The proportion of welded pipes in the overall production is constantly growing, which is explained by high adaptability and economic feasibility of obtaining such high-quality products. Welded pipes are made by various methods of electric welding (with a straight seam, with a spiral seam), furnace welding, resistance welding, etc. The production of electric welding pipes has become widespread, since this method produces products with a thin wall (0.5 mm or less), a larger diameter (up to 2400 mm or more), well-made seam and high surface quality. Industrial value received several ways to manufacture products. The most common is submerged-arc welding with a straight or spiral seam. Pipes of small and medium diameters, used mainly as structural and oil and gas pipelines, are produced by welding with alternating and direct current and arc heating of the edges of the rolled strip with a consumable electrode. The technological process consists of the following three operations: preparing the strip for molding; pipe molding, welding and calibration; pipe finishes.
In the production of ERW pipe, the blank is cold-rolled or pickled hot-rolled tape in rolls. The rolls are fed to the decoiler with a loading device. Next, the roll is unwound and subjected to editing on a sheet-straightening machine. The ends of the strip are cut with scissors to butt weld the rear end of the previous one and the front end of the next rolls. Further technological operations are similar to those discussed earlier. The prepared tape is subjected to molding on a continuous forming mill, butt-welding resistance in the welding unit of the mill. The resulting pipe is then subjected to editing in the calibration mill and the correct stand, and cut to length. The final processing of the pipes is carried out at the finishing site, where the pipes are straightened, trimmed at the ends on the trimming mills and tested on hydraulic presses.
Pros and cons of welded or electrically welded pipes
Of course, all the technological problems and energy costs in the production of straight and spiral pipes can not be compared with the efforts that the manufacturer must spend on the production of seamless pipes. The main advantage of this type of steel hire is relatively low cost.
Another undoubted advantage of welded pipes is their large diameter which can be 100 or more times the wall thickness. This makes the pipes lighter and therefore easier to transport.
- Welded pipes withstand pressure 10 times less than seamless ones. If seamless pipes with a minimum wall thickness must withstand a pressure of 20 megapascals (that is, about 200 atmospheres), then a pressure of 16 megapascals (160 atmospheres) is considered to be the maximum allowable for welded pipes.
- Welded pipes, as opposed to seamless, do not bend. If you need to change the direction of the gas or water supply, assembled from welded or electrically welded pipes, you will definitely have to use fittings.
- The technology itself for the production of welded pipes requires the use of such grades of steel that can be welded well – that is, they must be made of low-alloyed carbon steels with relatively little corrosion resistance.