Abstract
The electrochemical behavior of spirally-welded API steel was investigated at ambient temperature in 3.5% NaCl and 1M H2SO4 solution using linear polarization and electrochemical impedance spectroscopy (EIS) techniques. In order to reveal the corrosion resistance of different regions within the welded joint some significant characterization parameters in linear polarization and EIS curves were analyzed and compared. The surface morphology of corrosion products was also analyzed by scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS). The results showed that the corrosion resistance of the steel in both solutions at ambient temperature follows the order Weld Metal - Base Metal and HAZ. The corrosion of welded steel in sulfuric acid solution is more than that in NaCl solution.
Highlights
Carbon steels are the most important alloys used in petroleum and chemical industries since they account for over 98% of the construction materials
The weld metal (WM) and base metals have almost the same composition based on carbon equivalent calculations, the WM microstructure is noticeably different from the heat-affected zone (HAZ) as well as the unaffected base metal
The corrosion resistance calculated from electrochemical impedance spectroscopy (EIS) results shows the same trend as those obtained from polarization measurements
Summary
Carbon steels are the most important alloys used in petroleum and chemical industries since they account for over 98% of the construction materials. Of all the carbon steels, low carbon steels are widely used in oil / gas storage tanks and transportation pipelines because they display significant ductility, good weldability characteristics and possess reasonable strength and toughness [1,2,3]. These welded structures (pipe-lines, off-shore rigs, agitators, pumps, tanks etc.) are subjected to severe corrosion due to the aggressive chemical solutions [4,5,6] loaded with impurities (chlorides, sulphates etc.) [7,8,9]. The HAZ is the most sensitive region that is prone to corrosion due to the precipitation of chromium carbides [10, 11], which is of important concern in maintaining the integrity of pipelines, cylinders and tanks [12]
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