Carbon Steel Passivation: Formation of a Temporary Passive Film
Carbon steel passivation is a crucial process that helps extend the lifespan of this material.
What It Consists Of
Among various types of metals, carbon steel is the most vulnerable to atmospheric agents like air and water. Unlike stainless steel, it does not naturally possess a protective layer of chromium oxides and hydroxides that guards against corrosion. Therefore, carbon steel passivation artificially covers the metal to allow its use in different contexts.
In the industrial context, carbon steel alloys are used in a variety of applications. Normally, carbon steel requires a protective coating, which can be provided by painting or galvanic coating treatments. When this is not possible or practical, chemical passivation is performed, always preceded by a pickling action, whether mechanical or chemical. Passivation treatment is mainly applied to manufactured items such as prefabricated pipes or bars, inside tanks, heat exchangers, or valves.
The carbon steel passivation procedure involves exposing the material to alkaline solutions based on sodium salts or acidic phosphating agents. These agents, upon contact, create the passive layer through chemical reactions. This result can be achieved either by immersing the object in a tank containing acids or manually with the spray technique, depending on the characteristics and size of the object.
Products to use
Bama Carbopass and Bama Fosfiron are two examples: the first is a liquid product with a specific passivating action for carbon steel.
The second is a degreasing, decontaminating, and passivating liquid characterized by a dual cleaning and passivating action for carbon steel, capable of removing grease and salt residues and creating a protective anticorrosive film.
The procedure of passivation carbon steel consists in the exposure of the material to alkaline solutions based on sodium salts or acid-based phosphating agents that have the particular function - once in contact - to create the passive layer through chemical reactions.
This can be achieved by immersing the object in a tank containing acids or manually by spraying, depending on the characteristics of the object and its size.
However, it should be remembered that passivation on carbon steel is not eternal.
The non stainless alloy will tend by its nature in contact with oxygen to rust. For this reason, in order to better preserve the surface of the product before it enters into operation, protective oils of different formulations are applied at the request of the customer depending on the type of product and the service that the latter must perform.
If the surface must be free of any organic protective product, such as in applications for oxygen use, special ammonia-based papers are used to reduce and absorb the residual moisture inside the pipes or tanks.
Where required, Bama is also able to provide for nitrogen preservation of the treated items.
The substances used by Bama for the passivation of carbon steel are of its own production and fully comply with international standards on the subject.
