Fatigue performance of pre-strained pipes with girth weld defects: Full-scale experiments and analyses

The local deformation mechanism of pre-strained welded joints with defects was studied in the first part of this work. [Netto TA, Botto A, Lourenço MI. Fatigue performance of pre-strained pipes with girth weld defects: Local deformation mechanisms under bending. Int J Fatigue (2007), doi:10.1016/j.ijfatigue.2007.08.001]. It was shown that highly localized strains may develop at the tip of these defects, depending on their type (lack of fusion and lack of penetration) and size. Different levels of pre-straining do affect the fracture mechanics material parameters and subsequently can deteriorate the fatigue performance of these joints under operational cyclic loads. Here, the fatigue lives of pre-strained joints with different defects were obtained experimentally by means of full-scale specimens. Subsequently, both a finite element model and an algorithm based on linear fracture mechanics that accounts for the changes in the material properties due to pre-straining were used to estimate the fatigue life of typical joints. The results were compared and used to suggest guidelines to the development of weld acceptance criteria of reeled steel catenary risers.