Why do seamless steel pipes need pickling process?

In the rolling of seamless steel tube, especially in the production process of precise seamless steel tube, how on earth is the pickling process carried out? Today, Raymond steel tube company will unveil the mystery for you right away!

Summary of Acidic Pickling of Precision Seamless Steel Pipe

The method of removing oxide scale and rust on steel surface by acid solution is called pickling. Iron oxides (Fe3O4, Fe2O3, FeO, etc.) such as scale and rust react with acid solution to form salts which are dissolved in acid solution and removed. Acid for pickling includes sulphuric acid, hydrochloric acid, phosphoric acid, nitric acid and mixed acid.

Common medium for acid pickling of precision seamless steel pipe:

Sulfuric acid, nitric acid, phosphoric acid, hydrofluoric acid. In pickling, it is necessary to add acid pickling inhibitor to prevent acid from corrosion to metals.

Pickling Technology of Precision Seamless Steel Pipe

There are impregnation pickling, spray pickling and acid paste rust removal methods. Generally, dipping pickling method is used, and spraying method can be used in mass production. Iron and steel parts are usually pickled in 10% - 20% (volume) sulfuric acid solution at 40 C. When the iron content in the solution exceeds 80 g/L and ferrous sulfate exceeds 215 g/L, the pickling solution should be replaced. At room temperature, 20% - 80% (volume) hydrochloric acid solution is used to pickle steel, which is not easy to occur corrosion and hydrogen embrittlement. Because of the great corrosion effect of acid on metals, corrosion inhibitors need to be added. 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 peaks, the carrier needs to be pickled or alkali washed before use. Acid pickling is to use 6mol/L hydrochloric acid to soak for 2h or concentrated hydrochloric acid to heat and soak for 30min, filter, wash with water to neutral and dry. Acid pickling can remove impurities such as iron, aluminium, calcium and magnesium on the surface, but can not remove silanol group. The pickling carrier is suitable for the analysis of acidic samples.

Effect of Acidic Pickling on Precision Seamless Steel Pipe

The surface of precision seamless steel pipe is degreased and rusted to prepare for the next process. In the production process, the pickling process is to remove the oxide skin on the surface, and then after lubrication treatment (carbon steel-phosphorus saponification, stainless steel-butter lime, copper-aluminium tube-oil coating), with the old process-copper plating, and then deep drawing processing. If the pipes are not pickled, there may be oxides and oil stains on the surface, the phosphating liquid nuclear energy can not remove them, and the phosphating quality will be reduced.