In many years of pipe laying, no noteworthy incident has been monitored that could be associated with the mere existence of helical seam welds in large diameter pipes. In most of those few cases where buckling instability occurred, it was the lack of a mandrel, which was found as detrimental. The present paper discusses issues of pipeline design in terms of possible cold bending processes during pipe laying on the construction site. Cold bending in the field is introduced. Mechanical aspects of the elastoplastic structural behavior within and after the bending process are analyzed with respect to high grade pipeline steels. The mechanics of cold bending is explained and the Beam Theory in elastic and plastic stress-strain configurations is presented. The influence of the cold bending process on operating conditions and the ultimate limit state bursting are treated. Conclusions are drawn by comparing straight and cold bended pipe joints with respect to their burst behavior. The paper concludes with an analysis of the stresses in normal and tangential weld seam direction. Whenever a pipe joint is subjected to field cold bending significant residual stresses will be present in axial component direction, irrespective of the specific pipe production route. Residual stresses are a result of elastic-plastic strain formation during the cold bending process. Simulations show that increasing the steel grade may slightly reduce the relative magnitude of residual stresses. For the given burst pressure and forming angle, the stresses acting perpendicular to the helical weld seam reach values of 60 % of the hoop stress only. Finally, evidence has been given that helical seam welds do not have any negative impact on the pressure containment capacity of line pipe.


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    Titel :

    Strength and deformation characteristics of helical seam welded large diameter pipes. Field cold bending and related issues


    Beteiligte:

    Erschienen in:

    Drei R International ; 49 , Special 1: Pipeline Technology ; 6-11


    Erscheinungsdatum :

    2010


    Format / Umfang :

    6 Seiten, 12 Bilder, 3 Tabellen, 6 Quellen



    Medientyp :

    Aufsatz (Zeitschrift)


    Format :

    Print


    Sprache :

    Englisch





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