Microstructure evolution and electrochemical corrosion behavior of api x70 line pipe steel in differ

Pipeline steels play a critical role in applications such as oil and gas transmission, offshore drilling, and pressure vessels. To enhance their mechanical properties and provide better atmospheric corrosion protection, various heat treatment procedures are employed. In this study, we focus on X70 pipeline steel and investigate how altering its microstructure through heat treatment impacts its electrochemical corrosion behavior. Heat treatment parameters: Austenitizing temperatures:1000°C and 850°C, Quenching followed by tempering at 300°C, 450°C, and 600°C. Corrosion Assessment: Linear Sweep Voltammetry technique used & Specimens tested in different environments: Sea water (pH 8.2), 5% NaCl + 10^(-2) mol/l sodium thiosulphate (pH 3), 5% NaCl + 10^(-3) mol/l sodium thiosulphate (pH 5). Microstructural Insights: Heat-treated samples exhibit distinct phases. Notably, polygonal ferrite and fine-grained ferrite microstructures (at 600°C) show reduced corrosion rates compared to tempered martensitic microstructures (at 300°C). This research sheds light on the interplay between heat treatment, microstructure, and corrosion resistance in X70 pipeline steel, contributing to safer and more durable pipelines.