Surface oxide layer on crevice portion of stainless steel in high temperature high pressure water

Soma, Yasutaka   ; Kato, Chiaki   ; Yamamoto, Masahiro 

Surface oxide layers on crevice of 316L stainless steels in high temperature and high pressure water containing 2ppm dissolved oxygen (DO) were investigated by using SEM, STEM, and Raman spectroscopy. Effects of distance from open-mouse of the crevices (Y) and corresponding DO concentration on surface oxide layer were studied. Depending on the Y value, four different regions with different surface oxide layer were observed if the crevice were sufficiently narrow. The oxide layers were consisted of inner and outer oxide layer at the all regions. Change in composition of outer oxide layer clearly showed that the DO concentration decreased with increasing Y value. However, thickness of the inner oxide layer showed maximum value at certain Y value and then, decreased with the Y value. This behavior considered to be brought by differences in the DO concentration, ionic concentration and pH.