Seamless tubes are made by rolling a preheated billet between offset rolls to create a tube shell. The tube shell is then elongated in a multi-stand rolling mill (with a mandrel) to achieve the desired wall thickness and a limited range of diameters. Tube diameter can also be achieved with a sizing collar, but for significant diameter changes the tube is reheated and passed through a stretch-reducing mill – a multi-stand mill that reduces outside diameter but not wall thickness. The seamless range also includes Oil Country Tubular Goods (OCTG.)
Boiler tubing, the oil and gas industries and automotive transmission components are typical applications.
Welded tubes are made from hot rolled or cold reduced strip, sheet or plate. Welded tube includes hollow sections, black and galvanised gas/water pipe, scaffolding tube and large
diameter pipe. Small and medium diameters are produced in continuous, multiple-roll mills that progressively bend incoming, unheated strip into a circular cross-section prior to welding along the longitudinal seam. Tube may subsequently be cold-drawn through dies to achieve precise
dimensions and finish. Large diameters (400-1,600mm) are made from discrete plate which is welded in an “O” shape before being mechanically or hydraulically expanded. Spiral welded tube/pipe is available in diameters up to 2,500mm.
Welded tubes are used in a wide range of general engineering applications as well as in power generation plants, oil refineries, automotive manufacturing and furniture production.