Chemical Composition Difference
Q355NH: Contains alloy elements (0.25-0.55% Cu, 0.40-0.80% Cr, ≤0.50% Ni, ≤0.035% P) that are specially added to promote patina formation, with carbon content ≤0.18%
Ordinary carbon steel pipe: Only contains basic elements (Fe, C, Mn, Si), no corrosion-resistant alloy elements, and carbon content is generally 0.12-0.22%
Corrosion Resistance Difference
Q355NH: Forms a dense, self-healing patina in 6-12 months of natural weathering, reducing the corrosion rate to 1/4-1/10 that of ordinary carbon steel pipe, and does not require regular anti-corrosion coating maintenance in most outdoor environments
Ordinary carbon steel pipe: Forms loose, non-protective rust in the natural environment, the corrosion rate is fast, and it needs to be coated with anti-corrosion paint every 3-5 years, otherwise the substrate will be quickly corroded
Mechanical Properties Difference
Q355NH: Has higher strength, with minimum yield strength ≥355 MPa, tensile strength 470-630 MPa, and good low-temperature toughness (impact toughness ≥27 J at -20°C)
Ordinary carbon steel pipe: Lower strength, minimum yield strength ≥235 MPa, tensile strength 375-500 MPa, and poor low-temperature toughness, which is easy to brittle fracture in low-temperature environments
Long-Term Cost Difference
Q355NH: The initial procurement cost is 15-25% higher than ordinary carbon steel pipe, but it saves the long-term cost of coating, re-painting and maintenance, and the total life-cycle cost is 20-30% lower
Ordinary carbon steel pipe: The initial procurement cost is low, but the long-term maintenance cost is high, and the service life is only 1/2-1/3 of Q355NH in outdoor environments
Application Scope Difference
Q355NH: Suitable for outdoor structural applications with high corrosion resistance requirements, such as bridge support pipes, outdoor drainage pipes, architectural decorative pipes, and transmission tower support pipes
Ordinary carbon steel pipe: Suitable for indoor or low-corrosion environments, such as indoor water supply pipes, indoor structural support pipes, and temporary engineering pipes
