Seamless pipe VS ERW pipe:
The outer surface defects of the blanks used in seamless steel pipes cannot be eliminated by the hot rolling process. The defects can only be polished after the finished product is completed; the spiral path left after piercing can only be partially eliminated in the process of reducing the wall.
ERW steel pipe uses hot-rolled coils as raw materials. The surface quality of the coils is the surface quality of ERW steel pipes. The surface quality of hot-rolled coils is easy to control and high in quality. Therefore, the surface quality of ERW steel pipes is much better than that of seamless steel pipes.
2. Outer diameter tolerance
ERW steel pipe: It is cold-formed, 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 helpful to eliminate black leather buckles;
Seamless steel pipe: hot-rolled forming process is adopted, and its sizing is completed at about 8000C. The raw material composition, cooling condition and cooling state of the roll of the steel pipe have a great influence on its outer diameter, so it is difficult to accurately control the outer diameter and fluctuate The range is larger.
3. Wall thickness tolerance
ERW steel pipe: using hot-rolled coil as raw material, modern hot-rolling thickness tolerance can be controlled within 0.05mm, while seamless steel pipe is produced by round steel perforation method, the wall thickness deviation is large, and the subsequent hot rolling can partially eliminate the wall Thickness unevenness, but the most advanced unit can only be controlled within +5~10%t, which corresponds to 8.94mm thick steel pipe.
Seamless steel pipe: The limit of wall thickness control accuracy is 0.9mm.
ERW steel pipe: adopts cold bending forming, so the outer diameter control is accurate and the fluctuation range is small.
Seamless steel pipe: Hot-rolled forming process is adopted. The raw material composition of the steel pipe, the cooling condition and the cooling state of the roll have a great influence on its outer diameter, so it is difficult to accurately control the outer diameter and has a large fluctuation range.
5. Tensile test
The tensile properties of seamless steel pipes and ERW steel pipes conform to API standards, but the strength of seamless steel pipes is generally at the upper limit and the plasticity is at the lower limit. In comparison, the strength index of ERW steel pipes is in the best state, and the plasticity index is 33.3% higher than the standard. The reason is that the performance of hot-rolled coils, the raw material of ERW steel pipes, is guaranteed by means of microalloying smelting, out-of-furnace refining, and controlled cold and controlled rolling; seamless steel pipes mainly rely on means to increase carbon content, and it is difficult to ensure strength and plasticity. Reasonable match.
The raw material of ERW steel pipe, a hot-rolled coil, has a very high precision of controlled cold and controlled rolling during the rolling process, which can ensure the uniform performance of all parts of the coil.
7. Grain body
The hot-rolled strip, the raw material of ERW steel pipe, uses a wide and thick continuous casting billet, with a thicker fine-grained surface solidification layer, no columnar crystal regions, shrinkage holes and looseness, small composition deviation, and compact structure; in the subsequent rolling process In the middle, the application of controlled cold and controlled rolling technology further ensures the grain size of raw materials.
8. Anti-collapse test
ERW steel pipe is due to the characteristics of its raw materials and pipe-making process. Its wall thickness uniformity and ellipticity are far better than seamless steel pipes, which is the main reason why the collapse resistance performance is higher than that of seamless steel pipes.
9. Impact test
Since the impact toughness of the base material of ERW steel pipe is several times that of seamless steel pipe, the impact toughness of the weld is the key of ERW steel pipe. By controlling the impurity content of raw materials, the height and direction of slitting burrs, the shape of the forming edge, the welding angle, and the welding speed , Heating power and frequency, welding extrusion volume, intermediate frequency withdrawal temperature and depth, air-cooling section length and other process parameters ensure that the impact energy of the weld reaches more than 60% of the base metal. If further optimized, the weld impact energy can be close to that of the base metal. Material, so as to achieve seamless performance.
10. Blasting test
The blasting test performance of ERW steel pipe is much higher than the standard requirement, mainly due to the high uniformity of wall thickness and uniform outer diameter of ERW steel pipe.
The ERW steel pipe is cold-worked, and it has online straightening in the reduced diameter state, and the infinite multiple ruler is added, so the straightness is better; the seamless steel pipe is formed in the plastic state, plus the single ruler (continuous rolling is 3 ~4 times the ruler) The straightness of the pipe end is relatively difficult to control.
Seamless black steel pipe is made up of steel that has not being galvanized. Its name comes from the skin, dark-colored iron oxide coating on its surface. It is used in applications that does not requires galvanized steels.