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.
(3) Comparison of ERW and SMLS standards
General seamless hot-rolled steel pipe for fluid conveying, the standard is GB8163-87, its specifications are: outer diameter Ф32-630mm, wall thickness 2.5-75mm, steel grades are 10, 20, 09MnV, 16Mn. The American Petroleum Institute API 5L (41) standard is applicable to steel pipes for oil and natural gas transportation, including welded pipes and seamless pipes. ,B, X42, X46, X52, X56, X60, X65, X70, X80 are similar to the standard ISO3183-96 series standard and GB/T9711-97 series released in November 1997 and implemented in April 1998 standard. In view of the ISO, GB/T standards are derived from API 5L (41) standard. So compare GB8163-87 with API 5L(41).
The requirements of the two standards have the following characteristics:
1) The inspection items specified in GB8163-87 also have corresponding requirements in API 5L (41), and the completion of the indicators can meet the requirements of these items. 10, 20, 09MnV and 16Mn in GB8163-87 are respectively equivalent to A, B grades, X42 grades, X46 grades and X52 grades in API 5L (41).
2) The geometric dimensional accuracy requirements of steel pipes in GB8163-87 are lower than API 5L (41).
3) GB8163-87 and API 5L (41) have very different requirements for water pressure. The former clearly stipulates that ultrasonic waves or eddy currents can be used instead of water pressure, while the latter does not. This is extremely critical, because hydraulic inspection is one of the most important inspection items for steel pipes. Moreover, the former water pressure test value is lower than the latter requirement. For grades below X42, the standard water pressure test value of ERW pipe is consistent with GB8163-87 when it is not greater than Φ114.3mm; when it is greater than Φ114.3mm outer diameter, respectively 15% and 25% higher than seamless pipe requirements. For the pressure to be harsh, it requires that the hydraulic press must be equipped with some kind of automatic or interlocking mandatory device, record the pressure holding curve, and ensure the stable voltage time.
4) GB8163-87 is quite different from API 5L (41) in terms of non-destructive testing requirements. The former inspection item does not clearly stipulate that non-destructive testing is required, but it is mentioned under the water pressure inspection item that it is replaced by non-destructive testing. The water pressure statement; the latter requires the water pressure and the non-destructive inspection project to be carried out at the same time. The author believes that the latter regulations are more scientific and reliable. Practice has proved that whether ERW or SML steel pipes, the passage of water pressure does not necessarily mean that the pipes have no inherent serious defects, and such defects often have a great impact on the service life of the steel pipes. , become the focus of customer care. In addition, the pipe end crumple area under water pressure is also a high-incidence area for defects. Therefore, API 5L(41) not only requires hydraulic pressure and non-destructive testing at the same time, but also requires non-destructive testing of welds and pipe end crumples after hydraulic pressure to prevent cracks or defects from propagating and pipe due to hydraulic stress. End defect missed detection.
5) Flattening test: From the standard requirements, GB8163-87 is harsher than API 5L (41), but in fact, the strength and toughness of the weld seam of ERW steel pipe and the base metal match so that cracking often does not occur during pressing. Therefore, The flattening resistance of ERW steel pipe is no worse than that of seamless pipe.
(4) Comparison of the physical quality of ERW and SMLS steel pipes
After the quality inspection of Xi'an Pipe Research Institute and the ferrous metal inspection station of Shanghai Municipal Bureau of Technical Supervision, here are two prescribed B-grade Φ219×8.18 and X52-grade Φ323.9×6.4, and the collected domestic TS/52KΦ219×6ERW pipes , domestic 20 steel (equivalent to API B grade or X42 grade) Φ159×6, Mexican ST45 (equivalent to API X52 grade) Φ219×6 seamless pipe test data on its chemical composition, tensile properties, flattening properties, Impact toughness and appearance quality are classified and compared.
The components of the five steel pipes all meet the requirements of API 5L (41) and GB8163-87. The composition design of ERW is low C and high Mn, while SMLS is high C and low Mn. Obviously, the weldability of the former is better than that of the latter, which is more favorable for the welding of girth welds in field construction. SMLS has higher purity.
(5) Mechanical properties
1) The tensile properties meet the requirements of API 5L (41) and GB8163-87 standards, and the tensile properties of ERW and SML are equivalent.
2) It can be clearly found from the impact properties that the toughness of ERW steel pipe is better than that of SML, especially at low temperature.
3) The flattening performance shows that there are no cracks when the three ERW steel pipes are pressed together, while the #20 steel seamless steel pipe has micro-cracks, and the other is not cracked, indicating that the ERW steel pipe has better flattening performance.
(6) Appearance, size, process quality
1) Appearance dimensions and process quality meet the requirements of the two standards.
2) Judging from the actual measurement results of the product, the appearance geometry and appearance process quality of ERW are much better than SML steel pipes.
(7) The price comparison between ERW and SMLS steel pipes
Due to the advanced production technology and high production efficiency, the production cost of ERW steel pipe is much lower than that of seamless steel pipe. In general, the price per ton of ERW steel pipe is about 600-800 yuan lower than that of seamless pipe of the same material.
Permanent Steel Manufacturing Co.,Ltd as a carbon steel tube supplier, has years of experience in manufacturing of carbon steel pipe (SMLS/ERW/SSAW/LSAW), stainless steel tube, hollow section, pipe fittings. (Fluid Pipe/Boiler Tube/Fire Pipe/Line Pipe/Structure Tube)
