Galvanized Carbon steel square tube 40x40x2mm Z275 Pre Galvanized ASTM A500 Grade B Structural

This galvanized carbon steel square tube is formed from Z275 pre galvanized coil, which means the zinc coating is applied at the steel mill before the tube is welded rather than after. The 275 g per square metre total coating is the heavy end of the commercial pre galvanized range and gives a service life of roughly 20 to 25 years in rural and suburban atmospheres, according to ISO 9223 category C2 to C3 exposure.

The advantage of pre galvanized material over hot dip galvanized after fabrication is dimensional accuracy: there is no 60 to 120 micron zinc build up on the outside, so a 40 x 40 mm tube stays a 40 x 40 mm tube and slides into a connector as designed. The trade off is the cut end, where bare steel is exposed. We seal every cut end with a zinc rich wax during packing, and for outdoor work we recommend an additional cold zinc touch up on site at welded joints.

• Z275 Coating Weight: 275 g per square metre total zinc, both sides, verified by a strip sample from each coil and reported on the certificate.
• Dimension Stability: Because the coating is applied before forming, the outside dimension stays at 40 x 40 mm with a plus or minus 0.2 mm tolerance and no zinc build up at the corners.
• Grade B Structural Rating: ASTM A500 Grade B base steel gives 317 MPa minimum yield, so the galvanized finish does not come at the cost of structural capacity.
• Sealed Cut Ends: Cut ends are treated with a zinc rich wax and capped, which is the only practical way to protect the exposed steel in a pre galvanized section.
• Paint and Powder Adhesion: The light mill passivation is compatible with epoxy primer and powder coating after a standard degrease, so the tube can be finished in any colour.
• Consistent Zinc Adhesion: Bend and reverse impact tests are run every shift to confirm the coating does not flake at the corner radius during forming.

Outdoor frames are where this section earns its cost: carport and canopy posts, fence and gate frames, greenhouse structures, sign gantries, walkway handrails, solar mounting rails and livestock penning. It is also used indoors in wash down areas such as food packing halls, where a galvanized surface survives daily hose down better than painted black steel. For coastal sites within about 1 km of salt water we normally recommend hot dip galvanized after fabrication instead, because the cut ends and weld zones of a pre galvanized tube are the first points to show red rust.

Bundles are limited to 2 tons, strapped with three steel strips and wrapped in waterproof paper with a PVC sleeve, and the paper is kept dry because white rust forms quickly on galvanized surfaces stored under condensation. Bundles are stacked on timber dunnage in the container, never directly on the floor. Coating mass certificates and mill test reports to EN 10204 3.1 are supplied with every lot, and SGS or BV inspection is available before loading. CE, ISO 9001 and CNAS certification are held.

A field note worth passing to your fabricator: welded joints on pre galvanized tube must have the zinc removed within 25 mm of the weld before welding, otherwise the coating burns back and porosity appears in the seam. Grinding back and re coating with cold zinc gives a joint that outlasts the surrounding tube.