Hydrogen embrittlement represents an important issue with far-reaching implications across several industries and sectors. With the potential to cause sudden and catastrophic failures in critical components, its impact reaches diverse fields including aerospace and defense, the energy sector or the automotive sector, among others.
In light of the importance of addressing hydrogen cracking, we present a short guide for understanding this issue and the key strategies for preventing it.
What is hydrogen embrittlement?
The term describes the process by which hydrogen enters and diffuses into certain metals, causing them to become brittle and fracture.
Particularly harming on high-strength steels and other alloys, the phenomenon is behind significant reductions in metals’ ductility and load-bearing capacity, which ultimately makes them susceptible to sudden and catastrophic failure.
How to identify it?
A visual inspection might reveal several signs of hydrogen cracking, including the formation of cracks and fractures in areas of high stress, or changes in texture or appearance in surfaces.
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Additionally, mechanical testing techniques can be performed to confirm the presence of hydrogen embrittlement, including tensile tests (which measure ductility and tensile strength), fatigue tests, or tests aimed at assessing the material’s resistance to crack propagation.Moreover, microscopic analysis, non-destructive testing (such as ultrasonic or X-ray tests) and certain electrochemical techniques (including hydrogen permeation testing) can all expose potential embrittlement issues.
Causes of hydrogen embrittlement
Certain types of corrosion
Corrosion is a gradual degradation of materials due to chemical reactions, and certain forms of it may lead to hydrogen embrittlement (HE) by allowing the introduction of this element into the metal. These include:
- Galvanic corrosion: caused by two dissimilar metals being in electrical contact in a corrosive electrolyte. Hydrogen gas might be produced at the cathodic surface and then absorbed by the metal, leading to embrittlement.
- Pitting corrosion: a type of localized corrosion that leads to the formation of small pits or holes, which can act as initiation sites for hydrogen absorption and embrittlement.
- Crevice corrosion: typically takes place in confined spaces that facilitate more aggressive local chemistry, and translates localized hydrogen generation and absorption, potentially leading to hydrogen cracking.
The result of these and other types of corrosion is typically referred to as Stress-Corrosion Cracking (SCC) or Hydrogen-Assisted Stress Corrosion Cracking (HASCC).
Hydrogen absorption processes
Apart from corrosion, other electrochemical reactions such as electroplating or cathodic protection can lead to hydrogen being introduced into metals and then promoting embrittlement.
At the same time, processes at high temperatures (such as welding or casting) can involve hydrogen-rich environments where the element dissolves and becomes trapped within the structure after the metal cools.
Mechanical stresses that cause dislocations and micro-cracks, leading to pathways for hydrogen absorption. And so do certain chemical environments and reactions, such as acidic solutions or environments containing hydrogen sulfide (H₂S).
Environmental factors
Corrosive environments, moisture or high temperatures all represent potential causes behind the increase in hydrogen generation and absorption.
Impact of hydrogen embrittlement on material structure
- Reduced ductility
- Structural degradation
- Increased susceptibility to fracture
- Weakens atomic bonds (Hydrogen-enhanced decohesion or HEDE)
- Generates microstructural alterations
- Increases mobility of dislocations, leading to plastic deformation (Hydrogen-enhanced Localized Plasticity or HELP)
- Causes failure in critical components
Prevention of hydrogen embrittlement
Key mitigation strategies
- Materials that are less susceptible to hydrogen embrittlement should be chosen in the design phase. This includes austenitic stainless steels and certain nickel-based alloys, among others
- The application of protective coatings (nickel, cadmium or zinc plating) should be considered in order to act as surface barriers
- Limiting exposure to hydrogen-rich or corrosive environments
- Implementing hydrogen removal strategies, including baking and stress-relief annealing
Preventive technologies and methods
Cathodic protection has been successfully employed to prevent corrosion and hydrogen generation, and so have hydrogen barriers coatings.
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At the same time, the use of Non-Destructive Testing (NDT) facilitates the detection of early signs of hydrogen embrittlement before catastrophic failure occurs. Preventive environmental control policies also provide effective tools to reduce the rate of hydrogen production and thus minimize risk of embrittlement.
Design considerations
There are a number of design strategies that help minimize residual and operational stresses. For instance, it’s advisable to avoid sharp corners and sudden changes in cross-section, as these areas are known to concentrate stress and facilitate crack initiation. Regarding the choice of materials, thicker sections are advisable (as thinner sections are more susceptible to embrittlement).
Adopting a preventive perspective is key here, including the incorporation of redundancy in critical components to ensure that a single failure does not lead to catastrophic consequences.
Design must also facilitate easy inspection and maintenance processes, so that early signs of hydrogen cracking can be detected.
Materials processing
All practices on materials should take hydrogen embrittlement into consideration, from welding practices to thermal treatments, so that the introduction of hydrogen can be minimized.
Additionally, certain processes may benefit from performing them in a vacuum or under inert gas atmospheres, thus preventing hydrogen exposure.
Benefits of prevention
Increased durability and resistance of materials
Components maintain their mechanical properties and performance for longer, including their strength, ductility, and toughness. It’s a fundamental strategy for preventing premature failure.
Reduction of structural fault risks
The likelihood of micro-cracks forming and propagating within the material is reduced, including high-stress applications, where crack initiation can lead to catastrophic failure. The fight against hydrogen embrittlement is thus synonymous with improved structural integrity and a lower need for repairs and unplanned downtime.
Safety and reliability
Preventing hydrogen cracking can be a matter of life and death in industries such as aerospace, automotive, nuclear, and oil & gas. But that’s not all: successful protocols against this phenomenon ensure that materials perform predictably and reliably under all conditions, and help companies comply with certain stringent standards and regulations regarding material performance and safety.
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Cryospain: your ally against hydrogen embrittlement
As a leading company specializing in cryogenic engineering, at Cryospain we offer top expertise and services to help companies prevent hydrogen embrittlement (HE).
We are well-versed in managing hydrogen-related issues across a number of processes: from expert material selection and testing to successful thermal management. As such, we put our expertise at the service of companies looking to avoid hydrogen cracking in their processes and the serious consequences related to it.
Want to find out more about successful strategies to avoid hydrogen embrittlement and design an ad-hoc protocol that matches your needs? Get in touch with us and discover how we can help you.
