The Effect of Hydrogen Evolution on Acidification in Alloy 600 and 304 Stainless Steel Crevices at 288 C

Crevice experiments with 1 mm ID Alloy 600, 304L stainless steel, and platinum tubing have shown that to a large extent, equilibrium thermodynamics controls the mode and degree of crevice corrosion in aqueous systems at 288 C. When crevices enter a potential/pH region of thermodynamic instability for the crevice solution, direct reduction of water or hydrogen ions by the metal competes with macrocell acidification and the hydrogen fugacity strongly influences the degree of acidity which can be attained or maintained. The platinum system undergoes no such thermodynamic transition and acidification ceases only as the corrosion macrocell approaches equilibrium. Platinum crevice behavior indicates an upper limit of 0.60 V (SHE) for the Pt(II) oxide/Pt standard potential at 288 C.