How does 'Pitting Corrosion' lead to the failure of 17-7PH wave springs in marine environments?

Pitting corrosion is a localized form of corrosion that creates small holes or 'pits' in the material surface. In 17-7PH stainless steel, these pits occur when the passive film breaks down in the presence of chloride ions. Although the overall mass loss is negligible, the pits act as extreme stress concentrators. The stress intensity factor at a pit of depth $a$ can be approximated as $K_I = 1.12 \cdot \sigma \cdot \sqrt{\pi \cdot a}$. Once $K_I$ reaches the fracture toughness $K_{Ic}$ of the material, a crack propagates rapidly. Since wave springs are under constant or cyclic stress, pitting often transitions directly into stress corrosion cracking (SCC) or corrosion fatigue, leading to sudden, catastrophic failure without prior warning.