Square tube is formed by cold or hot rolled strip steel after welding or roll made of square steel. 

That quality testing whether the pipe has its own standards? About the detection methods for reference 

1 port. The end face of the integrity of the product requires cutting edge length greater than or equal to the size of the tip 100MM products, cutting-degree not greater than or equal 1mm. Slope of less than 200mm end product can not be greater than 1.5mm, cutting caused because the product does not allow port deformation, and at the ports will not allow the presence of burrs 

2 weld. Weld cracks are not allowed to open or opening of the welding class, the case of customer requirements, but far off the seam or weld reinforcement 

3 the convex portion of the sectional plane is also a requirement 

4 lengths. Length of the product if there is a length requirement, the first is to not allow the existence of joint, not shorter than the required length of the length of the 

5 Weld visually. Under the product online, the need to conduct a 100% visual detection of weld 

6. Acceptance criteria. Acceptance criteria square tubes have GB / T 3094, GB/T6728