How to clean and passivate large stainless steel surfaces - Shandong Jiugang Tisco Steel Co., Ltd.

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How to clean and passivate large stainless steel surfaces

Stainless steel and, to a lesser extent, aluminium, are among the most valuable metals. Both have the qualities of durability and corrosion resistance. Unfortunately, no one metal is perfect.

Both stainless steel and aluminium are susceptible to corrosion. This is why proper cleaning and passivation is so important when these metals are exposed to environments where corrosion can occur.

Before explaining the options for cleaning and passivation of large metal surfaces (stainless steel and aluminium), it is important to understand how corrosion is formed.

Stainless steel is a unique metal. It actually forms its own layer of iron-chromium oxide which acts as a corrosion protector. This layer protects the metal.

However, damage to the surface from corrosive chemicals, salt-saturated environments (such as continuous exposure to salt water) and mechanical action (such as cutting) will create openings in this layer. Welding can also damage the protective layer.

 

Unlike other metals, this one is unique in that it attempts to repair the surface naturally through chemical interaction between the oxygen in the environment and the stainless steel.

In the best case, this natural reaction will form a new bond with the same protective effect. The result is far from perfect, as some environments are full of contaminants. These contaminants precipitate where the original iron-chromium oxides cross.

These contaminants prevent the full interaction of oxygen and stainless steel. The resulting barrier does not form a barrier against corrosion, but traps the contaminants within it, creating the potential for corrosion.

The cost of repairing corrosion damage is very high. The US Department of Defense estimates that over $22 billion is spent annually on corrosion repair, maintenance and prevention. It is for this reason that governments and companies have invested so much effort in finding ways to clean and maintain metals, including stainless steel and aluminium. Proper cleaning plays an important role in the maintenance of metals (stainless steel).

Cleaning and passivation options

When it comes to passivation, there are many options. Ultrasonic, pickling and electrochemical processes can remove all corrosive contaminants and allow the protective coating of stainless steel to be restored. However, not all of them are capable or practical when it comes to cleaning and passivating large surfaces.

The following are the two most common processes.

1. Chemical pickling
2. Electrochemical
3. Chemical pickling
4. Chemical pickling, or just pickling, has a long history of cleaning stainless steel from corrosion. There is some flexibility in this process.

Chemical pickling agents made from nitric and hydrofluoric acids are applied to the surface to remove contaminants. Hydrofluoric acid removes contaminants, while nitric acid helps to activate the stainless steel surface and promotes passivation.

The application of pickling agents varies depending on the size of the surface. Common methods include brushing or spraying; however, in some applications it is also useful to immerse parts or large surfaces in a large bath filled with pickling solution. The advantage of immersion is that it allows the pickling solution to reach anywhere on the part/surface and cover hard-to-reach areas.

Despite the obvious disadvantages, pickling used to be preferred when cleaning larger surfaces as it provides faster results than other methods.

 

Pickling as a means of cleaning and passivation can actually be very dangerous.

Challenges associated with pickling

The chemicals used for pickling pose risks to workers and the environment. Workers exposed to nitric and hydrofluoric acids produced by pickling agents are at risk of tissue and bone damage. Burns are painful and common. Serious damage can occur to the eyes, heart, digestive and respiratory systems. Most companies that use acid washes require workers exposed to acid washes to wear breathing masks, full face masks, and acid-protective clothing, including gloves, overalls and footwear.

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