How is sulfuric acid used to clean steel before galvanizing?

Before galvanizing, steel must be cleaned to ensure the protective zinc coating adheres properly. This cleaning process, known as pickling, is used to remove scale—a layer of iron oxide crystals that forms on the surface of hot-rolled steel during production.12

During pickling, the steel is immersed in an acid solution, typically sulfuric acid or hydrochloric acid, which dissolves the iron oxide scale. To prevent the acid from also attacking or dissolving the underlying steel, chemical inhibitors are added to the solution.12

Depending on the form of the steel, this is performed in one of two ways:
* Continuous lines: Hot-rolled strips are pulled through a series of consecutive acid-containing tanks at a constant speed.1
* Batch operations: Long products, such as bars and wire rods, are placed on racks and immersed in long vats of acid.1

After the pickling process, the steel undergoes rinsing, neutralizing, and drying before it is ready for the galvanizing process.1