Corrosion is a significant cost to modern civilisation
Corrosion is a natural process converting a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials by chemical or electrochemical reaction with their environment. Corrosion decreases the longevity and alters the physical properties of the materials from which much of modern infrastructure is built. This is not only expensive to address, it is estimated the annual global cost is at least 3% of the world’s GDP but has caused environmental and physical harm. It is estimated that by the year 2100, global warming will have exacerbated the effects of corrosion and it will affect 1 in every 6 structures.
it is impossible to eliminate but corrosion detection and best practice can reduce its impact
Corrosion is impossible to stop altogether as the conditions where it occurs overlap significantly with the conditions for normal life i.e. the presence of oxygen, water and human habitable temperatures. Corrosion engineering aims to improve our understanding of corrosion and use this knowledge to minimise or prevent it. By helping us make better design and maintenance decisions it can maximise the lifespan of assets. It is estimated that 25% – 30% of annual corrosion costs could be saved if optimum corrosion detection and management practices were employed1.
There a various types of corrosion
As we said before, corrosion is the oxidation of metal and there are a number of different mechanisms through which this happens. The most common is atmospheric, whereby exposure to air oxidises the metal. Iron, the primary metal in steel and steel reinforced concrete, is highly vulnerable to atmospheric corrosion. This makes steel structures particularly susceptible to corrosion over time.
Other common corrosion types are galvanic, pitting, and crevice corrosion. Galvanic is when two different metals are in contact with each other. One metal begins to act as a cathode, and the other as an anode. The anode corrodes more rapidly than it would if it wasn’t in contact with the metal acting as a cathode, while this metal corrodes more slowly.
Pitting is a localised form of corrosion often seen in drainage pipes. This is when an oxide layer protecting a metal’s surface wears away unevenly, allowing for the oxidation of the metal, particularly in the presence of a corrosive aqueous solution.
Crevice involves the accumulation of water within small gaps or crevices in metal structures, leading to the presence of oxygen in relatively high concentrations. This rapidly increases the rate by which the structure becomes corroded.
Corrosion is driven primarily by exposure to water and oxygen in the atmosphere
Major factors influencing the rate of metal corrosion are temperature, humidity, salinity, air pollution and rainfall. Projections of steep increases in global mean temperature and rainfall due to climate change suggest corrosive environments will become more so in the future.
Corrosion causes more than just financial harm
Corroded and decayed infrastructure incurs high maintenance and replacement costs, half of these costs are caused by atmospheric corrosion. Some, if not all of this allocation of money, time and materials could have been used more productively elsewhere.
Unchecked corrosion also impacts public health and safety. The property destruction caused by collapsed infrastructure often results in injuries and fatalities. Even damage which prevents the use of structures like bridges and tunnels impacts quality of life and reduces economic activity. The derailment of a dangerous goods train carrying oil near Stewarton in Ayrshire, Scotland, caused localised fires. This was due to the collapse of a corroded underbridge that was unable to bear the weight of the train. More tragically, in 2022, a bridge spanning the Machhu river in Gujarat, India collapsed leading to the deaths of 136 people and 56 injuries. The causes were determined to poor maintenance and rusted cables.
Corrosion progresses slowly with exponentially growing repair costs
Due to the time it can take for corrosion to appear and progress, it can be easy to overlook or neglect the work required to detect and address. Doing so is a mistake, since, as the chart below shows, repair costs grow exponentially as corrosion progresses from early to advanced stages. Stage 1 refers to bubbling or cracked paint all the way through to Stage 4 where sections of metal are missing and there are holes in the structure. Stage 1 can usually be addressed by sanding and reapplying paint, Stage 4 requires replacement of the affected parts. This is an expensive task especially on large structures with many different parts that are structurally dependent on each other. Costs are in US dollars.
Detection is typically visual inspection and prevention commonly coating surfaces
The main method used to detect corrosion is visual inspection. However, the accuracy of these visual techniques is affected by lighting conditions and human subjectivity, which are variable. The process is also time-consuming using manual labour in order to interpret images and convert what they show into actionable reports.
Prevention of corrosion can involve simple techniques such as painting the steel or more sophisticated methods such as galvanising or plating using corrosion-resistant materials, such as zinc.
Corrosion detection and forecasting at Keen AI
Since 2020 Keen AI has been actively developing computer vision algorithms to consistently detect and grade corrosion in RGB images. Combining our corrosion detection pipeline with historic image and atmospheric data has enabled us to develop reliable models for forecasting the future state of steel towers. Our systems are used by some of the world’s leading asset operators. Our corrosion detection models have reduced analysis time by up to 91% and our forecasting models have reduced the number of surveys our customers have to do by 8.3%.
Read the Case Study from our work on transmission towers with National Grid and Contact us to learn more about Deepsteel and how it can help in the fight against corrosion.
Footnotes
1Corrosion challenges towards a sustainable society
2Advances in understanding atmospheric corrosion of iron
3Research Opportunities in Corrosion Engineering, National Academy of Sciences
