The investigation of NACE composition influence and testing condition on 20 steel corrosion rate and electrochemical characteristics https://doi.org/10.33108/visnyk_tntu2018.01.058

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Vol. 89 No. 1 (2018)
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Published: 20-03-2018
DOI: https://doi.org/10.33108/visnyk_tntu2018.01.058
Keywords:
corrosion rate, corrosion deep indicator, NACE environment, compromise corrosion potential, corrosion current, limiting diffusion current, Tafel constants

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Zvenomyra Slobodyan
Karpenko Physico-Mechanical Institute of the NAS of Ukraine, Lviv, Ukraine
Lyudmila Mahlatiuk
Karpenko Physico-Mechanical Institute of the NAS of Ukraine, Lviv, Ukraine
Roma Kupovych
Karpenko Physico-Mechanical Institute of the NAS of Ukraine, Lviv, Ukraine

Abstract

The influence of the NACE composition solutions (NACE-1: 3% NaCl + 0.25% CH3COOH; NACE-2: 5% NaCl + 0.5% CH3COOH) on the corrosion rate and the electrochemical characteristics of 20 steel is investigated. It is determined that in the acidic NACE-1 and NACE-2 weakly environments, the test time (2...72) hours increase leads to a significant reduction of 20 steel corrosion rate. This dependence is typical for neutral and weakly acidic environments in which corrosion products are deposited on the metal surface in the form of barrier film.
The difference between 20 steel corrosion rates in both NACE solutions in static and dynamic conditions is most noticeable in 24 hours. The corrosion rate in the flowing environment after 72 hours increases 7-12 times, which is caused by the acceleration of the oxygen transport to the metal surface and the barrier film
blurring.
The role of dissolved oxygen, as a depolarizer, is confirmed by polarization studies and gravimetric tests after oxygen removing. So, after nitrogen lancing of NACE solutions (complete removal of O2 is fixed polarographically), the steel corrosion rate was reduced by 11%.
The differences between the corrosion and electrochemical characteristics of 20 steel in NACE-1 and NACE-2 (icor, id, Еcor, bc та bа) are determined the lower solubility of O2 in solutions with a NaCl concentration greater than 3%.

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Vol. 89 No. 1 (2018)

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