PSI - Issue 71

Ajay Patel et al. / Procedia Structural Integrity 71 (2025) 196–202

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graphs of conductance and susceptance with time were plotted. Fig. 3 displays the conductance, and the susceptance signature plots for the undamaged mild steel specimen, as well as for various scenarios on days 10, 20, 30, and 40.

Fig. 3. Coupled admittance signature obtained for different days of corrosion exposure of mild steel coupon

3.1 Admittance signatures In Fig. 4(a), a rightward frequency shift is also observed in the signatures regarding the structural frequency. Conductance signatures offer more discernible and promising outcomes in identifying corrosion in mild steel coupons in the piezo resonance frequency range.

(a)

(b)

Fig. 4. Conductance signatures on (a) Structural (b) Piezo resonance frequency range To facilitate clear observations, Fig. 4(b) focuses on the piezo resonance frequency range of 190kHz-210kHz, allowing for a distinct view of signature changes. The plot reveals that as time progresses for the mild steel coupon immersed in the 3.5% NaCl solution, the corrosion intensifies. This is evidenced by a noticeable rightward frequency shift in the conductance and susceptance signatures. However, the conductance signatures exhibited more pronounced and discernible changes than the susceptance signatures. The root-mean-square deviation is a statistical measure used to quantify the amount of variation of data points from their mean value. It is defined in equation (8) (Bansal et al. (2022)). (%) = 100 × √ ∑ ( − 1 ) 2 = 1 ∑ ( 1 ) 2 = 1 (8) 3.2 Root mean square deviation (RMSD):