Advantages of hot rolled steel pipe:
It can destroy the casting structure of ingot, refine the grain of steel, and eliminate the defects of microstructure, so that the steel structure is dense and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the steel is no longer isotropic to a certain extent; the bubbles, cracks and porosity formed during pouring can also be welded under high temperature and pressure.

Disadvantages of hot rolled steel pipe:
1. After hot rolling, the non-metallic inclusions (mainly sulfides and oxides, as well as silicates) in the steel are pressed into thin sheets, resulting in delamination (sandwich) phenomenon. Delamination can deteriorate the tensile properties of the steel along the thickness direction, and interlaminar tearing may occur when the weld shrinks. The local strain induced by weld shrinkage is often several times of that at yield point, which is much larger than that caused by load;

2. Residual stress caused by uneven cooling. The residual stress is the internal self balance stress without external force. All kinds of hot-rolled section steel have this kind of residual stress. The larger the section size of general section steel is, the larger the residual stress is. Although the residual stress is self balanced, it has a certain influence on the performance of steel members under external force. Such as deformation, stability, anti fatigue and other aspects may have adverse effects.

3. The thickness and edge width of hot rolled steel products are not well controlled. We are familiar with thermal expansion and cold contraction. At the beginning of hot rolling, even if the length and thickness are up to standard, there will be a certain negative difference after cooling. The wider the side width of the negative difference is, the thicker the thickness is. Therefore, for large size steel, the width, thickness, length, angle and sideline of steel can not be too accurate.