Contrary to popular belief, stainless steels are susceptible to rusting. While it is not as common as iron rusting, it does happen so it’s important to take care of your stainless steel equipment.
The term ‘stainless’ is loosely used to describe any material that has a shiny surface and doesn’t rust easily, however there are many types and grades of steel that have different qualities based on the composition of the material. 304 steel, for example, is a grade of steel that contains both Chromium and Nickel. It also contains 70-80% iron and we all know iron rusts very easily. By adding Nickel and Chromium, the molecular structure of the material is changed. The material becomes passive, or will not actively rust. On a molecular level, it has a passivity layer, or film, to guard against rusting. As long as the invisible film is intact and not broken, the metal remains passive. If the passive film has been broken, the equipment starts to corrode and rust.
As opposed to passive, metals such as iron and steel are called active because they actively corrode in a natural environment when their atoms combine with oxygen to form rust.
Enemies of Stainless Steel
There are three basic things that can break down stainless steel’s passivity layer and allow corrosion to occur.
MECHANICAL ABRASIONS cause rusting because when a material scratches a piece of stainless steel, it damages the thin film. Examples of this include steel pads, wire brushes, and scrapers.
WATER comes out of the faucet in varying degrees of hardness. Depending on where you live, you may have hard or soft water. Hard water may leave spots and when heated, leave deposits behind that will break down the passive layer and rust stainless steel if left to sit. Soft water is less likely to have these minerals.
CHLORIDES are found nearly everywhere - in water, food, and table salt. One of the worst forms of chlorides can come from household and industrial cleaners.
Care and Cleaning Tips
By using proper tools and cleaning methods, stainless steel products can be kept rust free and looking great for many years of service. Below are a few tips to help:
- Use the proper tools
- 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 also can be used but the scrubbing motion must be in the direction of the manufacturers’ polishing marks.
- Clean with the polish lines
- 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 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. 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 also can attack stainless steel and cause pitting and rusting.
- 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 insure 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 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.
- Rinse, rinse, rinse
- If chlorinated cleaners are used, rinse and wipe equipment and supplies dry 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.
- Never use hydrochloric acid (muriatic acid) on stainless steel.
Published by NAFEM. To download NAFEM's Stainless Steel Equipment Care and Cleaning Brochure, click here.
Developed by Packer Engineering, Naperville, Ill., an independent testing laboratory.