The Science of Engineering: Corrosion Protection

Whenever metal comes in contact with moisture – whether it be a tank, a pipeline, a bridge support, or simply metal that is left outdoors – the metal corrodes.  It’s a problem that people have been trying to solve for 2,000 years, using the science of the times.

The earliest way to deal with corrosion was simply to choose the right metal or alloy.  For example, when iron corrodes, it produces rust, which flakes away and exposes more metal to corrosion.  Copper, on the other hand, forms copper oxide, which adheres tightly to the underlying metal and slows further corrosion. In the 18th century, ship hulls were clad with copper sheets, which corroded slowly.

Another early method of preventing corrosion is to coat it.  Initially the coating would be paint; over the centuries, more durable coatings were developed. 

By the early 19th century, scientists had developed an understanding of what causes corrosion.  Essentially, it’s an electro-chemical reaction.  As part of this reaction, the metal acts as an anode – that is, it surrenders free electrons.

One way to protect a metal structure is to provide a better anode, so that the metal being protected acts as a cathode.  This is called cathodic protection.

In 1824, the British navy built a ship, the HMS Samarang, in which iron blocks were attached to the copper hull.  The iron acted as an anode, preventing the copper hull from eroding. 

This technique was used for over a century to protect all sorts of metal structures and vessels from corrosion.  The problem with this technique is that the metal anode corrodes away and needs to be replaced (the metallic anode is sometimes called the “sacrificial metal”).

A newer and better solution is called impressed current cathodic protection (ICCP).  An electrical current is used to release free electrons, preventing the electro-chemical reaction that causes corrosion.  Thomas Edison experimented with ICCP in the 1890s, but lack of a good power source made the technique impractical.

Commercial ICCP was used to protect pipelines beginning in 1928, and became common in the 1930s.  The technology became more refined and sophisticated over time.  ICCP is not the standard mechanism for preventing corrosion in metal that is exposed to water.

Construction and engineering firms the construct tanks and pipelines deploy sophisticated ICCP systems to protect the metal from corrosion.