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Study on Effect of Buffer Capacity on Corrosion Performance of CRAs in Simulated Well Condition

Methodology to simulate actual oil and gas field condition in laboratory tests. A sulfide stress cracking test is carried out on 13% Cr stainless steel with various buffer solutions. Then, pH behavior was estimated. A suitable composition of the solution is proposed by using thermodynamic calculations.

Product Number: 51317--9283-SG
ISBN: 9283 2017 CP
Author: Masayuki Sagara
Publication Date: 2017
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The methodology how to simulate or realize an actual oil and gas field condition in laboratory tests is important to evaluate the actual corrosion performances of materials. The environmental factors such as partial pressure of H2S and CO2 temperature concentration of chloride ion and pH of the solution are essential to define the severity of corrosion condition. To consider the initiation of localized corrosion such as pitting or cracking in Corrosion Resistant Alloys (CRAs) it is important to research the stability of the passive film such as depassivation pH of the materials. The one of most important environmental factor which may have an impact on the stability of the passive film is pH of the solution. The local pH in the vicinity of surface of metals might fluctuate due to the result by the hydrolysis reaction of H2O combined with metallic cation which are released from the metal surface. It could be difficult to maintain the constant bulk pH value in a small volume vessel during the entire laboratory test duration (e.g. 720 hours) therefore the applications of buffer system are widely adopted. However the excessively stabilized buffer solution might give a different pH fluctuation behavior in the vicinity of metal surface from the actual corrosion environments. In this research the estimation of buffer capacity is conducted with some variations of buffering systems. The results of corrosion tests for martensitic stainless steels using the same bulk pH solution but the different buffer capacity will be presented to show the effect of local pH fluctuation at the surface of materials on the stability of the passive films. The candidates for the suitable buffering system that can simulate an actual oil and gas condition will be discussed.

Key words: Corrosion resistant alloy, Localized corrosion, Sulfide stress cracking, pH, Buffer solution, Acid, Carbon dioxide, Bicarbonate, Hydrogen sulfide.

 

The methodology how to simulate or realize an actual oil and gas field condition in laboratory tests is important to evaluate the actual corrosion performances of materials. The environmental factors such as partial pressure of H2S and CO2 temperature concentration of chloride ion and pH of the solution are essential to define the severity of corrosion condition. To consider the initiation of localized corrosion such as pitting or cracking in Corrosion Resistant Alloys (CRAs) it is important to research the stability of the passive film such as depassivation pH of the materials. The one of most important environmental factor which may have an impact on the stability of the passive film is pH of the solution. The local pH in the vicinity of surface of metals might fluctuate due to the result by the hydrolysis reaction of H2O combined with metallic cation which are released from the metal surface. It could be difficult to maintain the constant bulk pH value in a small volume vessel during the entire laboratory test duration (e.g. 720 hours) therefore the applications of buffer system are widely adopted. However the excessively stabilized buffer solution might give a different pH fluctuation behavior in the vicinity of metal surface from the actual corrosion environments. In this research the estimation of buffer capacity is conducted with some variations of buffering systems. The results of corrosion tests for martensitic stainless steels using the same bulk pH solution but the different buffer capacity will be presented to show the effect of local pH fluctuation at the surface of materials on the stability of the passive films. The candidates for the suitable buffering system that can simulate an actual oil and gas condition will be discussed.

Key words: Corrosion resistant alloy, Localized corrosion, Sulfide stress cracking, pH, Buffer solution, Acid, Carbon dioxide, Bicarbonate, Hydrogen sulfide.

 

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