Environmental Engineering Reference
In-Depth Information
Figure 3.34
Stress-time to fracture relationship for stress corrosion cracking of 0.8%
C steel in sodium acetate and acetic acid buffer solution showing the threshold stress.
The cause of SCC in this case has been the residual stress developed due to
riveting operations and concentrated sodium hydroxide present as corrosive in
these areas. Many alloy-environment combinations leading to SCC have been
discovered with the passage of time. It is a matter of concern that almost all alloys
of engineering interest are susceptible to this type of catastrophic degradation in
some environment or other, the only silver lining being that all alloys are not
susceptible to SCC in all environments. There is some specificity in this regard.
Earlier, the pure metals were considered to be immune to SCC. Though pure
metals have been induced to crack under severe test conditions in the laboratory,
practical instances are absent. On the other hand, their alloys show ready and
rapid cracking. A list of alloy-environment systems exhibiting SCC is presented
in Table 3.3. It should, however, be remembered that the table is not exhaustive;
newer combinations and newer environments causing SCC in a particular alloy
are being regularly discovered and are being added to this list. It is, therefore,
