Pickling & Passivation of stainless steel

PROTECTION FOR YOUR STAINLESS STEEL !.

Corrosion never sleeps !

A good stainless steel surface is clean, smooth and has no defects. A smooth surface finish is also crucial to corrosion resistance. Stainless Steel has a passive (protective) chromium oxide layer which protects the stainless steel from corrosion. When this passive layer is damaged , the surface will become active and therefore not corrosion resistant and starts “to rust “.

Corrosion

Corrosion of stainless steel can be caused by several defects in and on the surface, such as:

  • Heat Affected Zones (HAZ) due to welding
  • Weld defects
  • Iron Contamination
  • Rough Surface
  • Organic contamination
  • Aggressive chemicals

Pre-cleaning

Before carrying out pickling and/or passivation procedure, pre-cleaning is necessary to make sure the surface is free of grease, oil, dirt, atmospheric pollution. 

Pickling

The pickling process ( Circulation or immersion with INOX Pickling Liquid ) removes the passive layer and slightly etches the surface of the stainless steel in order to clean the surface propperly. ( Embedded steel, contamination by “fremdkorper”, heat tint ( HAZ) and weld scale ) . Because pickling liquid is highly corrosive / toxic and for each type of stainless steel  a different pickling procedures is required to avoid over etching, we advice to execute these works by specialistic companies ! 

Passivation

The chemical passivation process ( Circulation or immersion with INOX Passivation Liquid ) is a separate and totall different process then the pickling process. 

Instead of removing the passive layer, the passivation procedure forms or restores the Cr2O3 ( Chromium oxide layer = passive layer) in order to secure the corrosion resistance of the stainless steel.

This process can be applicated as an independent process to enrich or restore the already existing passive layer or to remove superficial rust/ fly rust.

This process can be applicated as an extra step after the pickling process to restore the passive layer over the clean pickled surface. 

For a clean stainless steel surface forms a passive layer the natural way ( air / ventilation) not always chemical passivation is required after the pickling process.   

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