Fundamental insights into the stabilisation and chemical degradation of the corrosion product scales

Xiaoqi Yue,Yong Hua,Lei Zhang

doi:10.1038/s41529-021-00152-x

Xiaoqi Yue, Yong Hua + Show 1 more

Open Access

https://doi.org/10.1038/s41529-021-00152-x

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Abstract

Carbonate stability plays a crucial role in clarifying the evolution and protection of the naturally formed corrosion scales on the steel surface in the application of geothermal production. In this paper, the stability of the corrosion scales from both micro and atomic level are studied via a combination of electrochemistry, surface analysis and first-principle calculation. The chemical and physical characterisation of various iron–calcium mixed carbonates are experimentally analysed and results are compared with the first-principle calculation. In the presence of Ca2+, the preferential loss of Ca during the dissolution experiments was observed, the interactions within the crystal weaken where Ca2+ co-precipitation, confirmed by a faster degradation rate for Ca0.51Fe0.49CO3 than FeCO3. This work reveals the degradation and protection performance of the naturally formed carbonate layers and provides insights into understanding the corrosion product stability and chemical breakdown of the corrosion scales.

Highlights

Ensuring engineering integrity while reducing the cost is the eternal topic for all industries such as oil and gas, geothermal, and nuclear
Since Fe atoms were replaced by Ca atoms within the crystal, the unit-cell volume of Ca1−xFexCO3 expends to a looser arrangement than FeCO3, and the unit-cell approaches the volume of CaCO3 as the increase in the mole fraction of Ca within the unit-cell
Combining the first-principle density functional theory (DFT) calculations and experimental validation is an effective way that can be used to elucidate the dissolution of corrosion product scales and protection performance to the steel surface

Summary

Introduction

Ensuring engineering integrity while reducing the cost is the eternal topic for all industries such as oil and gas, geothermal, and nuclear. Carbon steel was widely used in the industry such as oil and gas or geothermal productions based on its low cost and excellent mechanical performance[2,3,4,5,6]. Carbon steel was subject to corrosion in the presence of CO2, resulting in the fast iron dissolution, and followed by the development of the corrosion products gradually covering the surface and effectively reduce the corrosion behaviour[2,7,8]. Iron carbonate (FeCO3), for example, formed on the surface was considered as a natural protective scale to prolong the lifetime of carbon steel[2,7,9,10]. The coverage and compactness for the development of FeCO3 scales were fully discussed in the literature in terms of crystal sizes[13,14,15], orientation[16], solution pH12,17, and other factors[12,18]

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