What happens when stainless steel valves come into contact with sulfuric acid
What happens when stainless steel valves come into contact with sulfuric acid
Putting stainless steel valves into sulfuric acid will cause corrosion reaction, the specific situation is related to the concentration of sulfuric acid, temperature and stainless steel material and other factors:
Dilute sulfuric acid
At room temperature: In the dilute sulfuric acid environment at room temperature, some stainless steel will have a certain degree of corrosion. For example, the ordinary 18-8 chromium-nickel austenitic stainless steel (such as 304 stainless steel, 304L stainless steel, etc.), because it does not contain molybdenum, has poor corrosion resistance in dilute sulfuric acid and will gradually be corroded. The surface may appear rust spots, potholes and other signs of corrosion, with the extension of time, the structural strength of the stainless steel valve will gradually reduce, there may be leakage and other problems, affecting the normal use of the valve function.
When the temperature rises: when the temperature of dilute sulfuric acid rises, the corrosion rate of sulfuric acid on stainless steel will be significantly accelerated. This is because the rise in temperature will accelerate the rate of chemical reaction, so that the passivation film on the surface of stainless steel is more easily destroyed, thus accelerating the corrosion of sulfuric acid on stainless steel.
Medium concentration of sulfuric acid
Medium concentration of sulfuric acid is also strong corrosive to stainless steel. In this case, even stainless steel containing molybdenum elements, such as 316 stainless steel, 316L stainless steel, 316Ti stainless steel, etc., its corrosion resistance will be challenged. Long-term immersion in the medium concentration of sulfuric acid in the stainless steel valve, the surface corrosion will continue to intensify, the sealing performance of the valve, mechanical properties, etc. will be seriously affected, and eventually may lead to the complete failure of the valve.
Concentrated sulfuric acid
At room temperature: concentrated sulfuric acid at room temperature has strong oxidation, under certain conditions, the surface of stainless steel will form a dense passivation film, this passivation film can prevent further corrosion of sulfuric acid on stainless steel to a certain extent. Therefore, in a short period of time, stainless steel valves may not be significantly corroded. However, if the passivation film is damaged, such as mechanical wear, scratches, etc., sulfuric acid will quickly corrode stainless steel.
When the temperature rises: when the temperature of concentrated sulfuric acid rises, its oxidation will be further enhanced, and the corrosion of stainless steel will become more serious. High temperature concentrated sulfuric acid will destroy the passivation film on the surface of stainless steel, so that sulfuric acid can directly react with the metal elements inside stainless steel, resulting in greatly accelerated corrosion of stainless steel valves, and may even make the valve completely corroded in a short period of time.
Some ways to enhance the corrosion resistance of stainless steel in sulfuric acid
1.Alloying improvement
Add molybdenum element: such as 316 stainless steel (containing about 2-3% molybdenum) than 304 stainless steel in sulfuric acid corrosion resistance is better. Molybdenum can improve the corrosion resistance of stainless steel to reducing acids (including sulfuric acid) and enhance the stability of passivation film.
Nickel content adjustment: Appropriate increase of nickel content helps to improve the corrosion resistance of stainless steel in sulfuric acid. Nickel can make stainless steel obtain a single austenitic structure and enhance the corrosion resistance of the material.
2.Surface treatment
Passivation treatment:
A dense and continuous passivation film is formed on the surface of stainless steel by chemical method. For example, the surface of the stainless steel valve is treated with a strong oxidizing agent such as nitric acid. This film can prevent the contact of sulfuric acid with the stainless steel matrix, thereby improving corrosion resistance.
Coating coating:
Organic coatings: such as epoxy coatings, can form a layer of isolation on the surface of stainless steel to prevent sulfuric acid from contact with stainless steel.
Metal coating: such as nickel plating, chromium plating, etc., nickel and chromium themselves have good corrosion resistance, plating on the surface of stainless steel can enhance the overall resistance to sulfuric acid corrosion.
3.Control environmental factors
Temperature control: Try to reduce the temperature of the sulfuric acid environment, because increasing the temperature will accelerate the corrosion rate.
Concentration control: Avoid stainless steel valve contact with high concentration of sulfuric acid, reducing the concentration of sulfuric acid can reduce the degree of corrosion.
4.Cathodic protection
Adopt impressed current cathodic protection or sacrificial anode cathodic protection. However, this method may be difficult to implement for equipment with a more complex structure such as valves.
