Introduction to the corrosion of stainless steel pipes

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Introduction to the corrosion of stainless steel pipes: When stainless steel is corroded, its surface passivation film is damaged and the passivation layer dissolves. Such as the common general corrosion: This type of corrosion destroys the uniformity of most of the material on the surface; the corroded surface remains relatively uniform. It typically occurs in inorganic acids, non-oxidizing acid solutions, or highly corrosive thermal solutions. In areas where the corrosion resistance of steel is reduced, this type of corrosion intensifies significantly. Such as residual welding oxides, the powder layer removed by grinding carbon steel, etc. Stress corrosion cracking: It occurs when austenitic stainless steel cracks under the influence of chloride ions, mechanical stress, and temperature rise; stress corrosion cracking rarely happens below 60° or inside liquid cargo tanks. It occasionally occurs in heating coils (heating semi-solid oils containing chloride ions or being exposed to seawater ballast tanks containing chloride ions). Electrochemical corrosion: Dissimilar materials may experience electrochemical corrosion when connected by an electrolyte. When carbon steel and stainless steel are welded (as is the case in the fabrication of fixed joints), the reactive metal carbon steel suffers from accelerated corrosion. Driven by the electrolytic voltage, the electrolytic current between the two components induces electrochemical corrosion. Pitting (also known as pitted corrosion): Pitting is a type of corrosion that results in the formation of small holes or pitted areas on the surface of a metal, with a certain degree of solubility in those areas. For example, chlorides and iodides can penetrate into the etched layer, causing damage to the passivation layer; the halide ions prevent the passivation layer from repairing itself, which leads to rapid and localized pitting even through small cracks. Pitting begins in small cracks and gradually penetrates deeper into the metal; at this point, the corrosion accelerates, forming a deep and large cavity near the surface. Pitting is difficult to detect at first, and it is also quite hard to determine the extent of its corrosion. Defects such as dents or scratches on the passivation layer of a stainless steel surface, or the presence of iron particles or dust, as well as cratering, pores, and spatter on the welds, can all create weak points in the passivation layer. Pitting corrosion also occurs very easily when water is used as the ballast medium. Intergranular corrosion: In narrow gaps, such as those at flange or threaded connections, the passivation layer in these gaps can be damaged. In design, flange and threaded connections should be avoided as much as possible to prevent the formation of such gaps. During welding, phenomena such as undercutting should be avoided. Intergranular corrosion: Intergranular corrosion occurs in chromium-deficient areas, leading to a decrease in corrosion resistance, and it takes place in strongly acidic environments. The carbon content in stainless steel on chemical ships is below 0.03%; this value increases when the material is exposed to heat for extended periods. If the surface of the steel is contaminated by oil, greases, coatings, or paints, intergranular corrosion is likely to occur. The above 6 common types of stainless steel corrosion can easily occur during the transportation, cutting, manufacturing, welding, installation, and use of stainless steel