The fact is that the pickling time is basically dependent on the concentration of hydrochloric acid/ferric ions (iron salts) and the temperature of the pickling solution. Relationship of pickling time to zinc loading: It is a well known fact in hot dip galvanizing operations that over pickling of galvanized parts with protection leads to more zinc loading, i.e. "over pickling" increases zinc consumption.

Generally an hour in the pickling tank is sufficient to remove rust completely, and in some cases it is possible to leave the galvanized workpieces in the pickling tank overnight, i.e., for 10-15 hours, under the working conditions of the factory. Such galvanized workpieces are coated with more zinc than those pickled at the normal time.

Features

1, at room temperature, hydrochloric acid is more aggressive to metal oxides, but slower to dissolve base metals such as steel;

2, hydrochloric acid removes rust, causing less risk of corrosion and hydrogen embrittlement. After hydrochloric acid pickling, the surface of the workpiece is less residue, good quality of rust removal;

3, hydrochloric acid pickling of rust removal ability is almost directly proportional to its concentration;

4, concentrated hydrochloric acid is volatile, especially at high temperatures, the volatility is very fast, very easy to corrode the equipment, pollution of the environment, so hydrochloric acid is generally used in a concentration of not more than 15%, more than the concentration of this, the acid mist is larger, inconvenient to operate;

5, suitable for room temperature operation, the maximum operating temperature does not exceed 40 ℃.

Baidu Encyclopedia - Hydrochloric Acid Pickling Method