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Brief discussion on Crude oil and steel corrosion Print E-mail


K. Daniel Efird
  • Crude oil has a significant effect of the corrosion of steel in crude oil or brine mixtures, which effects are significantly different for different crude oils.
The specific crude oil produced from a field, has a major effect on the corrosion of steel in the crude oil or brine environment. The addition of crude oil to a brine lowers the measured corrosion rate of steel exposed to the mixture, but different crude oils have significantly different effects on steel corrosion, with identical brine compositions.
  • The differences in the observed steel corrosion behavior for different crude oils are in the degree of corrosion product protectiveness, and not in the rate of formation of the corrosion product.
  • Corrosion tests conducted on steel in brine environments without the crude oil present do not give a true picture of the behavior of steel in the crude oilor brine production environment. This 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.
  • The produced water level where accelerated corrosion of steel corrosion in crude oil production will occur can be identified with a high degree of accuracy and confidence. This can minimize operating expense by delaying the start of chemical treatment until it is actually necessary.
  • The expense of failure and replacement of downhole equipment and tubulars is minimized by identifying the produced water level where accelerated corrosion of steel will begin before it actually occurs in the operating system.
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. Consequently, corrosion tests conducted on steel in brine without the crude oil present do not give a true picture of the behavior of steel in the production environment. This leads 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.

Water related factors identified as controlling the corrosion of steel in production environments include pH, temperature, velocity, chloride, bicarbonate, organic acids, and acid gas partial pressure. These factors do not account for the effect of the crude oil on the corrosion process.
 
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