Effect of the Crude Oil on Corrosion of Steel in Crude Oil/Brine Production^☆

The specific crude oil present is shown to have a major effect on the corrosion of steel in crude oil/brine production environments. The addition of crude oil to a brine (chloride-containing water) lowers the measured corrosion rate of steel exposed to the mixture, but different crude oils can have significantly different effects on steel corrosion, with identical brine compositions. The primary effect of the crude oil on steel corrosion in crude oil/brine mixtures is apparently on the protectiveness of the corrosion product layer formed on the steel. The algebraic product of the organic nitrogen concentration in weight percent and the acid number exhibits an inverse relationship to the steel corrosion rate, implying that the organic nitrogen and acid contents of the crude oil are potentially major variables affecting corrosion product formation and resulting protectiveness. This means that corrosion tests conducted on steel in brine environments without the crude oil present cannot give an accurate picture of the behavior of steel in the crude oil/brine production environment, which can lead to gross errors when using the test results to estimate the potential corrosion problems and effects of corrosion inhibitor treatments in a crude oil production system. Corrosion tests simulating crude oil production systems must include the specific produced crude oil in the test environment if the test is to produce valid results.