Surface Treatments of Stainless Steel Flanges

Stainless steel is a very common material for flanges, and the commonly used surface treatments of stainless steel flanges include surface clear whitening treatment, surface mirror brightening treatment and surface coloring treatment.

Surface clear whitening treatment
Stainless steel flanges have to go through the bending process, binding process, welding process, artificial surface roasted heating treatment, etc., which will result in the black oxide skin on the surface of stainless steel flanges. The main composition of the black oxide skin is NiCr2O4 and NiF, and the black oxide used to be removed by the strong corrosive hydrofluoric acid and nitric acid. However, this method has the disadvantages of high costs, strong corrosion, causing damage to people’s health and bringing pollution to the environment, so it was gradually eliminated.

At present, there are two main ways to remove the oxide skin on surfaces of stainless steel flanges.
⑴ The sandblasting (shot blasting) method 
This method is shooting micro glass beads on surfaces stainless steel flanges so as to remove the black oxide skin.

⑵ The chemical method
This method is using the non-polluting pickling passivation paste and the normal temperature non-toxic cleaning solution with inorganic additives to immerse and then remove the black oxide skin on the surface, achieving the purpose of surface clear whitening treatment of stainless steel flanges. This method is suitable for the flanges which are large or have complex structures.

Surface mirror brightening treatment
According to the complexity of stainless steel flange products as well as different users’ requirements, surface mirror brightening treatment of stainless steel flanges can be divided into mechanical polishing, chemical polishing, electrochemical polishing, etc., which can make stainless steel flanges have the specular gloss. 

Surface coloring treatment
Surface coloring treatment of stainless steel flanges not only gives stainless steel flanges a variety of colors and increases the flanges’ types, but also improves the flanges’ wear resistance and corrosion resistance.

Several types of surface coloring treatments of stainless steel flanges are listed as follows.
⑴ The chemical oxidation coloring method 
In a specific solution, the color of the film is formed by chemical oxidation. 

⑵ The electrochemical oxidation coloring method
In a specific solution, the color of the film is formed by electrochemical oxidation.

⑶ The ion deposition oxide coloring method
Put stainless steel flanges on the vacuum coating machine for vacuum evaporation plating. Because of the large investment and the high cost of this method, it is not recommended for small batch of stainless steel flange products.

⑷ The high temperature oxidation coloring method
Immerse the stainless steel flanges in the fused salt, and keep the parameters of the stainless steel flanges so that the oxide film with the certain thickness can form on the surfaces of flanges and flanges can show a variety of different colors.

⑸ The gas pyrolysis coloring method
This method is relatively complex, which makes it seldom applied to the industry.
Source: China Stainless Steel Flanges Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

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