Corrosion experiments were conducted on API (1)5L X65 mild steel specimens in inhibited 1 wt% NaCl aqueous solutions saturated by CO2 at pH 5.0 and 25°C under silica sand deposits. Corrosion mechanisms of under deposit corrosion were investigated including localized/pitting attack. In a solution inhibited by a generic surfactant inhibitor, pitting corrosion occurred directly under each individual sand particle. It was concluded that the steel area in the immediate vicinity of the contact point with the sand particle was not inhibited leading to a galvanic effect. The uninhibited steel surface immediately underneath the sand particle becomes an anode with respect to the surrounding inhibited area which becomes a cathode forming a small galvanic cell. A large number of these galvanic cells amount to an accelerated rate of corrosion under the bed of sand particles. It was also found that this accelerated localized attack ceased after the sand particles were removed from the steel surface. In a solution using a non-surfactant inhibitor, this type of corrosion attack was not observed.

Subject
Pits, Steel surfaces, Sand, Uniform corrosion rate, Imidazolines, Silica, Sodium chloride solution, Chemical inhibition, Corrosion inhibitors, Steel, Pitting, Localized corrosion, Grain
Keywords:
CO2 corrosion, silica deposit, mild steel, pitting, localized corrosion, mechanisms
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2014
Association for Materials Protection and Performance (AMPP)
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