: The Sorey carbon nanopolymer material is processed using specific formulas and techniques, and then applied directly to the areas of the enamel-lined reactor where the enamel has cracked, in order to carry out repairs. This surface repair and protection method features strong adhesion, simple operation, and good corrosion resistance, preventing secondary chipping or cracking of the ceramic surface. However, it is important to use the appropriate formula and follow proper processing techniques during the repair process; otherwise, it will affect the service life of the repaired area. Sorey carbon nanopolymer materials exhibit excellent wear and corrosion resistance, as well as resistance to thermal cycling. They also possess high chemical stability and good physical and mechanical properties, allowing them to adhere firmly to metal surfaces without easily coming loose. After repair, a smooth glaze layer is formed on the surface of the cracked area of the enamel reactor, resulting in excellent performance in use.