Steel corrosion – the biological clock is ticking

Structural engineer, Professor Rob Melchers, could not have anticipated that his work on steel corrosion would land him in a biology lab.

What began as research into the corrosion of steel structures located in the sea now puts this internationally respected engineer in the lab, looking for traces of bacterial DNA which could be the key to predicting the durability of steel exposed to saltwater.

In the long-term, the findings may unlock the answer to slowing corrosion and increasing durability of steel infrastructure such as pipelines and nuclear waste systems.

"Even though rust is conventionally thought to be a chemical reaction between iron, water and oxygen, it is now commonly believed bacteria, particularly those in the ocean, are involved in steel corrosion," Melchers said.

"The sea is naturally full of bacteria, so we need to prove there is a link between the presence of certain bacteria and corrosion.

"Once we can do that, we can begin to predict more accurately how much corrosion there is likely to be."

Pinning down the elusive bacteria has proved more challenging than Melchers and his team anticipated.

"The patterns of behaviour displayed by bacteria are highly dependent on a range of conditions including temperature, pollution and water velocity," Melchers said.

"We wanted more convincing proof of which bacteria are involved, which is why we decided to look for bacterial DNA where the corrosion has occurred."

Funded by an Australian Research Council grant, the team has established a DNA testing facility at the University where a microbiologist is examining samples.

"We needed our own lab for this work – most biology laboratories are generally pretty pristine places, not really the environment for lumps of concrete and rust," Melchers said.

Using three-metre strips of steel sunk into several locations from Port Arthur to Townsville three years ago, the team is able to observe how the corrosion process occurs in tidal zones and in the atmosphere near the sea.

The team is also comparing corrosion in natural seawater and sterilised water to measure the effect of bacteria in different types of waters. The aim is to determine how these differences influence general and pitting corrosion.

"The deterioration of structural materials under adverse conditions – such as corrosion of steel in seawater environments – is a major cost to industry," Melchers said.

"Being able to predict how much corrosion is likely to occur under uncertain conditions over a period of time would be extremely useful in estimating reliability and durability.

"We want to strengthen our case scientifically, which is why we have turned to DNA analysis to strengthen our understanding of the influence of bacteria."