Cement Mortar Coated Steel Pipes for Corrosion Resistance
Cement mortar coated steel pipes are designed to provide enhanced durability and fire resistance. These pipes are filled with concrete, which has a high thermal capacity and can absorb significant amounts of heat energy. As a result, when exposed to fire, the temperature distribution within the pipe cross-section becomes uneven, effectively increasing the fire resistance time of the structure. This also helps slow down the heating rate of the steel column. In the event that the steel yields, the surrounding concrete can carry most of the axial load, preventing structural collapse. Additionally, the fire resistance of composite beams is improved because the heat from the top flange is transferred into the concrete, reducing the temperature of the steel beam.
Studies have shown that using cement mortar coatings can reduce the amount of fireproofing material needed by up to one-third or even two-thirds, depending on the specific fire resistance requirements. For example, achieving a 3-hour fire resistance rating can be done more efficiently with this method.
The strength grades of cement mortar used in these applications include M3, M5, M7.5, M10, M12.5, M15, M20, M25, M30, and M40. The mortar is categorized based on its purpose—masonry, plastering, and jointing—but these classifications are not directly related to the grade. After the application of cement mortar, an essential step is air drying. This involves leaving the structure in a natural environment for 2-3 days to prevent cracking due to impacts during transportation.
Steel components under external forces may experience some degree of deformation, instability, or fatigue. Hot-rolled steel products often face challenges in maintaining precise dimensions, especially in thickness and side width. Thermal expansion and contraction are common phenomena. Even if the initial dimensions meet standards, cooling can cause slight dimensional changes. The greater the negative difference in side width and thickness, the more pronounced the impact on performance. Therefore, for large steel sections, precision in edge width, thickness, length, angle, and edges is limited.
Internal corrosion protection of cement mortar coated steel pipes includes several methods such as three-layer polyethylene (3PE) coating for oil and gas pipelines, two-layer polyethylene (2PE), single-layer FBE (fusion-bonded epoxy), double-layer FBE, non-toxic IPN8710 macromolecular coatings for water supply, high-density polyethylene polyurethane foam insulation, and cement mortar lining. Epoxy coal tar fiberglass cloth coatings are also commonly used for anti-corrosion purposes.
These pipes have a wide range of applications including municipal engineering, where they are used for water supply systems, heating networks, and gas transmission. In the petroleum industry, they are suitable for transporting corrosive media. They are also widely used in sewage treatment projects and agricultural irrigation systems, where their corrosion resistance offers significant advantages over traditional steel structures, improving both fire resistance and safety.
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