Deformation behaviour of HFI-welded pipes – some examples of present applications –
In the last years requirements for laying and operation of pipelines have become more and more challenging. One the one hand this is related to national regulations and complex laying situations, such as pipeline installation in high density residential areas. One the other hand the pipe material and coating itself are exposed to multiple loads during laying activities and the use of pipelines, for example because of the geological conditions. In this report challenges for pipes and pipelines due to loading conditions during laying oper-ation are discussed with regard to High-Frequency-Induction- (HFI) welded pipes of Salzgitter Mannesmann Line Pipe. First the fitness for use during offshore reel-laying is demonstrated, with repeated plastic strains introduced into a pipeline, which may affect strength properties and deformation capacity of the line pipe material. A comparison is carried out between conventional small-scale reeling simulation tests on specimens and full-scale reeling simulation tests on pipes. Full scale reeling simulation is more and more demanded by customers to assure that the structural pipe behaviour meets the strain demands. Secondly, laboratory tests with respect to strain-based design requirements will be shown. Effects of external loads and ground movements on pipelines have moved into the focus of significant research topics for the past years, as pipelines are installed increasingly in remote and difficult ground areas. Also strain based design aspects have been included in a few design codes, e.g. DNV-OS-F101 or CSZ Z662-03. The pipeline’s structural resistance to such load scenarios like bending, which induce pronounced longitudinal strains and multi-axial stress-strain states in combination with internal pressure, have been investigated. A third example deals with the laying of a district heating pipeline under extremely severe conditions due to high density housing areas and traffic routes (cars, ships).