Valve Selection and Application Guide: From Material Properties to Installation and Maintenance

Valves play a crucial role in industrial applications. However, when dealing with corrosive media, selecting the correct valve material is of paramount importance. This article delves into the key considerations for selecting valve materials for different corrosive media and provides practical guidelines for valve selection, installation, and maintenance.

Key Considerations for Valve Material Selection in Corrosive Media:

In different corrosive media, the selection of valve materials is crucial. Here are the key points for selecting valves for some common corrosive media:

1. Valves for Sulfuric Acid Media:

Sulfuric acid is widely used as an industrial raw material and is one of the most corrosive media. Different concentrations and temperatures of sulfuric acid have varying corrosive effects on materials. Carbon steel and cast iron valves have good corrosion resistance for concentrated sulfuric acid with a concentration above 80% and a temperature below 80°C. However, they are not suitable for high-speed flowing sulfuric acid and pump valve applications. Fluoroplastics, such as lined fluorine valves (F46), offer better sulfuric acid resistance and are a more economical choice.

2. Valves for Hydrochloric Acid Media:

Most metallic materials are not resistant to hydrochloric acid corrosion. Rubber-lined valves and plastic valves (such as polypropylene and fluoroplastics) are the best choices for transporting hydrochloric acid. However, at temperatures exceeding 150°C or pressures greater than 16 kg, plastics become unsuitable, and alternatives like ceramic ball valves may be considered.

3. Valves for Nitric Acid Media:

Most metals are rapidly corroded by nitric acid. Stainless steel valves, especially those containing molybdenum (such as 316 and 316L), offer good corrosion resistance to nitric acid at room temperature. For high-temperature nitric acid, titanium and titanium alloy materials are commonly used.

4. Valves for Acetic Acid Media:

Acetic acid is one of the most corrosive organic acids. Stainless steel, especially molybdenum-containing 316 stainless steel, provides excellent resistance to acetic acid corrosion, even at high temperatures and with acetic acid steam. For high-temperature, high-concentration acetic acid or harsh requirements involving other corrosive media, high-alloy stainless steel valves or fluoroplastic valves may be used.

5. Valves for Alkali (NaOH) Media:

Steel is widely used in sodium hydroxide solutions below 80°C and 30% concentration. Stainless steel valves are also used in petrochemical plants at temperatures up to 100°C and concentrations below 75%. Titanium, titanium alloy valves, or high-alloy stainless steel valves are preferred for high-temperature alkali solutions.

6. Valves for Ammonia Media:

Most metals and non-metals have minimal corrosion in liquid ammonia and ammonia water. However, copper and copper alloys should be avoided.

7. Valves for Chlorine Media:

Most metal valves have limited resistance to chlorine gas corrosion, especially when accompanied by water. In such cases, fluorine valves are a good choice. For prolonged use, ceramic-lined valves may be considered to address issues of increased torque and aging of fluorine materials.

8. Valves for Saltwater (Seawater) Media:

Steel corrodes at a low rate in sodium chloride solutions and seawater. Various stainless steel valves exhibit low uniform corrosion rates, although localized corrosion may occur due to chloride ions. Grade 316 stainless steel valves are generally preferred.

9. Valves for Alcohol, Ketone, Ester, and Ether Media:

These media generally have low corrosivity, and valves made from common materials are suitable. However, care should be taken when selecting sealing materials to avoid compatibility issues with rubber seals and the media.

Valve Selection Guide:

Valve selection is crucial for industrial applications as it directly impacts the safety and efficiency of production processes. Here are some practical guidelines for valve selection:

1. Understanding Media Characteristics: Before selecting a valve, it is essential to understand the characteristics of the media, including chemical composition, temperature, pressure, and flow rate. Different media have varying corrosive and erosive effects on valve materials, necessitating the selection of appropriate materials.
2. Considering Operating Conditions: Select valves based on actual operating conditions, such as temperature, pressure, flow rate, and phase changes in the media. For high-temperature and high-pressure conditions, valves with appropriate resistance properties should be chosen.
3. Avoiding Common Mistakes: During the valve selection process, avoid common mistakes such as overestimating or underestimating valve sizes and ignoring media characteristics. Careful assessment and analysis ensure that the selected valves meet actual requirements, avoiding problems and risks later on.
4. Regular Maintenance and Inspection: Valves may experience sealing issues, sticking, or leakage after prolonged use. Therefore, regular maintenance and inspection are necessary. Check valve sealing performance, operating conditions, and component wear regularly to ensure proper operation and safety.

Valve Installation and Maintenance:

Proper valve installation and regular maintenance are essential for ensuring long-term stable operation. Here are some considerations:

1. Sealing Material Selection: Choose sealing materials based on media characteristics and operating conditions to ensure valve sealing performance. Common sealing materials include rubber, PTFE (Teflon), and metals, selected according to specific requirements.
2. Installation Position: Install valves correctly to ensure convenient operation and compliance with process requirements. Pay attention to valve orientation, position, and fixing methods during installation to prevent leakage or valve failure due to improper installation.
3. Operating Method: Select appropriate valve operating methods, such as manual, electric, or pneumatic, based on actual application requirements. Each operating method has its advantages and disadvantages, so choose according to specific needs.
4. Regular Maintenance: Regularly inspect valve sealing performance, operating conditions, and components. Perform maintenance and repairs promptly, including replacing sealing materials, lubricating components, and adjusting valve operation mechanisms, to ensure proper valve operation and safety.

Conclusion

In dealing with corrosive media, selecting the right valve material is crucial. Using incorrect valve materials can lead to equipment damage or accidents, emphasizing the importance of corrosion prevention. While stainless steel is often seen as a universal material, the selection of valve materials should be based on media characteristics and operating conditions. This article has introduced key points for selecting valves for nine common corrosive media, covering various industrial sectors. By understanding the characteristics of different media and the corrosion resistance of valve materials, we can better protect equipment, ensure stable operation of process systems, improve efficiency, reduce risks, and promote production safety.