With regards to corrosion, stainless steel is a very inventive material. In particular the good corrosion resistance combined with a fair price has made stainless steel the, by far, most commonly used material for “critical purposes”, including the food and pharmaceutical industries, household equipment and numerous applications within the chemical industry.
The great corrosion resistance of stainless steel is based upon the formation of an ultra-thin layer of chromium oxides on the steel. This film is only a few nanometers thick, and completely invisible, however, it’s sufficiently tight in order to isolate the steel from the surrounding environment. If, against all precautions, the chromium oxide film is perforated, it quickly reforms, and the steel is protected once again. Tis is called repassivation.
Unfortunately, things have a tendency to end up differently. I some cases, the oxide film may suffer a local breakdown, and no subsequent repassivation, and the result may be serious corrosion problems. Once the corrosion has started, penetration is likely to occur very quickly, and the use of stainless steel therefore often becomes a kind of “either or”. Either the steel repassivates or it doesn’t, and the difference in between the two extremes is sometimes very slim.
If we can prevent the corrosion from initiating, our steel will last (almost) to eternity. If not, severe corrosion will take place and the life-span of our equipment will be correspondingly short.