How to Clean Stainless Steel
Both indoor and outdoor stainless steel products require regular cleaning to preserve corrosion resistance and maintain a shiny appearance. Indoor stainless steel products typically have less damage and wear since they are not exposed to harsh outdoor elements. Outdoor stainless steel products such as railings, bollards, and bike racks require extra attention for ongoing maintenance and protection against rust and oxidation.
For stainless steel applications with minor staining, cleaning is relatively simple – soap and water followed by a clean-water rinse. Be sure that the stainless steel is cool to the touch before starting. A mild detergent or a diluted ammonia solution can also be used and then wiped down with a sponge, cloth, disposable wipe, or dried with an air blower.
If the stainless steel has become extremely dirty with signs of surface damage, alternative methods of cleaning may be required. When stainless steel care and maintenance requires the use of harmful chemicals, follow the safety instructions provided with the cleaning agents. Ensure that personal protective equipment is used in accordance with occupational health and safety guidelines. Conduct a test by applying the cleaning solution to a small, hidden area of the surface and checking the resulting finish.
Cleaning Process for Surface Stains and Discoloration
Wipe down with soap or detergent and warm water. Commercial solutions such as rubbing alcohol or acetone may also be helpful.
- Oil and grease marks
Rubbing alcohol, acetone, or methylated spirit can be used. Apply as many times as necessary with a clean, soft cloth until markings disappear.
- Burnt-on stains
Immerse in hot water and diluted ammonia or detergent. Remove the grime with a nylon brush and rinse with clean water. If necessary, use a fine abrasive powder but use with caution as abrasives will scratch polished surfaces.
- Coffee and tea surface stains
For tea stains, soak the stainless steel in hot water and sodium carbonate (washing soda). For coffee stains, soak in sodium bicarbonate (baking soda). Use a sponge or a soft cloth for cleaning if the object is too large for soaking.
- Oxidation and water stains
Use mild, non-abrasive cleansers with a soft cloth or sponge. Use clean water to rinse and let dry. Avoid scouring pastes. Cream detergents are also safe to use.
- Tough discoloration
Use domestic metal polish for discoloration. Chrome polishes for automotive parts are also effective. Treat the entire surface to avoid the appearance of discolored patches.
- Localized rust stains
Use a soft cloth to apply an oxalic acid solution. Leave on for a few minutes to dissolve contaminating particles. Once clean, rinse with clean water.
- Mortar splashes, cement, and limescale stains
Rinse off mortar or cement as soon as possible. Use a 10% or 15% phosphoric acid-based solution in warm water. Spread cleaner evenly over the surface, wait 30–60 minutes, then neutralize with an alkaline cleaner or diluted ammonia and rinse with clean water. For limescale stains, dilute one-part vinegar in three-parts water and use a nylon brush to apply.
Use a biodegradable graffiti-cleaning spray or wipes. Avoid using knives or hard scraping tools as these may cause damage to surfaces.
- Structural damage
Heavy damage includes compromises to the structure such as visible dents, cracks, breaks and rust that can undermine the integrity of a product. Heavily damaged products should be removed from service until a repair or replacement can be made. Any significant rust should be removed as soon as possible.
- Badly neglected and corroded surfaces
Minor damage: Stainless steel can be wiped using an all-purpose lubricant. Domestic stainless steel cleaners can also be useful. After wiping, rinse thoroughly with clean water. If rust remains, treat the corrosion as moderate. If rust returns in a short time, treat for iron or carbon steel contamination.
Moderate damage: Try a phosphoric acid-based stainless steel cleaner. Spread cleaner evenly over the affected surface and leave on for 30–60 minutes. Neutralize the acid with a spray-on alkaline cleaner. Wipe the surface clean with a paper towel, then rinse off residue with clean water. If rust remains, stainless steel may need to be treated for severe corrosion or be replaced. In the event that the rust returns, treat for iron or carbon steel contamination (see “Passivation” below).
Severe damage: Seek the help of a professional service provider. Serious rust treatments are highly corrosive and pose a risk to people and surrounding environments. Severe rust requires a pickling bath, typically containing hydrofluoric acid which is highly corrosive. Stainless steel can then be passivized with mild nitric acid.
A clean stainless steel surface can be re-damaged when exposed to extreme heat, chemicals, or mechanical damage. The iron may become exposed to rusting.
Passivation may need to be done regularly to prevent rust and maximize the inherent corrosion resistance of a stainless alloy as it is not a scale removal treatment. Ideally, the passive layer forms immediately after machining or passivation to cover the stainless steel surface. Realistically, particles and contaminants can adhere to the surface, and if allowed to remain, these foreign particles compromise the integrity of the original protective film.
A two-step process of passivation can provide the best corrosion resistance:
The part must first be thoroughly cleaned. Passivation cannot take place unless the stainless steel surface is clean and free from contamination and scale. Foreign matter may need to be removed by grinding, mechanical abrasion, or pickling which involves a nitric/hydrofluoric acid mixture.
- Passivating treatment
The stainless steel part is immersed in a passivating acid bath. Three methods can be used – nitric acid, nitric acid with sodium dichromate, or citric acid passivation. The passivation treatment varies based on chrome content and machinability of the stainless steel grade, as well as the acceptance criteria prescribed.
Brad Done is the vice president at Reliance Foundry Co Ltd. He has more than 25 years’ experience in the manufacturing of bollards and other outdoor metal products. Visit www.reliance-foundry.com to learn more.