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Carbon and alloy steels is often categorized by a range of traits which include
composition, microstructure, strength degree, materials processing, and heat treatment [1]. The
carbon and alloy steel categories chosen to the Technical Reference on Hydrogen
Compatibility of Components are based on qualities of the steels at the same time as accessible information. In
this chapter, the steels are distinguished from the major alloying elements, i.e., carbon and
manganese. Information on the compatibility of carbon steels with hydrogen gasoline exist mostly for your
following alloys: A106 Gr. B, A106 Gr. C, SA 105, and also the 10xx
steels. Additionally, a considerable quantity of data has become produced for that API 5L steels, grades
X42 to X80. Considering that a full range of properties in hydrogen gasoline isn't offered for every single steel, data
for all carbon steels are presented in this chapter. Though plain carbon ferritic steels exhibit
some metallurgical differences, the basic trends inside the information are expected to apply normally to this
class of steels.

Carbon steels are eye-catching structural materials in applications like pipelines since the
steels could be formed and welded, and adequate mechanical properties might be achieved through
normalizing heat treatment options or hot rolling. The API 5L steels could include additional alloying
elements, for example little quantities of niobium and vanadium. These "microalloying" additions as
well as processing via managed rolling impart a mixture of elevated power and
improved low-temperature fracture resistance.
In spite of the desirable properties of carbon steels, these components has to be utilised judiciously in
structures exposed to hydrogen gas. Hydrogen fuel degrades the tensile ductility of carbon steels,
especially within the presence of strain concentrations. Additionally, hydrogen gas lowers fracture
toughness, and specific metallurgical situations can render the steels vulnerable to crack
extension below static loading. Hydrogen gasoline also accelerates fatigue crack development, even at
relatively reduced hydrogen fuel partial pressures, suggesting that little fractions of hydrogen in gasoline
blends has to be thought of in fatigue life assessments. The severity of those manifestations of
hydrogen embrittlement will depend on mechanical, environmental, and materials variables.
Variables that influence behavior in hydrogen fuel include things like loading rate, load cycle frequency, gas
pressure, gas composition, as well as the presence of welds. Manage over these variables may permit
carbon steels to become utilized securely in hydrogen gasoline environments. For example, limiting the
magnitude and frequency of load cycling can boost the compatibility of carbon steels with
hydrogen fuel.
This chapter presents a selection of information for carbon steels in hydrogen fuel, including tensile and
crack development properties. The crack growth data emphasize fracture mechanics properties, given that
pipeline design can benefit from defect-tolerant style ideas, particularly for hydrogen
environments.