Why Choose SGCC Hot-Dip Galvanized Sheet Metal Fabrication Parts Outdoors?
2026-10-27
A site manager inspects an outdoor equipment enclosure after three years of service. The enclosure was made from cold-rolled steel with a powder coating. The coating has blistered along the bottom edge, and rust is bleeding from the fastener holes. The replacement unit is specified in SGCC hot-dip galvanized steel with no coating. The site manager wants to know whether the uncoated galvanized part will last longer than the coated cold-rolled part. The answer depends on the zinc layer and on how the part is fabricated. This guide explains why SGCC Sheet Metal Fabrication Parts are chosen for outdoor service and what to verify before ordering.
1. Why Does Outdoor Exposure Destroy Uncoated Steel Parts So Quickly?
Outdoor steel is attacked by three mechanisms at the same time. The first is moisture. Rain, dew, and humidity keep the steel surface wet for long periods, and the water acts as an electrolyte for the corrosion reaction. The second is chloride. Coastal air carries salt particles that deposit on the steel and accelerate the corrosion rate by a factor of three to five compared with inland air. The third is temperature cycling. The daily expansion and contraction cracks protective coatings and opens paths for water to reach the steel. A cold-rolled steel part with a paint coating will typically show rust at the edges and fasteners within two to three years in a coastal environment. The coating protects the flat surfaces, but the cut edges and the holes are not coated, and corrosion starts there. In our factory, we produce Sheet Metal Fabrication Parts in SGCC and in cold-rolled steel with coating. Cangzhou Shengsen Metal Products Co., Ltd. has been manufacturing sheet metal parts for over 15 years.
The key difference is that the galvanized part does not rely on a coating for protection at the edges. The zinc is part of the steel surface, and it protects the cut edge as well as the flat surface.
2. What Does the SGCC Zinc Layer Actually Do to Protect the Base Steel?
SGCC is a hot-dip galvanized steel sheet. The steel coil is passed through a molten zinc bath, and a metallurgical bond forms between the zinc and the steel. The zinc layer thickness is typically 60 to 275 grams per square meter, depending on the coating class. The zinc protects the steel in two ways. The first is a physical barrier. The zinc layer is continuous and covers the steel surface, so the steel is not exposed to the atmosphere. The second is sacrificial protection. Zinc is more electrochemically active than steel. When the zinc layer is scratched or cut, the zinc around the damaged area corrodes first and protects the exposed steel. This is why the cut edges of a galvanized part do not rust immediately. The table below shows the relationship between zinc coating weight and expected outdoor service life.
| Zinc coating weight (g/m²) | Salt spray resistance (ASTM B117) | Expected life in rural atmosphere | Expected life in coastal atmosphere |
| 60 | 72 – 120 hours | 5 – 8 years | 2 – 4 years |
| 120 | 200 – 300 hours | 10 – 15 years | 5 – 8 years |
| 180 | 400 – 600 hours | 15 – 20 years | 8 – 12 years |
| 275 | 800 – 1,000 hours | 20 – 30 years | 12 – 18 years |
In our factory, we verify the zinc coating weight of every incoming SGCC coil with a magnetic thickness gauge and with a stripping test. We also provide the mill certificate with the coating class for each batch. Cangzhou Shengsen Metal Products Co., Ltd. recommends a minimum coating weight of 120 grams per square meter for inland outdoor service and 180 grams per square meter for coastal service.
3. How Do Fabrication Processes Affect the Corrosion Resistance of Galvanized Parts?
Fabrication can damage the zinc layer, and the damage must be controlled. Cutting shears and laser cutting leave a cut edge where the steel is exposed, but the zinc adjacent to the edge provides sacrificial protection. Bending can crack the zinc layer on the outside of the bend if the bend radius is too small. Welding burns away the zinc in the heat-affected zone, and the exposed steel must be protected after welding. The table below shows the effect of each fabrication process and the recommended corrective action.
| Fabrication process | Effect on zinc layer | Corrective action |
| Shearing | Cut edge exposed; zinc adjacent provides protection | No action for indoor; apply zinc-rich paint for coastal |
| Laser cutting | Narrow heat-affected zone; minimal zinc loss | Inspect edge; touch up if required |
| Bending | Zinc may crack on outside radius if radius too small | Use bend radius at least 1.5 times thickness |
| Welding | Zinc burned away in heat-affected zone | Remove zinc before welding; apply zinc-rich paint after |
| Punching | Hole edge exposed; zinc adjacent protects | Deburr; touch up for coastal service |
Fabrication engineer's note: The most common cause of premature rust on a galvanized part is the failure to protect the weld zone. The zinc is burned away within 10 to 20 millimeters of the weld, and if the area is not painted with a zinc-rich coating, rust starts at the weld within months. In our factory, we remove the zinc from the weld area before welding and apply a zinc-rich primer after welding and cleaning. We also use a bend radius of at least 1.5 times the thickness to prevent zinc cracking. Cangzhou Shengsen Metal Products Co., Ltd. provides a fabrication and finishing specification with each order.
4. Why Does SGCC Outperform Painted Cold-Rolled Steel in Coastal and Industrial Environments?
In a coastal or industrial environment, the atmosphere contains chlorides and sulfur compounds that attack both the steel and the coating. A painted cold-rolled part is protected only where the coating is intact. When the coating is scratched or chipped, the steel is exposed, and the corrosion spreads under the coating, causing it to blister and peel. A galvanized part is protected even where the zinc is damaged, because the zinc around the damage corrodes first and protects the steel. The result is that the galvanized part does not develop the undercutting corrosion that destroys painted parts. In our factory, we have compared the two materials in a coastal test site. The painted cold-rolled panels showed rust at the scribe after 18 months. The SGCC panels with 180 grams per square meter coating showed no red rust after 36 months. Cangzhou Shengsen Metal Products Co., Ltd. can provide the test report on request.
The maintenance cost is also lower for SGCC. A painted part requires periodic inspection and touch-up painting, which is difficult for equipment installed in remote or elevated locations. A galvanized part requires only occasional cleaning to remove salt deposits, and it does not need repainting.
5. How Should Designers Specify and Verify SGCC Parts for Outdoor Service?
The specification should include five items. The first is the steel grade and the zinc coating class, expressed as grams per square meter or as a coating designation. The second is the bend radius requirement. The third is the welding and post-weld treatment requirement. The fourth is the cut edge and hole treatment requirement, especially for coastal service. The fifth is the acceptance test, which may include a zinc coating thickness measurement and a salt spray test on a sample. The verification at receipt should include a coating thickness check at three points on each part, a visual inspection for cracks at the bends, and a check of the weld touch-up. In our factory, we perform these checks on every production lot and provide the inspection report with the shipment. Cangzhou Shengsen Metal Products Co., Ltd. also provides a material certificate that traces the coil to the mill heat number.
We recommend that the designer specify the coating class based on the corrosivity category of the installation site. For rural and suburban sites, 120 grams per square meter is adequate. For urban and industrial sites, 180 grams per square meter is recommended. For coastal sites within 1 kilometer of the sea, 275 grams per square meter is recommended, together with a zinc-rich touch-up on all cut edges and welds.
Frequently Asked Questions About SGCC Sheet Metal Fabrication Parts for Outdoor Use
Summary for Designers and Fabrication Buyers
SGCC hot-dip galvanized Sheet Metal Fabrication Parts are chosen for outdoor service because the zinc layer provides both a physical barrier and sacrificial protection at cut edges and damaged areas. The service life depends on the zinc coating weight, the fabrication quality, and the environment. The specification should include the coating class, the bend radius, the welding and touch-up procedure, and the acceptance test. The verification should include a coating thickness check and a visual inspection of the bends and welds. Cangzhou Shengsen Metal Products Co., Ltd. has been manufacturing sheet metal fabrication parts for over 15 years and provides full material traceability and fabrication support for outdoor projects.
