Hydrogen can cause a number of
corrosion problems. Hydrogen embrittlement is a problem with
high-strength steels, titanium, and some other metals. Control is by
eliminating hydrogen from the environment or by the use of resistant
Hydrogen blistering can occur
when hydrogen enters steel as a result of the reduction reaction on a
metal cathode. Single-atom nacent hydrogen atoms then diffuse through
the metal until they meet with another atom, usually at inclusions or
defects in the metal. The resultant diatomic hydrogen molecules are then
too big to migrate and become trapped. Eventually a gas blister builds
up and may split the metal as shown in the picture below.
Hydrogen blistering is
controlled by minimizing corrosion in acidic environments. It is not a
problem in neutral or caustic environments or with high-quality steels
that have low impurity and inclusion levels.
The broken spring above on the
left was brought to the KSC
Materials Laboratory for failure analysis. Examination at high
magnification in the scanning electron microscope (above right) revealed
intergranular cleavage characteristic of hydrogen assisted cracking
(hydrogen embrittlement). The part was zinc plated during refurbishment,
and the hydrogen which entered the metal during the plating process had
not been baked out. A postplating bakeout procedure should be standard
for high strength steels.