Passivation of Stainless Steel

Our core business and area of expertise is the passivation of stainless steel.

Stainless steels get their corrosion resistant qualities from an extremely thin (invisible) layer that covers the surface. This is the chrome-oxide layer (or passive layer) and it forms spontaneously when the chromium within stainless steel is exposed to the oxygen in normal atmospheric conditions.

Depending upon the existing condition of your equipment, there may be a requirement for supplementary chemical cleaning processes. For example, degreasing, pickling or derouging.  These supporting processes are there to ensure that the surface is free of contaminants to facilitate effective passivation.


Chemical passivation is the process in which the stainless steel surface is exposed to (usually) an acid in order to remove any contamination and increase the chromium to iron ratio. This leaves the surface inert and in optimal condition for forming a dense chrome-oxide layer.

ASTM A967 ‘Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts’ defines passivation as:

“Stainless steels are auto-passivating in the sense that the protective passive film is formed spontaneously on exposure to air or moisture. The presence of exogenous surface contamination, including dirt, grease, free iron from contact with steel tooling, and so forth, may interfere with the formation of the passive film. The cleaning of these contaminants from the stainless steel surface will facilitate the sponteneous passivation by allowing the oxygen uniform access to the surface. The passive film may be augmented by chemical treatments that provide an oxidising environment for the stainless steel surface.”

Passivation should not be confused with pickling. Pickling is a chemical treatment utilising strong, corrosive acids that remove metallic contamination, welding and heat-treatment scales. The pickling process etches the steel and should not be used on machined or polished surfaces.

The Process

The final quality of the passive layer is entirely dependent upon the cleanliness of the surface. All oils, greases, metallic debris and oxide films must be completely removed. To achieve this, a variety of chemicals are employed. Their own effectiveness is largely determined by their respective formulation, concentration, temperature and contact time. 

Passivation of pipework and vessels

Onsite passivation is typically carried out by creating a circulation loop through the existing pipework and associated equipment. Vessels can be either filled with the various chemical products, or cleaned via spray-balls. In many cases, and depending upon material compatibility, your own in-line equipment can be used. Where this is not an option, we would create a temporary by-pass using our own pumps, heaters and flexible hoses.

Passivation of loose items

Passivation can also be carried out by immersing the component into a chemical bath, or by spraying the surfaces with specially formulated chemicals.

Documentation and Validation



SOP’s and all association documentation are produced in accordance with cGMP guidelines. We will generate bespoke RAMS for each project, including fully marked-up P&ID’s and GA’s showing temporary circulation loops and flushing sequences. All testing is performed with certified calibrated equipment.

Testing & Inspection

Upon completion, a variety of optional tests are available.  These include; ferroxyl testing, AES (Auger Electron Spectroscopy) to determine the chrome/iron ratio on the metal surface and passivity testing with an oxyliser


The chemical products we use have been designed to meet the highest requirements of validated cleaning procedures at pharmaceutical production sites. Suitable specific and non-specific methods are available in order to prove the absence of our products after the rinsing steps. The specific analytical methods have been validated according to ICH-guidelines. Furthermore, a scientific and risk-based toxicological assessment in the form of a complete PDE-documentation is available upon request


It is essential that your stainless steel systems and equipment are correctly cleaned and passivated before going into service. The cost of pre-commissioning passivation is much less than the costs associated with replacing corroded parts or failed product batches should the system be put into service without carrying it out. Routine cleaning and re-passivation should also be a part of your planned preventative maintenance.

Frequency will vary depending upon the use and design, but high-purity water systems in particular are corrosive and over time, will tarnish. A scheduled passivation process will keep the system in optimal condition and prevent (harder to resolve) issues such as rouging from developing.