Active undersea volcanoes pose increased corrosion risk
Article Type: Industrial news From: Anti-Corrosion Methods and Materials, Volume 61, Issue 5
A research team in Spain has proven, as suspected, that seawater polluted by an active undersea volcano decreases the corrosion resistance of austenitic stainless steels.
On October 10, 2011, a volcano erupted in the Atlantic Ocean near the island of El Hierro, in Spain’s renowned Canary Islands. A lucky team of researchers was able to obtain a seawater sample from this environment and explored whether or not seawater polluted by an active undersea volcano decreases the corrosion resistance of austenitic stainless steels.
When volcanoes erupt at sea, gases such as carbon dioxide and thermal water emissions are released. Although it has been long suspected that the associated decrease in the pH value of seawater was capable of modifying the corrosion behavior of materials that come into contact with this medium, it had never actually been proven.
In the April 2014 issue of CORROSION, the team describes their study of the semiconducting behavior of passive films formed on austenitic stainless steel (AISI 316L) in seawater polluted from the volcano of El Hierro Island vs normal, non-volcano-polluted seawater.
The researchers were motivated by “a lack of corrosion studies in seawater polluted by volcanic material”, says Jose García-Antón, a Professor in the Chemical and Nuclear Engineering Department at Universitat Politècnica de València in Spain. He notes:
Our work is new to the field of corrosion studies, because it’s very difficult to perform any kind of research under these environmental conditions or with this type of material.
Through a combination of polarization measurements, potentiostatic passivation tests, electrochemical impedance spectroscopy and capacitance measurements, García-Antón and colleagues proved that the seawater polluted by the volcano did significantly decrease the corrosion resistance of AISI 316L stainless steel.
Stainless steels are known for their resistance to general corrosion. In particular, AISI 316L stainless steels combine desirable mechanical properties and corrosion resistance, thanks to the addition of molybdenum and low carbon content. But even stainless steel is susceptible to localized corrosive attacks (e.g. pitting, intergranular and stress corrosion cracking) in highly electrical conducting environments such as seawater. Add an active volcano to the mix, and corrosion becomes an even bigger problem for marine infrastructure made of stainless steel; including bridges, wharfs, platforms and pipeline systems. García-Antón and colleagues confirmed that these corrosion problems become aggravated when the seawater environment is altered by acidic volcanic emissions because the resistance of the steel’s surface film is influenced by the surrounding seawater’s pH values.
The team found that when exposed to an active undersea volcano’s acidic environment, it worsened passivation kinetics, and the passive films that formed on AISI 316L stainless steel showed “a more defective structure”.
Our work can be taken into consideration to help prevent the corrosion of remotely controlled submarines used to search for new sea deposits, since these types of deposits tend to be found near active underwater volcanoes, says García-Antón.
“It also leads us to a better understanding of the types of materials that can provide a better performance in these environments”.
More information is available at: http://www.nace.org
