Stress corrosion cracking (SCC) is a failure mechanism that occurs when a material is exposed to a specific corrosive environment while under tensile stress. Even materials that normally perform well can fail unexpectedly due to the combined effect of stress and corrosion.
SCC is particularly dangerous because it can lead to sudden brittle fracture with little visible warning, even when the overall corrosion rate is low. It is a critical consideration in pipelines, pressure vessels, marine structures and chemical processing equipment.
Stress Corrosion is evidenced when the metal strength
loss resulting from the combined stress and corrosion
is greater than the effects of stress and corrosion
acting separately. The magnitude of the
combined effect is a measure of the susceptibility of
the material to stress corrosion.
Stress corrosion is generally evidenced as cracks
giving an appearance of brittleness in a material
which is otherwise has normal ductile
properties. The cracks may follow
intergranular paths which grow at relatively slow
velocities. If the load is constant
during the period of crack growth the cracks will
eventually reach a critical size to result in
material failure.
Some combinations of environment and material known
to cause stress corrosion are listed below.
| Material | Environment known to cause stress corrosion |
| Al alloys | Moist air, Sea Water, Chloride, Bromide and iodide solutions |
| Cu alloys | Ammonia solutions and vapours, amines, moist SO2, solutions of acetates, citrates formates, tartrates, nitrites and sodium hydroxide. |
| Ni alloys | Hydroxide solutions and hydrofluoric acid vapour |
| Ti alloys | Solutions of chlorides, bromides, and iodides, liquid N2O4, methanolic solutions and dry salts and elevated temperatures |
| Low strength ferritic steels | Solutions of hydroxides, nitrates, carbonates, phosphates, molybdates, acetates, cyanides, and liquid ammonia |
| High Strength ferritic steels | Moist air, water, aqueous and organic solutions. Susceptibility increases with increasing stregnth of materials |
| Stainless Steels | Solutions of chlorides , fluorides, iodides, bromides, sulphates , Phosphates, nitrates and polythionic acids |
Stress corrosion does not normally occur in
conditions in which the metal suffers from serious
general corrosion. It is therefore often
not noticed resulting in fracture without
warning.
The best methods of eliminating or minimising this problem are listed below:
Stress corrosion cracking (SCC) is a failure mechanism caused by the combined effect of tensile stress and a corrosive environment.
Common susceptible materials include stainless steels, aluminium alloys, copper alloys and high-strength steels under specific environmental conditions.
SCC occurs when tensile stress, a corrosive environment and a susceptible material are present simultaneously.
It can cause sudden brittle failure without significant general corrosion or visible warning signs.
Prevention includes material selection, stress reduction, coatings, and controlling environmental conditions.