Layers of iron oxide scale are more soluble in hydrochloric acid. Suitable
inhibitors eliminate the risk of overpickling. Hydrochloric acid pickles steel more swiftly than sulphuric acid. Hydrochloric acid produces a cleaner, smoother finished surface. This benefit
occurs because of three advantages: • the metal is attacked less by hydrochloric acid than sulphuric acid, resulting in greatly reduced pitting;
• rolled-in scale deposits are removed easily when using hydrochloric acid, whereas drastic overpickling of the rest of the part may occur when using sulphuric acid; and
• steel rinses better when pickled with hydrochloric acid.
Zinc consumption is reduced because of the pickled surface’s smoother finish.
This also greatly decreases the chances of steel having to be regalvanised due
to dross formation and the occurrence of voids in the zinc layer being reduced
significantly. Chloride salts, which may remain on the steel after rinsing, are more
compatible with flux solutions than sulphates. This reduces the contamination of
the flux baths, thereby providing further cost advantages. In an age of increasing pro-environmental initiatives, there is the added
comfort of knowing that spent hydrochloric acid can be recycled, thereby
obviating any requirement for dumping hazardous or toxic wastes and posing other
risks to the health of people and the environment.