Seamless pipe is manufactured by extruding the metal to the desired length; therefore ERW pipe have a welded joint in its cross-section, while seamless pipe does not have any joint in its cross-section through-out its length.In addition to the method of construction, the pressure capacity, cost, and the application of each kind of pipe vary from the other.

The cost difference between seamless and erw pipes

Since seamless pipes have a longer manufacturing process, and the operations here are multiple, the cost of seamless pipes is always higher in comparison to a welded pipe. ERW pipes make use of cold formed sheets, which are then joined together by high frequency welding, which is a relatively simple process, with the cost being fractional in comparison to the seamless variety.
For convenience of comparison, here are the main differences between ERW welded pipe and seamless steel pipe:

1. Outer diameter tolerance
ERW steel pipe: cold-forming and complete the size determination by reducing the diameter by 0.6%. The process temperature is basically constant at room temperature. Therefore, the outer diameter can be accurately controlled, and the fluctuation range is small, which helps eliminate the black leather buckle.
Seamless steel pipe: It adopts hot rolling forming technology and is shaped at about 8000℃. The material composition of the roller of the steel pipe, the cooling conditions and the cooling conditions have a great influence on its outer diameter, so it is difficult to accurately control the outer diameter and fluctuate in a large range.

2. Wall thickness tolerance
ERW steel pipe: Hot-rolled strip steel is used as the raw material. The thickness tolerance of modern hot-rolled strip steel can be controlled within 0.05mm, and seamless steel pipe is produced by round steel perforation, and the wall thickness deviation is large. Subsequent hot rolling can partially eliminate the wall thickness. The thickness is uneven, but currently the most advanced device can only be controlled within +5~10%t, which is equivalent to a steel tube with a thickness of 8.94mm.
Seamless steel pipe: The limit of wall thickness control accuracy is 0.9mm.

3. Ellipse
ERW steel pipe: cold-formed, with accurate diameter control and small fluctuation.
Seamless steel pipe: hot rolling forming process. The raw material composition of the roller, cooling conditions and cooling conditions have a great influence on the outer diameter of the steel pipe. Therefore, it is difficult to accurately control the outer diameter and the fluctuation range is large.

4. Tensile test
The tensile properties of seamless steel pipe and ERW steel pipe meet API standard, but the strength of seamless steel tubes is usually at the upper limit, and the plasticity is at the lower limit. In contrast, ERW steel pipe has the highest strength, and the plasticity index is 33.3% higher than the standard. The reason is that through micro-alloying smelting, refining outside the furnace, and controlled cold rolling, the performance of the raw materials of ERW steel pipe and hot rolled strips is guaranteed. Seamless steel pipe mainly rely on means to increase carbon content, making it difficult to ensure a reasonable match between strength and plasticity.

5. Hardness
The raw material of ERW steel pipe, namely hot-rolled strip coil, has high precision of controlling cooling and rolling during the rolling process, which can ensure the uniform performance of each part of the strip coil.

6. Grain
The raw material of the ERW steel pipe is a hot-rolled strip coil, which uses a wide continuous casting slab. The solidified surface has fine crystals, fine crystals, no columnar crystal area, shrinkage and looseness, small composition deviation, and dense structure; in the subsequent rolling During the manufacturing process, the application of intermediate cold rolling technology further ensures the grain size of the raw material.

7. Anti-collapse test
ERW steel pipe is characterized by its raw materials and pipe manufacturing process. Its wall thickness uniformity and ellipticity are far superior to seamless steel pipe, which is the main reason why the pressure resistance is higher than seamless steel pipe.

8. Impact test
Since the impact toughness of ERW steel pipe substrate is several times that of seamless steel pipe, the impact toughness of the weld is the key to ERW steel pipe. By controlling the content of impurities in the raw material, the height and direction of the longitudinal burr, the shape of the forming edge, the welding angle and welding speed, the heating power and frequency, the welding extrusion amount, the intermediate frequency extraction temperature and depth, the length of the air cooling section and other process parameters It can ensure that the impact energy of the weld reaches more than 60% of the base material. If it is further optimized, the impact energy of the weld close to the base material can be achieved achieve seamless performance.

9. Burst test
The blasting test performance of ERW steel pipe is far higher than the standard requirements, which is mainly due to the uniform wall thickness and uniform outer diameter of ERW steel pipe.

10. Straightness
ERW steel pipe is cold-worked and can be straightened online with a reduced diameter, and has an infinite multiple rule, so the straightness is better; seamless steel pipe is formed in a plastic state, plus the single rule (continuous rolling is 3~4 times rule) The straightness of the tube is difficult to control.

11. Appearance
The defects on the outer surface of the blank used in seamless steel pipe cannot be eliminated by hot rolling, and can only be polished after the finished product is completed. The spiral channel remaining after the perforation can only be partially eliminated during the wall reduction process. ERW steel pipe is made of hot rolled coil. The surface quality of the coil is the surface quality of the ERW steel pipe. The surface quality of the hot rolled coil is easy to control and high quality. Therefore, the surface quality of ERW steel pipe is far superior to that of seamless steel pipe.

12. Steel consumes 10,000 meters feet long
The wall thickness of the ERW steel pipe is uniform, and the wall thickness tolerance is negligible. The control accuracy limit of the wall thickness difference of the seamless steel pipe is ±5% t, and is generally controlled within ±5~10% t.

In order to ensure that the minimum wall thickness can meet the standard requirements and performance, it can only be solved by appropriately increasing the wall thickness. Therefore, in the casing of the same specification and the same weight, the ERW steel pipe is 5-10% or more longer than the seamless steel pipe, thereby reducing the consumption of steel pipe of 10,000 meters feet by 5-10%. Even if the price is the same, ERW bushings can actually save users 5% to 10% of procurement costs.