pipe mill

Steel Pipe and Manufacturing Processes


The advent of rolling mill technology and its development during the first half of the nineteenth century also heralded in the industrial manufacture of tube and pipe. Initially, rolled strips of sheet were formed into a circular cross section by funnel arrangements or rolls, and then butt or lap welded in the same heat (forge welding process).

Toward the end of the century, various processes became available for the manufacture of seamless tube and pipe, with production volumes rapidly increasing over a relatively short period. In spite of the application of other welding processes, the ongoing development and further improvement of the seamless techniques led to welded tube being almost completely pushed out of the market, with the result that seamless tube and pipe dominated until the Second World War.

During the subsequent period, the results of research into welding technology led to an upturn in the fortunes of the welded tube, with burgeoning development work ensuing and wide propagation of numerous tube welding processes. Currently, around two thirds of steel tube production in the world are accounted for by welding processes. Of this figure, however, about one quarter takes the form of so-called large-diameter line pipe in size ranges outside those which are economically viable in seamless tube and pipe manufacturing.

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Seamless Tube and Pipe

The main seamless tube manufacturing processes came into being toward the end of the nineteenth century. As patent and proprietary rights expired, the various parallel developments initially pursued became less distinct and their individual forming stages were merged into new processes. Today, the state of the art has developed to the point where preference is given to the following modern high-performance processes:

The continuous mandrel rolling process and the push bench process in the size range from approx. 21 to 178 mm outside diameter.

The multi-stand plug mill (MPM) with controlled (constrained) floating mandrel bar and the plug mill process in the size range from approx. 140 to 406 mm outside diameter.

The cross roll piercing and pilger rolling process in the size range from approx. 250 to 660 mm outside diameter.

Mandrel Mill Process

In the Mandrel Mill Process, a solid round (billet) is used. It is heated in a rotary hearth heating furnace and then pierced by a piercer. The pierced billet or hollow shell is rolled by a mandrel mill to reduce the outside diameter and wall thickness which forms a multiple length mother tube. The mother tube is reheated and further reduced to specified dimensions by the stretch reducer. The tube is then cooled, cut, straightened and subjected to finishing and inspection processes befor shipment.

Mannesmann plug mill process

Plug Mill Process, a solid round (billet) is used. It is uniformly heated in the rotary hearth heating furnace and then pierced by a Mannesmann piercer. The pierced billet or hollow shell is rollreduced in outside diameter and wall thickness. The rolled tube simultaneously burnished inside and outside by a reeling machine. The reeled tube is then sized by a sizing mill to the specified dimensions. From this step the tube goes through the straightener. This process completes the hot working of the tube. The tube (referred to as a mother tube) after finishing and inspection, becomes a finished product.

Welded Tube and Pipe

Ever since it became possible to manufacture strip and plate, people have constantly tried to bend the material and connect its edges in order to manufacture tube and pipe. This led to the development of the oldest welding process, that of forge-welding, which goes back over 150 years.

In 1825, the British ironware merchant James Whitehouse was granted a patent for the manufacture of welded pipe. The process consisted of forging individual metal plates over a mandrel to produce an open-seam pipe, and then heating the mating edges of the open seam and welding them by pressing them together mechanically in a draw bench.

The technology evolved to the point where strip could be formed and welded in one pass in a welding furnace. The development of this butt-welding concept culminated in 1931 in the Fretz-Moon process devised by J. Moon, an American, and his German colleague Fretz.

Welding lines employing this process are still operating successfully today in the manufacture of tube up to outside diameters of approx. 114 mm. Aside from this hot pressure welding technique, in which the strip is heated in a furnace to welding temperature, several other processes were devised by the American E. Thomson between the years 1886 and 1890 enabling metals to be electrically welded. The basis for this was the property discovered by James P. Joule whereby passing an electric current through a conductor causes it to heat up due to its electrical resistance.

In 1898, the Standard Tool Company, USA, was granted a patent covering the application of electric resistance welding for tube and pipe manufacture. The production of electric resistance welded tube and pipe received a considerable boost in the United States, and much later in Germany, following the establishment of continuous hot strip rolling mills for the production of the bulk starting material necessary for large-scale manufacture. During the Second World War, an argon arc welding process was invented – again in the United States – which enabled the efficient welding of magnesium in aircraft construction.

As a consequence of this development, various gas-shielded welding processes were developed, predominantly for the production of stainless steel tube.Following the far-reaching developments which have occurred in the energy sector in the last 30 years, and the resultant construction of large-capacity long-distance pipelines, the submerged-arc welding process has gained a position of pre-eminence for the welding of line pipe of diameters upward of approx. 500 mm.

Electric Weld Pipe Mill

Steel strip in coil, which has been slit into the required width from wide strip, is shaped by a series of forming rolls into a multiple length shell. The longitudinal edges are continously joined by high frequency resistance/induction welding.
The weld of multiple length shell is then head treated electrically, sized and cut to specified lengths by a flying cut-off machine. The cut pipe is straightened and squared at both ends.
These operations are followed by ultrasonic inspection or hydrostatic testing.

Steel Pipe and Manufacturing Processes Introduction The advent of rolling mill technology and its development during the first half of the nineteenth century also heralded in the industrial


Seamless Pipe Mills and Finishing Lines

Our focus on innovative technology and plant reliability allows to deliver equipment that produces high-end quality products with outstanding investment and operational costs to customers.

Experience in the design of innovative seamless pipe plants and equipment for hot rolling and cold finishing alongside important investments in R&D activities allow to manufacture and supply turnkey equipment globally. Our product portfolio covers complete Seamless Pipe Mill Plants (2 Rolls / 3 Rolls Hot Rolling Mill Lines, Expander Mill Lines) producing tube sizes with ranges up to 28” and a production capacity stretching from 100.000 to 1.000.000 tonnes per year.

In addition to this, Danieli Centro Tube is a leading supplier of Finishing Lines (Heat Treatment, Quality Assurance, Upsetting, Beveling and Threading lines) for both welded and seamless pipe applications in relation with the different market segments.

Also included in our scope of supply are:

  • The CRP (Cross Rolling Piercing Mill) – original and innovative design of this equipment allow piercing round billets into a shell. The mill comes equipped with cone-type or barrel-type rolls arranged either in the vertical or horizontal position according to the customers’ requirements;
  • The FQM™ (Fine Quality Mill) – at the heart of the seamless pipe production process and is responsible for shaping the wall thickness close to the final target value and elongating the inlet shell. This technology is suitable for a wide range of pipe sizes and steel grades, the process is flexible and appropriate for both high and low production;
  • The FQT (Fine Quality Train) is a new process for the production of seamless pipe for finished pipes with diameter from 73 mm up to 460 mm that reduces the number of deformation steps from three to two by removing the reheating furnace and relevant intermediate cooling bed as well as the SM/SRM control pulpit.
    This means also a reduction both of the plant layout length and foundation work necessary with the traditional solution.
  • The HPE (Hot Pull Elongator) is an innovative rolling machine including a bench with idle roll stands where a pierced hollow bloom is deformed on a mandrel. This process is particularly dedicated to small/medium diameter pipes up to 245 mm, highly reducing the layout and height of building besides also the cost of technological equipment with respect to traditional mandrel mills (floating or retained).
    Many other features of these innovative mills contribute to reach state-of-the-art solutions, with simplified production of small lots and increased efficiency in rolling, allowing relevant savings both in CapEx and OpEx.
  • The HTM (hydrotester) – allows to perform hydrostatic tests on seamless and welded pipes in complete safety. Equipment design includes high flexibility and versatility. Two different hydrostatic testing machines are available: the four-column type and the two-beam type, depending on the customer’s output these can be equipped with either one or two heads;
  • Danieli CM (Carbide Tipped Circular Saws) – designed to cut a wide range of products and steel grades, for example solid bars, profiles, single pipes, tube layers, tube samples and couplings. The CM comes in either a vertical or a horizontal arrangement depending on the specific application and layout.
  • Danieli TSM (Tube Straightening Machine) – unique design offering enhanced efficiency, improved quality and superior technology and safety, high quality processed pipes are also ensured. Equipment allows to straighten tubes by both deflection and cross section ovalisation.

All of the above-mentioned equipment can be supplied as part of the seamless pipe mill or as stand-alone equipment.

LONG PRODUCTS Seamless Pipe Mills and Finishing Lines Our focus on innovative technology and plant reliability allows to deliver equipment that produces high-end quality products with ]]>