Cement Mortar Coated Steel Pipes for Corrosion Resistance
Cement mortar coated steel pipes are designed with a layer of concrete inside, which has the ability to absorb and store significant amounts of heat. This characteristic leads to an uneven temperature distribution within the pipe's cross-section when exposed to fire, effectively increasing the fire resistance duration. As a result, the heating rate of the steel column is slowed down, and once the steel begins to yield, the surrounding concrete can take on most of the axial load, preventing structural collapse. The fire resistance of composite beams is also improved due to the heat transfer from the top flange of the steel beam to the concrete. According to experimental data, using cement mortar coatings can reduce the amount of fireproof paint needed by up to one-third to two-thirds or even more when achieving a 3-hour fire resistance rating.
The strength grades of cement mortar used in these pipes include M3, M5, M7.5, M10, M12.5, M15, M20, M25, M30, and M40. Depending on their intended use, mortar is categorized into masonry, plastering, and jointing, though this classification is unrelated to the grade designation. After the application of cement mortar, a crucial step is air drying, which involves leaving the structure in a natural environment for 2–3 days. This process helps prevent cracks caused by impact during transportation.
Steel components under external forces can still be affected in terms of deformation, stability, and fatigue resistance. Hot-rolled steel products often face challenges in maintaining precise dimensions, especially in thickness and side width. Thermal expansion and contraction are well-known phenomena—despite meeting size standards at the time of hot rolling, there may be slight dimensional deviations after cooling. The greater the negative difference in side width and thickness, the more pronounced the performance differences become. Therefore, for large steel sections, it's difficult to achieve extremely high precision in edge width, thickness, length, angle, and corners.
Internal corrosion protection for cement mortar coated steel pipes includes various methods such as three-layer polyethylene (3PE) and two-layer polyethylene (2PE) coatings for oil and gas pipelines, single- and double-layer fused epoxy (FBE) coatings for similar applications, non-toxic macromolecular coatings like IPN8710 for water supply systems, and high-density polyethylene polyurethane foam insulation. Additionally, internal cement mortar lining is commonly used in water supply pipelines to prevent corrosion. Other options include anti-corrosion treatments using epoxy coal tar and fiberglass cloth.
These cement mortar coated steel pipes have a wide range of applications. In municipal engineering, they are ideal for high-rise building water supply systems, heating networks, and underground water transmission pipelines. In the petroleum industry, they are used for transporting corrosive media in pipelines, as well as in chemical, pharmaceutical, and textile sectors. In sewage treatment, they are suitable for discharge pipes, sewage lines, and anti-corrosion projects in biological pools. In agriculture, they provide excellent corrosion resistance for irrigation, deep well, and drainage systems, enhancing the fire resistance and fire protection properties of steel pipes compared to traditional steel structures.
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