Corrosion and protection of black steel seamless pipe

The black steel seamless pipe is a very thin, firm and stable chromium-rich oxide film (protective film) formed on its surface to prevent the continuous infiltration and oxidation of oxygen atoms, so as to obtain the ability to resist rust. Once for some reason, this film is continuously damaged, oxygen atoms in the air or liquid will continue to infiltrate or iron atoms in the metal will continue to separate out, forming loose iron oxide, and the metal surface will be continuously corroded.

Common types of corrosion

1) On the surface of the black steel seamless pipe, there are deposits of dust or dissimilar metal particles containing other metal elements. In the humid air, the condensed water between the adhesion and the black steel seamless pipe connects the two into one. The micro-battery triggers an electrochemical reaction, and the protective film is damaged, which is called electrochemical corrosion.

2) Organic juices (such as vegetables, noodle soup, etc.) adhere to the surface of black steel seamless pipes. In the presence of water and oxygen, organic acids are formed, and organic acids will corrode the metal surface for a long time.

3) The surface of the black steel seamless pipe contains acid, alkali and salt substances (such as alkali water and lime water splashing on the decoration wall), causing local corrosion.

4) In the polluted air (such as the atmosphere containing a large amount of sulfide, carbon oxide and nitrogen oxide), when encountering condensed water, it will form liquid spots of sulfuric acid, nitric acid and acetic acid, causing chemical corrosion.

Anticorrosion method

1) The anti-corrosion of black steel seamless pipe shall be covered by epoxy coal tar paint according to the requirements of the drawings, and coated with glass fiber cloth and coated with top paint for anti-corrosion.

2) The construction process of the outer wall: pipe rust removal → primer coating → first topcoat → second topcoat → glass fiber cloth → topcoat → topcoat;

3) The inner wall construction process: pipeline rust removal → primer coating → first topcoat → second topcoat → third topcoat

1) Derusting of black steel seamless pipe
Before priming, the surface of the pipe should be cleaned of grease, ash, rust, and iron oxide scale. The quality standard of sandblasting and rust removal reaches Sa2.5 level.

2) Apply primer after rust removal on the surface of the pipe, and the time interval between them should not exceed 8 hours. When applying primer, the base surface should be dry. The primer should be brushed evenly and fully, and there should be no coagulation or blistering, and the two ends of the tube should not be brushed within the range of 150-250mm.

3) After the primer surface is dry, apply the topcoat and wrap the glass cloth. The time interval between the primer and the first topcoat should not exceed 24 hours.

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