Abstract
Background: Trial productions of API-X65, API-X70 steels have been undertaken at Rourkela steel plant (RSP) and Bokaro steel limited (BSL) in collaboration with R&D Center for iron and steel and the requisite mechanical properties have been successfully met in industrial heats. One of the important aspects to assure good performance of pipeline steels is to minimize cracking susceptibility when exposed to sour environments. Hence, the present work focuses on characterization of newly developed API X65 and 70-line pipe steels on terms of HIC and SSC phenomenon in sour gas media and possibility to develop HIC and SSC resistant steel.
Methods: Hydrogen-induced cracking (HIC) resistance and sulphide stress corrosion (SSC) behavior of commercially produced API X65 and API X70 steels were characterized as per NACE standards. Results: Newly produced API X65 and API X70 line pipe steels showed poor resistant to HIC and SSC in sour gas environment. From Electrochemical corrosion studies it was concluded that chemisorbtion film formed on the surface responsible for auto-catalytically generating hydrogen at the surface, increasing the probability for diffusion of hydrogen. To explore the possibility of improving the HIC and SSC performance of these steels in hydrogenated and sour gas environments, laboratory heat making trial was undertaken with controlled addition of Cu at levels of 0.14, 0.26 and 0.36 wt% to API X65 steel. The addition of Cu to API X65 steel has immensely beneficial by increasing the corrosion resistant of the steel by altering the surface film and restricts the hydrogen diffusion. Also the Cu has improved the HIC and SSC resistant of the steel because of low diffusion of hydrogen.Keywords: API steel, hydrogen induced cracking (HIC), sulphide stress corrosion cracking (SSC), corrosion, sour gas environment, electrochemical impedance spectroscopy (EIS).
Graphical Abstract
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