Pickling process

It is an important link in the production process of stainless steel pipe fittings, which is to remove oxides, impurities and welding slag on the surface of the pipe after pickling treatment.

(1) Acid leaching: Dilute nitric acid or dilute hydrochloric acid, and the soaking time is generally 3-5 minutes.

(2) Water wash: The frequency of washing is usually 3 times, each time about 1-2 minutes.

(3) Alkali wash: Use sodium hydroxide or sodium phosphate and last 3 minutes.

(4) Rewash

Pickling principle

    After the production of buttweld elbow , tee, reducer, cap and flange, acid solution is used to remove the oxide and rust on the surface of the steel. The oxides of iron such as oxide skin and rust (Fe3O4, Fe2O3 etc) react chemically with the acid solution to form salts that dissolve in the acid solution and are removed.

    Steel parts are generally pickled in 10% to 20% sulfuric acid solution at a temperature of 40°C.  When the iron content in the solutuion exceeds 80 g/L and ferrous sulfate exceeds 215 g/L, the pickling solution should be replaced. The metal surface becomes silver after pickling, while passivating the surface to improve the corrosion resistance of stainless steel.

    When pickling, non-ferrous metals should be avoided to contain acid to away seconfary pollution and foreign boday damage. After pickling, it should be neutralized with clean water, then dried and painted in time to avoid oxidation again.

Pickling solution

Acid for pickling includes sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid and mixed acid. The most commonly used are sulfuric acid and hydrochloric acid.

Pickling technique: dip pickling and spray pickling.

Late cleaning of pipe fittings

(1) Food grade cleaning: To meet food hygiene standards

(2) Radioactive cleaning: Remove radioactive material

(3) vew-spuelen: To meet pure water cleaning standards in the pharmaceutical or microelectronics industries.

After-pickling maintenance

For finished stainless steel, it is not recommended to use the pickling process again, because the surface passivation film maybe dissolved, thereby reducing the corrosion resistance of stainless steel. If there is rust, it can be cleaned with a special cleaning agent.