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Corrosion Science 50 (2008) 2456–2464

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Corrosion Science
journal homepage: www.elsevier.com/locate/corsci

The effect of pre-corrosion and steel microstructure on inhibitor performance in
CO2 corrosion
L.D. Paolinelli a, T. Pérez b, S.N. Simison a,*
a
b

División Corrosión – INTEMA, UNMdP, Ave. Juan B. Justo 4302, B7608FDQ, Mar del Plata,Argentina
Centro de Investigaciones Industriales (CINI), Simini 250, 2804 Campana, Argentina

article

info

Article history:
Received 4 June 2007
Accepted 17 June 2008
Available online 4 July 2008
Keywords:
A. Carbon steel
B. EIS
C. CO2 corrosion
C. Steel microstructure
C. Imidazolines

abstract
The importance of chemical composition and microstructure on CO2 corrosion of carbonand low alloy
steels has been widely recognized, still contradictory results can be found in the literature. The aim of
this work is to assess the relationship between microstructure, surface condition and inhibitor efficiency
in CO2 corrosion. A C–Mn steel with two different microstructures was tested in a deoxygenated 5% wt.
NaCl solution saturated with CO2 at 40 °C, pH 6. A commercialimidazoline-based inhibitor was added
after different pre-corrosion periods. The results obtained showed that pre-corrosion decreases the inhibitor efficiency, but that its impact is microstructure dependent.
Ó 2008 Elsevier Ltd. All rights reserved.

1. Introduction

E0 ¼ À0:622 V ðSCEÞ

The widespread use of carbon and low alloyed steels in the
petroleum industry is primarily due to economicreasons. Nevertheless, their corrosion resistance is limited in certain oil and gas
environments with high chloride and carbon dioxide concentrations. Depending on their chemical composition and manufacturing processes, carbon and low alloyed steels may have different
microstructures which influence their mechanical properties and
corrosion resistance.
CO2 corrosion, usually referred to as sweetcorrosion, is one of
the most severe forms of attack in the oil and gas production and
transportation [1,2].
CO2 dissolves in water giving carbonic acid which is dissociated,
decreasing the solution pH.
It is widely known that CO2 increases the corrosion rate of C–
Mn and low alloy steels mainly because of its effect on hydrogen
evolution reaction [3,4].
In pH > 4 solutions, the H+concentration is small so H2CO3 presence allows for higher reduction rates, and therefore increases the
corrosion rate.
There is a possibility of H2CO3 and HCOÀ direct reduction
3
according to these equations [5]:

2HCOÀ þ 2eÀ ! H2 þ 2CO2À
3
3

2H2 CO3 þ 2eÀ ! H2 þ 2HCOÀ
3

* Corresponding author. Tel.: +54 223 4816600; fax: +54 223 4810046.
E-mail address: ssimison@fi.mdp.edu.ar (S.N.Simison).
0010-938X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.corsci.2008.06.031

ð 1Þ

ð2Þ

E0 ¼ À0:856 V ðSCEÞ
At pH > 5, the direct reduction of bicarbonate ion can become
meaningful as its concentration increases with pH.
The dominant anodic reaction in CO2 corrosion is the electrochemical dissolution of iron into ferrous ion.
As a consequence ofcorrosion processes, a layer of corrosion
products is formed on the surface of the steel. Its protection properties depend on the environmental conditions as well as on the
characteristics of the material. The presence of iron carbonate
(FeCO3) is commonly related with the formation of protective layers [6–11]. Because of its low solubility (pKsp = 10.54 at 25 °C [12]),
FeCO3 precipitates whenferrous cations (Fe2+) interact with carbonate (CO2À ) and bicarbonate (HCOÀ ) ions in the solution. The
3
3
surface scales formed below 40 °C in chloride media containing
carbon dioxide consist mainly of cementite (Fe3C) with some
FeCO3 and steel alloying elements [1]. Fe3C is part of the original
steel microstructure and accumulates on the surface after the preferential dissolution of...