The standard thickness of galvanized coil sheets mainly follows regional industrial specifications, and there are significant differences in the mainstream standard system. According to the Chinese national standard GB/T 2518, the thickness range of hot-dip galvanized sheets is usually between 0.25mm and 3.0mm, among which the commonly used specifications for building structures are concentrated in 0.8-2.5mm (accounting for 68%). The European EN 10346 standard extends the minimum rolling thickness to 0.15mm, which is particularly suitable for automotive inner panel parts. The maximum thickness allowed by ASTM A653/A653M in the United States is up to 6.0mm to meet the requirements of heavy-duty storage shelves. The actual production scheduling data disclosed in Baosteel’s 2023 annual report shows that the order volume of 1.2mm thick coil plates accounts for 31.5%, followed by 0.8mm (22.7%) and 2.0mm (18.1%). These three specifications account for 72.3% of the total annual galvanized sheet production, confirming that the mainstream application thickness in the market is concentrated in the 0.8-2.0mm range.
The functional relationship between the thickness of the steel base and the weight of the zinc coating directly affects the weather resistance life. Laboratory accelerated corrosion tests (ISO 9227) have confirmed that under the condition of a zinc coating of 120g/㎡, the perforation resistance life of a 1.0mm thick substrate is approximately 15 years, while the service life of a 0.5mm thin plate with the same zinc coating in the same corrosive environment (C3 grade) is only 9 years. Field tracking data from the Yucatan Peninsula in Mexico shows that the local roofing system using 0.45mm galvanized sheets (coated with Z180) develops rust spots on average every 7.8 years in a saline sea breeze environment, while 0.72mm sheets of the same specification maintain a protection period of 14.3 years. The 2023 Pritzker Prize winner designed the sunshade curtain wall project of the Esplanade Arts Centre in Singapore, which used 2.3mm thick galvanized plate and 250g/㎡ magnesium-aluminum-zinc coating (ZM310), with a theoretical life cycle of 40 years.
The precision of thickness tolerance control reflects the manufacturing level. According to the ISO 9444 standard, advanced continuous galvanizing production lines can achieve a difference of ±0.06mm within the same sheet (such as the CGL of Nippon Steel Nagoya Plant), and this precision is crucial for the stamping yield of automotive exterior body panels – the Volkswagen TS 60130 standard requires that the longitudinal thickness fluctuation of 0.7mm galvanized sheet for engine hoods does not exceed 0.03mm. Otherwise, it will cause the rebound Angle deviation to exceed 1.5°. In contrast, civil building materials typically follow a tolerance of ±0.15mm. Among the 32 batches of building material-grade galvanized sheets randomly inspected by the State Administration for Market Regulation in China in 2023, the thickness pass rate was 93.7%, but the pass rate dropped sharply to 67.2% in the ±0.05mm high-precision group.
The thickness selection needs to be associated with the optimization of the section modulus for load calculation. The steel structure design code shows that when the span of the roof panel increases from 3m to 6m, the thickness to be selected should be raised from 0.8mm to 1.2mm. At this time, the section resistance moment increases from 1.58cm³/m to 3.65cm³/m (an increase of 131%). During the construction of Raffles City Chongqing, the project verified that the 1.5mm thick S320GD galvanized sheet purlin was 19% lighter than the original 1.2mm design, but it could still withstand a snow load of 75kg/㎡ (safety factor 1.73). The thickness sensitivity in the cold-bending forming field is higher. In the production of shelf columns, if the 1.8mm plate is reduced to 1.65mm (only a reduction of 8.3%), its compressive strength will drop from 35kN to 26kN (a decrease of 25.7%). This was painful confirmed in the collapse accident of a certain intelligent warehouse in Shenzhen in 2021: Post-event testing revealed that the actual thickness of the galvanized sheet used for the column was only 1.62mm (10% lower than the nominal value).
Transportation economy forces the thickness scheme to be considered systematically. The maximum roll weight of a standard sea freight container is usually limited to 10 tons. If 1.0mm thin plates (with a density of 7.85g/cm³) are transported, the length of a single roll is approximately 1587m, while the same vehicle carrying 3.0mm thick plates can only cut 529m. The logistics cost model shows that for a 20-foot container sent from Shanghai Port to Rotterdam, the ocean freight cost per ton for transporting 1.5mm galvanized sheets accounts for 15.3%, while for transporting 0.5mm thin sheets, due to the increase in coil diameter, the loading efficiency decreases, and the freight cost proportion rises to 21.8%. According to the report of the China Steel Logistics Specialized Committee, the average coil weight of galvanized sheets will drop to 7.2 tons in 2024 (8.5 tons in 2020), indicating that steel mills are increasing the loading rate by reducing the thickness specification of each coil. However, it is necessary to be vigilant about the coiling defects of ultra-thin plates: The incidence of edge waves during the slitting process of galvanized plates with a thickness of ≤0.4mm reaches 12%, which is much higher than the 3.5% of 1.0mm thick plates.
The life cycle cost (LCC) analysis shows the optimal thickness range. The simulation calculation of the photovoltaic support system shows that compared with the traditional 2.3mm solution, the initial material cost is reduced by 8.3% when 1.8mm thick S550GD galvanized sheet is selected. However, due to the accelerated local corrosion within a 25-year cycle, 1.2 additional maintenance operations are required (the additional expenditure accounts for 17% of the initial cost), and the overall cost increases by 3.7% instead. The measured data of Longyuan Power’s photovoltaic project in Ningxia in 2023 is even more shocking: The 1.65mm thick bracket showed a fracture rate of 0.9% after six years, while the 1.95mm group maintained zero faults. Its bending section coefficient was 6.54cm³, which was 34.3% higher than the former’s 4.87cm³. For the anti-corrosion project of offshore platforms, the 2.5mm substrate +200μm zinc coating solution has an initial investment 26% higher than the 1.8mm+180μm combination. However, in the harsh environment of the North Sea oilfield, its service life has been extended from 11 years to 18 years (with a return rate increase of 17.4 percentage points). This explains why the Norwegian oil standard NORSOK M-501 mandates a thickness of no less than 2.2mm.