Why the seamless steel pipe should carry out the pickling process?
The method of removing oxide scale and rust from steel surface by acid solution is called acid pickling. Iron oxides (Fe3O4, Fe2O3, FeO, etc.), such as oxide scales and rust, react with acid solutions to form salts dissolved in acid solutions and are removed. Sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid and mixed acid are used for acid pickling.
The common medium for pickling of seamless steel pipe:
Sulfuric acid,nitric acid,phosphoric acid,hydrofluoric acid.Acid pickling inhibitor must be added in acid pickling to prevent acid from corroding metal.
Seamless steel pipe pickling process:
The main methods are pickling acid washing, spraying acid washing and acid ointment removing.In general, impregnation acid washing is widely used,and injection method can be used in mass production.Iron and steel parts are usually pickled in 10% to 20% (volume) sulfuric acid solution at a temperature of 40 degrees Celsius.When the iron content in solution exceeds 80g/L and ferrous sulfate exceeds 215g/L,acid pickling fluid should be replaced.At room temperature,20% ~ 80% (volume) of hydrochloric acid is used to pickle steel,which is not easy to cause corrosion and hydrogen embrittlement.Because of the corrosive effect of acids on metals,corrosion inhibitors are needed.After cleaning, the surface of the metal is silver white,and the surface is passivated to improve the corrosion resistance of the stainless steel. In order to eliminate the adsorption on the surface of diatomite support and reduce the tailing of chromatographic peaks, the carrier should be pickled or washed before being used. Pickling is to carry the carrier with 6mol/L hydrochloric acid to boil 2H or concentrated hydrochloric acid to heat to dip and boil 30min, filtering, washing with water to neutral, drying. Pickling can remove impurities such as Fe, Al, Ca and Mg on the surface, but can not remove silanol. Acid pickling carrier is suitable for the analysis of acid samples.
The effect of pickling of seamless steel pipe:
The surface of seamless steel pipe is degreasing and rust removing, so as to prepare for the next process. In the process of production, the process of acid pickling is to remove the surface oxide skin, after the lubrication treatment (carbon steel – phosphorus saponification,stainless steel-calf lime,copper aluminum tube – oiling),the old process – copper plating), and then drawing deep processing. If the steel pipe is not pickled and the surface may contain oxide and oil,the phosphating solution can not remove nuclear energy and the quality of phosphating will be reduced.