Acid coating, more commonly known as pickling, is the chemical process used to remove rust, scale and other contaminants from metal surfaces. Before galvanizing or epoxy coating in particular, having a completely clean steel surface has a direct impact on final coating quality.
Why Does It Matter So Much?
Any oxide or dirt layer left on the surface prevents the subsequent coating from bonding fully to the metal. This can lead to premature coating failure or inadequate corrosion protection.
Stages of the Process
The pickling process typically consists of pre-cleaning, immersion in an acid bath, rinsing and drying, forming a solid foundation for the coating steps that follow. In practice, steel is most often pickled in hydrochloric acid at roughly 10-18% concentration and near-ambient temperature, or in sulfuric acid at around 60-80°C at lower concentrations — the choice depends on the type and amount of scale to be removed, per standard practice referenced in ASTM A143 and ISO 8407.
