Factorial design used to study the corrosion of API K55 steel in wells caused by chloride brines
brine, corrosion, corrosion rate, ANOVA, steel API K55
Chloride brines are widely used in the petroleum industry, participating in the formulations of drilling muds, completion brines, etc. In some wells, the brines remain for long time trapped in the annular space above the packer. Therefore, they must have anticorrosive characteristics to guarantee a longer time between of interventions to replace equipaments. In this context, the present work aims to evaluate the influence of pH and concentrations of sodium chloride, sodium bisulfite and corrosion inhibitor about the API K55 steel’s corrosion rate using a factorial design 24 with a central point and also verify the corrosion inhibitor’s efficiencies in the various brines’ compositions. Bases on NACE TM169, the corrosion rate tests were made in triplicate based on the mass difference. The steel specimen were exposed to brines in rotating oven at 90ºC and 274,20 psi of manometric pressure during 24 hours, being cleaning with hydrochloridric acid, tin II Chloride and antimony III oxide solution. It was found the sodium bisulfite concentration effect wasn’t statistically significant in a 95% confidence interval. The effects of sodium chloride concentration, pH interaction with corrosion inhibitor concentration, pH and corrosion inhibitor were statistically significant within the same confidence interval. Using ANOVA, it was verified the statistical model that fit the observed values was predictive with determination coefficient equal to 99.46%. According to the results, the corrosion inhibitor’s highest efficiency was 72,90%, at pH 7.0 and 0,48% v/v of corrosion inhibitor.