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51318-10970-Performance of API 5L X65 in a 'sweet' followed by 'sour' environment

Picture for Performance of API 5L X65 in a 'sweet' followed by 'sour' environment
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The corrosion behaviour of X65 steel in a mixed 1% H2S (in CO2) brine after exposure to a pure CO2-saturated brine at 40°C. The objective was to identify the scales formed and understand their effect on the corrosion performance of X65 steel upon transition from pure sweet to sour conditions.

Product Number: 51318-10970-SG
Author: Maria Eleni Mitzithra / Shiladitya Paul
Publication Date: 2018
Industry: Corrosion Monitoring and Control
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This paper reports the corrosion behaviour of X65 steel in a mixed 1% H2S (in CO2) brine after exposure to a pure CO2-saturated brine at 40°C. The objective of the study was to identify the scales formed and understand their effect on the corrosion performance of X65 steel upon transition from pure sweet to sour conditions. Electrochemical testing indicated reduced general corrosion rate during the exposure to pure CO2 environment, which is mainly attributed to the formation of protective but porous siderite scale. After the introduction of mixed CO2/H2S gas, the corrosion rate decreased further for a short period due to precipitated mackinawite above the existing siderite. As H2S and brine were diffusing through the pore network in siderite, the corrosion rate exhibited an increasing trend due to the accelerating effect of the formed mackinawite within the intermediate layers and on the steel surface. Owing to the possible development of internal stresses in the newly formed scale, the existing siderite layers were ruptured, leading to the precipitation of more mackinawite and promoting further the dissolution of ferrite into the solution. The estimated corrosion rates indicated that the uniform attack is more widespread than the local attack.

Key words: X65 steel, 1% H2S/CO2 mixture, protective iron carbonate, mackinawite, uniform corrosion

This paper reports the corrosion behaviour of X65 steel in a mixed 1% H2S (in CO2) brine after exposure to a pure CO2-saturated brine at 40°C. The objective of the study was to identify the scales formed and understand their effect on the corrosion performance of X65 steel upon transition from pure sweet to sour conditions. Electrochemical testing indicated reduced general corrosion rate during the exposure to pure CO2 environment, which is mainly attributed to the formation of protective but porous siderite scale. After the introduction of mixed CO2/H2S gas, the corrosion rate decreased further for a short period due to precipitated mackinawite above the existing siderite. As H2S and brine were diffusing through the pore network in siderite, the corrosion rate exhibited an increasing trend due to the accelerating effect of the formed mackinawite within the intermediate layers and on the steel surface. Owing to the possible development of internal stresses in the newly formed scale, the existing siderite layers were ruptured, leading to the precipitation of more mackinawite and promoting further the dissolution of ferrite into the solution. The estimated corrosion rates indicated that the uniform attack is more widespread than the local attack.

Key words: X65 steel, 1% H2S/CO2 mixture, protective iron carbonate, mackinawite, uniform corrosion

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51318-10964-Sour TLC

Product Number: 51318-10964-SG
Author: Gaute Svenningsen / Jon Kvarekvål
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In this work, sour TLC was systematically studied in autoclaves with a special holder that exposed one side of the TLC coupon while the back side was exposed to cooling liquid.

 
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51318-10990-Localized Corrosion of Mild Steel under Iron Sulfide Layers in CO2/H2S Environment

Product Number: 51318-10990-SG
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Publication Date: 2018
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Mild steel specimens (API 5L X65) were pretreated to form a pyrrhotite layer on the surface using high temperature sulfidation in oil, then exposed to a range of aqueous CO2 and H2S corrosion environments, leading to initiation of localized corrosion.

 
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