As we know, ordinary steel (whether carbon steel or alloy steel), if left in the atmosphere for a long time, oxidizes on the surface and produces a yellowish-brown deposit, commonly called “rust,” which is metal corrosion. Ordinary steel is mainly an iron–carbon alloy; without special additives, its chemical stability in water and moist air is very poor. When no oxygen is present, iron forms white ferrous hydroxide of very low solubility; when oxygen is present together with water, ferrous hydroxide is quickly oxidized to brown ferric hydroxide. Ferric hydroxide is even less soluble in water than ferrous hydroxide and forms a loose layer covering the metal. It is not firmly bonded to the metal surface and cannot protect the iron from further corrosion. As oxygen continues to enter, corrosion proceeds continuously, and ferric hydroxide continually converts into complex hydrated iron oxide.
The metal corrosion described above is an electrochemical change. Metal corrosion occurs by two processes: chemical change and electrochemical change. Corrosion of metal in dry gas or in a non-electrolytic liquid is a chemical process, with no current generated during corrosion. It includes corrosion in high-temperature gases, steam, and various organic liquids. Corrosion of metal in electrolyte solutions and moist air is an electrochemical process. It is due mainly to the potential difference between the metal and the electrolyte solution, which causes ions to transfer from the metal into the solution (or the reverse process) and thereby produces corrosion. It comprises two processes: oxidation (dissolution of the metal) and reduction (evolution of hydrogen, reduction of oxygen, deposition of metal from solution, etc.). During electrochemical corrosion of metal, electric current is usually generated at the same time.
To prevent metal corrosion, chromium, nickel, and other metallic elements are added to steel in sufficient amounts to change the internal structure of the metal and promote formation of a dense oxide film on the steel surface, thereby preventing further corrosion. Prefabricated direct-buried insulated pipe of this type has strong corrosion resistance and is commonly referred to as prefabricated direct-buried insulated pipe. The corrosion resistance of prefabricated direct-buried insulated pipe is due mainly to the presence of chromium. When chromium content reaches 10–12% or more, the steel becomes what is commonly called “stainless steel.” In fact the term “stainless steel” is not entirely accurate, because prefabricated direct-buried insulated pipe is not completely “stainless”; this depends on its specific operating conditions. So-called “stainless” is only relative to ordinary carbon steel. For example, workpieces made of chromium stainless steels such as 2Cr13, 3Cr13, and 4Cr13, if surface finish is not very high, may still form a thin layer of “yellow rust” even when working in the atmosphere. Within the same grade of stainless steel, improving workpiece surface finish can enhance corrosion resistance.
The above is Jinan Insulated Pipe We hope this introduction to the corrosion-resistance features of ordinary prefabricated direct-buried insulated pipe is helpful. Follow us for more industry news. https://www.sdhpgy.com
