Corrosion behavior of carbon steel pipelines under different deposits in oil and gas transportation

The corrosion behavior of X65 carbon steel under different deposits in CO2 saturated formation water was studied by weight loss measurements, electrochemical measurements, wire beam electrode and microscopic analysis. The results show that the corrosion rate of the steel slightly decreases by being covered with sand, clay or ferrous carbonate. However, covered with ferrous sulfide, elemental sulfur or mixture, the corrosion rate obviously accelerates, especially in the specimen covered with elemental sulfur. The corrosion rate of the specimen covered with mixture deposits also significantly increases, in which elemental sulfur plays a dominant role. The significant increase in corrosion rate of the specimen covered with elemental sulfur is attributed to the self-catalytic action of elemental sulfur on the cathodic reaction of steel corrosion. The current and potential distributions of wire beam electrodes indicate that the potentials of the electrodes covered with mixture deposits are more positive than those without deposits. During the corrosion, severe localized corrosion occurs on the electrodes under mixture deposits. The current and potential maps of wire beam electrodes can effectively reflect the localized corrosion behavior of the steel under deposits due to the change of local environment.