Effect of impurities in steel and ppb level of chloride in bulk water on electrical conductivity of stainless steel's crevice solution in high temperature water

Soma, Yasutaka   ; Komatsu, Atsushi ; Kato, Chiaki   

In this study, the effect of impurities in steel and ppb level of chloride in bulk water on electrical conductivity of stainless steel's crevice solution (K) has been studied. Crevice specimens were made of as-polished Type-316L stainless steel (standard-SS), standard-SS exposed to 60% nitric acid to dissolve sulfur containing inclusions (acid-picked SS), and 316EHP steel in which sulfur and phosphorous concentration was decreased compared to standard-SS (EHP-SS). These crevice specimens were immersed into 561 K, 8 MPa water the K values were measured as a function of time with stepwise increase in dissolved oxygen levels. In addition, effect of 50 ppb Cl added to bulk water was investigated using standard-SS crevice. The all of the standard-SS, acid-picked SS, and 316EHP showed similar K vs time curves. It can be concluded that impurities dissolved from the steel itself do not significantly contribute to the increase of K. The effect of 50 ppb Cl on K vs time curve was obvious because maximum K value became more that 2 times larger than the solution without Cl addition. This indicate that small concentration of impurities can be migrated into the crevice.