Effect of pH on SCC Behavior of SA516Gr70N Steel in NaCl/Na₂S Solution

Electrochemical behavior, stress corrosion cracking (SCC) and SCC mechanism of SA516Gr70N steel in alkaline sulfide solution with different pH values were studied by electrochemical measurements, U-bend tests, slow strain rate tests (SSRT) in combination with fracture morphology observation with scanning electronic microscopy (SEM). The results show that SA516Gr70N steel exhibited a certain SCC susceptibility in alkaline sulfide solution, and the SCC was controlled by a mixture of anodic dissolution and hydrogen-induced cracking, in which hydrogen-induced cracking played a leading role. With the increase of pH, both the SCC susceptibility and the corrosion rate of SA516Gr70N steel decreased. The increase of pH could accelerate the anodic passivation, and slow down the cathodic hydrogen evolution reaction, thereby inhibiting local anodic dissolution and hydrogen-induced cracking, and reducing the SCC sensitivity of SA516Gr70N steel.