Effects of Oxygen, Salt, and pH Level on Corrosion Rate of Drill-Stem Steel

摘要

A technique proposed to control corrosion of the drill pipe is removal of oxygen from the drilling fluid. One approach to oxygen reduction is to substitute an anaerobic gas for air in the drilling fluid. A critical question to be answered when designing the anaerobic gas generator is what level of oxygen concentration is acceptable within the inert gas such that a low corrosion rate will be maintained. A laboratory program was done to answer this question. The program was designed to determine the effect of oxygen content, salt concentration and pH level on the corrosion rate of plain carbon steel. The corrosion rate of steel was found to decrease with increasing salt concentration at fixed pH levels and with oxygen contents in solution at equilibrium with air at 90 exp 0 C. The corrosion rate was found to decrease with increasing pH at fixed concentrations of salt and oxygen at 90 exp 0 C. The corrosion rate was also found to be proportional to the dissolved oxygen concentration at fixed pH levels and salt concentration. It is recommended that the anaerobic gas generator be designed to lower the oxygen concentration one order of magnitude below that in solution in equilibrium with air, that is, to approximately 500 ppB at 90 exp 0 C. (ERA citation 08:020183)