Differences between Seamless Tube and ERW Tube

The question "Shall I use seamless tubes or ERW tubes for my project?" is coming up over and over. Each of the two has different advantages and disadvantages, which should be pondered to take a proper decision:
 

Seamless tube (SMLS) VS ERW tube:

1. Appearance
The outer surface defects of the blanks used in seamless steel tubes 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 tube uses hot-rolled coils as raw materials. The surface quality of the coils is the surface quality of ERW steel tubes. 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 tubes. 

2. Outer diameter tolerance

Seamless steel tube: 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 tube have a great influence on its outer diameter, so it is difficult to accurately control the outer diameter and fluctuate The range is larger.

ERW steel tube: 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;

3. Wall thickness tolerance

Seamless steel tube: The limit of wall thickness control accuracy is 0.9mm.

ERW steel tube: 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.

4. Ovality

Seamless steel tube: 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.

ERW steel tube: Adopts cold bending forming, so the outer diameter control is accurate and the fluctuation range is small.

5. Hardness
The raw material of ERW steel tube, 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.

6. Tensile test
The tensile properties of seamless steel tubes and ERW steel tubes conform to 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 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 tubes, is guaranteed by means of microalloying smelting, out-of-furnace refining, and controlled cold and controlled rolling; seamless steel tubes mainly rely on means to increase carbon content, and it is difficult to ensure strength and plasticity. Reasonable match.

7. Grain body
The hot-rolled strip, the raw material of ERW steel tube, 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. 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.

9. Anti-collapse test
ERW steel tube 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 tubes, which is the main reason why the collapse resistance performance is higher than that of seamless steel tubes.

10. Blasting test
The blasting test performance of ERW steel tube is much higher than the standard requirement, mainly due to the high uniformity of wall thickness and uniform outer diameter of ERW steel tube.

11. Straightness

The ERW steel tube 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 tube 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.

Go here to learn more about " Seamless pipe vs Welded pipe"

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