Forming seamless tube and pipe

Nowadays tube and pipe manufacturers in the Middle East all have a system in place, enabling the production process from the steelworks to the finished tube to be continuously monitored and documented for total traceability and effectively controlled on the basis of quality criteria.

As for the tube industry, the GCC and Middle East are proving to be increasingly attractive markets for international tube manufacturers. Some of the growth sectors include oil and gas technology, petrochemicals, water and electricity supply, drainage as well as construction. Huge investments by the government as well as private sector have been made in this sector and more are in the pipeline.

Satish Khanna, General Manager, Al Fajer Information and Services, said, "The Gulf has the largest concentration of energy resources in the world, with oil producing countries in the region estimated to have spent about Dhs182.5 billion (US$50 billion) to increase their current oil production or on new explorations by the year-end."

Khanna added, "The global demand for energy, infrastructure development, construction projects, water and air conditioning supply and automobiles - the key sectors that drive the tube and pipe industry -- will continue to grow in the coming years."

A considerable proportion of the seamless tube and pipe manufactured undergo subsequent cold forming. The main purpose of these cold working processes is to achieve closer wall thickness and diameter tolerances, an improvement in surface finish and specific mechanical properties in the tube. Cold forming also serves to expand the product mix toward the lower end of the OD and wall thickness scales. One of the processes that predominate in this respect is cold drawing.

Cold drawing
Seamless precision steel tube has been standardised in DIN 2391 for the diameter range from 4 to 120mm and wall thickness from 0.5 to 10mm. In addition, however, non-standardised intermediate sizes and tube up to up to 380mm outside diameter with wall thickness up to 35mm can also be manufactured by cold drawing.

There are three processes employed for the cold drawing of tube: hollow drawing, stationary or floating plug drawing, and drawing over a mandrel, also known as drawing on-the-bar.

Because of the lack of an internal tool, in hollow drawing only the outside diameter of the tube is reduced and the outside surface polished in the die, with the wall thickness undergoing no more than negligible change in both absolute terms and in respect of its tolerances.

In plug drawing, a plug which is either fixed to a mandrel bar or a so-called floating plug (this lodges in the forming zone as a result of its particular shape and the forming pass it produces) forms an annular gap with the block die through which tube is drawn. This reduces within close tolerances both the outside and inside diameters, and thus also the wall thickness, as well as smoothing and polishing both the outside and inside surfaces. In general, a fixed, stationary plug is used to produce reductions in area of up to 45% per draw. Drawing over a floating plug is predominantly employed for small-diameter tubes and greater lengths, and particularly when the stock is taken from a coil and, following drawing, re-coiled on a capstan.

In drawing over a mantel, the tube is pulled through the die with the aid of an inserted mandrel bar, with the outside and inside diameters, and also the wall thickness, again undergoing reduction. The possible reductions in area per draw are higher than in the case of plug drawing, but the length of tube is limiteFashion & Celebrity News