The Standards
Chinese Standards are often different, the tensile strength could be different.
Read your local standards and ask questions before searching factories.
The relevant standard to refer to should be:
AS/NZS 11632009 is the standard for Cold-formed structural steel hollow sections
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2. Different Grade, Zinc Coating, Tolerance, wall thickness
c250, C350. C450
Depending on the job the steel used for, consult the surveyor what grade and legal standards of thickness. For example, the thickness used in suppporting must be a 3.5mm or above.
For Example, the post support must fit snugly into the tube, if the wall size is not aligned, it doesn't fit, the whole steel lot could be written off.
3. Choose a reputable factory and do Quality Control before shipment
4. Anti-Dumping Duty
All tube are taxed heavily unless exempted. Worked out the final costs to ensure a fair costs comparison.
The goods subject to measures are: Certain electric resistance welded pipe and tube made of carbon steel, comprising circular and non-circular hollow sections. Normally referred to as either CHS (circular or oval hollow sections) or RHS(rectangular or square hollow sections) collectively referred to as hollow structural sections (HSS), including CHS with other than plain ends, such as threaded, swaged and shouldered.