Does 304 Stainless Steel Pipe need Passivation?

As we all know, 304 stainless steel pipes are added with chromium, nickel and other metal elements, and the composition is relatively high, which is easy to oxidize into a high-density passivation film. However, in some environments, such as coastal areas or humid warehouses, chloride ions can easily penetrate and corrode the passive film of stainless steel, and stainless steel will gradually corrode and rust over time. Passivation treatment can improve the corrosion resistance of stainless steel pipes.

Does 304 stainless steel pipe need passivation treatment? What are the benefits of passivating stainless steel pipes?

Passivation is a passivation film produced on the surface using chemical reagents under the action of metal. It is very thin, dense, has good coverage and is firmly adsorbed. It is usually a compound that oxidizes metals. It completely separates the metal from the corrosive medium, prevents the metal from contacting the corrosive medium, basically stops the metal from dissolving, and forms a passive state to achieve the anti-corrosion effect.

After passivation treatment, it has the characteristics of not increasing the thickness and changing the color of the 304 stainless steel pipe, improving the precision and added value of the product, making the operation more convenient; since the passivation process is carried out in a non-reactive state, the passivation agent can be added and used repeatedly , so it has a longer life and more economical cost; passivation promotes the formation of an oxygen molecular structure passivation film on the metal surface. The film layer is dense and has stable performance. It also has a self-repairing effect in the air, so it is different from the traditional anti-rust oil coating. Compared with other methods, the passivation film formed by passivation is more stable and corrosion-resistant.

However, it should be noted that if there is surface dirt on the 304 stainless steel pipe before passivation, it should be cleaned mechanically, and then deoiled and degreased. If the passivation solution cannot remove grease, the presence of grease on the surface will affect the quality of passivation. Therefore, oil removal and degreasing cannot be omitted. Alkali solution, emulsifier, organic solvent, steam, etc. can be used. For the passivation solution, HNO3 should be controlled between 20% and 50%. According to electrochemical tests, the quality of the passivation film treated with an HNO3 concentration less than 20% is unstable and prone to pitting corrosion, but the HNO3 concentration should not be greater than 50%. To prevent over passivation.

In addition, the 304 stainless steel pipes used in some outdoor equipment and home hardware products in coastal areas also need to be passivated. There are more saline-alkali substances in offshore areas, and the blown sand contains salt and minerals. It is easy to cause corrosion when sticking to the surface of stainless steel, so passivation processing is generally performed to prevent it from oxidizing and rusting.

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