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How to choose the valve according to the pipeline medium?

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Corrosion is one of the dangerous and costly hazards of chemical ecuipment. If ignored, it can cause catastrophic equipment failures. Generally, corrosion occurs when the protective film at the surface of themetal breaks down. From a scientific standpoint, 60% of the damage to chemical equipment is linked to corrosion.


In the fluid pipeline system, the valve regulates the flow. Therefore, youshould understand the most suitable material when selecting chemical valves. While most folks see stainless steel as the universal material regardless of the environmental condition), it can be dangerous. Let's look at some key points of material selection commonly used in chemical data.



Sulphuric acid


Sulphuric acid is an important raw material with a variety of uses but remains a strong corrosive medium. Although cast iron and carbon steel give better corrosion resistance for concentrated Sulphuric acid at temperatures above 80 , they are not the best for high-flowing Sulphuric acid. Ordinarily. 316 stainless steel has little effect on Sulphuric acid. Research suggests that type 304 is resistant to corrosion at room temperature up to 3%, while type 316 is resistant up to 20% at 50.The added molybdenum gives the latter better corrosion resistance.


That said, the pump valves for Sulphuric acid should be made of high salloy stainless steel. Another more economical choice is fluoroplastics.




Acetic acid


Ordinary steel can be corroded by acetic acid at all temperatures. Even at lower concentrations, the corrosion rate can increase in cathodic current density. The best valves to suit this corrosive acid are stainless steel (316 and 316L) that contains molybdenum. Such metals offer better resistance than 304 and 321.


And they can handle glacial acetic acid up to temperatures of 80 . If nitric acid is at a high temperature, titanium and alloys of titanium can be used. If only a small amount of iron is allowed into the medium, you should avoid ordinary stainless steel.



Hydrochloric acid


Hydrochloric acid is corrosive when it gets into contact with different materials. Metals like steel, cast iron, titanium, and copper will suffer an attack at all temperatures and concentrations.


While stainless steel is not resistant to hydrochloric acid, you can use Vyalves that feature high-silicon Ferro molybdenum-below 50 C. Other special metals like zirconium, tantalum, and titanium have a strong passivation tendency and can be used as a hydrochloric acid medium. 

Plastic and rubber valves also offer good corrosion resistance.




Nitric acid


Due to its oxidizing nature, nitric acid can cause corrosion to metals-the concentration depends on the nature of the material. However, it offers better corrosion resistance at room temperature. While ordinary steel (304 and 321) won't work with nitric acid, those that contain molybdenum (316 and 316L) work seamlessly. Plus, dilute nitric acid will react with rnagnesium, zinc, and more. It behaves differently from less reactive metals like silver and copper. For high-temperature nitric acid, yeou should choose valves that feature titanium and titanium alloys.


Without the right material for the valve, the fluid system could face avoidable risks associated with corrosion. We recommend that you use this guide to select a quality valve for your applications. The best material will reduce the chance of premature valve replacement.

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