In the rolling process of seamless steel pipe, especially precision seamless steel pipe, pickling process is very important, which can remove the oxide scale and rust on the surface. How is the pickling carried out?

Overview of pickling

The method of removing oxide scale and rust on steel surface by acid solution is called pickling. Oxide scales, rust and other iron oxides (Fe3O4, Fe2O3, FeO, etc.) react with the acid solution to form salts, which are dissolved in the acid solution and removed. Acid used in pickling includes sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, mixed acid, etc.

Common medium for pickling

Sulfuric acid, nitric acid, phosphoric acid, hydrofluoric acid. Corrosion inhibitor must be added during acid pickling to prevent acid from corroding metal.

Pickling process of seamless pipe

The main methods are impregnation acid washing, spray acid washing and acid cream derusting. Generally, dipping acid washing method is used, and spray method can be used in mass production. Steel parts are generally pickled in 10% - 20% (volume) sulfuric acid solution at 40 ℃. When the iron content in the solution exceeds 80g / L and ferrous sulfate exceeds 215g / L, the pickling solution should be replaced. Under normal temperature, pickling steel with 20% - 80% (volume) hydrochloric acid solution is not easy to occur corrosion and hydrogen embrittlement. Due to the great corrosion effect of acid on metal, it is necessary to add corrosion inhibitor. After cleaning, the metal surface becomes silver white and passivates the surface to improve the corrosion resistance of stainless steel.

In order to eliminate the adsorption on the surface of diatomite carrier and reduce the tailing of chromatographic peak, the carrier should be acid washed or alkaline washed before use. Pickling is to soak the carrier with 6mol / L hydrochloric acid for 2h or heated with concentrated hydrochloric acid for 30min, filter, wash with water to neutral, and dry. Pickling can remove iron, aluminum, calcium, magnesium and other impurities on the surface, but can not remove the silanol group. The acid washing carrier is suitable for the analysis of acid samples.

Effect of pickling on seamless pipe

The surface of precision seamless steel pipe should be degreased and derusted so as to prepare for the next process. In the production process, the pickling process is to remove the oxide scale on the surface, and then after lubrication treatment (carbon steel phosphorous saponification, stainless steel butter lime, copper aluminum tube oil coating), and then drawing and deep processing. If the steel pipe is not pickled, there may be oxides and oil stains on the surface, which can not be removed by phosphating solution, and the quality of phosphating will be reduced.