PSI - Issue 59

Liubomyr Poberezhnyi et al. / Procedia Structural Integrity 59 (2024) 158–166 Liubomyr Poberezhnyi et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 3. OCP kinetic vs Ag/AgCl RE for welded joint zones in 3.5% NaCl solution.

The weld metal consistently maintained the lowest value of the OCP throughout the experiment. By the end of the measurements, it was 37 mV lower than the BM and 70 mV lower than the HAZ. This significant difference could potentially lead to galvanic corrosion, particularly if there are defects in the anti-corrosion coating. Comparing the results of potentiodynamic tests of the base metal and the welded metal (Fig.4), the difference between the corrosion potentials is only 15 mV, which is lower than that observed between the OCPs (37 mV). After 150 min in a 3.5% NaCl solution within the range of – 0.43…– 0.47V, an inflection is observed, indicating the formation of corrosion products on the sample’s working electrode surface. However, after 190 minutes of exposure to the NaCl solution, the inflection disappears, and the corrosion current increases up to 10 times. The reason for this behavior may be the influence of chlorides, which destroy the protective film of oxidation products and facilitate further corrosion.

Fig. 4. Potentiodynamic curves for specimens without isolation (black and red – BM, blue – WM; time after adding 3.5 % NaCl solution). Test performed with scan rate 0.25 mV/s.

Due to the limitations of the methodology used, it was not possible to conduct a potentiodynamic test exclusively for the HAZ. Based on experimentally obtained electrochemical characteristics of welded joint (table.2), the corrosion rate was calculated. Notably, the corrosion rate for the welded metal is 2.5 times greater than of the base metal.