Longitudinal seam steel pipes are produced from strip steel, and the pipes obtained by longitudinal welding on high-frequency welding equipment are called straight seam welded pipes. In recent years, longitudinally welded pipes have been widely used in the petroleum and gas industry, fluid transportation projects, building structures, transmission steel pipe towers, etc., and have played a huge role in the construction of the national economy.
Longitudinal welded pipe can be divided into:
1. High frequency straight seam welded pipe (ERW)
Straight seam high-frequency welded pipe is a welded pipe that is continuously produced on the production line using steel strip (coil) as the raw material and high-frequency welding technology.
The material strength is generally below 450MPa, and the materials include J55, L450, X60, Q235, Q345, Q420, Q460. The diameter range of the longitudinally welded pipe is 14-610mm, and the wall thickness is 1-23.8mm.
Longitudinal high frequency welded pipe adopts multi-frame continuous forming process, high production efficiency (production speed 15-40m/min), the production line has complete sizing, straightening, rounding and other equipment, and the steel pipe is in roundness, straightness and The welding aspect is better.
2. Submerged arc straight seam welded pipe (LSAW)
Submerged arc longitudinal seam welded pipe is produced by using a single steel plate as raw material, through JCO or UOE forming, submerged arc welding or submerged arc welding combined with other welding processes. Common ones are X70, X80, X120, etc. The diameter of LSAW pipe is 400-1422mm and the wall thickness is 8-44.5mm.
In terms of welding, edge milling machining is used; in terms of forming, in addition to conventional JCO and UO technologies, some manufacturers use incremental forming (PFP) technology and roll bending (RBE) technology; in terms of welding , The automatic pre-welding machine with argon gas protection or CO2 gas protection and special multi-wire (4 wire and 5 wire) internal and external submerged arc welding equipment are used, and square wave power supply and power wave power supply device are used; in terms of diameter expansion, The full length of the pipe adopts mechanical expansion; in terms of inspection, it is necessary to conduct online flaw detection on the plate, perform automatic ray + automatic wave flaw detection + water pressure test after welding the steel pipe, and perform secondary online or offline ray + wave flaw detection after expansion.
Due to the limitation of the coil width and production equipment, the domestically produced longitudinally welded pipes are stably produced. The welded pipe diameter is 580mm and below is the longitudinal high frequency welded pipe, and the large size is the longitudinal submerged arc welded pipe.
The power source of the longitudinal welded pipe manufacturer can use a single power source or multiple independent power sources as the power source of multi-wire submerged arc welding. The use of a single power source only requires relatively simple equipment. However, it is often difficult to adjust the arc power individually; although the independent power supply has more complicated equipment, each of the arc powers can be adjusted independently. At the same time, different current types and polarities can be used, so that a very ideal welding state can be achieved. To achieve an ideal welding state, multiple independent power sources are generally used as the power source for multi-wire submerged arc welding. When using different power connection methods for welding seams, there will often be quite different weld cross-section topography. The main reason for this situation is that different power connections will produce different levels of interference between arcs.
Under normal circumstances, compared to the use of AC power, if the DC power supply is used, the welding wire will have a larger weld penetration. In the process of multi-wire submerged arc welding, the previous arc is usually used to ensure sufficient penetration, and the subsequent arc adjusts the melting width. Therefore, the DC-AC hybrid power supply configuration method is usually used in the longitudinally welded pipe multi-wire submerged arc welding of the longitudinally welded pipe manufacturer, that is, the DC power supply is used as the front welding wire, the DC power supply is reversely connected, and the AC welding wire is used as the welding wire. The welding wire behind.
When welding, the manufacturer of double-sided submerged arc welding longitudinal seam steel pipe covers a layer of granular flux on the welding area, and the arc burns under the flux layer to melt the end of the welding wire and the local base material to form a weld. Under the action of arc heat, the upper part of the flux melts the slag and metallurgically reacts with the liquid metal. The slag floats on the surface of the molten metal pool, on the one hand, it can protect the weld metal, prevent air pollution, and produce physical and chemical reactions with the molten metal, and the weld metal's extreme and performance. On the other hand, manufacturers of double-sided submerged arc welding longitudinal seam steel pipes can also cool down the weld metal slowly. Submerged arc welding can use a larger welding current. Compared with manual arc welding, its big advantages are good welding seam and high welding speed. Therefore, the manufacturer of double-sided submerged arc welded straight seam steel pipe is particularly suitable for welding the straight seam of large workpieces. And most of them use mechanized welding. Submerged arc welding has been widely used for welding carbon steel, low alloy structural steel and stainless steel.https://www.permanentsteel.com/productshow/erw-steel-pipe.html