A Brief Discussion on Non-metallic Equipment with High Corrosion Resistance

Graphite equipment is expensive, prone to mechanical damage, and requires fire protection

This post was last edited by Wang Genrong on 2021-5-3 09:20. Let’s first discuss the characteristics of chemical equipment made from graphite (taking graphite heat exchangers as an example): The impermeable graphite material boasts excellent corrosion resistance, and it is widely used in the manufacture of heat exchange, absorption, and reaction equipment. It is also employed in the production of various types of towers and containers, such as those used in cooling, distillation, evaporation, filtration, washing, and many other chemical processing applications. Impervious graphite materials can be used to manufacture graphite pressure vessels (Grade A4); such equipment must comply with the mandatory standard: GB/T21432-2008 Graphite Pressure Vessels. Chemical equipment made of graphite can resist corrosion by most inorganic and organic acids; it remains unaffected by hydrochloric acid at any concentration when used at its boiling point for extended periods, by sulfuric acid at 75% concentration when used at its boiling point for extended periods, and by hydrofluoric acid at 60% concentration when used at its boiling point for extended periods ； Graphite-based chemical equipment also possesses a certain degree of alkali resistance; for example, graphite heat exchangers can be used for extended periods in boiling ammonia solutions of any concentration without suffering from corrosion. However, such equipment is not resistant to corrosion caused by strongly oxidizing acids and strong bases – its resistance to substances such as sodium hydroxide, potassium hydroxide, nitric acid, and fuming sulfuric acid is relatively poor. Although impervious graphite materials possess excellent corrosion resistance and thermal conductivity, as well as high chemical stability, they are not suitable for withstanding mechanical stress. Due to their complex manufacturing processes, special care must be taken during lifting, transportation, installation, and use: 1. When handling or lifting them, it is necessary to do so gently; they should not be dragged on the ground. Graphite components must not be moved using prying tools or tied up directly with steel wires. Protective measures should be taken for those graphite parts that are exposed outside the metal casing. 2. During installation, if welding or gas cutting is required on the steel shell, care must be taken to protect the graphite components and seals (water can be filled inside the shell); otherwise, the graphite components should be removed. For two-way anti-corrosion heat exchangers, operations such as being near open flames or carrying out cutting and welding must be avoided. 4. When opening the inlet valve of the equipment, it should be done slowly to avoid strong impact from the material. 5. The medium, temperature, and pressure ranges to be used must strictly comply with the equipment specifications; it is not allowed to operate above the specified temperature or pressure limits, nor should there be sudden changes in temperature or pressure. 6. When using the heat exchanger as a heater during startup, cold material should be fed first, followed by steam ； When used as a cooler or condenser, the cold medium should be passed through first followed by the material, but the temperature must not drop below the material’s freezing point. When shutting down, the process should be reversed to avoid sudden changes in temperature. 7. For the plate-and-frame heat exchangers, a few hours after the new equipment is first put into use, it is necessary to check whether the cooled water or condensed water discharged contains components of the material being processed; in the event of any leakage, the tie rod bolts of the longitudinal spring compensators should be adjusted promptly. 8. During operation, non-condensable gases within the equipment should be removed promptly. 9. If the materials and cooling water contain substances that tend to crystallize or form scale, thereby blocking the flow channels, regular cleaning is necessary. Chemical cleaning or mechanical cleaning can be employed depending on the specific circumstances. 10. During use, it is necessary to regularly check whether the discharged cooling water or condensate contains components of another material; if any leakage or cross-contamination is detected, the machine should be stopped immediately for maintenance. 11. In winter, when the equipment is being tuned or not in use, drain all the materials as well as the condensate and cooling water from it to prevent damage to the equipment due to freezing.

The price of graphite equipment is fairly reasonable; compared to other anti-corrosion equipment, it is relatively cheap

GB/T21432-2008 should be a recommended standard. Graphite equipment has its advantages, but it also has its limitations. It is necessary to consider whether the resin used for impregnation can withstand the corresponding medium and operating conditions.

Enameled equipment cannot withstand F-ion media and strong alkalis; it can handle most other substances fairly well. It performs particularly well when used under high temperature and low pressure conditions. In terms of heat conduction, after metals and graphite, enamelled materials come next. Graphite is the cheapest option for corrosion resistance, and its heat conduction properties are close to those of metals, making it very effective. However, graphite tends to flake off over time, so it cannot be used in applications where high cleanliness of the material is required. Equipment lined with fluoropolymer materials offers excellent corrosion resistance, but its performance is poor under high temperature and low pressure conditions; the heat conduction rate is very low, resulting in long heating and cooling times

You’re very down-to-earth. Your company deals with enamel and fluoropolymer lining, but you don’t just keep saying that enamel and fluoropolymer lining are the best; your evaluations are quite fair! Only such discussions are meaningful. Unlike some people who right away start talking about how great their own products are; some even pretend to be customers who have used a certain product in order to promote it (when in fact they themselves are the owner of that company):handshake