March/April 2013

Exposing the cracks

Sergei Shipilov reveals the perils of corrosion

By Alexandra Lopez-Pacheco

Sergei Shipilov, research professor of materials science and engineering at the University of North Texas, specializes in corrosion science and engineering, including stress corrosion cracking (SCC), corrosion fatigue and hydrogen embrittlement. He has penned over 100 scientific papers and book chapters in his areas of expertise and edited the two-volume “Environment-Induced Cracking of Materials” (Elsevier, 2007) and “Minimizing Infrastructure Corrosion” (NACE, 2009). In his presentation, “Materials Degradation and Corrosion in a Sustainable Society,” Shipilov raises the alarm on the costly impact corrosion has on industry and on society – not just in dollars but also in lives.

CIM: Why is corrosion such a critical issue today?

Shipilov: Corrosion is coming to the forefront because there was never before such a large volume of ageing infrastructure that required maintenance. The direct cost of corrosion in Canada is around $41 billion, with indirect costs essentially doubling that amount. It is also a major contributor to environmental pollution due to leakage of hazardous materials from pipelines, vessels and nuclear reactors.

For instance, corrosion was a factor in the world’s worst chemical disaster in Bhopal, India, in 1984, which took the lives of 3,800 people and some 15,000 from related illnesses. Because of North America’s ageing infrastructure, corrosion has become a major public safety concern. Some examples include the Minneapolis bridge collapse in 2007, which killed 13 people, and the Montreal bridge collapse in 2006, which killed five people, including a pregnant woman.

It is important to understand that corrosion itself is not the problem. It is a natural phenomenon like snow or rain. But it can create problems. The problems manifest as a loss of structural integrity. If corrosion does not affect structural integrity, all is well. But if it does, bridges fall. The problem is how corrosion impacts complex engineering structures and high-risk technologies.

CIM: One of your areas of research is SCC. Can you explain what this is?

Shipilov: If you look at the statistics on failures in engineering structures in a wide variety of industries, 40 to 65 per cent of all failures are due to this type of fracture. To explain SCC, let’s use the example of a concrete bridge in Toronto. In that environment, a lot of salt is used during the winter season. Salt is a very corrosive environmental factor. Through cracks in the concrete, salt can reach the bridge’s reinforcing bars, leading to corrosion and rust. Rust increases the bars’ volume, so it starts to push the concrete in different directions, potentially resulting in a piece of concrete falling off the bridge.

One of the biggest issues today is that the materials we use age and, over time, their properties change. Material transforms and becomes brittle over the years so it can no longer withstand the same pressure and/or deformation. We need to recognize how materials have degraded over the years.

CIM: When it comes to new structures, is there anything that can be done to reduce future corrosion?

Shipilov: Engineers should be familiar with the critical combinations of environmental factors and materials in order to avoid them in next-generation systems. This is critical because environmental factors in corrosion and SCC are often specific to the material. In some combinations, the environment accelerates corrosion, while in others the combination is all right. For each material, there is a specific environment that will or will not accelerate deterioration. If you recognize this, you can prevent corrosion. For example, hot aqueous chlorides readily cause SCC in stainless steels but do not have the same effect on carbon steels, aluminum or other non-ferrous alloys.

The biggest problem is that we do not educate engineers in this field. SCC is the number one type of corrosion; in fact, it is responsible for more catastrophic structural failures than all other forms combined. However, the number of people studying it is very small and the number of people who understand it is even smaller.

SCC is a very complicated field because it is situated at the intersection of materials science, chemistry, mechanics and engineering. There are not many specialists in this field because there is no university program that combines these disciplines. The first step is creating publicity to draw attention to this issue.

Book Sergei Shipilov as a Distinguished Lecturer or learn more about the CIM Distinguished Lecturers Program.

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