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According to the different corrosion mechanism of pipeline, pipeline corrosion can be divided into the following types:
1. Oxygen absorption corrosion
Petroleum and its products often contain water and dissolved oxygen. The corrosion of molecular oxygen in water is carried out through oxygen consumption reaction on cathode.
2. Sulfur dioxide corrosion
As the materials transported often contain sulfur, the sulfur content in the pipeline will accumulate more, and the sulfur dioxide in the accumulated water at the bottom of the pipeline can generate acid regeneration cycle reaction on the steel pipe. First of all, ferrous sulfate is produced by the reaction of sulfur dioxide, oxygen and iron, and then ferrous sulfate is hydrolyzed into oxide and free acid. The free acid accelerates the corrosion of iron to form new ferrous sulfate. Ferrous sulfate is hydrolyzed again, which accelerates the corrosion of pipeline bottom.
3. Hydrogen sulfide corrosion
Petroleum often contains a large amount of hydrogen sulfide. Hydrogen sulfide gas itself does not cause corrosion to the pipeline. However, when it meets the water in the pipeline to form a solution, it will ionize hydrogen ions and corrode the pipeline. At the same time, hydrogen sulfide solution will be oxidized to form sulfuric acid, which will aggravate the corrosion of pipeline.
4. Carbon dioxide corrosion
Atmospheric precipitation contains carbon dioxide. Carbon dioxide dissolves in water and forms carbonic acid. The acidity in carbonic acid is corrosive to pipelines. Since most pipelines are made of steel, steel is an iron carbon alloy. Both iron and carbon can conduct electricity, and a galvanic cell is formed between relatively active iron and relatively weak carbon. Under this action, the corrosion reaction speed is accelerated, and all the above corrosion effects can be accelerated.
5. Bacterial corrosion
There are many kinds of bacteria in the pipeline, which can metabolize salt and corrode the iron in the pipeline.