Control Valve Selection Guide for the Chemical Industry

Control Valve Selection Guide for the Chemical Industry
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Choosing the right valve material for a chemical process is critical due to the diverse and often corrosive nature of the chemicals involved. There is a common misconception that stainless steel is a universal material for all conditions, but this is not accurate. Each chemical medium requires specific consideration based on its nature, concentration and temperature.

Valve Material Selection

Acetic Acid

Acetic acid is one of the organic acid corrosive substances, ordinary steel in different concentrations and temperatures of acetic acid will be seriously corroded, stainless steel is excellent acetic acid resistant materials, molybdenum-containing 316 stainless steel can also be applied to high temperature and dilute acetic acid vapor. For high temperature and high concentration of acetic acid or contain other corrosive media and other demanding requirements, can choose high alloy stainless steel control valves or fluorine plastic valves.

Hydrochloric Acid

Hydrochloric acid corrodes most metallic materials, including stainless steel. Valves containing molybdenum and high ferrosilicon can be used at 50℃ and 30% concentration. Industrial valves for conveying hydrochloric acid generally choose rubber lined and plastic valves, they have better corrosion resistance. General metal materials in nitric acid will be rapidly corroded and destroyed, stainless steel has a wide range of applications in nitric acid resistant materials. In different concentrations of nitric acid at room temperature, stainless steel has good corrosion resistance. Please note that the corrosion resistance of molybdenum-containing stainless steel to nitric acid is not only worse than ordinary stainless steel, but the performance is even inferior to molybdenum-free stainless steel such as 304. For high temperature nitric acid, titanium and titanium alloy materials are usually required.

Most metallic materials are not resistant to hydrochloric acid corrosion (including a variety of stainless steel materials), molybdenum-containing high-silicon iron can only be used for 50 ℃, 30% of the following hydrochloric acid. Contrary to metallic materials, most non-metallic materials have good corrosion resistance to hydrochloric acid, so rubber lined valves and plastic valves (such as polypropylene, fluorine plastic, etc.) is a better choice for conveying hydrochloric acid.

Nitric Acid

Nitric acid will quickly corrode and destroy general metal materials, but room temperature has good corrosion resistance of stainless steel and is widely used to transport nitric acid, but note that molybdenum-containing stainless steel performance is worse than ordinary stainless steel. If it is high temperature nitric acid, need titanium and titanium alloy materials to resist.

Sulfuric Acid

Sulfuric acid is highly corrosive and widely used in industrial applications. Different concentrations and temperatures of sulfuric acid have different degrees of corrosion of the material. For concentrated sulfuric acid with a concentration above 80% and a temperature below 80°C, carbon steel valves and cast iron valves are not suitable. Ordinary stainless steel has limited corrosion resistance. Therefore, industrial valves used to transport sulfuric acid are usually high silicon cast iron valves and high alloy valves. Due to the superior sulfuric acid resistance of fluoroplastics, fluorine lined valves are a more economical and reliable choice.

Chemical Valve Function

Chemical processes involve handling a variety of liquids and gases, requiring valves for the following operations:

(1) Open or close the flow.
(2) Control the flow rate.
(3) Prevent or allow backflow.
(4) Regulate or relieve pressure.

Valves are categorized according to their linear or rotary motion and the shape of their closing member (e.g., gate, globe, plug, diaphragm, or butterfly valves). Some valves require manual actuation, while others require an electric actuator for remote, frequent or automatic operation.

Valve Components

Valve Body

The valve body holds all internal parts and includes the flanges. It contains the shut-off elements that regulate the flow of fluid. The seat is attached to the valve body to ensure tight closure. The valve stroke is the distance from fully open to fully closed of the closing element.

Valve Stem

The valve stem connects the actuator to the shutoff element through the bonnet and packing box to prevent leakage. Some valves, such as rotary plugs and some spherical designs, do not have caps.

Cap

The cap is usually screwed or bolted to the valve body and needs to be removed for maintenance.

Actuator Selection

Pneumatic Actuators

Pneumatic actuators suitable for frequent operation and fast response, usually operating at 2-10 bar, commonly 4-6 bar. Types include piston (for large valves) and diaphragm (for regulating service).

Electric Actuators

Electric actuators are common in power stations due to the availability of field power and ease of installation. They can be slow and cumbersome and require fail-safe design for power outages.

Hydraulic Actuators

Hydraulic actuators For large, high-pressure valves that require frequent operation.

Valve Ratings

Valve pressure ratings indicate their ability to withstand pressure over a specific temperature range and are usually based on standards such as ASME/ANSI B16.34. High temperatures or high pressures can reduce the rating, and valve selection usually focuses on temperature suitability.

Conclusion

Selecting chemical valves requires knowledge of the chemistry, temperature and pressure of the medium. Key considerations include material corrosion resistance, operating torque, safety features, and valve function (e.g., open/close or modulating). Proper valve selection ensures safe, efficient and reliable chemical processing. Important Tools.