The chemical cleaning of steel surfaces by dissolving or loosening scale with acid. Sulfuric, hydrochloric, nitric and hydrofluoric acids in various combinations with water are used. Sulfuric-hydrochloric acid mixtures are used for plain carbon steels and low-alloy steels. Most pickling solutions include organic inhibitors, which minimize pitting and hydrogen pickup. Time in the pickling solution must be limited to minimize hydrogen pickup.