Corrosion handbook
10 06/21
Hydrogen-assisted cracking
Hydrogen-assisted cracking is caused by the diffusion of hydrogen atoms into the
metal. The presence of hydrogen in the lattice weakens the mechanical integrity
of the metal and leads to crack growth and brittle fracture at stress levels below
the yield strength. Like stress corrosion cracking, it can lead to sudden failure of
metal parts without any detectable warning signs.
In common applications, hydrogen damage is usually only relevant for high-
strength hardened steels.
As with SCC, three different conditions must be present at the same time
(see Fig. 10)
• Material (e.g. high strength, hardened steels)
• Stresses (applied or residual)
• Hydrogen source
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Fig. 10: Factors required for the occurrence of hydrogen-assisted cracking.
The source of hydrogen can be a production process such as steel making,
pickling and electrogalvanizing (primary hydrogen-assisted cracking). A
secondary source can be the hydrogen formed during a corrosion process
occuring in-use, which then diffuses into the material (secondary hydrogen-
assisted cracking). During the corrosion process, hydrogen is formed and diffuses
into the material. This hydrogen intake leads to a decrease in the toughness or
ductility of a metal.