Material Explanation/Data
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Material Explanation/Data

This document describes how and why stainless steel rusts and properly clean and care for it. The following data was developed for the North American Food Equipment Manufactures (NAFEM). NAFEM has granted permission for reprint.

Stainless Steel and Rust, Care and Cleaning

Contrary to popular belief, stainless steels are susceptible to rusting.

Corrosion on metals is everywhere. It is recognized quickly 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, contain chromium and nickel; and 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, 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 stain-less. If the passive film of stainless steel has been broken, equipment starts to corrode. At its end, it rusts.

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
  2. Deposits and water
  3. Chlorides

Mechanical abrasion means those things that will scratch a steel surface. Steel pads, wire brushes and scrapers are prime examples.

Water comes out of the faucet in 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.

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.

So what does all this mean? Don’t Despair!

Here are a few steps that can help prevent stainless steel rust.

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. Never use hydrochloric acid (muriatic acid) on stainless steel.
  8. Regularly restore/passivate stainless steel.

Cleaning 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 or cloth

Restoration/Passivation

Benefit, Super Sheen.

 

 

Review

  1. Stainless steels rust when passivity (film-shield) breaks down as a result of scrapes, scratches, deposits and chlorides.
  2. Stainless steel rust starts with pits and cracks.
  3. Use the proper tools. Do not use steel pads, wire brushes or scrapers to clean stainless steel.
  4. Use non-chlorinated cleaners at recommended concentrations. Use only chloride free cleaners.
  5. Soften your water. Use filters and softeners whenever possible.
  6. Wipe off cleaning agent(s) and standing water as soon as possible. Prolonged contact causes eventual problems.

To learn more about chloride-stress corrosion and how to prevent it, contact the equipment manufacturer or cleaning materials supplier.

Developed by Packer Engineering, Naperville, Ill., an independent testing laboratory.

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