High Frequency Inductive (HFI) welding is a highly productive process for the fabrication of longitudinally welded pipes from hot rolled strip. Longitudinally welded HFI-Pipes are nowadays used in the most diverse range of applications. Typical applications are for example, pipelines for the conveyance of liquid and gaseous hydrocarbons, potable and utility water, brine, district heating systems, hollow sections and Oil Country Tubular Goods (OCTG). HFI-Pipes are increasingly coming into use in the offshore sector, in competition with SAW and seamless pipes. The precondition for their use in this case is the capability for production of pipes with increasing wall thicknesses and very tight and homogenous geometric tolerances. Mannesmann Fuchs Rohr (mills in both Siegen and Hamm, Germany) produces HFI pipes in O.D. 4”-20” (114.3 - 508.0 mm) with wall thicknesses up to t = 0.81” (20.6 mm). Special requirements originating from the offshore sector are thus last but not least fulfilled via the use of high quality primary material with large pipe wall thicknesses.
Key steps of the process chain of the production process as well as significant properties of HFI-Pipes from Mannesmann Fuchs Rohr regarding the use in the offshore-sector are discussed. Very important from the production process point of view is the welding technology. A uniform heating of the strip edges is indispensable. Therefore the High Frequency Induction Welding plays a key role since it enables the use of welding frequencies in the lower range of the HF technology. Through this especially in the case of welding higher wall thickness’ the heating of the entire strip edge at the corners as well as in the middle of the strip is ensured. Another important production step is the sizing of the pipe string. This sizing influences the mechanical values of the pipe as well as the geometrical values. Both result in good properties regarding the use in the offshore sector. The third explained partial stage of the production process is the US testing of the weld seam.
Besides the properties of the black pipes Mannesmann Fuchs Rohr offers a special coating system for the offshore sector. This so called rough coating is designed on the basis of the well known 3-layer PE- and PP-coating of Mannesmann (MAPEC) and is furthermore characterised by a rough surface. The rough surface has in this case different advantages regarding the additional application of heavy coating, the forces during pipe laying and safety aspects.
HFI-Pipes from Mannesmann Fuchs Rohr have been used in several projects over a period of more than 10 years. Different projects and the experiences of the customers are described.