Views:5 Author:Site Editor Publish Time: 2019-06-03 Origin:Site
Steel pipes can be made into seamless steel pipes and welded steel pipes. Among them, ERW steel pipe is the main variety of welded steel pipe.
Today, we are going to talk about two kinds of steel pipes used as raw materials for oil casing: seamless casing and ERW casing.
Seamless casing -- a casing made of seamless steel pipe
Seamless (Seamless) pipe, refers to the four methods of hot rolling, cold rolling, hot drawing, cold drawing made of steel pipe. The tube itself does not have any welds.
ERW casing -- the casing made of electric welded pipe
ERW(Electric Weld) pipe refers to the direct-welded pipe made through high-frequency resistance welding. The raw material steel plate (coil) of ERW welded pipe is made of low carbon microalloy steel by TMCP(thermo-mechanical Control Process) rolling.
The outside diameter tolerance
Seamless steel tube: the use of hot rolling forming process, its sizing is completed in about 8000C, steel tube raw material composition, cooling conditions and the cooling state of the roller have a greater impact on its outside diameter, so the outside diameter control is difficult to be accurate, and the fluctuation range is large.
ERW steel tube: cold bending molding, through 0.6% reducing the diameter to complete the diameter, the process temperature is basically constant at room temperature, so the outer diameter control accurate, small fluctuation range, is conducive to the elimination of black buckle;
The wall thickness tolerance
Seamless steel tube: it is produced by perforating round steel, the wall thickness deviation is large, the subsequent hot rolling can partially eliminate the wall thickness non-uniformity, but the most advanced unit can only control within ±5 ~ 10%t.
ERW steel pipe: hot rolled strip coil is used as raw material, and the thickness tolerance of modern hot continuous tie can be controlled within 0.05mm.
The defects on the surface of the blank used in seamless steel pipe cannot be eliminated by hot rolling process. In the process of wall reduction, only partial elimination can be achieved for the spiral track left after perforation.
ERW steel tube USES hot rolled coil as raw material, the surface quality of coil is the surface quality of ERW steel tube, and the surface quality of hot rolled coil is easy to control and high quality, so the surface quality of ERW steel tube is far better than seamless steel tube.
Seamless steel tube: the use of hot rolling forming process, steel tube raw material composition, cooling conditions and the cooling state of the roller have a greater impact on the outside diameter, so the outside diameter control is difficult to be accurate, and the fluctuation range is large.
ERW steel tube: cold bending forming, so the outside diameter control is accurate, the fluctuation range is small.
Seamless steel pipe and ERW pipe tensile performance indexes accord with standard of API, but the strength of the seamless steel tube is generally in the ceiling, the plastic is in lower limit, by comparison, ERW steel pipe strength index in the best state, plasticity index is higher than the standard 33.3%, the reason for the ERW steel tube of raw materials - hot rolled coil is depend on the performance of micro alloying of smelting, refining outside the furnace and controlled rolling of cooling means to guarantee; Seamless steel tube mainly depends on the means of increasing carbon content, it is difficult to ensure the reasonable matching of strength and plasticity.
The raw material of ERW steel tube, hot rolling strip coil, has very high precision in the process of rolling, which can ensure the uniform performance of each part of the strip coil.
The raw material of ERW steel tube -- hot rolling coil adopts wide and thick continuous casting billet, with thick fine grain surface solidification layer, no columnar crystal zone, shrinkage cavity and loose, small composition deviation, compact structure; In the subsequent rolling process, the application of cold controlled rolling technology further ensures the grain size of raw materials.
Collapse resistance test
ERW steel tube because of its raw materials, the characteristics of the pipe production process. The uniformity and ellipticity of its wall thickness are much better than that of seamless steel pipe, which is the main reason of higher crushing resistance than that of seamless steel pipe.
Several times due to the impact toughness of ERW steel pipe to seamless steel tube, the impact toughness of welds is the key of ERW steel pipe, by controlling the impurity content of raw material, slitting, molding of edge burr height and direction form, Angle of welding, welding speed, heating power and frequency, welding extrusion amount, intermediate frequency withdraws from the depth, temperature and air cooling length of process parameters to ensure the weld to that of the parent metal of more than 60%, further optimization, such as can realize welding seam impact energy is close to the parent metal, so as to achieve performance as seamlessly.
The blasting test
The blasting test performance of ERW steel tube is much higher than the standard requirements, mainly due to the high wall thickness uniformity of ERW steel tube and uniform outside diameter size.
Seamless steel tube in the plastic state forming, plus single foot (continuous rolling for 3 to 4 feet) tube end straightness is relatively difficult to control;
ERW steel pipe belongs to cold processing, and in the state of reducing diameter with online straightening, plus is infinite times feet, so the straightness is better.
Steel consumption of 10 thousand meter footage casing
The wall thickness of ERW steel tube is uniform, and its wall thickness tolerance can be ignored, while the control accuracy limit of the wall thickness difference of seamless steel tube is ±5%t, generally controlled in ±5 ~ 10%t. In order to ensure that its minimum wall thickness can meet the standard requirements and service performance, only an appropriate increase in wall thickness to solve. Therefore, in the same specification and weight of casing, ERW steel pipe is 5 ~ 10% longer than seamless steel pipe, which reduces the steel consumption of 10 thousand meters of casing steel by 5 ~ 10%. Even at the same price, ERW casing virtually saves users 5 ~ 10% of the purchase cost.
But is now at home and abroad, or use more seamless, because in the ERW casing steel grade can only control the highest K55, if high steel grade and then we also don't have the production capacity, domestic for ERW market now, do the casing or Japanese production equipment and production process can reach a certain level, but also just can produce the N80 if want to production to the higher grade of steel P110 or currently has the certain difficulty, so the ERW now can only do table form.