Pickling: processes and application

Metal pickling: chemical treatment for clean surfaces

To ensure the best results in each industrial surface coating operation, a basic preliminary treatment is first carried out on each type of material — pickling.

There are many advantages offered by this solution, such as restoring a clean surface free of contaminants, removing oxides of possible welding, and creating a uniform base colour.

Pickling and passivation treatments are usually performed because the surface remains bare after the former and a protective coating is necessary. Chrome plating and anodizing are two other treatments that can be performed after pickling.

Stainless steel pickling: why it is as fundamental as with iron and other metals

While pickling is a necessary treatment for iron, it is mistakenly believed that it this is not the case for stainless steel. Indeed, stainless steel is coated with a layer of chromium oxide which makes the surface corrosion resistant, non-stick and resistant to chemical agents.

However, it can lose its passivation and return to its natural state, that is, like other untreated metal alloys. There are many reasons for this, for example, welding that risks generating carbides inside the stainless steel alloy. These compounds are formed at very high temperatures (between 300°C and 900°C), causing the loss of passivation.

If this happens, the steel must be pickled to clean the surface again, followed by another passivation process.

Impreglon uses the pickling method before applying any type of coating, whether to make the surface resistant to corrosion and chemical agents (coatings with the Halar® or Rilsan systems) or non-stick, smooth and hard (Teflon PFA and PTFE coatings used in the TempCoat® system).