Helium, being monatomic, as opposed to hydrogen which is diatomic (H2), is the smallest molecule.
It will migrate through steel.
A steel tank of helium will slowly lose pressure, until it has an internal pressure near the partial pressure of helium in the surrounding environment.
Helium tanks are often made of aluminum wrapped with fiberglass/epoxy to slow this process.
Helium, being monatomic, as opposed to hydrogen which is diatomic (H2), is the smallest molecule. It will migrate through steel. A steel tank of helium will slowly lose pressure, until it has an internal pressure near the partial pressure of helium in the surrounding environment. Helium tanks are often made of aluminum wrapped with fiberglass/epoxy to slow this process.