According to the manufacturing method, steel pipes can be divided into two categories: seamless steel pipes and welded seam steel pipes. Among them, ERW steel pipe is the main variety of welded steel pipe. Today, we mainly talk about two kinds of steel pipes used as raw materials for petroleum casing: seamless casing and ERW casing.
Seamless casing made of seamless steel pipes; seamless steel pipes refer to steel pipes manufactured by four methods: hot-rolled, cold-rolled, hot-drawn, and cold-drawn. There is no weld seam on the pipe body itself.
ERW (Electric Resistant Weld) steel pipe made of electric welded pipe refers to a straight seam welded pipe manufactured by a high-frequency resistance welding process. The raw material steel plate (coil) of ERW welded pipe is made of low-carbon microalloy steel rolled by TMCP (Thermo-Mechanical Control Process).
1. Seamless steel pipe with outer diameter tolerance: hot-rolled forming process, shaped at around 8000C. The raw material composition, cooling condition and cooling state of the roller have a great influence on its outer diameter, so the outer diameter control is not easy to be accurate, and the fluctuation range is large. ERW steel pipe: It is cold-formed, sizing 0.6%. The process temperature is basically constant at room temperature, so the outer diameter is controlled accurately and the fluctuation range is small, which is beneficial to eliminate black leather buttons;
2. Wall thickness tolerance seamless steel pipe: It is produced by perforating round steel with large wall thickness deviation. Subsequent hot rolling can partially eliminate uneven wall thickness, but the most advanced units can only be controlled within ±5~10%t. ERW steel pipe: Using hot rolled coil as raw material, the thickness tolerance of modern hot rolling can be controlled within 0.05mm.
3. Appearance The external surface defects of the blank used in seamless steel pipes cannot be eliminated by the hot rolling process, and can only be polished off after the finished product is completed; the spiral path left after perforation can only be partially eliminated during the wall reduction process. ERW steel pipe uses hot rolled coil as raw material. 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 the quality is high. Therefore, the surface quality of ERW steel pipe is much better than that of seamless steel pipe.
4. Oval seamless steel pipe: hot-rolled forming process. The raw material composition of the steel pipe, the cooling conditions and the cooling state of the roll have a great influence on its outer diameter, so the outer diameter is difficult to accurately control, and the fluctuation range is large. ERW steel pipe: cold-formed, accurate outer diameter control, small fluctuation range.
5. Tensile test The tensile performance indicators of seamless steel pipes and ERW steel pipes meet API standards, but the strength of seamless steel pipes is generally at the upper limit and plasticity at the lower limit. In comparison, the strength index of ERW steel pipe is in the best state, and the plastic index is 33.3% higher than the standard. The reason is that the performance of hot-rolled coils of the raw materials of ERW steel pipes is guaranteed by means of microalloying smelting, out-of-furnace refining, controlled cold and controlled rolling, etc.; seamless steel pipes mainly rely on means to increase the carbon content, and it is difficult to ensure strength and plasticity. Reasonable collocation.
6. The hot-rolled coil of the raw material of the hardness ERW steel pipe has extremely high precision during the rolling process, which can ensure the uniformity of the performance of each part of the coil.
7. The raw material of grain size ERW steel pipe-hot rolled coil adopts wide and thick continuous casting billet, which has a thicker fine-grained surface solidification layer, no columnar crystal regions, shrinkage and pores, small composition deviation, and compact structure; in the follow-up The application of controlled cold and controlled rolling technology in the rolling process further ensures the grain size of the raw materials.
8. The 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 to ERW steel pipe. By controlling the impurity content of the raw material, the height and direction of the cutting burr, the shape of the forming edge, the welding angle, the welding speed, the heating power and frequency, the welding extrusion amount, the intermediate frequency drawing temperature and depth, and the air-cooled section length and other process parameters Ensure that the weld impact energy reaches more than 60% of the base metal. If further optimized, the impact energy of the weld can be close to that of the base material to achieve seamless performance.
10. Blasting test The performance of the blasting test of ERW steel pipe is much higher than the standard requirement, mainly due to the high uniformity of the wall thickness and uniform outer diameter of the ERW steel pipe.
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