Abstract
The microstructure and corrosion resistance in H2S environments for various zones of X80 pipeline steel submerged arc welded joints were studied. The main microstructures in the base metal (BM), welded metal (WM), coarse-grained heat-affected zone (CGHAZ), and fine-grained heat-affected zone (FGHAZ) were mainly polygonal ferrite and granular bainite; acicular ferrite with fine grains; granular bainite, ferrite, and martensite/austenite constituents, respectively. The corrosion behavior differences resulted from the microstructure gradients. The results of the micro-morphologies of the corrosion product films and the electrochemical corrosion characteristics in H2S environments, including open circuit potential and electrochemical impedance spectroscopy, showed that the order of corrosion resistance was FGHAZ > BM > WM > CGHAZ.
Highlights
X80 pipeline steel is a low-carbon and low-alloyed steels made by thermo-mechanical controlled rolling technology
In Hydrogen sulfide (H2 S) environments, a layer of sulfide corrosion product film can be gradually formed on the surface of pipeline steel, and its compact structure is conducive to reducing the corrosion rate [13,14]
The Evolution solution was purged with H2 S for 24 h, and H2 S flow was maintained during the test duration
Summary
X80 pipeline steel is a low-carbon and low-alloyed steels made by thermo-mechanical controlled rolling technology. In H2 S environments, the corrosion rate of pipeline steel is mainly related to the temperature, pH value, and H2 S partial pressure [6]. With the increase of the temperature and H2 S partial pressure, the corrosion rate of pipeline steel decreases first and increases [7,8]. Higher H2 S partial pressure increases the possibility of serious pitting corrosion in pipeline steel [10]. In H2 S environments, a layer of sulfide corrosion product film can be gradually formed on the surface of pipeline steel, and its compact structure is conducive to reducing the corrosion rate [13,14]. The order of the corrosion resistance of X80 pipeline steel welded joints is BM > HAZ > WM in an alkaline soil solution [20]. The H2 S corrosion resistance and the characteristics of the sulfide corrosion products of the X80 pipeline steel submerged arc welding (SAW) joints were studied
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