According to the manufacturing method, steel pipes can be divided into two categories: seamless steel pipes and welded steel pipes. Among them, ERW steel pipes are the main kind of welded steel pipes. Today, we mainly talk about two kinds of steel pipes used as casing raw materials: seamless casing pipes and ERW casing pipes.
Seamless casing pipe – casing pipe made of seamless steel pipe; Seamless steel pipe refers to steel pipe made by four methods of hot rolling, cold rolling, hot drawing and cold drawing. The pipe body itself has no welds.
ERW body – ERW (Electric Resistant Weld) steel pipe made of electric welded pipe refers to longitudinal seam welded pipe made by high frequency resistance welding. Raw steel sheets (coils) for electric-welded pipes are made from low-carbon micro-alloy steel rolled by TMCP (thermomechanical controlled process).
1. O.D. tolerance seamless steel pipe: using hot-rolled forming process, sizing is completed at about 8000°C. The composition of the raw material, the cooling conditions, 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 the fluctuation range is large. ERW steel pipe: it is formed by cold bending, and its diameter is reduced by 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 conducive to the elimination of black leather buckles;
2. Seamless steel pipe with wall thickness tolerance: It is produced by perforating round steel, and the wall thickness deviation is large. Subsequent hot rolling can partially eliminate the unevenness of the wall thickness, but the most modern machines can only regulate it within ±5~10%t. ERW steel pipe: When using hot rolled coil as raw material, the thickness tolerance of modern hot rolling can be controlled within 0.05mm.
3. Defects in the outer surface of the workpiece used for the appearance of seamless steel pipe cannot be eliminated in the hot rolling process, but can only be polished after the finished product is completed, the helical stroke left after punching can only be partially eliminated in the process of reducing walls. ERW steel pipe is made from hot rolled coil as raw material. The surface quality of the coil is the same as the surface quality of ERW steel pipe. The surface quality of hot rolled coils is easy to control and is of high quality. Therefore, the surface quality of ERW steel pipe is much better than that of seamless steel pipe.
4. Oval seamless steel pipe: using hot rolling 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 it is difficult to accurately control the outer diameter, and the fluctuation range is large. ERW steel pipe: produced by cold bending, the outer diameter is precisely controlled, and the fluctuation range is small.
5. Tensile test The tensile properties of seamless steel pipe and ERW steel pipe are in accordance with API standards, but the strength of seamless steel pipe is generally at the upper limit, and the ductility is at the lower limit. On the contrary, the strength index of ERW steel pipe is in the best condition, and the plasticity index is 33.3% higher than the standard. The reason is that as a raw material for ERW steel pipe, the performance of hot rolled coil is guaranteed by micro-alloy smelting, out-of-furnace refining, and controlled cooling and rolling; plastic. Reasonable coincidence.
6. The raw material of ERW steel pipe is hot-rolled coil, which has extremely high precision in the rolling process, which can ensure the uniform performance of each part of the coil.
7. Raw material of ERW hot rolled steel coil pipe with grain size adopts wide and thick continuous casting billet, the surface fine-grain solidification layer is thick, there is no area of ​​columnar crystals, shrinkage porosity and pores, composition deviation is small. , and the structure is compact; control in the subsequent rolling process The use of cold rolling technology additionally ensures the grain size of the raw material.
8. The slip resistance test of ERW steel pipe is related to the characteristics of the raw material and the manufacturing process of the pipe. The wall thickness uniformity and ovality are much better than seamless steel pipes, which is the main reason that the collapse resistance is higher than that of seamless steel pipes.
9. Impact test Because the toughness of the base material of ERW steel pipe is several times higher than that of seamless steel pipe, the 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 cutting burr, the shape of the forming edge, the welding angle, the welding speed, the heating power and frequency, the welding extrusion volume, the intermediate frequency retraction temperature and depth, the length of the air cooling section and other process parameters are guaranteed. Energy weld impact reaches more than 60% of the base metal. With further optimization, the impact energy of the weld can be close to the energy of the base metal, which ensures trouble-free operation.
10. Explosive testing The explosive testing performance of ERW steel pipes is much higher than the standard requirements, mainly due to the high uniformity of wall thickness and the same outer diameter of ERW steel pipes.