The Nickel Advantage - Nickel in Stainless Steel - Eurometaux

Chapter 2
Corrosion Resistance
Nickel contributes
to corrosion “
resistance.
”
Stress Corrosion Cracking There are many different types of stress corrosion cracking
(SCC). Austenitic stainless steels have very good stress corrosion cracking reistance in
hydrogen sulphide environments, such as are found in the natural gas sector. Austenitic
stainless steels and more recently duplex stainless steels have shown excellent long term
performance and guidelines for their use can be found in standards such as NACE
MR0175/ISO 15156.
Chloride stress corrosion cracking has been studied for years, and many people are familiar
with the “Copson Curve,” derived from testing in aggressive boiling magnesium chloride. It
has shown that the ferritic stainless steels without a nickel addition are superior to the
standard stainless steels with 6-12% nickel. Alloys with more than 45% nickel were found
to be virtually immune to cracking in magnesium chloride. In practice, most other chloride
solutions are far less aggressive than the magnesium chloride, and while grades such as 304
and 316L are generally avoided, the stainless alloys with 6% molybdenum have sufficient
resistance in most cases, as do the duplex stainless steels.
Figure 10:
Copson Curve – Effect of nickel on
the susceptibility of stainless steels
to chloride stress corrosion cracking
in boiling magnesium chloride.
1000
Cracking
Breaking time (hr)
100
10
Minimum time to cracking
No cracking
Innovative use of stainless
steel for solar reflectance
and energy savings
Photo courtesy of:
Rafael Vinoly Architects PD
[Pittsburgh convention centre]
1
Indicates
commercial wire
Did not crack in
30 days
0 20 40 60 80
Nickel (%)
PAGE 26
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