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51313-02144-Localized Corrosion of Mild Steel under Silica Deposits in Inhibited Aqueous CO2 solutions

Picture for Localized Corrosion of Mild Steel under Silica Deposits in Inhibited Aqueous CO2 solutions
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Product Number: 51313-02144-SG
ISBN: 02144 2013 CP
Author: Jin Huang
Publication Date: 2013
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In upstream oil and gas pipelines solids (such as sand) deposit on the bottom of the pipeline and form a bed or layer when the flow rate is low. Observations of localized corrosion in these conditions have lead to the need to understand the corrosion mechanisms involved in under deposit corrosion. A solid sand bed results in a covered area where the water chemistry is different from adjacent areas exposed to the bulk solution and may form a concentration cell. The deposit also limits the access of inhibitor to the metal surface. The formation of concentration cell and limitation of inhibitor access result in the potential of locally accelerated corrosion.


Electrochemical experiments were conducted on an X65 mild steel sample covered by sand at test conditions of pH 5.0 and 25°C in a 1 wt% NaCl solution saturated by CO2. Linear polarization resistance is used to calculate the general corrosion rate of the steel over a period of 24 hours or longer. An Atomic Force Microscopy (AFM) technique was used to study the structure of adsorbed pure Imidazoline inhibitor (K1) molecules on sand surface using a quartz crystal. AFM was also used to investigate the strength of adsorption between inhibitor molecules and the substrate surface. It was observed that a pure Imidazoline based inhibitor was not able to reduce the corrosion rate of the steel underneath the sand particles and pits were found at those areas. Pits penetration rate was calculated using infinite focus microscopy (IFM) measurement. From experimental studies it was concluded that inhibitor K1 did go through the sand deposit and reach the steel surface. Adsorption of this pure Imidazoline inhibitor on sand surface was not the cause that leads to global loss of inhibitor. However when sand deposit was present the steel surface was not uniform with respect to corrosion. Sand covered areas become less easily to both corrosion and inhibitor which promotes the formation of concentration cell and leads to accelerated localized corrosion.

Key words: CO2 corrosion sand deposit mild steel localized corrosion mechanisms 

In upstream oil and gas pipelines solids (such as sand) deposit on the bottom of the pipeline and form a bed or layer when the flow rate is low. Observations of localized corrosion in these conditions have lead to the need to understand the corrosion mechanisms involved in under deposit corrosion. A solid sand bed results in a covered area where the water chemistry is different from adjacent areas exposed to the bulk solution and may form a concentration cell. The deposit also limits the access of inhibitor to the metal surface. The formation of concentration cell and limitation of inhibitor access result in the potential of locally accelerated corrosion.


Electrochemical experiments were conducted on an X65 mild steel sample covered by sand at test conditions of pH 5.0 and 25°C in a 1 wt% NaCl solution saturated by CO2. Linear polarization resistance is used to calculate the general corrosion rate of the steel over a period of 24 hours or longer. An Atomic Force Microscopy (AFM) technique was used to study the structure of adsorbed pure Imidazoline inhibitor (K1) molecules on sand surface using a quartz crystal. AFM was also used to investigate the strength of adsorption between inhibitor molecules and the substrate surface. It was observed that a pure Imidazoline based inhibitor was not able to reduce the corrosion rate of the steel underneath the sand particles and pits were found at those areas. Pits penetration rate was calculated using infinite focus microscopy (IFM) measurement. From experimental studies it was concluded that inhibitor K1 did go through the sand deposit and reach the steel surface. Adsorption of this pure Imidazoline inhibitor on sand surface was not the cause that leads to global loss of inhibitor. However when sand deposit was present the steel surface was not uniform with respect to corrosion. Sand covered areas become less easily to both corrosion and inhibitor which promotes the formation of concentration cell and leads to accelerated localized corrosion.

Key words: CO2 corrosion sand deposit mild steel localized corrosion mechanisms 

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