ERW (high frequency straight seam welded pipe) steel pipe blanks are manufactured by hot-rolled steel strip cold rolling forming, while SML (seamless steel tube) steel pipe blanks are formed by perforating round steel in the hot-rolled state. Obviously, the SML formed in the hot-rolled state has a large gap between the grain size and the denseness of the structure of the tube compared with the ERW tube, and the properties caused by it must be very different.
(1) Excellent tube blank quality
Compared with the billet of the SML steel pipe, the design of the chemical composition of the ERW steel pipe is more scientific and reasonable. ERW special steel grades are characterized by high purity. By taking off S, De-P, de-aeration treatment and other methods make S, P content can be controlled at o. Below 005%, N content can be controlled below 0.008%, the shape of inclusions can be controlled to be spherical, and the number of them is greatly reduced. The content of C is controlled below 0.1%, which makes it easy to perform girth welding including the construction process.
(2) Advantages of geometric size
It can be seen from the comparison of the dimensional deviation of ERW steel pipes that ERW steel pipes have higher dimensional accuracy than SML steel pipes. This is because the SML steel pipe is continuously perforated in a hot rolling mill, while the ERW steel pipe is formed from a steel strip under cold rolling. In contrast, ERW steel pipes have more control over appearance dimensions than SMI. Steel tubes are easier to implement. Because of this, the appearance quality of ERW steel pipes has fewer defects, and the appearance quality is better than SML steel pipes.
(3) Comparison of ERW and SML standards
General seamless hot-rolled steel pipe for fluid transportation, the standard is GB8163-87, its specifications are: outer diameter 32-630mm, wall thickness 2.5-75mm, steel grades 10, 20, 09MnV, 16Mn. The American Petroleum Institute API SL (41) standard is applicable to steel pipes for petroleum and natural gas transportation, including welded pipes and seamless pipes, and its specifications are outside diameter ≠ lO. 3 ～ ≠ 2032. Omm, wall thickness is 1.7 ～ 31.8mm, steel grades are A25, A, B, X42, X46, X52, X56, X60, X65, X70 and X80. Similar to this standard are IS03183-1996 series standards and GB / T 9711-1997 series standards issued in November 1997 and implemented in April 1998. ISO, GB / T standards are derived from APISL (41) standards.
(4) Physical quality comparison between ERW and SML steel pipes
① Chemical composition. From the comparison of the physical composition of ERW and SML steel pipes, it can be seen that the composition of the five steel pipes all meets the requirements of API SL (41) and GB 8163-87. The composition design of the ERW steel pipe is low C and high Mn, while the SML steel pipe is high C and low Mn. Obviously, the former has better weldability than the latter. Higher purity than SML.
② Mechanical properties.
a. The tensile properties meet the requirements of API SI_ (41) and GB 8163-87 standards. The tensile properties of ERW and SML steel pipes are equivalent.
b. It can be clearly found from the impact properties that the toughness of ERW steel pipes is better than that of SML steel pipes, especially at low temperatures.
c. According to the flattening performance, no cracks occurred when the three ERW steel pipes were pressed, and the micro-cracks appeared on the seamless steel pipe of No. 20 steel, which indicates that the ERW steel pipe has better resistance to flattening.
③ Appearance dimensions and craft quality. From the statistical results of the steel tube geometric size and appearance process quality:
a. Appearance size and process quality meet the requirements of two standards;
b. From the physical measurement results of the product, the appearance geometry and appearance quality of ERW steel pipes are much better than SML steel pipes.
(5) Price comparison between ERW and SML steel pipes Due to advanced production technology and high production efficiency, the production cost of ERW steel pipes is much lower than that of SML steel pipes.
In general, the price per ton of ERW steel pipe is about 600-800 yuan lower than that of SML steel pipe of the same material. Take ordinary steel ERW steel pipe as an example, such as Q235A / B or SS400, 12 ", 323.9 × 8, the tax price per ton is 3500 ~ 3600 yuan; and pipeline steel series, such as X42, 12", 323.9 × 8, per ton The price including tax is 4,000 to 4,100 yuan, which is much lower than the price of similar SML steel pipes.
In recent years, countries are actively studying the use of ERW steel pipes to replace SML steel pipes and spiral welded pipes. Currently used in oil and gas pipelines are spiral submerged arc welded pipe (SSAW), straight seam submerged arc welded pipe (LSAW), resistance welded pipe (ERW). When the diameter is small (such as 152mm or smaller), SML steel pipe is used .
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