FAQ
STAINLESS STEEL
Stainless steel, also known as Inox steel or Inox from French “inoxydable“, is a steel alloy with a minimum of 10.5% chromium content by mass.
Stainless steel does not readily corrode, rust or stain with water as ordinary steel does, but despite the name it is not fully stain-proof, most notably under low oxygen, high salinity, or poor circulation environments. There are different grades and surface finishes of stainless steel to suit the environment the alloy must endure. Stainless steel is used where both the properties of steel and resistance to corrosion are required.
Stainless steel differs from carbon steel by the amount of chromium present. Unprotected carbon steel rusts readily when exposed to air and moisture. This iron oxide film (the rust) is active and accelerates corrosion by forming more iron oxide, and due to the greater volume of the iron oxide this tends to flake and fall away. Stainless steels contain sufficient chromium to form a passive film of chromium oxide, which prevents further surface corrosion by blocking oxygen diffusion to the steel surface and blocks corrosion from spreading into the metal’s internal structure, and due to the similar size of the steel and oxide ions they bond very strongly and remain attached to the surface.
Passivation only occurs if the proportion of chromium is high enough and oxygen is present.
Contrary to popular belief, Stainless Steels are susceptible to rusting.
Corrosion on metals is everywhere. We recognize it quickly on iron and steel as unsightly yellow/orange rust. Such metals are called “active” because they actively corrode in the natural environment.
Stainless steels are passive metals because they contain other metals, like chromium and nickel.
400 series stainless steels contain chromium while 300 series contain both chromium and nickel.
Metals are crystalline solids made up ion atom arrangements like tinker toys. With 12-30% chromium, an invisible passive film covers the steels surface acting as shield against corrosion. The metal becomes “passive” toward corrosion.
As long as the film is intact; not broken or contaminated, the metal is passive and stain-less.
There are three basic things which can break down your stainless steel’s passivity layer and allow corrosion to rear its ugly head.
- Mechanical abrasion
- Deposits & water
- Chlorides
Mechanical abrasion means those things that will scratch the steel’s surface . Steels pads , wire brushes and scrapers are prime examples.
Water comes out of our tap in varying degree of hardness. Depending on what part of the country you live in, you may have hard or soft water. Hard water may leave spots. Also when heated, hard water leaves deposits behind that if left to sit, will break down the passive layer and rust your stainless steel. Other deposits from food preparation and service must be properly removed.
Cholorides are found nearly everywhere. They are in water , food and table salt. One of the worst perpetrator of chlorides can come from household and industrial cleaners.
In a nutshell:- Stainless Steels do rust when
Passivity (film Shield) breaks down
By scraps and scratches
By deposits and chlorides
Here are a few steps that can help prevent stainless steel rust.
- Use the proper tools : when cleaning you stainless steel products, take care to use non-abrasive tools. Soft cloths and plastic scouring pads will not harm the steels passive layer. Stainless steel pads can also be used but the scrubbing motion must be in the direction of the manufacturers polishing marks. Step 2 tells you how to find the polishing marks.
- Clean with the polish lines : some stainless steels come with visible polishing lines or “grain.” When visible lines are present, you should always scrub in a motion that is parallel to them.When the grain cannot be seen play it safe and use a soft cloth or plastic scouring pad.
- Use alkaline, alkaline chlorinated or non-chloride containing cleaners: while many traditional cleaners are loaded with chlorides, the industry is providing an ever increasing choice of non-chloride cleaners. Is you are not sure of your cleaner’s chloride content contact your cleaner supplier. If they tell you that your present cleaner contains chlorides, ask if they have an alternative. They probably will. Also, avoid cleaners containing quaternary salts as they also can attack stainless steel and cause pitting and rusting.
- Treat you 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. Salts in a properly maintained water softener are your friend. If you are not sure of the proper water treatment, call a treatment specialist.
- keep your food 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 your stainless steel equipment, remember the single most likely cause of damage is chlorides in the water. Heating cleaners that contain chlorides has a similar effect.
- Rinse , Rinse , Rinse: If chlorinated cleaners are used you must rinse, rinse, rinse and wipe dry immediately. The sooner you wipe off standing water ,especially when it contains cleaning agents, the better. After wiping the equipment down, allow it to air dry for the oxygen helps maintain the stainless steels passivity film.
- Never use hydrochloric acid (Muriatic acid) on stainless steel
- Regularly restore / passivate stainless steel
| Job | Cleaning agent | Comments |
| 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 of cloth |
| Restoration / Passivation | Benefit* , Super Sheen* |
* Diversey / Ecolab products
Passive Film Breakdown
If the passive film of your stainless steel has been broken, your equipment will begin the long walk down the dark road of corrosion. At its end; rust.
The first signs are on the microscopic level. If you were to look at them under a microscope or through a magnifying glass, you would see small pits and cracks staring back at you. Given time, these pits and cracks will grow and deepen while all the time exuding unsightly, red-orange rust. More severe and visible cracking can also take place.