1. Comparison of wall thickness tolerance between erw steel pipe
and seamless steel pipe
ERW steel pipe: hot-rolled coil is used as raw material, the thickness limit of modern hot-joining can be controlled within 0.05mm, and the seamless steel pipe is produced by round steel perforation, the wall thickness deviation is large, and the subsequent hot rolling can partially eliminate the wall. Thickness unevenness, but the current advanced unit can only be controlled within ±5~10%t, corresponding to the thickness of 8.94mm steel pipe.
Seamless steel pipe: The limit of wall thickness control accuracy is 0.9mm.
2. ERW steel pipe and seamless steel pipe compared with outer diameter tolerance
ERW steel pipe: adopts cold-bending forming, and the sizing is completed by 0.6% reduction. The process temperature is basically constant at room temperature, so the outer diameter control is accurate and the fluctuation range is small, which is good for eliminating black leather buckle;
Seamless steel pipe: It adopts hot-rolling forming process, and its sizing is completed at 8000C. The raw material composition, cooling conditions and cooling state of the steel pipe have a great influence on the outer diameter, so the outer diameter control is difficult to be accurate and fluctuates. The range is large.
3. Comparative tensile test of erw steel pipe and seamless steel pipe
The tensile performance indexes of seamless steel tubes and erw steel tubes are in line with API standards, but the strength of seamless steel tubes is generally at the upper limit and the plasticity is at the lower limit. In comparison, the strength index of erw steel tubes is in an excellent state, and the plasticity index is higher than the standard 33.3%. The reason is that the performance of the raw material of the erw steel pipe-hot rolled coil is guaranteed by means of microalloying smelting, refining outside the furnace and controlled cooling and rolling; the seamless steel pipe mainly relies on the means of increasing the carbon content, and it is difficult to ensure the strength and plasticity. Reasonable match.
4. ERW steel pipe and seamless steel pipe compared ovality
ERW steel pipe: cold-formed, so the outer diameter control is accurate and the fluctuation range is small.
Seamless steel pipe: The hot rolling forming process, the raw material composition of the steel pipe, the cooling condition and the cooling state of the roll have a great influence on the outer diameter, so the outer diameter control is difficult to be accurate and the fluctuation range is large.