Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
Emmanuel Georgiou, Dirk Drees Falex Tribology N.V., Wingepark 23B, B3110, Rotselaar, Belgium
Tribocorrosion is a key issue in Industry Corrosion is a naturally occurring phenomenon that results in the degradation of materials due to a chemical and/or electrochemical reaction of their surface with the surrounding environment. Examples of corrosion are found in many applications ranging from aeronautical, automotive, naval, and the construction industry, over home appliances, water systems, pipelines, and ‘bio’ applications. A recent report by NACE International (The Worldwide Corrosion Authority) indicates that in the US alone, $2.2 trillion are spent on corrosion issues, whereas the annual cost of corrosion worldwide is estimated to be over 3% of the world’s GDP.
Tribology is the combined term for friction and wear phenomena, and these also occur at the surface of components, and are in interaction with their environment. Because both mechanisms can occur simultaneously and both influence the surface of a component, it is clear that they can strongly influence each other in a dynamic process. This simultaneous positive or negative synergy of damage mechanisms at the surface, or the study of it, is called Tribocorrosion.
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Tribocorrosion: risks and potentials
Corrosion phenomena can be significantly accelerated by the simultaneous occurrence of a mechanical load on the surface: the formation of cracks and surface defects, along with surface strain and stress fields lead to faster diffusion of corrosive ions or the destruction of protective layers (depassivation). In Figure 1 indicative examples of corrosion related failures in a German and an American chemical plant are shown. Up to 50% of the reported corrosion damage occurs from an interaction between corrosion and mechanical loading: corrosion fatigue, stress corrosion cracking, wear and erosion.
Some obvious examples of tribocorrosion can be found in many off-shore applications, but also in dentistry (brackets) and other biomaterial applications, since the human body is also a source of electrolytes. The occurrence of tribocorrosion isn’t always recognized in field practice. Examples are the accelerated corrosion of steel conveyors exposed to ambient air of high relative humidity, the failure of electrical connectors in the automotive industry, the erosion wear of turbine blades, etc. In any case, the question is: “How can we minimize the risk of corrosion in mechanical systems and in particular tribo-systems?
Figure 1. Failure-statistics of large chemical process plant in (a) Germany and (b) United States (taken from Corrosion Engineering: Principles and practice, McGrawHill, 2008). 32 LUBE MAGAZINE NO.136 DECEMBER 2016
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