Comment by nwallin

Hydrogen is soluble in most metals. It will just diffuse right into it, like air flowing through a foam filter.

Added bonus: if the metals in question form chemical bonds with hydrogen, (titanium in particular) it will happily do so, even if it's deep inside the metal. The metal will turn very brittle very quickly if it's exposed to molecular hydrogen.

https://en.wikipedia.org/wiki/Hydrogen_damage