Fig. 1 Schematic diagram of the corrosion products causing bright speckles in 3.5 wt% NaCl solution

Fig. 2 Schematic diagram of the ESPI test system

Fig. 3 Current-time curve of 304 stainless steel at 0.35 V (SCE) polarization in 3.5 wt% NaCl solution, pits a-h indicate the occurrence time of speckles A-H (as shown in the following Fig. 4) and the corresponding current

Fig. 4 ESPI images collected at different time when speckles occurred: a 14 s; b 27 s; c 41 s; d 45 s; e 52 s; f 72 s; g 90 s; h102 s

Fig. 5 Calculated pitting current of a single pit at 0.35 V (SCE) polarization in 3.5 wt% NaCl solution

Fig. 6 SEM images of pits Ap a, Bp b, Cp c, Dp d, Ep e, Fp f, Gp g, Hp h, which correspond to the speckles A-H in Fig. 4

Fig. 7 Geometric parameters of pits with different growth time: a length and width of pit mouth; b area of pit mouth

Fig. 8 Calculated growth rate of a pit mouth at different time: a growth rate of pit mouth length and width; b growth rate of pit mouth area

Fig. 9 Calculated pitting current density of a single stable pit at 0.35 V (SCE) polarization in 3.5 wt% NaCl solution

Fig. 10 SEM image of pit mouth lace cover at 0.35 V (SCE) polarization in 3.5 wt% NaCl solution