In a piping system, two pipes of the same nominal diameter or of different diameters are connected to form a complete pipe. A corner stainless steel fitting is required. This corner stainless steel fitting is called a stainless steel elbow.
The chemical process that removes the oxide layer from the surface of stainless steel slows the rate of corrosion of the metal. This is the pickling passivation of stainless steel, which removes the scale and rust on the surface of stainless steel. A very thin passivation film is formed on its surface, which completely separates the metal from the corrosive medium, prevents the metal from contacting the corrosive medium, and forms a passivation state to prevent corrosion. The whole process is as follows: surface cleaning - degreasing - water cleaning - pickling - passivation - clean water rinsing - drying.
There are three surface treatment methods for stainless steel pipe fittings:
1. Surface treatment: After processing, a black oxide film will be formed on its surface.
The original method is to use nitric acid and hydrofluoric acid strong corrosion method to remove foreign matter on the surface. However, this method pollutes the environment and is harmful to human body. Moreover, it is expensive and highly corrosive. So, this method has been eliminated.
At present, the most widely used oxide film treatment methods are:
(1) Chemical method: Treat with non-polluting pickling passivation paste. At room temperature, the non-toxic cleaning solution is leached with organic additives to beautify the surface of stainless steel. After treatment, its surface is basically free of light color.
(2) Sandblasting: remove the black oxide film on the surface by spraying glass beads.
2. Bright treatment of the surface: The gloss of the surface can be obtained by chemical polishing process, electrochemical polishing process, mechanical polishing process and other methods according to different requirements.
3. Surface coloring method: Surface coloring can not only increase the color of stainless steel elbow, but also improve the wear resistance and corrosion resistance of stainless steel elbow.
There are five coloring methods as follows.
(1) Chemical oxidation method
(2) Electrochemical oxidation coloring
(3) Ion deposition oxide coloring method
(4) High temperature oxidation coloring
(5) Gas-phase pyrolysis colorimetric method
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