What causes hydrogen blistering? Hydrogen ions are reduced
to hydrogen atoms that adsorb on the steel surface. Some of
the hydrogen atoms will diffuse through the steel and
accumulate at hydrogen traps, typically voids around
inclusions. When hydrogen atoms meet in a trap and combine,
they form hydrogen gas (H2) molecules in the trap. The
accumulation hydrogen gas inside the extremely small cavity
will lead to the buildup of excessive internal hydrogen
pressure. At certain times, this internal hydrogen pressure
will become sufficient to cause the steel to blister.
Blisters occur usually in low strength steels (<80ksi
yield strength) and are formed preferentially along
elongated nonmetallic inclusions or laminations in line pipe
steek
