Stainless Steel Cleaning, Pickling and Passivation

Here at UNIQUE we have developed a tailor-made process with specific chemistry to provide the ideal metal surface treatment process for high integrity stainless steel products.
From our new bespoke 10,000 sqft metal treatment facility in Oldham, Greater Manchester we are able to offer our clients a value centric service which is underpinned by our commitment to quality and backed up by our ISO 9001accreditation.

Our Capabilities

2 x 5 tonne Overhead Cranes
14500 Litre Pickling Bath 6m x 2m
12m x 9m Purpose built chemical cleaning area
In house Automatic Effluent Plant to safely dispose of waste liquids
Lean production process to ensure on time deliveries.
Passivation testing
Ferroxyl testing

The Nature of Stainless Steel

Stainless steel is essentially an iron alloy that is composed of at least 10.5% chromium  and less than 1.2% carbon. The chromium properties provide stainless steel with superior corrosion resistance.

The main requirement for stainless steels is that they should be corrosion resistant for a specified application or environment. The selection of a particular “type” and “grade” of stainless steel must initially meet the corrosion resistance requirements. Additional mechanical or physical properties may also need to be considered to achieve the overall service performance requirements.

The Stainless Steel Process

Cleaning (Degreasing)

The first step in the process is a deep clean of the metal using our own branded Unique degreasing agent. This prepares the substrate by removing rust, grease, oils and other foreign deposits.  The cleaning phase will brighten up the surface of the stainless steel. Degreasing the substrate is essential for proper pickling and uniform formation of the passive layer.

Unique P1 is an acid based cleaner This product works to remove oil, grease, smut and other inorganic contaminates. This product prepares the substrate for pickling.


Pickling removes the passive layer in addition to a small amount of metal from the surface of the stainless steel. This process is traditionally carried out by submerging the fabrication in a bath or via spray. After pickling, they surface of the stainless will start to oxidise when exposed to oxygen in the air. It is this critical process that restores the corrosion resistance of the stainless steel.

UNIQUE P2 is a liquid pickling agent that is used when maximum corrosion resistance is needed. This product removes free iron contamination, the passive layer, and exposes the bare substrate. Exposing the substrate is essential to developing a thick and uniform passivation layer, giving your stainless maximum corrosion resistance.

UNIQUE P3 Is a thickened pickling paste specifically designed for welds and vertical surfaces.

Benefits of Pickling:

  • Dissolves thermal oxides after welding, annealing etc.
  • Provides a chemically clean, uniform finish.
  • Removes surface contaminants.
  • Passivate the surface as well as chemically cleaning.


Although this process occurs naturally on the surface of stainless steel, it is often useful to accelerate and assist in the development of the passivation layer. Passivation occurs when chromium oxidises with the oxygen in the air to form a corrosion resistant passivation layer. This process can be accelerated and assisted with a passivation product, ensuring the development of a uniform and thick passive layer.

UNIQUE P4 Passivator works by oxidising any remaining free iron on the surface after the cleaning and pickling stage. The use of this product ensures that there is no brown staining or flash clouds after the pickling process.

Benefits of Passivation:

  • Dissolves surface “free iron” particles.
  • Increases corrosion resistance
  • Removes surface contaminants
  • Instantaneously forms passive oxide layer.