New Mechanism on Synergistic Effect of Nitrite and Triethanolamine Addition on the Corrosion of Ductile Cast Iron

K T Kim,B T Lim,H B Park,Y S Kim,H Y Chang

doi:10.1155/2016/4935602

Abstract

In general, we compared the different inhibition mechanisms of organic inhibitor with that of anodic inhibitor. When triethanolamine or nitrite was added separately to tap water for inhibiting the corrosion of ductile cast iron, large amounts of inhibitor were needed. This is because the corrosion inhibitors had to overcome the galvanic corrosion that occurs between graphite and matrix. In this work, we investigated the corrosion of ductile cast iron in tap water with/without inhibitors. The corrosion rate was measured using chemical immersion test and electrochemical methods, including anodic polarization test. The inhibited surface was analyzed using EPMA and XPS. Test solutions were analyzed by performing FT-IR measurement. When triethanolamine and nitrite coexisted in tap water, synergistic effect built up, and the inhibition effect wasca.30 times more effective than witnessed with single addition. This work focused on the synergistic effect brought about by nitrite and triethanolamine and its novel mechanism was also proposed.

Highlights

Many research studies have reported about the different kinds of corrosion in nuclear power plants
In a previous study [12], we described the corrosion inhibiting mechanism of nitrite ion on the passivation of carbon steel and ductile cast iron (DCI) in nuclear power plants: the corrosion of carbon steel and DCI is immensely mitigated by the addition of NaNO2
When 5,000 ppm of corrosion inhibitors was added to tap water, the corrosion rates of DCI increased regardless of the concentration of nitrite or TEA

Summary

Introduction

Many research studies have reported about the different kinds of corrosion in nuclear power plants. Nitrogen, or oxygen atoms and organic heterocyclic compounds containing polar groups [6,7,8,9,10] These compounds adsorb and form a covalent bond on the metal surface [11]. They may act as a barrier film by blocking anodic and cathodic active sites or decreasing electroactive species transport rate to or from the metal surface Corrosion inhibitors, such as nitrite, chromate, silicate, molybdate, and hydrazine, are usually used for mitigating problems caused by corrosion. Nitrite ion is required to oxidize the surface of matrix: it is required to passivate the galvanic corroded area Since it is adsorbed on the surface of graphite, a greater amount of corrosion inhibitor has to be added to DCI than to carbon steel. We proposed the mechanism of the synergistic effect elicited by two inhibitors

Experimental Procedure

Corrosion Tests

Results

Discussion

Conclusions