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Stainless Steel Passivation

Passivation is the process of making a material ‘passive’, usually by the deposition of a layer of oxide that adheres to the metal surface. In air, passivation affects the properties of almost all metals, notable examples being aluminium, zinc, titanium, and silicon (a metalloid). In the context of corrosion, passivation is the spontaneous formation of a hard non-reactive surface film that inhibits further corrosion. This layer is usually an oxide or nitride that is a few nanometres thick.

SPL offers two types of stainless-steel passivating depending on your requirements:

Nitric acid passivation

Nitric acid with sodium dichromate passivation

At SPL, we offer two options for corrosion resistant materials:

Nitric Acid & Dichromate

Nitric Acid Only

REACH Compliant Method

The stainless-steel passivation process removes all surface impurities and stimulates the development of an oxide film which protects the component from rust and corrosion. In general, all tanks are made up specifically for the job at hand which means you can always be assured of a fresh solution.

Pre-treatment: All components are pre-treated with a degreaser to remove grease, oils, coolants, machining chips and other microscopic contaminants.

Nitric Acid Passivation: Suited to Chromium-Nickel Grades (300 Series) and Grades with 17% Chromium or more (except 440 Series).

Nitric Acid with Sodium Dichromate Passivation: Suited to straight Chromium Grades (12-14% Chromium), High Carbon-High Chromium Grades (440 Series) and Precipitation Hardening Stainless.


After electroplating, and heat-treatment if required, a chromate conversion coating is usually applied, giving the coating its well-known golden appearance. Such a treatment can double the corrosion resistance, and a thin conversion coating can maintain a bright as-plated finish and does not appreciably affect the electrical conductivity of the surface, nor its solderability.

Coloured (Cadmium & Zinc)

Coloured passivate for cadmium or zinc surfaces provides a yellow colour.

Olive Drab Passivate

Olive Passivate produces a heavy olive drab chromate coating on zinc or cadmium plated surfaces. Olive-Drab provides the maximum salt spray and abrasion resistance of any type of chromate dip and is a satisfactory product for meeting Government specifications for this type of finish. 


Olive-Drab produces an excellent base for subsequent painting and can replace organic type primers for this purpose. The smooth glossy olive drab colour produced is an outstanding final finish for many types of applications. Olive-Drab will withstand salt spray testing of 150 -225 hours before the appearance of white rust and 400 – 750 hours before the appearance of red rust.


In-house masking design and manufacture capability