What are the details of pickling and passivating seamless steel pipes

First, what is the process principle of pickling and passivating seamless steel pipes?

(1) Pickling process: Pickling mainly utilizes acid solutions (such as hydrochloric acid, sulfuric acid, nitric acid, etc.) to chemically react with rust, oxide scale, and other impurities on the surface of seamless steel pipes, dissolving and removing them. This process cleans the surface of the steel pipe, preparing it for subsequent passivation treatment. Pickling alone removes rust, oxide scale, oil, and other impurities from the surface of the seamless steel pipe using acid solutions. Commonly used acids include sulfuric acid, hydrochloric acid, and phosphoric acid. Pickling methods include immersion pickling and spray pickling. Immersion pickling involves immersing the steel pipe in an acid solution, allowing the acid solution to fully react with the impurities on the surface of the steel pipe; spray pickling involves spraying an acid solution onto the surface of the steel pipe through a nozzle, a method that can treat the steel pipe surface more evenly.

(2) Passivation process: Passivation forms a dense passivation film on the surface after pickling. This film is mainly composed of metal oxides or hydroxides. Common passivation methods use passivating agents such as chromates and nitrates. Taking chromate passivation as an example, chromates react with metal ions on the surface of the steel pipe to form a chromium-containing passivation film. This film prevents corrosive media such as oxygen and moisture from contacting the steel pipe substrate, thus greatly improving the corrosion resistance of the steel pipe.

Second, what are the performance characteristics of pickled and passivated seamless steel pipes?

(1) Excellent corrosion resistance: The passivation film effectively isolates the steel pipe from the external corrosive environment, enabling it to exhibit good corrosion resistance in the atmosphere, water, and some weakly corrosive chemical media, extending the service life of the steel pipe.

(2) Good surface quality: Pickling makes the surface of the steel pipe smooth and clean, without oxide scale and rust. This not only benefits subsequent processing (such as welding, painting, etc.) but also ensures that impurities will not affect the transported medium during use (such as in the food and pharmaceutical industries). 

(3) Clean Surface: Pickling effectively removes impurities from the surface of the steel pipe, making it smoother and more even, providing a good foundation for subsequent processing (such as painting, electroplating, etc.).

(4) Relatively Low Cost: Compared to pickled and passivated seamless steel pipes, pickled seamless steel pipes have lower costs due to the absence of the passivation process, making them an economical choice in situations where corrosion resistance requirements are not particularly high.

Third, where are pickled and passivated seamless steel pipes applied?

(1) Chemical Industry: Used for transporting various corrosive chemical raw materials and products, such as acids, alkalis, and salt solutions. For example, in pipeline systems transporting dilute sulfuric acid and sodium hydroxide solutions in chemical plants, pickled and passivated seamless steel pipes can resist the corrosion of these chemicals.

(2) Food and Pharmaceutical Industry: Ensures pipeline cleanliness and hygiene, preventing rust and other impurities from contaminating products. Used in food processing to transport fruit juice, milk, and other foods, and in pharmaceutical processes to transport raw materials and finished products, ensuring product quality and safety. 

(3) Marine Engineering: In marine environments, due to the strong corrosiveness of seawater, pickled and passivated seamless steel pipes can resist seawater erosion and can be used in pipeline systems of some offshore platforms.

(4) Construction Industry: In building structures, pickled seamless steel pipes can be used in situations where appearance requirements are not particularly high, but surface rust removal is necessary, such as building scaffolding and support structures.

(5) General Industrial Fields: Used in situations where corrosion resistance requirements are not extremely high, but surface cleaning is required, such as some ordinary machinery manufacturing and simple fluid transportation pipelines. For example, pickled seamless steel pipes can meet basic usage requirements in ventilation duct systems of some small factories.