About Stainless Steel

Stainless Steel

Laboratory metalware consumables are manufactured from corrosion-resistant 304 stainless steel. Laboratory cleanliness and stainless steel are closely related. Stainless steel provides corrosion resistance that is necessary to limit product contamination.

It is immune to sterilising solutions, most of the organic chemicals and dyestuffs, and a wide variety of inorganic chemicals.

Stainless steel is an extremely durable surface.

Stainless Steel 304

Stainless Steel 304 alternatively known as an 18/8 Alloy, is designed for corrosion resistance and durability. The 304 series stainless steels have approximately 18% chromium and 8% nickel and are non-magnetic. This is an optimal grade with superior corrosion resistance when compared with the magnetic lower cost stainless steels.

How is it “Stainless”?

With approximately 18% chromium in the steel it makes it rust resistant and known as stain ‘less’. The chromium in the steel combines with oxygen in the atmosphere to form a thin, invisible layer of chrome-containing oxide, called the passive film. If the metal is cut or scratched and the passive film is disrupted, more oxide will quickly form and recover the exposed surface, protecting it from corrosion. The passive film requires oxygen to self-repair, so stainless steels have poor corrosion resistance in low-oxygen conditions. Also chlorides will attack and destroy the passive film.

High Temperatures

Normal temperature range -196°C to +550°C.

Suitable for intermittent use up to 870°C.

Continuous use of 304 in the 550°C-870°C range is not recommended as corrosion resistant properties are affected leading to pitting. Nickel or zirconium products are more suited for this elevated temperature range.

Corrosion Resistance

Water

Stainless steel is metallurgically incapable of rusting in water. Tough stains or the appearance of what looks like rust are a result of water-borne minerals or particles.

There may be occasions when “rust stains” appear but this is a result of iron particles from an outside source in water supply. These can be removed with cleaners containing oxalic acid or dilute solution containing phosphoric acid. Do not use steel wool pads as they leave small particles that will develop into rust spots.

Acids

Sulphuric

No corrosion resistance from dilute to concentrated amounts.

Hydrochloric

Chlorides pose high risk of pitting corrosion, depending on concentrations.

Hydrofluoric

No corrosion resistance.

Phosphoric

With concentrations up to 80% at room temperature, the beaker provides excellent corrosion resistance. Increasing the concentration and raising the temperature degrades stainless steel 304 corrosion performance.

Nitric

With concentrations up to 60% at room temperature, the beaker provides excellent corrosion resistance. Increasing the concentration and raising the temperature degrades stainless steel corrosion performance.

Alkalis

The majority of alkali solutions do not affect stainless steel.

Cleaning

Stainless steels need to be cleaned to preserve corrosion resistance. Any contamination of the surface by dirt, or other material, hinders the natural passivation process and traps corrosive agents, thus reducing corrosion protection. Some form of routine cleaning is necessary to preserve the appearance and integrity of the surface and actually thrive with frequent cleaning. Unlike some other materials, it is impossible to “wear out” stainless steel by excessive cleaning.

Contaminates will vary greatly in their effect on appearance and corrosion. While some may be easily removed, others may require specific cleaners for effective removal and it may be necessary to identify the contaminate or experiment with various cleaners.

Stainless steel metalware consumables can be autoclaved and are resistant to sanitizing agents.

Ultrasonic Cleaning

Clifton ultrasonic water baths can be a useful cleaning process. The ultrasonic activity, in a water based detergent solution removes debris and dirt.

Do not use chloride-containing detergents or carbon steel or wire wool brushes.