Stress Corrosion Cracking Case Study
1. Introduction of Stress Corrosion Cracking
Stress Corrosion Cracking (SCC) is the growth of cracks with a under the combined
effects of a static stress and a specific chemical environment. All SCC failures
involve a macroscopic brittle performance, and the ductility of the material is reduced.
It is universally acknowledged that there is no single mechanism for stress corrosion
cracking (Ford, 1984). Stress corrosion spectrum (Parkins, 1972) demonstrates the
significant alloy-environment the mechanism involved. Stress corrosion spectrum is
shown as Figure 1.
Figure.1 Stress corrosion spectrum
Stress Corrosion Cracking contains two main stages: …show more content…
Figure 2 Dislocation movement in SCC
As shown in Figure 2 the “step” formed after slip is an active site for the initiation of a stress-concentration pit. And pits are important for cracks generation. The pit formation is
precursor to stress corrosion cracking. If some pits are formed in proper condition,
growth of crack takes place and propagation happens.
Chu et al. (2004) had demonstrated microcracks during initiation. In Chu’s experiment
X-65 pipeline steel samples were exposed to synthetic soil environment for 61 days and
111 days, and the morphology of two samples are shown in Figure 3. It was concluded
that majority of initiated microcracks were generated from pits at metallurgical
discontinuous points like grain boundaries and banded phases.
Figure 3 SEM images for 61 days exposure sample (a) and 111 days exposure
In practice, initiation is negligible, and few efforts are made to inhibit initiation.
Because in fabrication defects are enough for initiation sites, which means in …show more content…
Prevention of Stress Corrosion Cracking
There are three key factors for stress corrosion cracking: stress, environment and
susceptible material. So, the prevention of SCC includes elimination of one of three
factors: remove stress, avoid the susceptible environment or modify microstructure of
2.1 Remove stress
In most cases it is impossible to remove the working stress of components,
which components are designed to bear. But reducing the residual stress is an
effective method to control stress corrosion cracking. Usually annealing is
adapted to relieve residual stress inside, but annealing is not effective for large
components to relive residual stress, sometimes unexpected phases form during
Another way to remove stress is avoid stress concentrators like notches, which
can prevent stress concentration and reduce stress inside.
2.2 Avoid the susceptible environment Controlling environment is usually not possible to prevent SCC. The methods to
control the environment in service includes mixing inhibitors, modifying the
electrode potential of the alloy, and isolating the alloy by coatings.
2.3 Modify microstructure of