Premature corrosion failure of structural highway components made from weathering steel

Weathering steel (or Cor-Ten Steel) is a very common material that has been used for many years for steel construction in the field of transportation. The chemical composition of weathering steel is able to promote, after exposure in the atmosphere, the formation of a stable and protective oxide layer reducing remarkably the corrosion rate. The weathering steel was used for structural components (guard-rails) on the Brennero Highway for about 30 years, showing a generally good behaviour. However, in some cases, a very strong corrosive attack was noted, causing a degradation of the structure. The origin of this failure was not clear. The subject of this work is an extensive failure analysis investigation, studying the materials after different exposure time in the highway environment with the aim of finding the reasons of the early failures. The main parameters studied are: the materials quality and the characteristics of the surface oxide, the micro and macro climate conditions, the shape of the components (which can favour the accumulation of humidity or rain), the presence close to the weathering steel of special conditions (concrete, pollution, etc.). The results showed that the materials used in the last 30 years are, from a metallurgical, microstructural and electrochemical point of view, very close to each other and they satisfy the standard specifications, while more critical are the climatic conditions, both in a general and in a local sense, and the geometrical parameters. For this reason a protocol for the correct use of weathering steel for this application is proposed including further protective steps in the case of critical situations. (C) 2002 Elsevier Science Ltd. All rights reserved.