All grades of stainless steel will stain and discolour due to surface deposits and can never be accepted as completely maintenance free. In order to achieve maximum corrosion resistance the surface of the stainless steel must be kept clean. Provided the grade of stainless steel and the surface finish are correctly selected and cleaning schedules carried out on a regular basis, good performance and long service life are assured
Surface contamination and the formation of deposits must be prevented. These deposits may be minute particles of iron or rust from other sources used on the building of new premises and not removed until after stainless steel items have been fixed. Industrial and even naturally occurring atmospheric conditions can produce deposits which can be equally corrosive e.g. salt deposits and marine conditions.
A working environment which offers more aggressive conditions, e.g. hot humidity, such as in a swimming pool, increases the speed of discolouration and therefore requires the maintenance to be on a more frequent basis. Modern processes use many cleaners, sterilizers and bleaches for hygienic purposes. All these proprietary solutions, when used in accordance with makers instructions are safe but not if incorrectly used, (e.g. warm surface of any quality of stainless steel). Strong acid solutions are sometimes used to clean masonry and tiling of buildings but they should never be permitted to come into contact with metals, including stainless steel. If this should happen the acid solution must be removed immediately by copious applications of water.
Where surface contamination is suspected, immediate attention to cleaning will encourage a trouble free product. Food handling, pharmaceutical, aerospace and certain nuclear applications require extremely high levels of cleanliness applicable to each industry. Advice is often sought concerning the frequency of cleaning stainless steel and the answer is quite simple ‘clean the metal when it is dirty in order to restore its original appearance’. This may vary from one to four times a year for external applications or it may be once a day for an item in hygienic or aggressive situations. Frequency and cost of cleaning is lower with stainless steel than with any other materials and will often outweigh the initial higher cost of this superior product.
Stainless steel is easy to clean. Washing with soap or a mild detergent and warm water followed by a clear water rinse is usually quite adequate for domestic and architectural equipment. An enhanced aesthetic appearance will be achieved if the cleaned surface is finally wiped dry. Where stainless steel has become extremely dirty with signs of surface discolouration (perhaps following a period of neglect or misuse) methods of cleaning are detailed in the table below.
|Routine cleaning, all finishes||Soap or mild detergent and water (such as fairy liquid)||After application, use a sponge or clean cloth to rinse with warm, clean water and then wipe dry if necessary|
|Fingerprints, all finishes||Soap and water or organic solvent such as Acetone or Alcohol||After application, use a sponge or clean cloth to rinse with warm, clean water and then wipe dry if necessary|
|Stubborn stains, discolouration all finishes||Mild cleaning solutions such as abrasive free stainless steel cleaning creams.||After application, use a sponge or clean cloth to rinse with warm, clean water and then wipe dry if necessary|
|Oil/Grease marks, all finishes||Soap and water or organic solvent such as Acetone or Alcohol|
|Rust and other corrosion products, all finishes||Oxalic Acid. The cleaning solution is applied with a swab, allowed to stand for 14-20 minutes before being washed away with water.||May continue using mild cleaning cream to give a final clean After application, use a sponge or clean cloth to rinse with warm, clean water and then wipe dry if necessary|
|Scratches on brush satin finished finish||Slight scratches: impregnated nylon pads. Polishing with scurfs dressed with iron free abrasives.
Deeper scratches: apply in direction of polishing
|Do not use ordinary steel wool. Iron particles can become embedded in stainless steel and cause further damage|
Acids should only be used for on site cleaning when all other methods have been proved unsatisfactory. Rubber gloves should be used and care taken to see that acid cleaners are not spilt over adjacent areas. Special precautions are necessary with oxalic acid. Solvents should not be used in enclosed places. Smoking must be avoided when using solvents. In all instances follow the manufacturer’s safety instructions.
In general, cleaning is carried out to restore the original surface appearance to prevent corrosion and maintain hygienic conditions.
Stainless steel is easy to clean, and washing with soap or a mild detergent and warm water, followed by a clear water rinse is usually quite adequate for domestic, architectural and commercial catering equipment. If the water is hard, the steel should then be dried with a soft cloth to prevent water spotting.
Thorough cleaning is particularly important in catering and medical applications where cleanliness is required not only for aesthetic purposes but also for hygiene. Stainless steel’s smooth and pore-free surface does not harbour bacteria and is easily cleaned, if necessary using the most vigorous techniques.
When the steel has become extremely dirty, perhaps following periods of neglect or after being subjected to a particularly aggressive environment, mild abrasion only, such as scrubbing with a nylon or other non-scratching scourer, my be necessary. Ordinary steel wool soap pads should never be used as they may leave particles of mild steel on the surface of the stainless steel which may cause localised areas of rusting. Stainless steel soap pads, however, are quite suitable.
A bright annealed of 2B finish will be permanently marked by the use of abrasives which therefore should be avoided at all costs. Discolouration, heavy dirt or rust which may resist normal cleaning methods can be removed using a proprietary stainless steel cleaner followed by a clear water rinse.
Some deposits and stains encountered in catering and medical applications can be difficult to remove.
It should be noted that nearly all abrasive cleaners will scratch the bright annealed or 2B finish of stainless steel. On other finishes the cleaner should be used in the direction of the polish. A clean dust and grit free cloth should be used to avoid scratching. In all cases, the mildest cleaning procedure that will do the job efficiently should be used.