By Leyla Alieva, CEO & Co-Founder, NEOL Copper Technologies
Hydrogen, being the most abundant element there is, makes up approximately 75% of the mass of the universe and is considered by many to be the most essential element to achieving net zero. However, hydrogen also contributes to a great amount of mechanical damage. This is caused by two separate occurrences: hydrogen embrittlement and hydrogen wear which can cause significant damage to metals and reduce the lifespan of the machinery.
Although these two occurrences might seem similar, there are some significant differences between the two, and by understanding these differences we can combat the negative effects of both, and ultimately improve the performance and longevity of our machines.
The term hydrogen embrittlement is used to describe the process whereby metals become brittle and fracture as a result of absorbing hydrogen. It is a common issue for steel makers, lowering the level of stress required for cracks to appear in the metal and therefore reducing its load-bearing capabilities.
Hydrogen embrittlement typically occurs during the manufacturing process, or in other situations where hydrogen is present or produced, such as electroplating. When hydrogen atoms come into contact with a susceptible metal – at room temperature or higher – they can enter into the metal lattice and diffuse through the grains. These atoms then come together, forming small bubbles at the metal grain boundaries (the interface between two grains of the same material). The bubbles then increase pressure between the metal grains, forming tiny cracks inside the material and lowering its ductility.
Fortunately, hydrogen embrittlement is nothing new, and there has been plenty of research conducted into methods for preventing it. There are ways in which we can limit metal’s exposure to environments that introduce hydrogen during manufacture, and post-fabrication heat treatments that can be used to diffuse absorbed hydrogen before embrittlement happens.
There are also several industry tests that can be performed to determine if a certain process will lead to hydrogen embrittlement, including the ASTM F519 test used to evaluate plating/coating processes and service environments.
Hydrogen wear isn’t as well documented as embrittlement, but it is no less important. It works in a similar way, with hydrogen invading the metal surface, but instead of happening during production it occurs during the process of friction.
As metals surfaces connect with each other they generate heat and pressure, causing the particles to separate. This provides gaps which allow hydrogen atoms to infiltrate the metal, pushing out its own particles and causing the deterioration of that machine part. The hydrogen itself can emerge from moisture that has found its way to the friction point and, in many cases, is a byproduct of the lubricant used to protect the machine.
An example of this in action is what has become known as white etching cracking (WEC). WEC is a common cause of bearing failure in wind turbine gearboxes, responsible for around 60% of bearing failures in the industry and illustrates the damage hydrogen can cause in areas of high friction – leading to expensive maintenance and replacement costs.
Though research into hydrogen wear isn’t as commonplace as it is for embrittlement, there has still been a considerable amount conducted. Not only that, but this research has also led to a major discovery; that hydrogen wear can be used to polish a friction surface, and copper can be introduced to control it and prevent the hydrogen atoms from causing damage.
Although both types of mechanical degradation originate from the same source, they produce completely different outcomes. Where hydrogen embrittlement presents a major threat to metals, causing them to become brittle and susceptible to fractures and should avoided wherever feasible, hydrogen wear, if properly managed, can be utilised to enhance machine performance.
Being able to differentiate between the two is essential in order to enhance the longevity and functionality of machinery. Whilst we continue to move towards a future where hydrogen is expected to play a significant role in reaching net-zero carbon emission goals, it is crucial that we address the growing effect that hydrogen has on metals.
We must continue to deepen our understanding of hydrogen wear and hydrogen embrittlement, in order to continue to develop the knowledge and solutions we need to overcome the emerging challenges presented by them. By doing this, we can work towards reducing the waste caused by mechanical failure and towards green energy.
