Steel plate pickling is a metal surface treatment process employed to remove impurities from steel plate material. A strong acidic solution referred to as pickle liquor is used to remove these impurities; this substance is also commonly used to clean steel in numerous steelmaking processes. Impurities can include:
• Inorganic contaminants;
Many working processes that operate at high temperatures leave a layer of oxide or scale on the surface of a material. In order to eliminate the scale a workpiece can be dipped into a tank of pickle liquor. The main acid within this substance is hydrochloric acid, which pickles very quickly whilst reducing base metal loss. Steels featuring alloy content greater than 6% are pickled in two different stages with a number of different acids.
Steel plate that has undergone acid pickling will oxidise once exposed to the atmosphere, especially when conditions are of moderately high humidity. Therefore a thin layer of lubrication or a waterproof coating is added to protect the material from moisture in the air. This film must be removed before any fabrication, painting or plating processes take place.