Why do impurities such as ferric tetraoxide and carbon appear in carbon steel pipelines?
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Medium: Butene, with impurities such as sec-butanol and water. This pipeline is the butene circulation pipeline in the hydration section of the same plant for both Unit A and Unit B. The pipeline is made of carbon steel. Inspection revealed a large amount of black impurities in the pipeline, which affected the centrifugal pump. Analysis and testing revealed carbon, iron, and iron tetraoxide. I need help understanding how such impurities are formed.
Looking at the products \"carbon, iron, and ferric oxide,\" it can be seen that carbon steel has been oxidized; are there any photos of the corroded areas? Today, I came across a case of biological corrosion in an olefin heat exchanger.
Thank you for your reply. There are no photos of corrosion at the moment, but based on the appearance of the impurities, they appear as black flaky pieces that can easily break into black powder; these impurities seem to have some magnetic properties. How does the oxidation of carbon steel lead to the formation of iron tetraoxide?
Thank you for your reply. There are no photos of corrosion at the moment, but based on the appearance of the impurities, they appear as black flaky pieces that can easily break into black powder; these impurities seem to have some magnetic properties. How does the oxidation of carbon steel lead to the formation of iron tetraoxide?
Iron oxides include FeO (ferrous oxide), Fe2O3 (iron oxide), and Fe3O4 (ferric oxide, which can be considered as FeO·Fe2O3). Generally, the scale consists of 3 layers: the outermost layer is iron oxide, the middle layer is ferric oxide, and the innermost layer is ferrous oxide. As for carbon deposits, it’s necessary to look into the previous processing steps involved~~
It’s possible it has been oxidized; that’s just my opinion
Thank you for your answer. Could you explain in detail how these three layers of oxide are formed?
In the atmosphere, iron is first oxidized to ferrous oxide, then further oxidized to black ferric oxide, and subsequently oxidized to the reddish-brown ferric oxide that we are familiar with.
Pipelines inside carbon steel are generally in anaerobic conditions; how could they be the same as those in the atmosphere?
Oxygen penetrates into carbon steel; the outermost layer is essentially completely oxidized, forming iron oxide. The middle layer is partially oxidized and partially not oxidized, resulting in ferric oxide (that is, one part iron oxide and one part ferrous oxide). The innermost layer is essentially not fully oxidized, consisting of ferrous oxide~~