Despite what you’ve heard, stainless steel IS susceptible to rusting. Corrosion on metal is common. It is easily recognizable on iron and steel as unsightly yellow/orange rust. Such metals are called “active” because they actively corrode in a natural environment, when their atoms combine with oxygen to form rust.
Stainless steels are passive metals because they contain other metals, like chromium, nickel and manganese, that stabilize the atoms.
- 400 series stainless steels are called ferritic, contain chromium, and are magnetic
- 300 series stainless steels are called austenitic, and contain chromium and nickel
- 200 series stainless, also austenitic, contains manganese, nitrogen and carbon
- Austenitic types of stainless are not magnetic, and generally provide greater resistance to corrosion than ferritic types
With 12-30 percent chromium content, an invisible passive film covers the steel’s surface, acting as a shield against corrosion. As long as the film is intact and not broken or contaminated, the metal is passive and stainless. If the passive film of stainless steel has been broken, equipment starts to corrode. As the corrosion continues, the steel will rust.
Enemies of Stainless Steel
There are three basic things which can break down stainless steel’s passivity layer and allow corrosion to occur:
1. Mechanical abrasion. Mechanical abrasion refers to objects that will scratch a steel surface. Steel pads, wire brushes and scrapers are prime examples.
2. Deposits and water. Tap water has varying degrees of hardness. Depending on what part of the country you live in, you may have hard or soft water. Hard water may leave spots, and when heated leave deposits behind that if left to sit, will break down the passive layer and rust stainless steel. Other deposits from food preparation and service must be properly removed.
3. Chlorides. Chlorides are found nearly everywhere. They are in water, food and table salt. One of the worst chloride perpetrators can come from household and industrial cleaners.
Here are some best practices that can help prevent stainless steel rust.
1. Use the proper tools and clean with the polish lines. When cleaning stainless steel products, use non-abrasive tools. Soft cloths and plastic scouring pads will not harm steel’s passive layer. Stainless steel pads can be used, but the scrubbing motion must be in the direction of the manufacturer’s polishing marks. Some stainless steel comes with visible polishing lines or “grain.” When visible lines are present, always scrub in a motion parallel to the lines. When the grain can’t be seen, play it safe and use a soft cloth or plastic scouring pad.
2. Use alkaline, alkaline chlorinated or non-chloride containing cleaners. While many traditional cleaners are loaded with chlorides, the industry is providing an ever-increasing selection of non-chloride cleaners. If you are not sure of chloride content in the cleaner used, contact your cleaner supplier. If your present cleaner contains chlorides, ask your supplier if they have an alternative. Avoid cleaners containing quaternary salts; it can attack stainless steel and cause pitting and rusting.
3. Treat your water. Though this is not always practical, softening hard water can do much to reduce deposits. There are certain filters that can be installed to remove distasteful and corrosive elements. To ensure proper water treatment, contact a treatment specialist.
4. Keep your equipment clean. Use alkaline, alkaline chlorinated or non-chloride cleaners at recommended strength. Clean frequently to avoid build-up of hard, stubborn stains. If you boil water in stainless steel equipment, remember the single most likely cause of damage is chlorides in the water. Heating cleaners that contain chlorides have a similar effect.
5. Rinse, rinse, rinse. If chlorinated cleaners are used, rinse and wipe equipment and supplies immediately. The sooner you wipe off standing water, especially when it contains cleaning agents, the better. After wiping equipment down, allow it to air dry; oxygen helps maintain the stainless steel’s passivity film.
6. Never use hydrochloric acid (muriatic acid) on stainless steel. If used, hydrochloric acid can cause cracking, corrosion and pitting on stainless steel.
7. Regularly restore/passivate stainless steel. This is discussed in the recommended cleaners chart below.
Recommended Cleaners for specific situations
|Routine cleaning||Soap, ammonia, detergent, Medallion||Apply with cloth or sponge|
|Fingerprints & smears||Arcal 20, Lac-O-Nu Ecoshine||Provides barrier film|
|Stubborn stains & discoloration||Cameo, Talc, Zud, First Impression||Rub in direction of polish lines|
|Grease & fatty acids, blood, burnt-on-foods||Easy-off, De-Grease It Oven Aid||Excellent removal on all finishes|
|Grease & oil||Any good commercial detergent||Apply with sponge or cloth|
|Restoration/Passivation||Benefit, Super Sheen|