Moiré based method for real-time crevice corrosion monitoring

Abstract

A novel real-time technique was developed to monitor localized corrosion occurring over a metal surface. It is an optical method based on the Moiré technique that has undergone further improvements and fine tuning for more accurate measurements. Upon testing, good agreements were obtained with the microscopically determined penetration depth. Application for this technique was demonstrated through real-time monitoring of crevice corrosion activity occurring on the surface of AISI 316 (UNS S31600) stainless steel immersed in 3% NaCl at 60 C. The crevice was an artificial clear glass/metal crevice with a gap thickness of 5 lm. Based on the findings of these results it was shown that this method can effectively and accurately be used to monitor crevice corrosion.

Visualization of pH and pCl Distributions: Initiation and Propagation Criteria for Crevice Corrosion of Stainless Steel

“…13 Metastable (micro) pits are sometimes observed at the initial stage of crevice corrosion, particularly in stainless steels. [14][15][16][17][18][19][20][21][22] Oldfield and Sutton found the formation of micro pits just before the initiation of the crevice corrosion for type 316 stainless steel in a 1 M NaCl solution. 14 Kehler and Scully demonstrated a strong correlation between the event rates for metastable pitting and the crevice corrosion resistance of alloys 625 and 22.…”

Sudden pH and Cl− Concentration Changes during the Crevice Corrosion of Type 430 Stainless Steel

“…The initiation mechanism of the crevice corrosion of stainless steels is roughly classified into three types, namely, the passive dissolution, [4][5][6][7] IR-drop, [8][9][10][11][12] and metastable pitting mechanisms. [13][14][15][16][17][18][19][20][21][22][23][24] In the passive dissolution mechanism, which was described by Oldfield and Sutton et al, [4][5][6][7] H + accumulates inside the crevice with time, which causes depassivation, followed by active dissolution of the steel surface. In the IR-drop mechanism, which was described by Pickering et al, [8][9][10][11][12] when the electrode potential difference in a crevice mouth and a deep position becomes sufficiently large, the lower electrode potential inside the crevice reduces the stability of passivity.…”

“…In the IR-drop mechanism, which was described by Pickering et al, [8][9][10][11][12] when the electrode potential difference in a crevice mouth and a deep position becomes sufficiently large, the lower electrode potential inside the crevice reduces the stability of passivity. In the metastable pitting mechanism, [13][14][15][16][17][18][19][20][21][22][23][24] Stockert and Böhni et al suggested that crevice geometry stabilizes the initiation of metastable pits inside a crevice, and that the corrosion morphology changes from pitting to general dissolution inside the crevice. 15 Sulfide inclusions also act as the initiation sites of metastable pits inside the crevices.…”