Internal reversible hydrogen embrittlement [3] can occur after a very small average concentration of hydrogen has been
absorbed from the environment. However, the local concentration of hydrogen may be greater than average bulk values,
because the absorbed hydrogen diffuses into the interface between grains or preferentially in to the grain boundary. The
mechanical effects may leads to loss of ductility to cracking. Internal reversible hydrogen embrittlement has also been
termed slow rate embrittlement and delayed failure. Heavy levels of cold working, especially in parts that are not
subsequently stress relieved, can create residual stress levels that are very near the yield strength of the material. This is an
ideal situation for hydrogen-assisted cracks to propagate.