Effects of Corrosion Potential, Dissolved Oxygen, and Chloride on the Stress Corrosion Cracking Susceptibility of a 316NG Stainless Steel Weld Joint

The effects of applied potential, dissolved oxygen (DO), and chloride ion (Cl⁻) on the stress corrosion cracking (SCC) susceptibility of a 316NG weld joint and sensitized 316NG stainless steel (SS) were studied. Meanwhile, corrosion potential related SCC mechanisms in Cl⁻-contaminated water and both the feasibility of potentiostatic control of the potential and slow strain rate tensile (SSRT) method on SCC behavior assessment were discussed. Results showed that the heat-affected zone  (HAZ) and weld region adjacent to the fusion line were sensitive to SCC at high corrosion potential, which was attributed to the high residual strain in this region. The SCC susceptibility of weld joint and base metal in Cl⁻-contaminated water increased dramatically when the corrosion potential reached the pitting potential (E_pit). When the applied potential E was below E_pit, both annealed and sensitized specimens showed mechanical-controlled ductile cracking. When the corrosion potential was above E_pit, the annealed specimen showed pitting-initiated transgranular cracking, while the sensitized specimen showed pitting-initiated intergranular cracking. The detrimental effects of DO and Cl⁻ could be underestimated by the SSRT method for materials with lower SCC susceptibility. Potentiostatic control of the potentials during SSRT test was more aggressive than controlling the DO conditions, thus more effective for detecting cracking for SCC-resistant materials.