Taking into account the various qualities, wall thickness, and diameters in which customers require finished pipes, Mild Steel Hot Rolled Coils in such required qualities are produced from established manufacturers in preferred coil weights of 18 to 10 tonnes. Each coil is tested for chemical composition, mechanical and physical properties, and if found to pass the test, the coils are moved on to the slitting line.
The coils are slit at the slitting line to the required width as per the pipe diameters to be rolled. The slit- widths are continuously re-coiled on recoiler drums to obtain what are called strips. The ends of the individual small coils are tack welded and unloaded on the re-coiler trolley.
These coiled strips are moved over with the help of overhead cranes to any of the 3 pipe manufacturing lines which are suitable for manufacturing pipes of,
A) 15mm NB to 40mm NB
B) 40mm NB to 100mm NB
C) 125mm NB to 300 mm NB
depending on the diameter to be manufactured. The coils are stored in the strip storage area of the concerned processing line.
The required quality checks, like edge quality, thickness, width, surface defects etc. are exercised during the process of slitting.
The coiled slits are then mounted on the de-coiler (or Pay off Reel) at the start of each processing line. The front end of the strip is opened and fed into the shear to obtain a perfect straight cut.
The tail-end of the previous strip duly sheared is welded on to the front -end of the succeeding strip on the welding table so as to obtain a continuous length of strip for rolling into pipes. The strips the passes through the pinch rolls and the stamping unit (where the companies name, brand etc. are stamped), down to looping cage. Thereafter, the strip moves through a series of horizontal forming rolls gradually forming itself into "U" shape and then "O" shape.
The kissing edges of the strip are then heated by means of a High Frequency Induction Welding Unit situated in each of the 3 processing lines, and the pipe is almost simultaneously passed through a pair of vertical rolls, where the edges are pressed together to form a complete pipe.
In the process of welding the pipe, bead lines (excess material) are formed on the outside surface as well as the inside surface of the pipes.