Talking about the corrosion of metals by petrochemical chlorides
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In chloride media, chlorides are divided into two types: inorganic chlorides and organic chlorides. The former is generally brought in from crude oil, while the latter is a product of the production process, that is, it gets mixed in during production. The corrosion of carbon steel by chlorides is essentially uniform corrosion accompanied by hydrogen embrittlement. The corrosion of stainless steel is pitting corrosion. According to some experimental data, the order of the resistance of common stainless steels to chloride-induced pitting, from lowest to highest, is 304 → 304L → 1Cr13 → 316 → 316L → 321 → 347. In engineering, measures to prevent chloride corrosion are primarily considered from the following aspects: (1) Improving the desalting process of crude oil so that NaCl, MgCl2, and CaCl2 in the crude oil are removed to a large extent before distillation. (2) Inject ammonia, alkali, water, and corrosion inhibitors into key areas (such as the tower top condensation system). The purpose of injecting ammonia and alkali is to neutralize HCl, while the purpose of injecting water is to dilute HCl. When the concentration of Cl ions drops below 100 PPm, corrosion is reduced. General engineering requirements specify that the Cl ion concentration should be kept at 50 PPm or below. (3) Select suitable materials, such as carbon steel-stainless steel composite steel plates.
In the petrochemical industry, chlorides mainly originate from crude oil and the production process. Chlorides cause significant corrosion of metals, especially carbon steel and stainless steel. Carbon steel is subject to uniform corrosion and hydrogen embrittlement, while stainless steel primarily suffers from pitting corrosion. To reduce the corrosion of metal equipment caused by chlorides, protection can be achieved by improving the crude oil desalination process, injecting ammonia, alkalis, water, or corrosion inhibitors at key locations, and selecting appropriate materials. For example, controlling the Cl- concentration below 50 PPm in the tower top condensation system can effectively reduce the corrosion rate. .