Pickling, degreasing, passivation are processes that may be required in pipeline drawing and installation. Pickling: The method of using acid solution to remove the oxide and rust on the surface of steel is called pickling. It's a way of cleaning metal surfaces. This is usually done in conjunction with pre-passivating treatment. Generally, the parts are immersed in an aqueous solution such as sulfuric acid to remove the oxide film on the metal surface. It is the pre-treatment or intermediate treatment of electroplating, enamel, rolling and other processes. The oxides of iron such as oxide skin and rust (Fe3O4, Fe2O3, FeO, etc.) react chemically with the acid solution to form salts that dissolve in the acid solution and are removed. Acid for pickling includes sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, chromic acid, hydrofluoric acid and mixed acid. The most commonly used are sulfuric acid and hydrochloric acid. The pickling process mainly includes dip pickling, jet pickling and acid paste rust removal. Generally, the immersion pickling method is used, and the spray method can be used in mass production. The industrial concentrated sulfuric acid sold on the market usually contains H2SO475%~97% (mass fraction), you can also choose brown industrial sulfuric acid solution, which contains H2SO475%~78%(mass fraction). Steel parts are generally pickled in 10% to 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 normal temperature, the steel is pickled with 20% ~ 80%(volume) hydrochloric acid solution, which is not prone to excessive corrosion and hydrogen embrittleness. Because the acid has a great effect on the corrosion of metals, it is necessary to add corrosion inhibitors. After cleaning, the metal surface becomes silver-white, and the surface is passivated to improve the corrosion resistance of stainless steel. The process of using sulfuric acid solution with a concentration of 5% to 20% to remove the oxide skin and adhesive salts on the surface of the workpiece is called sulfuric acid pickling. In order to eliminate the surface adsorption of the diatomite carrier and reduce the chromatographic peak tailing, the carrier should be pickled or alkali washed before use. Pickling is to soak the carrier in 6mol\/L hydrochloric acid for 2h or heated in concentrated hydrochloric acid for 30min, filter, wash with water until neutral, and dry. Pickling can remove impurities such as iron, aluminum, calcium and magnesium from the surface, but cannot remove the silanol group. Pickling carrier is suitable for analyzing acid samples. Deester: pipelines, valves and other degreasing (degreasing) treatment, is in special occasions, such as the need to ban oil media, as well as oxygen pipelines and liquid oxygen pipelines need degreasing, general air separation industry and gas industry pipelines, most of the valves are required to degreasing. General degreasing agents are acetone, trichloroethylene, tetrachloroethylene, carbon tetrachloride, etc., but acetone, tetrachloroethylene, carbon tetrachloride toxicity are relatively large, and they are generally banned now, and trichloroethylene is used more, and the degreasing effect fully meets the requirements. Degreasing method, wiping method, circulation washing method. Whether degreasing is qualified shall be tested by oil detector. Passivation: Passivation is the method of transforming the metal surface into a state that is not easy to be oxidized, and delaying the corrosion rate of the metal. In addition, an active metal or alloy, in which the chemical activity is greatly reduced, and become a precious metal state phenomenon, also called passivation. Passivation: If the corrosion products generated by the action of the metal due to the medium have a dense structure, form a thin film (often invisible), closely covered on the surface of the metal, then the surface state of the metal is changed, so that the electrode potential of the metal greatly jumps in the positive direction, and becomes a blunt state of corrosion resistance. For example, when Fe→Fe2, the standard potential is -0.44V, and after passivation, it jumps to 0.5 ~ 1V, showing the corrosion resistance of precious metals, and this film is called passivation film. The passivation of metals may also be spontaneous (e.g. the formation of an insoluble compound on the surface of the metal, an oxide film). In industry, passivating agents (mainly oxidants) are used to passivate metals to form a protective film. Common examples: cold concentrated sulfuric acid, cold concentrated nitric acid and iron, aluminum can be passivated. The mechanism of passivation can be explained by the film theory, that is, passivation is due to the interaction between metal and oxidizing substances, which generates a very thin, dense, good covering performance, and firmly adsorbed passivation film on the metal surface. This film exists as an independent phase, usually a compound of oxidized metals. It plays the role of completely separating the metal from the corrosive medium, preventing the metal from contacting the corrosive medium, so that the metal basically stops dissolving and forming a blunt state to achieve the role of anti-corrosion.