According to the manufacturing method, steel pipes can be divided into two categories:
seamless steel pipes and welded 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 oil casing: seamless casing and ERW casing.
Seamless casing - casing made from seamless steel pipe
Seamless pipe refers to the steel pipe manufactured by four methods of hot rolling, cold rolling, hot drawing and cold drawing. The tube body itself does not have any welds.
ERW casing - casing made from electric welded pipe as raw material
ERW steel pipe (Electric Resistant Weld) refers to a straight seam welded pipe manufactured by a high frequency resistance welding process. The raw steel plates (coils) of ERW welded pipes are low-carbon microalloyed steels rolled by TMCP (Thermo-Mechanical Control Process).
1. Outer diameter tolerance
Seamless steel pipe: The hot-rolled forming process is adopted, and the sizing is completed at about 8000C. The composition of the raw material 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 control is difficult to be accurate and fluctuate. Larger range.
ERW steel pipe: It is formed by cold bending, and the diameter is reduced by 0.6% to complete the sizing. The process temperature is basically constant at room temperature, so the outer diameter is accurately controlled and the fluctuation range is small, which is conducive to eliminating black leather buckles;
2. Wall thickness tolerance
Seamless steel pipe: It is produced by round steel perforation, and the wall thickness deviation is large. The subsequent hot rolling can partially eliminate the uneven wall thickness, but the current 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 continuous rolling can be controlled within 0.05mm.
3. Appearance
The defects on the outer surface of the billet used in the seamless steel pipe cannot be eliminated by the hot rolling process, and the defects 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 pipes use 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 has high quality. Therefore, the surface quality of ERW steel pipes is much better than that of seamless steel pipes.
4. Ovality
Seamless steel pipe: The hot-rolled forming process is adopted. The composition of the raw material 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 control accurately, and the fluctuation range is large.
ERW steel pipe: It is formed by cold bending, so the outer diameter is controlled accurately and the fluctuation range is small.
5. 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.
6. 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.
7. 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.
8. 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.
9. Impact test
Since the impact toughness of the base metal 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 slitting burr, 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, length of air cooling section and other process parameters ensure that the impact energy of the weld reaches more than 60% of the base metal. material for seamless performance.
10. Blasting test
The blasting test performance of ERW steel pipe is much higher than the standard requirements, mainly due to the high uniformity of wall thickness and uniform outer diameter of ERW steel pipe.
11. Straightness
The seamless steel pipe is formed in a plastic state, and the straightness of the pipe end is relatively difficult to control with a single ruler (continuous rolling is 3 to 4 times the ruler);
ERW steel pipe is cold-worked, and it has on-line straightening in the state of reduced diameter, plus it is infinitely multiplied, so the straightness is better.
12. Steel consumption of casing with 10,000 meter footage
The wall thickness of ERW steel pipe is uniform, and its wall thickness tolerance can be ignored, while the control accuracy limit of the wall thickness difference of seamless steel pipe is ±5%t, which is generally controlled at ±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% longer than the seamless steel pipe, or even more, which reduces the steel consumption of the 10,000-meter footage casing by 5-10%. Even at the same price, ERW bushing virtually saves 5-10% of the purchase cost for the user.
