Longitudinally Welded Steel Pipes
For the manufacture of these high quality longitudinally welded pipes steel strip in coils are needed.
The steel strip, coming out from the decoiler, forms an endless strip since the tail end of one coil is welded to the leading end of the next. This strip is continuously cold – formed into an open seam tube. The seam is welded by ERW method (Electric Resistance Welding) using 400 kHz high frequency electric current. In high – frequency welding practically only the ‘skin’ of the strip edges to be welded are raised to welding temperature. Welding takes place when the edges are pressed together. Continuous control of the welded seam carried out by an ultrasonic tester, ensures that any defect is spotted out in time.
According to the requirements customer’s specifications, scarfing of the external and internal flash of the seam is carried out in order to obtain a smooth surface. If required by the same specifications, normalizing of the weld seam is carried out using medium frequency electric current (2,7 kHz).
The endless tube strand obtained in this way, after being cooled passes through the sizing mill for accurate sizing to the final diameter and for the straightening. Then is conveyed through the traveling cut – off unit where it is automatically cut into the required lengths (from 2 to 16 meters). These lengths are submitted to end facing and threading according to the specifications, as well as to testing and quality control on special machinery.
Finally they are given the stipulated protective coating (galvanizing, painting etc.). These pipes are manufactured by the above Cold Finishing process with sizes from 4 ½ to 10 ¾ inches outside diameter.
The system of tube and pipe manufacturing described above, produces pipes of high strength, high quality and reliability, having accurate dimensions and shape and a smooth surface.
These longitudinally welded steel pipes measure from ½ to 10 ¾ inches (21.3 to 273 mo) outside diameter.