How to clean and disinfect stainless steel

Why is 304 and 316 Stainless Steel ideal for hygiene conscious environments?

The benefit of stainless steel furniture is that it’s tough and long-lasting. In addition, our 304 and 316 ranges have excellent corrosion resistance due to the formation of a chromium passivation layer. This makes them suitable for use in hygiene-conscious environments such as the food processing and pharmaceutical sectors.

It's important to understand that stainless steel must contain at least 10.5% chromium to form a passive layer on the surface: the more chromium content in the stainless steel, the better its corrosion resistance. In comparison, our 304 Stainless steel contains 18-20% Chromium.

This Chromium forms an invisible passive layer of Chromium Oxide on the stainless steel surface to protect itself from exposure to contaminants and therefore corrosion. If the surface is physically (due to scratches or dents) or chemically damaged, the ion in the stainless steel is exposed which causes the staining (rouging). The passive layer will repair itself once the source of the damage is removed and chemical treatment has been used. A very clean surface is a critical prerequisite to the formation of this passive layer and chemical treatments can enhance the passive layer.

We've created a handy Stainless Steel Care Guide to help advise on your cleaning needs.

Stainless Steel needs to be regularly cleaned and disinfected to ensure its continued suitability in the food processing and pharmaceutical sectors. 304 and 316 Stainless Steel is particularly well-suited to these environments thanks to it being extremely tolerant of the chemical detergents required to keep the furniture clean.

Does Stainless Steel rust?

No, stainless steel does not rust. If the stainless steel is continually left exposed to external contaminants, the steel can rouge (commonly referred to as rust). While rust may be flaky in appearance, rouge is a stain to the steel which can vary in colour from orange to red or black depending on the chemical build up on the surface. There are chemical treatments that can remove any deposits that have built up to remove rouging on the stainless steel.

What causes stainless steel to rouge?

Halides that include chloride, fluoride, bromide and iodide can damage the stainless steel surface and therefore destroy the passivation film. It’s worth noting that chloride ions are widely present in salt, bleach and disinfectant. If the stainless steel is in contact with these for a long time without being cleaned off, then the oxide film will be damaged and rouging will occur. Biofilms (invisible communities of microorganisms that cling to the stainless steel surface) or physical damage i.e. scratches can also cause rouging to stainless steel.

Stainless steel also reacts with certain elements in the air and water and can cause discoloration. The tables below show how much concentrate of each of the following corrosives that 304 and 316 stainless steel can handle:

304 GRADE

Corrosive	Strength	Temp
Chloride Ions	Up to 200ppm (mg/litre)	-
Acetic Acid	20%	80°C
Formic Acid	90%	20°C
Phospohoric Acid	20%	60°C
Nitric Acid	20%	50°C
Sulphuric Acid	90%	20°C
Bleach (neat)	None	-
Salt water & air	Dependant on finish*	-

316 GRADE

Corrosive	Strength	Temp
Chloride Ions	Up to 1000ppm (mg/litre)	-
Acetic acid	50%	Boiling Temp
Formic acid	100%	60°C
Phosphoric Acid	20%	Boiling Temp
Tartaric acid	60%	80°C
Sulphuric Acid	20%	20°C
Bleach (neat)	Heavily diluted (1/10 water)	-
Salt water & air	Dependant on finish*	-

*It is proven that 316 lasts much longer in seaside environments. The finish on the stainless steel is therefore important; 316 has a smoother surface due to its lower Ra value and therefore will be more resistant to corrosion and also less chance of harbouring bacteria and other microbes due to the smoother surface.

Insufficient cleaning and the atmosphere in which the stainless steel furniture is in can contribute to rouging occurring. By keeping to a regular cleaning routine and using the right chemicals, rouging can easily be prevented.

How should Stainless Steel be cleaned

The hygiene team needs to regularly clean and disinfect Stainless Steel to ensure it remains hygienic. This involves chemicals being sprayed onto the contaminated surface before it is rinsed off and neutralised so that the surface can repassivate.

Cleaning removes unwanted substances such as food remnants, dirt and impurities whereas disinfection kills harmful bacteria and other biofilms / microorganisms. This process can be achieved by chemicals, heat, ultraviolet light, ultrasonic waves or radiation.

Disinfectant, with proper use, will kill or inactivate 100% of disease producing microorganisms (vegetative bacteria, viruses and fungi) and the surface may or may not require pre-cleaning.

Sanitiser can also be used on pre-cleaned surfaces as it reduces microorganisms on the surface but does not necessarily eliminate all of them.

Suggested methods of cleaning can include:

Issue	Cleaning Solutions	Cleaning Methodology
Routine cleaning	Use mild detergent such as ProKlenz NpH or use a more aggressive alkaline such as STERIS CIP 100, both used at between 1 and 5% in warm water, or use disinfectants or sterilant such as STERIS Vesta-Syde SQ disinfectant or STERIS Sporklenz RTU sterilant. (Suitable precautions should be taken when using alkaline detergents.)	Sponge, rinse with clean water / IPA and wipe dry
Fingerprints	Soap/warm water or Acetone, Alcohol	Rinse with clean water / IPA and wipe dry
Rouging and other discolouration	STERIS CIP 200 or similar – this will remove rouging and help with repassivation.	The cleaning solution can be applied with a swab and allowed to stand for the recommended time before being rinsed away. Rinse well with clean water / IPA. (Precautions for acid cleaners should be observed)