| Letter to wise people |
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Dear madam, Dear sir,
Since long time people and companies worldwide struggle with an anomaly that still survives in most languages. French people call it “acier inoxydable”, in German the same material is called “rostfreier Stahl” and in Dutch dictionaries “roestvrij staal” is considered to be an appropriate terminology; in English it’s called “Stainless steel”. So what’s the problem? All these expressions give the impression as if this type of steel will never rust: A major misunderstanding ! It already starts with a simple parapet in a coastal area. Several flat owners guarantee me that their parapet possesses an infinite life, just because their supplier told them that stainless steel never rusts. Yet, several of these flat owners are suddenly confronted with reality; their precious stainless steel nevertheless starts corroding. What has happened in several cases is that the parapet has been made of the basic stainless steel AISI 304. This type of material is not resistant to the chlorine rich sea climate. And when you weld this metal without precautions, the final result could be intergranular corrosion and stress corrosion cracking as well; these types of corrosion deliver nice pictures indeed, yet many worries as well. Would the use of 316L stainless steel be a solution? For many applications the failure risk would be reduced indeed, yet also 316L can fail fast and catastrophically. Using stainless steel is not just a matter of common sense, yet also knowledge on ‘what’s possible and what’s not’ and on ‘what influences what’ is a matter of life to stainless steel.
The previous list of aspects ‘to be taken into account’ looks straightforward for most people, until they reach the word ‘aftercare’. An adequate aftercare of stainless steel components and constructions is of utmost importance indeed. Do you for example realise that it is not very wise to cut or grind conventional steel or copper when stainless steel is near? Also removing rust from stainless steel surfaces by means of a classic steel brush is a ‘not done’. Another, astonishing rule: never write with a pencil on stainless steel; and finally … Never believe the fairytale that stainless steel does not need passivation. Passivation of welded stainless steel is a stringent “MUST” when you want to guarantee the safe future of the stainless steel constructions in your company. So, to finalise this plee: dear editors, please remove from your dictionaries all terminology that suggests that there exists something like a steel that never rusts. In Dutch wise people use ‘roestvast staal’, and this terminology is already in many dictionaries indeed. So take up the challenge … enrich your language.
Sincerely yours, Dr. ir. Frans Vos General Manager Materials Consult bvba
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So, is the use of stainless steel always a source of worry? Certainly not. Stainless steel can indeed be the miracle solution for many applications, yet for other applications a conventional steel covered with an appropriate coating could be as suitable as well. Materials selection is a matter of choosing the material “in function of the application, the way of construction, the environment to which the material will be exposed, the process conditions and the proper aftercare”. Only by taking all these aspects into account, it will be possible to determine whether the use of stainless steel is adequate and, if so, which type of stainless steel is most suitable.
