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Corrosion in Oil field environments

Oil field production environments can range from practically zero corrosion to severely high rates of corrosion. Crude oil at normal production temperatures (less than 120°C) without dissolved gases is not, by itself, corrosive.

The economics of controlling corrosion in many oil fields are dependent on efficient separation of crude oil from other species. While the rates may vary, the species causing the most problems are nearly universal. Carbon dioxide and hydrogen sulphide gases, in combination with water, define most of the corrosion problems in oil and gas production. Other problems include microbiological activity and the solids accumulation.

The mechanisms of carbon dioxide corrosion are generally well defined; however, the reality inside a pipeline becomes complicated when carbon dioxide acts in combination with hydrogen sulphide gas, deposited solids, and other environments. Hydrogen sulphide gas can be highly corrosive, but can, in some cases, form a protective sulfide scale that prevents corrosion. Microorganisms can attach to pipe walls and cause corrosion damage. Solids, such as formation sand, can both erode the pipeline internally and cause problems with under-deposit corrosion, if stagnant.

Oxygen is not found in oil reservoirs and much is done to ensure that no oxygen enters the production environment; however, in many cases, a few parts per million (ppm) of oxygen will enter the pipelines, greatly exacerbating corrosion problems.

External corrosion problems in oil and gas production normally are similar to those found in the pipeline industry. But since the lines are shorter and smaller in diameter, their economic impact on the total cost of production is limited. Atmospheric corrosion of structures and vessels is a problem for offshore fields and those operating near marine environments. Improvements in the quality of protective coatings for offshore environments have dramatically reduced the frequency of repainting platforms and tanks.

Reference: www.corrosioncost.com