Update README.md

Multiple grades of stainless steel are already well proven
for this type of environment, and are listed in technical
standards such as the ASME Boiler and Pressure Vessel Code,
and EN 13445-2. What these have in common is that they
have an austenitic microstructure that enables them to
operate at temperatures of as low as -273°C.
Resisting hydrogen embrittlement
The other big issue is the potential for hydrogen
embrittlement of steels and metals in general. Sensitivity
to hydrogen embrittlement varies, depending on the
material. High-strength steel, titanium and aluminium
alloys are all vulnerable to hydrogen embrittlement.
Sensitivity also varies between different types of stainless
steel.
Austenitic stainless steels have higher resistance to
hydrogen embrittlement than ferritic and martensitic
alloys, as hydrogen’s rate of diffusion through the material
is low. Therefore, along with the low-temperature ductility,
this makes austenitic stainless steel a good option for
hydrogen storage.
The risk of hydrogen embrittlement increases with the
pressure. There is little risk of hydrogen embrittlement at
low pressures. As such, most stainless steels are suitable
for storing or transporting hydrogen when pressure is not
excessive.
However, as the pressure rises, so does the force that
pushes atoms into the internal surface of a tank. As a
result, it becomes more likely that hydrogen atoms will
diffuse into the steel matrix of tank walls or the body
of pipework. As austenitic stainless steel has a lower
diffusivity of hydrogen than other stainless steel types,
it is the preferred material – especially in many storage
applications that operate in the range of 200 bar, with
some sites working at up to 800 bar.
Alloying elements in the stainless steel also play a role
in reducing susceptibility to hydrogen embrittlement.
The industry has a rule of thumb that the most suitable
materials are low-carbon austenitic stainless steels with
around 12 – 13% nickel, and 2 – 3% molybdenum. This
combination of nickel and molybdenum has been found
to resist the diffusion of hydrogen, making it particularly
attractive for hydrogen storage and transport tanks as the
industry develops.
This is a current area of research for Outokumpu’s
metallurgists who are working on a long-term project that
has the goal to fully understand how the alloying elements
influence how hydrogen diffuses into the material, and
eventually find the optimum alloy to avoid hydrogen
embrittlement.
Storage and transport tanks
The storage of compressed hydrogen will require robust
tanks. The basic construction of these will be based on a
tank or cylinder with an inner and outer shell, with the
inner shell containing the hydrogen and the outer having
the purpose of resisting the internal pressure.
Four design options are available:
y Type I with walls made from metal alloys that have the
capability to contain up to 200 bar.
y Type II tanks with a metal inner skin and an outer
that is cylindrically covered with resin-soaked glass or
carbon fibres to provide capability of withstanding up to
1000 bar.
y Type III uses a metal liner fully covered by a carbon fibre
outer, which has the capability of withstanding up to
350 or 700 bar, which is the standard for vehicles.

README.md

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+datasets:
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+language:
+- en
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+pipeline_tag: question-answering
+---