Open a quotation for galvanized tube and you will see codes like Z40, Z60 or Z80 next to the coating line. If you have never ordered tube before, these codes look like factory jargon — but they are simply the coating weight, and they are the single biggest lever on both price and service life.
What the Z-number means
The Z-class states the total zinc coating weight on both surfaces, in grams per square metre:
| Class | Coating weight (both sides) | Typical feel |
|---|---|---|
| Z40 | 40 g/m² | Indoor or mild-duty fabrications |
| Z60 | 60 g/m² | General outdoor fabrication |
| Z80 | 80 g/m² | More demanding outdoor exposure |
Note: Z-classes belong to hot-dip-coated strip. Yuanheng’s tube is pre-galvanized — coating graded in Z-classes: Z40 / Z60 / Z80 (40 / 60 / 80 g/m²).
More zinc means more corrosion protection — and a higher material cost. The goal is not “as much as possible” but matching the class to the environment and the product’s expected life.
How to choose a class
As a general industry approach:
- Indoor, dry environment (furniture, shelving, display racks): Z40 is commonly sufficient, especially when the tube will be powder-coated afterwards.
- General outdoor use (fencing, gates, greenhouse structures): Z60 is a common middle ground.
- Humid, coastal or higher-corrosion environments: Z80, or Z-class plus additional surface treatment — worth discussing explicitly with your supplier.
Two practical warnings:
- Environment matters more than product type. The same greenhouse frame needs a different class in a dry inland region than on a humid coastline.
- Whatever class you agree, write the acceptance criteria into the order — coating weight, measurement method and sampling — so inspection is not a matter of opinion.
Coating and downstream finishing
A major reason fabricators choose pre-galvanized tube is what happens after purchase: the uniform, thinner coating on flat surfaces takes powder coating and electrophoretic finishing well, which is why it dominates furniture frames, racking and fitness equipment. If your product is finished rather than bare, tell your supplier — the recommended coating class may differ.
FAQ
Can I order a coating weight between the standard classes? Non-standard coating weights can be requested and are confirmed before quoting — send the target value with your sizes.
Is a heavier coating always more corrosion-resistant? Within the same environment, more zinc generally means longer life. But the right question is “enough for my environment and product life”, not “maximum”.
How do I verify the coating I received? Agree the measurement method and sampling plan before order confirmation, then arrange inspection against those agreed criteria.
Specifying tube now? Yuanheng rolls pre-galvanized tube in walls from 0.6 to 2.5 mm with Z40/Z60/Z80 (40/60/80 g/m²) coating, from 1-ton lots. Send your specification →