1. External diameter tolerance
Seamless Pipe: It is difficult to control the outer diameter of seamless pipe accurately and fluctuate in a larger range because of its raw material composition, cooling conditions and cooling state outside the roll.


ERW pipe: cold forming, sizing by reducing the diameter by 0.6%, the process temperature is basically constant at room temperature, so the outer diameter control is accurate, the fluctuation range is small, which is conducive to eliminating the black buckle;


2. Wall Thickness Tolerance
Seamless tube: The accuracy limit of wall thickness control is 0.9mm.


ERW pipe: With hot rolled coil as raw material, the thickness of modern hot connection can be controlled within the tolerance range of 0.05 mm, while seamless pipe can be produced by round steel piercing with deviation of wall thickness. Secondly, the wall thickness can be partially inhomogeneous by hot rolling, but the most advanced unit can only be controlled at [5] 10% t, corresponding to the thickness of 8.94 mm steel pipe.


3. Elliptical
Seamless pipe: Hot rolling process, raw material composition of steel, cooling condition and roll cooling condition have great influence on its outer diameter, so it is difficult to control the outer diameter accurately and fluctuate in a larger range.
ERW pipe: cold forming is adopted, so the outer diameter control is accurate and the fluctuation range is small.


4. Tensile test
The tensile properties of seamless and ERW pipes meet API standards, but the strength of seamless pipes is generally in the upper limit and the plastics is in the lower limit. Compared with the strength of ERW pipes, the plasticity index is higher than the standard 33.3%. Because the performance of raw material-hot rolled coil of ERW pipes depends on microalloy smelting, furnace smelting and cold controlled rolling. To ensure seamless steel pipe mainly depends on the means of increasing carbon content. It is difficult to ensure strength and reasonable collocation.


5. Hardness
The control of cold rolling precision of ERW pipe raw material - hot rolled coil is very high in rolling process, which ensures the uniformity of coil components.


6. Crystals
The raw material of ERW pipes-hot rolled coil has wide thickness of continuous casting billet, thicker grain surface solidification layer, no columnar area and loose shrinkage, small composition and dense structure. In the subsequent rolling process, the application of medium and controlled cold rolling technology further ensures the grain size of raw materials.


7. Crushing test
ERW pipe is characterized by its raw material and pipeline technology. Its wall thickness is uniform, ellipticity is far superior to seamless tube, the main reason why the anti-fragmentation performance of seamless tube is higher than that of seamless tube.


8. Impact test
Because of the impact toughness of ERW pipe base in seamless pipe for many times, the impact toughness of weld is the key of ERW pipe. By controlling the impurity content of raw material, cutting height and direction, forming edge shape, welding angle, welding speed, heating power and frequency, welding extrusion quantity and length of air-cooled section, the welding shadow can be ensured. Sound, up to 60% of the base metal, such as further optimization, materials, in order to achieve seamless performance.


9. Blasting test
The blasting test performance of ERW pipe is much higher than the standard requirement, mainly from the uniformity of wall thickness and diameter of ERW pipe.


10, straight line
ERW tube is cold-processed, straightened in the state of reduced diameter, and infinite, so straightness is better; seamless tube in the plastic forming state, with a measuring instrument (rolling volume of 3-4 times the scale) tube straightness is relatively difficult to control.


11. Appearance
Seamless tube used for billet surface defects can not be eliminated by hot rolling process, only after finished products, polishing defects; for spiral holes, in the process of reducing the wall, can only be part of the elimination. ERW pipe is made of hot rolled coil. The surface quality of coil is the surface quality of ERW pipe. The surface quality of hot rolled coil is easy to control and high quality. Therefore, the surface quality of ERW pipe is better than that of seamless pipe.