Valves play a critical role in various industrial applications, regulating the flow of fluids and gases to ensure smooth operations. However, their exposure to corrosive environments poses a significant challenge, necessitating effective anti-corrosion measures. Among these, protective coatings and corrosion inhibitors stand out as primary methods to safeguard valves from degradation caused by exposure to corrosive mediums and atmospheric conditions.

Protective Coatings

Coating, a widely utilized anti-corrosion measure, serves as both a protective layer and an identifying marker on valves. Typically composed of synthetic resin, rubber slurry, vegetable oil, or solvent, it shields the metal surface from direct contact with corrosive mediums and the atmosphere. This method is commonly employed in environments exposed to water, salt water, seawater, and mild atmospheric corrosion. Periodic reapplication of corrosion-resistant paint, usually every six months to a year, safeguards the valve's inner cavity against corrosion by water, air, and other media.

Corrosion Inhibitors

Corrosion inhibitors play a crucial role in controlling corrosion by promoting battery polarization. These inhibitors are primarily used in media and fillers to slow down equipment and valve corrosion. For instance, the addition of oxidizing agents like copper sulfate or nitric acid can passivate stainless steel in sulfuric acid, forming a protective film on the surface. Similarly, sodium nitrite added to water prevents valve corrosion during pressure testing. Specialized esters are also used for specific requirements.

To protect valve stems from asbestos packing corrosion, corrosion inhibitors and sacrificial metals are applied to the stem's surface. Sodium nitrite and sodium chromate form a passivation layer on the stem's surface, enhancing its corrosion resistance. Zinc powder serves as a sacrificial metal, reducing chloride contact with the valve stem and preventing corrosion. Additionally, incorporating corrosion inhibitors like red lead and calcium lead acid into paint prevents atmospheric corrosion.

Electrochemical Protection

Electrochemical protection, encompassing anodic and cathodic protection, utilizes sacrificial metals like zinc to shield iron components from corrosion. Cathodic protection is particularly favored in large and critical valves due to its cost-effectiveness. Zinc is also introduced into asbestos packing to provide cathodic protection to the valve stem.

Environmental Control

Controlling the corrosive environment around valves is essential for minimizing corrosion. While broad-spectrum environmental control is challenging, measures such as deoxidizing boiler water and adjusting pH levels in refining processes can be effective. Regular valve cleaning, purging, and lubrication help mitigate environmental corrosion, especially in environments prone to dust, water vapor, and smog.

Enhanced Processing Technology and Valve Structure

Effective corrosion protection begins with thoughtful design and manufacturing processes. By addressing structural deficiencies and adopting appropriate processing methods, valves can better withstand various working conditions. Solutions like solution quenching treatment for austenitic stainless steel parts and improving valve stem surface roughness help combat corrosion effectively. Measures to prevent abrasion and friction corrosion, such as selecting corrosion-resistant materials and improving surface hardness, further enhance valve longevity and performance.

In conclusion, the protection of valves against corrosion demands a comprehensive approach, starting from the design phase and continuing through manufacturing, installation, and maintenance. By implementing suitable coatings, corrosion inhibitors, electrochemical protection, and environmental control measures, along with advancements in processing technology and valve structure, the service life and performance of valves can be significantly enhanced. With diligent attention to corrosion prevention, industries can ensure the reliability and longevity of their valve systems, contributing to the efficiency and safety of their operations.