ABSTRACT The knowledge of girth weld tensile behaviour is an essential issue to be considered in the definition of a welding procedure for seamless linepipe, subject to in-plane bending, such as during laying applications. In particular, the evaluation of the behaviour in direction transverse to the welding should be carried out, according to DNV standards. In this paper, a joined application of experimental testing and Finite Element Analysis is carried out to characterize the tensile behaviour of both weld metal and heat affected zone material, until rupture, that is beyond the onset of plastic collapse, in direction transverse to the weld.
INTRODUCTION Advanced techniques for the assessment of safety of components just like girth welds are nowadays available even for very severe applications. In particular, procedures for the defect tolerance critical assessment, based on the most modern Fracture Mechanics concepts reported in BS 7910 (2005), R6 (2000), SINTAP (1999), API RP 579 (2007), have been developed even for extreme conditions just like reeling installation, where the pipeline and its girth weld are loaded under displacement control, at high values of plastic deformations. Some of the most recognized procedures are presented in the widely recognized standards DNV OS-F101(2007) and DNV RP-F108 (2006) where the calculation route is presented in the form of modifications to the BS 7910 procedure to adapt it to strain-based situations. The evaluation of girth weld tensile behaviour, in direction transverse to the welding, is also recommended by DNV to investigate the actual weld joint load bearing capability, when subjected to in-plane bending, as in the case of reel-laying installation. The use of weld and base material curves, in transverse direction, could provide essential information for possible refinement of defect assessment procedures, especially taking into account the actual plastic deformation pattern associated to the weld-to-base material strength mismatch.