Influence of KBr concentration on corrosion behaviors of 13Cr stainless steels under high temperature and high pressure

Recently, the use of bromine completion fluids in the oil and gas industry has caused numerous severe corrosion problems of the oil well casing and tubing, particularly the localized corrosion failure. Bromine completion fluids, such as KBr solution, are highly corrosive to steels. Even if the stainless steel is subjected to a high concentration of bromate under high temperature and pressure, it can still experience severe corrosion failure risks. In this study, the influence of KBr concentrations on corrosion behaviors of plain and super 13Cr steels under high temperature and pressure was investigated by corrosion simulation, scanning electron microscopy (SEM) observation, and electrochemical measurements. The results show that both plain and super 13Cr steels exhibit good corrosion resistance in KBr solutions with various concentrations regarding average corrosion rate, which is either mild or moderate. However, the local corrosion rates of plain and super 13Cr steels are serious or extremely serious. With the increase of bromide concentration, the free corrosion and pitting potentials of plain 13Cr steel significantly decrease. Both the average and local corrosion rates increase significantly. For super 13Cr steel, the pitting potential decreases, whereas the free potential remains relatively stable. The average corrosion rate of super 13Cr steel shows a lower scope of change than the local corrosion rate, which increases significantly and indicates that super 13Cr steel is much more corrosion resistant than plain 13Cr steel, but its local corrosion sensitivity is still high. Laser scanning confocal microscopy (LSCM) results show that both plain and super 13Cr steels exhibit serious pitting corrosion in a KBr solution with a concentration of 1.40 g·cm^-3, and this is related to the aggressiveness of Br^-. Compared with plain 13Cr steel, super 13Cr steel shows a lower pitting sensitivity; however, its pitting corrosion risk cannot be ignored.