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, discolor 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. The frequency and cost of cleaning of stainless steel are lower than for many other materials and this will often out-weigh higher acquisition costs.

Why Maintenance is Recommended

Surface contamination and deposit formation are the key factors that can lead to a drastically decreased lifespan of the stainless steel. These pollutants may be tiny iron and rust particles from other non-stainless steel surfaces that are being used and not subsequently removed in the adjoining areas. Industrial, domestic and other climatic conditions can result in corrosive deposits. One such example is of marine salt deposits.

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Maintenance During Installation

There should be no particular problems with the cleaning of new manufacturing systems, but if the time has been extended, further effort might be needed. In cases of suspected surface contamination, prompt cleaning attention would encourage trouble-free service life. A high level of cleanliness can be required for food handling, pharmaceutical, and aerospace applications.

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On-Going Maintenance

Advice on the duration of cleaning of items in stainless steel is often needed and the response is to simply clean the metal surface when it is dirty to preserve its original appearance. For external applications this can range from two to five times per year or can be once a day for hygienic or urgent situations.

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Tips on Good Housekeeping During Manufacturing

The setting up of carbon and free iron on stainless steel can be contaminating, resulting in rapid corrosion. Workshops and machinery dedicated to steelworks are suitable, whereas other steels are not obtained from in a workshop, as well as:
● Tools used for other metals
● Wire brosses, fastening belts, grinding wheels
● Shop racks of steel
● Melting or welding sparks to contaminate
● Equipment for handling
● Manufacture of corresponding carbon steel

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Causes of Corrosion

Here is a list of some of the common reasons for untimely rusting of the stainless steel surface:

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●  Chemical Attack

Chemicals such as hydrochloric acid and solutions rich in chlorides (usual salts) cause excessive corrosion in stainless steel. Chromium added in stainless steel prevents the corrosion of the metal but the formation and preservation of chromium oxide are impaired by salts and acids.

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●  Improper Installation

When mounted with non-stainless steel or iron tools that scrape or bite the surface, Rust may start to develop on stainless steel. In the case of a disturbance, ferrous tool particles can stick on the stained surface and can avoid a re-formation of the chromium oxide layer. Good stainless steel has an overall chromium distribution through the material, but maltreatment may result in the chromium being unbalanced, hence causing corrosion.

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●  Structural damage

Somehow if there happens to be a crack or dent on the surface of the stainless steel, any liquids may be trapped inside the vacuum hence produced. In such a case, if the liquid is salty water then there is a possibility of corrosion within the steel.

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●  Galvanic corrosion

When two distinct metals are immersed in a conducting solution and are electrically connected, galvanic corrosion occurs. There is a secured metal (the cathode), and the other is corroded (the anode). Compared to that when the metal is uncoupled, the attack rate on the anode is accelerated.

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Methods to Clean Stainless Steel Surfaces

The cleaning of heavy stainless steel objects such as bars, pipes, sheets, tubes etc require extra efforts for polishing.

Some of the easy and widely used methods for cleaning stainless steel surfaces are:

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●  Passivation Treatment

Stainless steel that is usually composed of chromium, iron and nickel is an iron-based alloy. It derives its corrosion resistant properties from chromium. As oxygen is exposed, chromium constitutes a thin film of chromium oxide covering the surface of the rusting stainless steel. This passivation is intended to form the chromium oxide layer.

It is a two step procedure

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❖ Cleaning - The steel surface needs to be washed thoroughly. Unless the surface is clear and free of contamination, inoxidable stains can not be passivated. In extreme circumstances, external substances can need to be separated by grinding or mechanical abrasion or by beating prior to the passivation. 

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❖ Passivating treatment - In a passivating acid bath, the stainless steel is immersed. One out of the three passivating methods can be employed: passivation from nitric acid, passivation from sodium dichromate to nitric acid or passivation from citric acid. The treatment of passivation depends on the amount of chromium present in the stainless steel.

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● Pickling Treatment

The passivation improves the resistance to corrosion of stainless steel items, the processing of this material does not remove numerous imperfections.

Pickling is a typically acid based treatment where hydrochloric or sulfuric acid treatment technique is used that allows the oxide and the heat tint to be removed during the dissolution of steel spots in the piece. However, the pickling process is very imprecise, with many disadvantages, including strict EPO laws. The acid solution degrades with age, and the quantity of surface material extracted can vary greatly, making it difficult to obtain reliable results.

"Pickling Paste" is an industrial hydrofluoric and nitric acid substance used in the thickener-used to pickle welds and correct spots.

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