What is rust?
It is a heterogeneous layer of oxidation products of iron and its alloys, such as steel, in water, humid atmosphere or soil, containing mainly iron oxides and hydroxides. Commonly, the term "rust" also refers to layers of oxidation products of other metals, including the oxidation of iron in dry gases or the oxidation of non-ferrous metal alloys (e. g. scale, deposits, passive layers). With enough time, oxygen and water, the whole mass of iron will eventually completely rust and disintegrate. A popular method of preventing corrosion (rusting) is cathodic protection. It involves connecting the outer anode to the protected structure in the form of metal, which has a standard potential lower than the material of the protected structure.
Why is rust dangerous?
In addition to the fact that rust irritates the human skin, its very presence weakens and even destroys the original structure on which it is formed. One example where rust had a huge impact was the Silver Bridge disaster in West Virginia in 1967. The steel suspension bridge collapsed in less than a minute, killing 46 people!
The bridge was named the "Silver Bridge" because it was the country's first painted aluminum bridge. It was designed with a twenty-two foot carriageway and one five foot walkway. Some unique engineering techniques have been used on the Silver Bridge, such as “High Tension” eyelet chains, a unique anchoring system and “Rocker” towers. The Silver Bridge was the first suspension bridge of its type to be built in the United States.
In the 1960s, no good corrosion resistant materials were known. The eyelet chains were made of innovative at the time carbon steel, which, as we know, is not sufficiently resistant to atmospheric agents, let alone chemical agents. Rust took as many as 40 years to cause stress corrosion cracking and corrosion fatigue to turn an ordinary day into a horror.
Although the collapse of the Silver Bridge was a disaster, there were positive aspects to its failure. Bridge inspections are now more routine and thorough due to the Silver Bridge. Engineers now have more knowledge about corrosion fatigue and stress corrosion, allowing them to design and build better structures. With today's technology, as well as better design techniques and materials, there is hope that the Silver Bridge disaster will never happen again.
