Effect of Thermomechanical Processing and Crystallographic Orientation on the Corrosion Behavior of API 5L X70 Pipeline
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IN recent years, more pipelines have been manufactured on order to meet the world’s growing energy need. A key factor in maintaining energy supply through pipelines is improving the corrosion resistance of the pipeline steel, especially under severe service conditions. A report from the National Association of Corrosion Engineers (NACE), the internationally renowned authority in corrosion, placed the global cost of corrosion at a whopping 2.5 trillion USD, an equivalent of 3.4 pct of the entire world’s GDP.[1] Such striking statistics shows the overwhelming impact of corrosion on our infrastructures. Corrosion is a means through which metals achieve thermodynamic stability after being transformed by processing.[2] With oxidation and reduction occurring on the pipeline steel during the
ENYINNAYA OHAERI, JOSEPH OMALE, UBONG EDUOK, and JERZY SZPUNAR are with the Department of Mechanical Engineering, College of Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, SK S7N 5A9, Canada. Contact e-mail: [email protected] Manuscript submitted December 18, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
corrosion process, water reduction reaction may result in the release of hydrogen gas. This is also similar during uncontrolled cathodic protection of pipelines, as the production of hydrogen becomes imminent at highly cathodic potentials.[3,4] In the case of pipelines, corrosion behavior becomes even more complex in service environments containing other hydrogen-producing species. Corrosion in pipelines is closely related to various environmental factors. The presence of corrodents such as sulfides, chlorides, and carbonates highly influence the corrosion behavior of pipeline steel.[5] Some of these species interfere with the corrosion potential of carbon steel, while others destabilize passivation film and enhance anodic sensitivity.[6,7] However, the combined activities of acetic acid and sodium chloride within the vicinity of pipeline steel further increase the corrosion rate.[8] Thus, it is important to properly understand the role of metallurgical variables in altering corrosion resistance of pipeline steel. Many corrosion studies have focused mainly on electrochemical testing of pipeline steels for different applications. Less consideration is given to the effect of hot rolling on electrochemical response of steels. Interestingly, a recent study established that pitting corrosion resistance in 316LVM austenitic stainless steel was increased at 111- and
011-oriented planes compared to other planes of lower atomic density.[9] Also, crystallographic orientation of grains has been proposed as a major corrosion controlling factor for commercial grade titanium.[10] Since corrosion is a surface phenomenon, the effect of plane orientation at the steel surface remains an important aspect. The idea of creating a material with the dominance of a particular preferred orientation is simply referred to as crystallographic texture. Even though variations in texture are commonly seen across pipeline steel
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