Stainless Steel - Cleaning, Care and Maintenance

Topics Covered

Background

Why Maintenance is Necessary

Maintenance During Installation

On Going Maintenance

Good Housekeeping During Manufacturing

Cleaning Methods

Passivation Treatments

Pickling Treatments

Precautions

Acids

Solvents

Chlorides

Background

The attractive and hygienic surface appearance of stainless steel products cannot be regarded as completely maintenance free. All grades and finishes of stainless steel may in fact stain, discolour or attain an adhering layer of grime in normal service. To achieve maximum corrosion resistance the surface of the stainless steel must be kept clean. Provided the grade, condition and surface finish were correctly selected for the particular service environment, fabrication and installation procedures were correct and that cleaning schedules are carried out regularly, good performance and long life will be achieved. Frequency and cost of cleaning of stainless steel is lower than for many other materials and this will often out-weigh higher acquisition costs.

Why Maintenance is Necessary

Surface contamination and the formation of deposits are critical factors which may lead to drastically reduced life. These contaminants may be minute particles of iron or rust from other non-stainless steels used in nearby construction and not subsequently removed. Industrial, commercial and even domestic and naturally occurring atmospheric conditions can result in deposits which can be quite corrosive. An example is salt deposits from marine conditions.

Working environments can also create more aggressive conditions, such as the warm, high humidity atmosphere above indoor swimming pools. These environments can increase the speed of corrosion and therefore require more frequent maintenance. Modern processes use many cleaners, sterilisers and bleaches for hygienic purposes. All these proprietary solutions, when used in accordance with their makers' instructions are safe, but if used incorrectly (e.g. warm or concentrated) can cause discolouration and corrosion on the surface of stainless steels. Strong acid solutions (e.g. hydrochloric acid or "spirits of salts") 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 water flushing.

Maintenance During Installation

Cleaning of new fabrications should present no special problems, although more attention may be required if the installation period has been prolonged. Where surface contamination is suspected, immediate attention to cleaning will promote a trouble-free service life. Food handling, pharmaceutical and aerospace applications may require extremely high levels of cleanliness.

On Going Maintenance

Advice is often sought concerning the frequency of cleaning of products made of stainless steel, and the answer is quite simply "clean the metal when it is dirty in order to restore its original appearance". This may vary from once to four times a year for external applications or it may be once a day for an item in hygienic or aggressive situations. In many applications the cleaning frequency is after each use.

Good Housekeeping During Manufacturing

Stainless steel can be contaminated by pick-up of carbon steel ("free iron") and this is likely to lead to rapid localised corrosion. The ideal is to have workshops and machinery dedicated to only stainless steel work, but in a workshop also processing other steels avoid pick-up from:

         Tooling used with other metals

         Grinding wheels, wire brushes, linishing belts

         Steel storage racks

         Contamination by grinding or welding sparks

         Handling Equipment

         Adjacent carbon steel fabrication

Cleaning Methods

Stainless steel is easy to clean. Washing with soap or a mild detergent and warm water followed by a clean water rinse is usually quite adequate for domestic and architectural equipment. An enhanced appearance will be achieved if the cleaned surface is finally wiped dry. Specific methods of cleaning are as in Table 1.

Sections below give passivation treatments for removal of free iron and other contamination resulting from handling, fabrication, or exposure to contaminated atmospheres, and pickling treatments for removal of high temperature scale from heat treatment or welding operations.

Passivation Treatments

         Grades with at least 16% chromium (except free machining grade such as 303), 20-50% nitric acid, at room temperature to 40oC for 30-60 minutes.

         Grades with less than 16% chromium (except free machining grades such as 416), 20-50% nitric acid, at room temperature to 40oC for 60 minutes.

         Free machining grades such as 303, 416 and 430F, 20-50% nitric acid + 2-6% sodium dichromate, at room temperature to 50oC for 25-40 minutes.

Pickling Treatments

         All stainless steels (except free machining grades), 8-11% sulphuric acid, at 65 to 80oC for 5-45 minutes.

         Grades with at least 16% chromium (except free machining grades), 15-25% nitric acid + 1-8% hydrofluoric acid, at 20 to 60oC for 5-30 minutes.

         Free machining grades and grades with less than 16% chromium such as 303, 410 and 416, 10-15% nitric acid + 0.5-1.5% hydrofluoric acid, at 20 to 60oC for 5-30 minutes.

"Pickling Paste" is a commercial product of hydrofluoric and nitric acids in a thickener - this is useful for pickling welds and spot contamination, even on vertical and overhanging surfaces.

Table1. Methods of Cleaning Stainless Steel

Problem

Cleaning Agent

Comments

Routine Cleaning
All finishes

Soap or mild detergent and water (Preferably warm)

Sponge, rinse with clean water, wipe dry if necessary. Follow polish lines.

Fingerprints
All finishes

Soap and warm water or organic solvent (eg acetone, alcohol, methylated spirits)

Rinse with clean water and wipe dry. Follow polish lines.

Stubborn Stains and Discolouration.
All finishes.

Mild cleaning solutions, eg. Jif, specialty stainless steel cleaners.

Use rag, sponge or fibre brush (soft nylon or natural bristle. An old toothbrush can be useful). Rinse well with clean water and wipe dry. Follow polish lines.

Lime Deposits from Hard Water.

Solution of one part vinegar to three parts water.

Soak in solution then brush to loosen. Rinse well with clean water.

Oil or Grease Marks.

All finishes.

Organic solvents (eg. acetone, alcohol, methylated spirits, proprietary "safety solvents"). Baked-on grease can be softened beforehand with ammonia.

Clean after with soap and water, rinse with clean water and dry. Follow polish lines.

Rust and other Corrosion Products.

Embedded or Adhering "Free Iron".

Rust stains can be removed by adding one part of nitric acid to nine parts of warm water. Leave for 30 to 60 minutes, then wash off with plenty of water, and flush any drains thoroughly. See also previous section on Passivating.

Rinse well with clean water. Wear rubber gloves, mix the solution in a glass container, and be very careful with the acid. (see Precautions for acid cleaners)

Routine Cleaning of Boat Fittings.

Frequent washing down with fresh water.

Washing is recommended after each time the boat is used in salt water.

Cooking Pot Boiled Dry.

Remove burnt food by soaking in hot water with detergent, baking soda or ammonia.

Afterwards clean and polish, with a mild abrasive if necessary. See comments re steel wool.

Dark Oxide From Welding or Heat Treatment.

"Pickling Paste" or pickling solutions given on previous page.

Must be carefully rinsed, and use care in handling (see Precautions for acid cleaners).

Scratches on Polished (Satin) Finish.

Slight scratches - use impregnated nylon pads. Polish with scurfs dressed with iron-free abrasives for deeper scratches. Follow polish lines. Then clean with soap or detergent as for routine cleaning.

Do not use ordinary steel wool - iron particles can become embedded in stainless steel and cause further surface problems. Stainless steel and "Scotch-brite" scouring pads are satisfactory.

Precautions

Acids

Acids should only be handled using gloves and safety glasses. Care must be taken that acids are not spilt over adjacent areas. All residues must be flushed to a treated waste stream. Always dilute by adding acid to water, not water to acid. Use acid-resistant containers, such as glass or plastics. If no dulling of the surface can be tolerated a trial treatment should be carried out; especially for pickling operations. All treatments must be followed by thorough rinsing.

Solvents

Solvents should not be used in confined spaces. Smoking must be avoided when using solvents.

Chlorides

Chlorides are present in many cleaning agents. If a cleaner containing chlorides, bleaches or hypochlorites is used it must be afterwards promptly and thoroughly cleaned off.

 

Source: Atlas Steels Australia

 

For more information on this source please visit Atlas Steels Australia

 

Date Added: Jan 11, 2002 | Updated: Jun 11, 2013
Ask A Question

Do you have a question you'd like to ask regarding this article?

Leave your feedback
Submit