Coating steel pipes are steel pipes with a plastic anticorrosive layer fused to the inner surface (or both inner and outer surfaces) via spraying, rolling, dipping, or absorbing processes. Plastic-lined steel pipes, also known as steel-plastic composite pipes, are based on ordinary carbon steel pipes and are lined with a chemically excellent thermoplastic plastic. After cold-drawing or blow molding, they combine the mechanical properties of steel pipes with the corrosion resistance of plastic pipes.

In people's lives, with the significant increase in the usage of steel products, their applications have also become more specialized. Among them, coated steel pipes and plastic-lined steel pipes have a wide range of applications and are quite similar in many aspects. But what are the differences between them? Next, the editor will illustrate several points of detail for everyone.

Section 1: In terms of technology:

Plastic Coating Process: After the steel pipe is pre-treated, a glue adhesive is evenly applied to the outer wall of the plastic pipe, which is then placed inside the steel pipe to expand and form a steel-plastic composite product.

The plastic coating process involves heating steel pipes after pre-treatment, followed by high-speed plastic coating, and then curing to form a steel-plastic composite product.

Layer and Coating Thickness

The plastic coating thickness of the plastic-coated steel pipe should meet the requirements for coating thickness as specified in the CJ/T136 standard. The coating thickness of the coated steel pipe should comply with the requirements for coating thickness as outlined in the CJ/T120 standard.

Section 3: Raw Material Variations

 Neoprene piping materials are typically purchased as hot-dipped galvanized steel pipes, with the inner zinc coating difficult to completely remove, significantly affecting adhesion; however, plastic-coated steel pipes use welded pipes as raw materials, adopting advanced foreign production technology. The surface of the steel pipe is treated with an external zinc-nickel alloy coating, and the inner wall is lined with high-temperature熔结high molecular weight, non-toxic powder. The products comply with the Ministry of Construction's CJ/T120-2008 standard (replacing J/T120-2000), and the pipeline and inner wall hygiene standards meet the "Hygienic Safety Evaluation Specification for Drinking Water Transmission and Distribution Equipment and Protective Materials" (2001).

Section 4: Differences in Thermal Expansion and Contraction

The lining pipe tends to shrink in diameter due to the thicker lining layer and the greater shrinkage of the plastic layer, with a tendency to shorten in length. It is particularly unsuitable for large-diameter pipes. After undergoing a boiling test, most lining pipes will exhibit delamination. A clear difference is observed through the boiling test: after 24 hours of boiling at 95°C, the ordinary lining pipe shows localized delamination at the interface between the steel pipe and the lining layer. After boiling for 48 to 72 hours, some lining pipes may have the lining layer protruding 2 to 3mm.

Modified epoxy resin used in coated steel-plastic pipes, particularly large-diameter ones, has a thermal expansion coefficient very close to that of steel, significantly reducing thermal shrinkage.