The difference between seamless pipe and erw pipe

1. Different concepts

Seamless steel pipes are perforated from a whole piece of round steel, and the steel pipes without welds on the surface are called seamless steel pipes; ERW is a hot-rolled coil that is formed by a forming machine and uses the skin effect of high-frequency current. The proximity effect causes the edge of the tube blank to be heated and melted, and pressure welding is carried out under the action of the squeeze roller to realize the produced product.

2. Outer diameter tolerance

ERW steel pipe: It is cold formed and the size is determined 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 to eliminate the black leather buckle.

Seamless steel pipe: adopts hot-rolling forming process and is shaped at about 8000℃. The raw material composition, cooling conditions and cooling conditions of the steel pipe roll have a great influence on its outer diameter, so it is difficult to accurately control the outer diameter and fluctuate in a large range.

4. Ovality

ERW steel pipe: cold-formed, accurate outer diameter control, small fluctuation range; seamless steel pipe: hot-rolled forming process, the raw material composition of the steel pipe, cooling conditions and the cooling state of the roll have a great influence on its outer diameter, so external It is difficult to control the diameter accurately, and the fluctuation range is relatively large.

5. Appearance

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 far better than seamless steel pipes. .

6. Straightness

Seamless steel pipes are formed in a plastic state, and it is relatively difficult to control the straightness of the pipe end with a single ruler (continuous rolling is 3 to 4 times ruler); ERW steel pipes are cold processed and have online straightening in the reduced diameter state. In addition, it is infinite times the ruler, so the straightness is better.

3. Wall thickness tolerance

Seamless steel pipe: It is produced by round steel perforation method, and the wall thickness deviation is large. The subsequent hot rolling can partially eliminate the unevenness of the wall thickness, but the most advanced unit can only be controlled within ±5～10%t; ERW steel pipe ：Using hot-rolled coils as raw materials, the thickness tolerance of modern hot-rolling can be controlled within 0.05mm.

7. Tensile test

The tensile properties of the seamless steel pipe and the ERW steel pipe are in line with the API standard, but the strength of the seamless steel pipe is generally at the upper limit and the plasticity is at the lower limit. In comparison, the strength index of the ERW steel pipe is in the best state, and the plasticity index is 33.3% higher than the standard. The reason is that the performance of the hot-rolled coil, the raw material of ERW steel pipe, is guaranteed by means of microalloying smelting, out-of-furnace refining, and controlled cooling and rolling; a reasonable match.

8. Hardness

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

9. Grain size

The raw material of ERW steel pipe, the hot-rolled coil, is a wide and thick continuous casting billet, with a thick fine-grained surface solidification layer, no columnar crystal region, shrinkage cavity and looseness, small composition deviation and dense structure; in the subsequent rolling process Among them, the application of controlled cooling and controlled rolling technology further ensures the grain size of raw materials.

10. Anti-collapse test

ERW steel pipes are characterized by their raw materials and pipe-making processes. Its wall thickness uniformity and ovality are far superior to those of seamless steel pipes, which are the main reasons why the collapse resistance is higher than that of seamless steel pipes.

11. 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 seam 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 material. If further optimized, the weld impact energy can be close to the base material. Material to achieve seamless performance.

12. 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.

13.Consumption of steel for 10,000-meter footage casing

The wall thickness of ERW steel pipe is uniform, and its wall thickness tolerance can be neglected. The control accuracy limit of seamless steel pipe wall thickness difference is ±5%t, and it is generally controlled at ±5-10%t. In order to ensure that the minimum wall thickness can meet the standard requirements and performance, the solution 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% longer than the seamless steel pipe, or even more, which reduces the steel consumption of the casing for 10,000 meters by 5-10%. Even at the same price, ERW casing virtually saves users 5-10% of the purchase cost.