Effect of Microstructure and Texture Evolution on the Electrochemical Corrosion Behavior of Warm-Rolled API 5L X70 Pipel

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PIPELINES remain a convenient means of transporting oil and natural gas from one point to another. These assets play a crucial role in meeting the world’s energy demand. So, good quality steels are required for their construction. Steel classification places more emphasis on material strength, with little consideration toward corrosion dynamics within the operation environments. In our service (i.e., H2S-containing environment), pipelines often experience unforeseen damage due to cracking. Some reviews[1,2] have recommended

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] MUHAMMAD ARAFIN is with the Research and Development Center, EVRAZ North America, 100 Armour Road, P.O. Box 1670, Regina, SK S4P 3C7, Canada. FATEH FAZELI is with CanmetMATERIALS, Natural Resources, Hamilton, ON, L8P 0AS, Canada. Manuscript submitted June 6, 2019.

METALLURGICAL AND MATERIALS TRANSACTIONS A

that pipeline property enhancement is necessary for optimum reliability. However, this should be performed cautiously to avoid jeopardizing other inherent mechanical properties. Recent studies[3,4] are directed toward broadening the applications of steel through improvement in microstructure and crystallographic texture. There are correlations between corrosion in pipeline steel and its inherent structure, especially when subjected to hydrogen environments.[5–7] Certain microstructural features, such as inclusions, segregation, or precipitates, could serve as promoters of corrosion in steels through hydrogen embrittlement (HE) mechanisms.[8,9] For instance, the susceptibility to HE in X50 pipeline material varied from predominantly ferrite-pearlite to martensitic after heat treatments.[10] The transgranular cracks observed within the ferrite-pearlite microstructure initiated around non-metallic inclusion particles. Contrarily, the martensitic steels failed by intergranular cracking without significant contributions from inclusions. Also, hydrogen-induced cracking (HIC) was previously identified at oxide inclusions of Al-Mg-Ca, precipitates of (Ti-Nb)N, and other elements such as Mo-Mn-S.[5,11] These

multicomponent inclusions were mostly found around segregations in the mid-thickness region of X70 pipeline steel. Consequently, embrittlement caused by the entry of hydrogen into steel may cause HIC. Numerous scenarios of pipeline failures across the world have been attributed to the HE phenomenon, as well as other related corrosion causes.[12–14] Therefore, it is imperative to investigate processing methods that could potentially lead to the development of corrosion-resistant steels with formidable texture. The production of pipeline steel plates is done to achieve excellent properties at a minimal cost. However, contemporary steels are of higher quality compared with the older grades with large amounts of impurities. This is primarily due