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From Pits To Cracks: A Review Of 45-Years Of Published Research On Surface Trenches In Low Alloy Steels Exposed To H2S-Containing Environments

From Pits To Cracks: A Review Of 45-Years Of Published Research On Surface Trenches In Low Alloy Steels Exposed To H2S-Containing Environments
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Carbon and low alloy steels (CS and LAS, respectively) used for exploration and production in the oil and gas (O&G) industry are normally exposed to environments that may contain H2S in a wide range of concentrations. In aqueous solutions, H2S acts as a cathodic poison.1,2 A cathodic poison inhibits the recombination of atomic hydrogen to H2, and as a result, favors its absorption by the metal.1,2 In the presence of a susceptible microstructure and the simultaneous effect of applied or residual tensile  stress, a crack can nucleate and propagate, when a critical concentration of hydrogen is reached in the metal.3 This environmentally assisted cracking (EAC) phenomenon is known as Sulfide Stress Cracking (SSC).2 SSC is commonly addressed as a case of hydrogen embrittlement (HE) damage.2

Product Number: 51322-17957-SG
Author: Dannisa R. Chalfoun, Teresa E. Perez, Mariano Iannuzzi, Mariano A. Kappes
Publication Date: 2022
Industries: Oil and Gas , Coatings
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$20.00
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Surface trenches are described as elongated pits or blunt cracks with a large depth (d) to width (a) ratio that occur as the result of an environmentally and stress-assisted damage. Trenches may represent a transition from pits to cracks in stressed carbon and low alloy steels specimens when exposed to H2Scontaining solutions under certain experimental conditions. In the literature, surface trenches are also known as deep or sharp pits, small blunt cracks, stress-induced microgrooves, fissures, cracklets, or microcracks. Since these features were first presented in 1977 by Dunlop, many authors have typically reported their depth while others have included the shape aspect ratio (d/a) for a more consistent characterization. In 2000, Pargeter published a flowchart to distinguish pits from cracks based on the microscopy analysis of the cross-sections of tested samples. In the absence of detrimental phases such as hard microstructures, and for indications with a depth higher than 250 µm, Pargeter classified cracks as features that presented sharp tips and parallel sides. However, indications with depths below the 250 µm limit reported in the literature remain unclassified according to Pargeter’s guidelines. In recent years, efforts have been made to clarify the limits between trenches with respect to pits and cracks.

Surface trenches are described as elongated pits or blunt cracks with a large depth (d) to width (a) ratio that occur as the result of an environmentally and stress-assisted damage. Trenches may represent a transition from pits to cracks in stressed carbon and low alloy steels specimens when exposed to H2Scontaining solutions under certain experimental conditions. In the literature, surface trenches are also known as deep or sharp pits, small blunt cracks, stress-induced microgrooves, fissures, cracklets, or microcracks. Since these features were first presented in 1977 by Dunlop, many authors have typically reported their depth while others have included the shape aspect ratio (d/a) for a more consistent characterization. In 2000, Pargeter published a flowchart to distinguish pits from cracks based on the microscopy analysis of the cross-sections of tested samples. In the absence of detrimental phases such as hard microstructures, and for indications with a depth higher than 250 µm, Pargeter classified cracks as features that presented sharp tips and parallel sides. However, indications with depths below the 250 µm limit reported in the literature remain unclassified according to Pargeter’s guidelines. In recent years, efforts have been made to clarify the limits between trenches with respect to pits and cracks.

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