Abstract
In this study, an optimum tempering temperature after a thermo-mechanical control process (TMCP) was proposed to improve the hydrogen-induced ductility loss of high-vanadium X80 pipeline steel. The results showed that with increasing tempering temperature from 450 to 650 °C, the size and quantity of granular bainite decreased but the spacing of deformed lath ferrite and the fraction of massive ferrite increased. The number of fine vanadium carbides increased as well. However, as the tempering temperature increased to 700 °C, the microstructure of T700 steel completely converted to massive ferrite and the grain size became larger. Additionally, the amount of nanoscale precipitates decreased again, and the mean size of precipitates evidently increased in T700 steel. The steel tempering at 650 °C, containing the most vanadium precipitates with a size less than 20 nm, had the lowest hydrogen diffusion coefficient and the best resistance to hydrogen-induced ductility loss.
Highlights
IntroductionWith the continuous exploitation of petroleum and natural gas in remote areas, long distance oil/gas pipeline transportation is facing enormous challenges [1,2]
Over the past decades, with the continuous exploitation of petroleum and natural gas in remote areas, long distance oil/gas pipeline transportation is facing enormous challenges [1,2].More and more severe service environment and the self-acidity of oil and gas both put forward more stringent requirements on mechanical properties and corrosion resistance for pipeline steel [3]
After long-term research, hydrogen-induced corrosion failures have been summarized as two main types, hydrogen embrittlement (HE) and hydrogen-induced cracking (HIC) [2,4,5,6]
Summary
With the continuous exploitation of petroleum and natural gas in remote areas, long distance oil/gas pipeline transportation is facing enormous challenges [1,2]. More and more severe service environment and the self-acidity of oil and gas both put forward more stringent requirements on mechanical properties and corrosion resistance for pipeline steel [3]. After long-term research, hydrogen-induced corrosion failures have been summarized as two main types, hydrogen embrittlement (HE) and hydrogen-induced cracking (HIC) [2,4,5,6]. A large number of hydrogen atoms penetrating into steel is the main cause of failures. The hydrogen atoms move to the steel surface by reduction of hydrogen ions from external acidic environment and enter steel through physisorption, driven by van der Waals’ forces, and chemisorption successively [7]
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