Highly alloyed stainless steels have been exposed to natural
chlorinated and chlorine-free seawater at 35 C. Simulated
tube-tubesheet joints, weld joints and galvanic couples with
titanium, 90/10 CuNi and NiAl bronze were tested and
evaluated for corrosion. The corrosion rates of various
anode materials - zinc, aluminium and soft iron - were also
determined. Finally the risk of hydrogen embrittlement of
tubes of ferritic stainless steels and titanium as a
consequence of cathodic protection was studied. An attempt
was also made to explain the cracking mechanism of the
ferritic steels by means of transmission electron
microscopy.
One important conclusion of the project is that chlorinated
seawater is considerably more corrosive to stainless steels
than chlorine-free water, whereas chlorination reduces the
rate of galvanic corrosion of copper materials coupled to
stainless steels. Hydrogen embrittlement of ferritic
stainless steels and titanium as a consequence of cathodic
protection of carbon steel or cast iron in the same
structure can be avoided by strict potentiostatic control of
the applied potential.