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The Influence of Electrochemical Potential and Stress-Level on Trench Nucleation on Ni-Bearing Low Alloy Steels in Sour Environments

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The presence of trenches on low alloy steels (LAS) in sour environments at the open circuit potential (OCP) has been reported since 1977. Originally, they were classified as deep and elongated localized corrosion pits. Recently, many authors have referred to them as “stress-induced grooves.

Product Number: 51323-19030-SG
Author: Dannisa R. Chalfoun, Mariano A. Kappes, Teresa E. Perez, Mariano Iannuzzi, José Luis Otegui, Ricardo M. Carranza
Publication Date: 2023
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$20.00
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Surface trenching of low alloy steels in H2S-containing solutions refers to a characteristic damage morphology, somewhere between elliptical deep pits and blunt cracks. Trench occurrence has been reported after tests in sour environments in the presence of applied loads, such as constant load tests, three-and four-point bending tests, and slow strain rate tests. These features can act as crack initiation sites in sulfide stress cracking (SSC) tests for material selection and qualification, often conducted at the open circuit potential. How different material, environment and mechanical variables influence trenches formation are still under study. In this work, the effect of the electrochemical potential and stress-level on trench formation and growth are explored on Ni-bearing steels up to 5 wt.%. The results obtained herein verified the anodic nature of trench formation. Additionally, under an anodic polarization, a critical stress value for trench formation, σtrench, was estimated from slow strain rate tests and finite element modeling. The observed dependencies with the electrochemical potential and the stress-level confirmed that trenches can be considered as a form of environmental-assisted cracking.

Surface trenching of low alloy steels in H2S-containing solutions refers to a characteristic damage morphology, somewhere between elliptical deep pits and blunt cracks. Trench occurrence has been reported after tests in sour environments in the presence of applied loads, such as constant load tests, three-and four-point bending tests, and slow strain rate tests. These features can act as crack initiation sites in sulfide stress cracking (SSC) tests for material selection and qualification, often conducted at the open circuit potential. How different material, environment and mechanical variables influence trenches formation are still under study. In this work, the effect of the electrochemical potential and stress-level on trench formation and growth are explored on Ni-bearing steels up to 5 wt.%. The results obtained herein verified the anodic nature of trench formation. Additionally, under an anodic polarization, a critical stress value for trench formation, σtrench, was estimated from slow strain rate tests and finite element modeling. The observed dependencies with the electrochemical potential and the stress-level confirmed that trenches can be considered as a form of environmental-assisted cracking.

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