A “Toolbox” for Forensic Engineers

Materials in Distress 57
Figure 2.20 Stress corrosion cracking in silver-plated brass goblet.
Most of the higher strength engineering metals may suffer stress corrosion
failure if the conditions are right. Stainless steels and aluminum
alloys are susceptible in chloride (Cl – ) environments. One obvious remedy
for all is to eliminate or significantly reduce the level of residual stress
resulting from forming or welding processes. Hydrogen is also a troublesome
element in this respect as it is believed it may form molecular hydrogen
within the crack region and extend the crack by causing an internal
gas pressure, or the formation of solid hydrides within the microstructure
that can also subject the crack to additional mechanical stress. These
stresses may extend the cracks themselves or enhance the corrosion mechanism
as before. Examples of both these types of failure are discussed in
later chapters.