Comparison of ERW pipe and seamless pipe (SMLS):
(1) Superior tube blank quality
Compared with the tube blank of SMLS steel pipe, the design of chemical composition of high frequency welded pipe (ERW) is more scientific and reasonable.
ERW special steel grades are characterized by high purity. Through de-S, de-P, degassing, Ca treatment and other methods, the content of S and P can be controlled below 0.005%, the content of N can be controlled below 0.008%, the shape of inclusions can be controlled to be spherical, and the number of inclusions can be greatly reduced . The C content is controlled below 0.1%, so that the welding including the construction process of girth welding has good welding performance, and the increase in strength is to prevent the growth of austenite grains by adding trace alloying elements such as Nb, V, and Ti. At the same time, gap strengthening is increased to improve the toughness and strength of the steel. The tube blank of SMLS steel pipe is generally made of A3, #20 steel, 16Mh and other materials. The purity of the material is poor, and the C content is high, generally around 0.2%, which is not conducive to the girth welding in construction. The strength is acceptable, but Poor toughness.
Another major difference between ERW steel pipe blanks and SMLS steel pipe blanks is that the former is made of hot-rolled steel strips by cold rolling, while the latter is formed by perforating round steel in a hot-rolled state. Obviously, the grain size and the weave density of the SMLS tube blank formed in the hot rolling state are quite different from those of the ERW tube blank, and the properties that can be caused by this must also be very different.
(2) Advantages of geometric size
No matter from the comparison of the data or the comparison of the measured data in the data, the dimensional accuracy of ERW steel pipe is higher than that of SMLS. This is because the seamless pipe is formed by continuous perforation of the round steel in the hot rolling mill, while the ERW steel pipe is formed from the steel strip in the cold rolled state. In contrast, ERW is easier to implement than SMLS in terms of external dimensions. Because of this, the appearance quality of ERW steel pipe has fewer defects, and the appearance quality is also better than that of SMLS steel pipe.
In addition, due to the use of the computer flying saw, the precision of the fixed-length rate and the fixed-length length of the high-frequency welded pipe is high.
Since the high-frequency welded pipe is made of hot-rolled steel strip with high rolling precision, its thickness is easy to control, and the steel pipe with thinner wall thickness and higher steel grade can be produced according to the design requirements. For example, after several repeated demonstrations, the pipes used in the West-East Gas Pipeline Project are basically determined to use X70 steel grade, with a wall thickness of 14.7mm and Ф1016mm. The steel grade is increased, the wall thickness is reduced, and the project investment is relatively reduced, about 5 billion yuan . The wall thickness of seamless pipes is often limited by perforation technology and production costs, and thin-walled steel pipes are very difficult.