PSI - Issue 36

Tetyana Kalyn et al. / Procedia Structural Integrity 36 (2022) 313–317 T. Kalyn, L. Poberezhny, P. Popovych et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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Polarization curves recorded for the 17H1S steel in the NS4 solution without and with adding AA at different concentrations are shown In Fig. 2. Increasing inhibitor concentration leads to deacreasing in corrosion current density. The highest effect of inhibition was revealed at concentration of AA of 1.0 g/l, which is in a agreemebt with the gravimetric results (Table 2).

Fig. 2. Polarization curves for the 17H1S steel in the NS4 medium without and with addition of AA.

It is known that AA forms complex compounds with metals through the – OH groups of the lactone ring. Sekine et al. (1988) discussed the formation of complexes – water-soluble chelates of Fe (II), which slightly reduced the inhibitory effect at increasing the concentration of more than 200 ppm AA. The pH of the NS4 test solution without AA was 8.5-8.6, but the pH was decreased with increasing AA concentration as shown in Table 3. According to Ferreira et al (2004), pH influenced on forms of AA, which can exist in non-ionized and ionized forms.

Table 3. The pH value of the NS4 solution in the presence of AA AA concentration. g/l pH 0.2 7.45 0.4 7.36 1.0 7.02 1.5 6.61

According to Ferreira et al. (2004) AA in pH range of 6.61 … 7.75 is almost completely converted into monoascorbate anions, which are easily oxidized to dehydroascorbic acid and it hydrolyzes to 2.3-diketogluconic acid at pH>7. Therefore, it can be assumed that inhibitory protection of the steel in the test solution is associated with adsorbtaion of dehydroascorbic acid (at lower concentrations of AA) or unoxidized ascorbate ions (at higher concentrations of AA) depending on AA concentration. 4. Сonclusions The AA inhibited corrosion of the 17H1S steel in the near-neutral NS4 solution. The results of electrochemical and weight loss measurements showed that AA can be used as corrosion inhibitor for the 17H1S pipeline steel in the NS4 solution simulating soil environment. The maximum corrosion protection degree of 88% was revealed at AA concentration of 1 g/l. Acknowledgements The research was implemented with the grant support of the National Research Fund of Ukraine (project № 2020.01/0417).