Advantages of ERW High-Frequency Welded Pipe

First, the technical development process of ERW steel pipe at home and abroad

High-frequency welded pipe (ERW) is a hot rolled coil formed by the molding machine, the use of high-frequency current skin effect and proximity effect, so that the edge of the billet is heated and melted, and pressure welding is carried out under the action of the extrusion roll to achieve the production. High-frequency resistance welding method began to be applied to welded pipe production in the 1950s. In the past decade, its production technology is becoming more and more perfect, product quality continues to improve. First of all, the quality of raw materials used in the production of ERW has improved significantly, the steel composition design of low C, low P, S, micro-alloying; smelting process of converter smelting, ladle refining, vacuum degassing, continuous casting and the use of new technologies; rolling process of controlled rolling, control of the use of cooling technology to make large and medium-caliber ERW steel pipe with the appearance of the appearance of the dimensions of the hot-rolled steel strip, appearance and quality, physical and chemical properties have improved dramatically. The second is the large and medium caliber ERW steel pipe. Secondly, large and medium-diameter ERW steel pipe molding welding heat treatment and other processes in the production process to achieve automatic computer control, high-frequency welding process heat input energy along with the computer's automatic compensation system has been effectively controlled to prevent the welding heat input energy caused by low cold welding, false welding and high heat input energy caused by over-burning. Medium-frequency heat treatment temperature control makes the heat treatment process can achieve the best results according to the process requirements, effectively ensuring the quality of the weld and heat-affected zone. In addition, the progress of testing technology, the realization of online or offline full weld ultrasonic or eddy current inspection, hydraulic test can also be monitored in the computer, according to the requirements of the pressure test and pressure stabilization.ISO9000 series of standards and the promotion and implementation of APIQ1 specification, so that the large and medium-diameter ERW steel pipe production, inspection, sales and service is in a whole process of quality assurance. In recent years, countries are actively studying the use of high-frequency welded pipe (ERW) steel pipe instead of seamless pipe and spiral welded pipe, in industrially developed countries, the diameter of high-frequency welded pipe in the Ф610mm below, the proportion of ERW has reached about 70%.

ERW and SAW, SML comparison of various performance indicators

1, ERW and SAW comparison

(1) As the length of SAW weld is about 4-5 times longer than the length of ERW weld, the inner weld tumor has no process ability to remove, so it inevitably increases the friction of the inner wall of the pipeline when conveying media. While the ERW weld length is short, the internal weld tumor can be removed, the medium flowing in the pipe, the pipe wall resistance is relatively small compared to the spiral submerged arc welded steel pipe, which reduces the amount of oil mixing and reduces the temperature rise generated by the resistance is very favorable to reduce the amount of oil products transported.

(2) According to the residual stress measurement results show that the ERW welded pipe circumferential molding internal stress is small, for the pipe is favorable. For SAW welded pipe, because of its large weld zone, weld stress has tension and pressure, the stress state is more complex than the ERW pipe, which is related to the spiral welded pipe molding process. The inner surface is elastic complex tensile stress, axial stress is +450Mpa, circumferential stress is +344 Mpa, this kind of large range of tensile stress in the weld and heat-affected zone of the inner wall will have an adverse effect on the inner wall defects of the initiation of cracking and stress corrosion.

(3) Due to the SAW weld length is about 4-5 times the length of the high-frequency straight seam pipe weld length, the finished pipe weld treatment of anti-corrosion treatment is more difficult; ERW steel pipe has a short weld (compared with the spiral seam steel pipe), the pipe wall thickness is uniform, the length of the pipe is stable, geometric dimensions of the high precision, corrosion prevention and assembly welding quality is easy to ensure.

2、Comparison of ERW and SML

(1) Superior billet quality

High-frequency welded steel pipe billet and SML steel pipe billet compared to the chemical composition of the design is more scientific and reasonable.

ERW special steel grade is characterized by high purity. Through the de-S, de-P, degassing, Ca treatment and other methods to make the S, P content can be controlled at 0.005% below, N content can be controlled at 0.008% below, the inclusions can be controlled for the form of spherical, and its number is greatly reduced. c content is controlled at 0.1% below, so that the welding, including the construction process of the ring weld has a good weld performance, and the increase in the strength of the Nb, V, Ti and other micro-alloying elements, to stop the austenitic alloying elements, to stop the austenitic alloying elements. Trace alloying elements to prevent the growth of austenite grain, while increasing the gap strengthening to improve the toughness and strength of steel. The SML steel pipe billet is generally A3, 20 steel, 16Mh and other materials, the purity of the material is poor, the C content is high, generally in the 0.2% or so, is not conducive to the construction of the ring welded butt joints, the strength is still good, but the toughness is poor.

ERW steel pipe billet and SML steel pipe billet is another major difference: the former is manufactured by cold roll forming with hot rolled steel strip, while the latter is a garden steel in the hot rolled state by the perforated molding. Obviously, the hot rolled state of the formation of the SML billet grain size and organization of the degree of density and ERW billet compared to a large gap, which can cause the performance of the inevitable and fasteners are very different.

(2) Geometric advantages

Whether from the information comparison, or information in the measured data comparison, ERW steel pipe than SML dimensional accuracy. This is due to the fact that seamless pipes are formed by continuous perforation of garden steel in a hot rolling unit, while ERW steel pipes are formed from steel strip in a cold rolled state. In contrast, ERW is easier to implement than SML in terms of dimensional control of appearance. Because of this, ERW tubes have fewer appearance quality defects and better appearance quality than SML tubes.

In addition, due to the use of computerized flying saws, the sizing rate and sizing length of HF welded pipes are more accurate. As the high-frequency welded pipe is manufactured by hot rolled steel strip with higher rolling precision, its thickness is easy to control, and the pipe with thinner wall thickness and higher steel grade can be produced according to the design requirements. Such as the West-to-East Gas Pipeline Project, after several iterations of demonstration, is now basically determined to use X70 steel grade, wall thickness of 14.7mm, Ф1016mm steel pipe, steel grade to improve the wall thickness down, the relative reduction of engineering investment, about 5 billion yuan. The wall thickness of the seamless pipe is often subject to the limitations of perforation technology and production costs, thin-walled steel pipe is very difficult.