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Pickling of seamless steel pipes

Pickling of seamless steel pipes

In the rolling of seamless steel pipes, especially in the production process of precision seamless steel pipes, the pickling process is very important to remove the oxide scale and rust on the surface. So how does the pickling process of seamless steel pipes proceed?

Overview of pickling of seamless steel pipes

The pickling of seamless steel pipes is a method of using acid solution to remove oxide scale and rust on the surface of steel, called pickling. Iron oxides such as scale and rust (Fe3O4, Fe2O3, FeO, etc.) react chemically with the acid solution to form salts which are dissolved in the acid solution and removed. Acids for pickling include sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid and mixed acids.

Common media for seamless steel pipe pickling

Sulfuric acid, nitric acid, phosphoric acid, hydrofluoric acid. When pickling, be sure to add pickling corrosion inhibitor to prevent the acid from corroding the metal.

Seamless steel pipe pickling process

There are mainly dip pickling method, spray pickling method and acid paste derusting method. Generally, the dipping and pickling method is used, and the spray method can be used in mass production. Steel parts are generally pickled in a 10%-20% (volume) sulfuric acid solution at a temperature of 40°C. When the iron content in the solution exceeds 80g/L and ferrous sulfate exceeds 215g/L, the pickling solution should be replaced. At room temperature, the steel is pickled with 20% to 80% (volume) hydrochloric acid solution to prevent over-corrosion and hydrogen embrittlement. Since acid has a great corrosion effect on metals, corrosion inhibitors need to be added. After cleaning, the metal surface becomes silvery white, and the surface is passivated to improve the corrosion resistance of stainless steel. In order to eliminate the adsorption on the surface of the diatomaceous earth carrier and reduce the tailing of the chromatographic peak, the carrier needs to be acid washed or alkali washed before use. Pickling is to soak the carrier with 6mol/L hydrochloric acid for 2 hours or heat and soak with concentrated hydrochloric acid for 30 minutes, filter, wash with water to neutrality, and dry. Pickling can remove iron, aluminum, calcium, magnesium and other impurities on the surface, but cannot remove silanol groups. The pickling carrier is suitable for analyzing acidic samples.

The role of seamless steel pipe pickling

Pickling degreases and derusts the surface of seamless steel pipes in preparation for the next process. In the production process, the pickling process is to remove the surface oxide scale, and then go through lubrication treatment (carbon steel-phosphorous saponification, stainless steel-butter lime, copper aluminum pipe-oiling), using the old process-copper plating), and then For drawing and deep processing. If the steel pipe is not pickled, there may be oxides and oil stains on the surface, and the nuclear energy of the phosphating solution cannot remove them, and the quality of phosphating will be reduced.