HIGHLIGHTS
- Exposure to hydrogen can compromise the integrity of
certain metals. - Hydrogen embrittlement can cause hydrogen leaks and
subsequent fires. - Proper material selection and design measures can
reduce and mitigate risks associated with hydrogen
embrittlement.
Hydrogen embrittlement is a critical concern in industries
utilizing hydrogen, posing significant safety concerns if not
adequately addressed. Incompatible materials can lead to leaks and
hydrogen fires or explosions. In this article, we’ll present a
high-level overview of embrittlement, focusing on hazards and
mitigation strategies.
What Is Hydrogen Embrittlement?
Hydrogen embrittlement is a phenomenon where metals become
brittle and susceptible to cracking with exposure to pressurized
hydrogen.
Although a highly complex and nuanced topic, the gist is this:
In pressurized hydrogen environments, hydrogen atoms can dissociate
into individual hydrogen ions at the surface of the metal and
migrate into the bulk metal.
Hydrogen atoms are incredibly small — the smallest on the
periodic table of elements. Once in the bulk metal matrix, hydrogen
degrades the material strength by causing discontinuities at grain
boundaries, inclusions, and dislocations, recombining into
molecular hydrogen in voids, assisting with crack growth, and other
internal effects. The result is a reduction in the ductility and
strength of the material.
A microscopic view of
hydrogen embrittlement of Inconel. Image from Iannuzzi, Mariano
& Barnoush, Afrooz & Johnsen, Roy. (2017). Materials and
Corrosion Trends In Offshore and Subsea Oil and Gas
Production.
Although some metals are more susceptible than others, the
impact of hydrogen on metals is also a function of exposure
environment (pressure, temperature, and gas composition) as well as
stress. Without the metal being in a stress state, environmental
embrittlement will not propagate cracks, even if the metal is
embrittled.
Further reading: for an in-depth look at the
science behind hydrogen embrittlement, see this article by
H2Tools.
Hydrogen-induced
cracking. Photo by CEphoto, Uwe Aranas.
Hazards Of Hydrogen Embrittlement
Embrittlement poses a severe risk in industries utilizing
hydrogen, such as energy, manufacturing, transportation, and
aerospace. When a metal’s integrity is compromised it can lead
to leaks and combustible mixtures, which can result in a fire or
explosion.
- Material Integrity Compromise: Hydrogen
embrittlement compromises the integrity of metals, potentially
leading to catastrophic failures. This is a critical concern since
the reliability of components is paramount to hydrogen combustion
safety. - Leakage Risks: Incompatible materials can
develop cracks due to hydrogen embrittlement, resulting in the
potential for leaks. Hydrogen is highly flammable when mixed with
oxygen; even small leaks can pose significant safety risks. - Hydrogen Fires: Where hydrogen leaks and
combines with air or oxygen, it can create an easily ignitable
mixture which can lead to fires or explosions. These can be highly
destructive and pose severe risks to personnel, equipment, and
facilities.
Case Example: Hydrogen Bus Refueling Station Failure
In 2012, hydrogen embrittlement led to a pressure relief valve
failure at the AC Transit Facility in Emeryville, CA, a refueling
station for hydrogen-powered buses.
Hydrogen refueling
station in Emeryville, California. Image courtesy of wlbutler.com.
Sandia National Laboratory (Livermore, CA) conducted an
extensive metallurgical analysis of the failed valve. It concluded
that incompatible materials (440C Martensitic stainless steel) and
deviations in the manufacturing process led to hydrogen
embrittlement and, ultimately, the failure of a PRD nozzle.
Comparison of an exemplar
nozzle with the failed PRD nozzle. Image from Harris, San
Marchi Sandia Report SAND2012-8642 Investigation
of the Hydrogen Release Incident at the AC Transit Emeryville
Facility.
Fortunately, backup venting systems functioned properly, and no
one was harmed in the subsequent hydrogen release, but the incident
caused the precautionary evacuation of a one-block radius. Like
many hydrogen failures, it caused understandable concern and
damaged the public perception of this emerging technology.
Mitigating Hydrogen Embrittlement Risks
Over more than 35 years, WHA International has investigated
fires, explosions, and incidents involving hydrogen. Hydrogen
embrittlement is one of the hazards evaluated in WHA’s Hydrogen Combustion Risk Analysis (HCRA)
services. This systematic process aims to identify potential risks
in hydrogen systems and recommend design changes to enhance safety.
Key mitigation strategies include:
- Material compatibility assessment: Conduct
thorough assessments to identify metals susceptible to hydrogen
embrittlement. WHA recommends the use of test data to assess a
metals’ vulnerability to embrittlement. Implementing compatible
materials is crucial for preventing embrittlement-related failures
as well as leaks. - Design modifications: Implement design
modifications to mitigate the risks associated with hydrogen
embrittlement. This may include changes to materials, increasing
the factor of safety, making adjustments to the exposure
environment, and suggesting component and system design
modifications. - Reducing the probability of ignition: Identify
potential ignition sources in and around a hydrogen system. Since
flammable mixtures of hydrogen and are or oxygen need very little
energy to ignite, completely eliminating the ignition risk is not
always possible. Therefore, mitigation strategies are focused on
reducing the probability of ignition and the likelihood of hydrogen
mixing with an oxidizer to create flammable mixtures. - Reducing the consequence of ignition: Design
best practices also include fail-safe measures like automated
shutoff systems, venting systems, ventilation, and barriers to
protect personnel and nearby equipment in case of ignition.
Further reading: learn more about WHA’s
Hydrogen Fire Risk Management Philosophy.
In 2019, a hydrogen tank
explosion killed two people and injured six in Gangneung, South
Korea. Courtesy of Gangwon Fire HeadQuarters. Though this incident
is not attributed to hydrogen embrittlement, it demonstrates the
explosive potential of hydrogen leaks.
Protect Your Personnel And Equipment Around Hydrogen
Hydrogen embrittlement is a serious concern that demands
attention in industries utilizing hydrogen. By understanding the
hazards associated with incompatible materials and implementing
mitigation strategies, companies can enhance the safety of their
hydrogen systems.
The content of this article is intended to provide a general
guide to the subject matter. Specialist advice should be sought
about your specific circumstances.
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