Effects of chloride ions on corrosion of ductile iron and carbon steel in soil environments

Yarong Song,Peng Zhao,Guangming Jiang,Ying Chen,Yimei Tian

doi:10.1038/s41598-017-07245-1

Yarong Song, Peng Zhao + Show 3 more

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https://doi.org/10.1038/s41598-017-07245-1

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Journal: Scientific Reports	Publication Date: Jul 31, 2017
Citations: 123	License type: open-access

Affiliation: Tianjin University, University of Queensland

Abstract

Chloride is reported to play a significant role in corrosion reactions, products and kinetics of ferrous metals. To enhance the understanding of the effects of soil environments, especially the saline soils with high levels of chloride, on the corrosion of ductile iron and carbon steel, a 3-month corrosion test was carried out by exposing ferrous metals to soils of six chloride concentrations. The surface morphology, rust compositions and corrosion kinetics were comprehensively studied by visual observation, scanning electron microscopy (SEM), X-Ray diffraction (XRD), weight loss, pit depth measurement, linear polarization and electrochemical impedance spectroscopy (EIS) measurements. It showed that chloride ions influenced the characteristics and compositions of rust layers by diverting and participating in corrosion reactions. α-FeOOH, γ-FeOOH and iron oxides were major corrosion products, while β-Fe8O8(OH)8Cl1.35 rather than β-FeOOH was formed when high chloride concentrations were provided. Chloride also suppressed the decreasing of corrosion rates, whereas increased the difficulty in the diffusion process by thickening the rust layers and transforming the rust compositions. Carbon steel is more susceptible to chloride attacks than ductile iron. The corrosion kinetics of ductile iron and carbon steel corresponded with the probabilistic and bilinear model respectively.

Highlights

Corrosion of ferrous metals in soil is one of the major causes of durability problems of water, sewage, oil and gas distribution systems
The surface of ductile iron exposed to soils with different chloride contents gradually transferred from an initial grey-brown appearance to red-brown or yellow-brown after longer exposure (Fig. 2a; Supplementary Fig. S2a)
The effects of chloride ions in saline soils on corrosion of ductile iron and carbon steel were investigated in terms of surface morphology, rust compositions and corrosion kinetics

Summary

Introduction

Corrosion of ferrous metals in soil is one of the major causes of durability problems of water, sewage, oil and gas distribution systems. The electrochemical process is highly influenced by the development of rust oxide layers as well as the film/droplet formation on the metal surface, which are in turn controlled by local environments, i.e. moisture, oxygen, temperature, soluble salts and so forth[7]. The study of those factors influencing the corrosion of ferrous metals in soils has a long and substantial history. Allam et al.[16], focusing on atmospheric situations, revealed that chloride ion only functioned during the corrosion initiation and failed to penetrate through the thick rust layer at later stages. Speaking, previous studies failed to support a clear correlation between the chloride concentration and corrosion rates, especially for the corrosion process in soil environments

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