Østby, Erling (SINTEF Materials and Chemistry, Trondheim, Norway) | Nyhus, Bård (SINTEF Materials and Chemistry, Trondheim, Norway) | Hauge, Mons (StatoilHydro ASA, Trondheim, Norway) | Levold, Erik (StatoilHydro ASA, Trondheim, Norway) | Sandvik, Andreas (StatoilHydro ASA, Trondheim, Norway) | Thaulow, Christian (Norwegian University of Science and Technology, Trondheim, Norway)
In this paper results from experimental investigations and numerical modeling of the strain capacity in SENT (Single Edge Notched Tension) specimens are presented. Both SENT specimens with defects in the pipe base material and in weldments are considered. The weld metal is about 10% overmatched compared to the base material. The results show that the overmatching on average leads to an increase in strain capacity, however, a much larger scatter in the results is observed for specimens with the defect in the weld material. The paper also demonstrates that 3D FE simulations are very well capable of reproducing the physics observed in the experiments.
Prediction of strain capacity of pipelines with defects is an important part of strain-based fracture assessment. The strain capacity can be influenced by several different parameters, e.g. defect size, weld metal mismatch, and crack growth resistance. The scatter in these parameters also plays an important role, and will have an effect on how to define appropriate safety factors. A thorough understanding of the influence played by the different factors is vital in order to obtain robust strain-based fracture assessment schemes. SENT specimens have recently been proposed as an interesting candidate for fracture mechanics testing of pipelines and associated weldments (see Nyhus et al. (2003)). The SENT specimen displays a similar ligament deformation pattern and constraint level as found for cracks in pipes. In this paper we apply testing of SENT specimens to investigate some of the above mentioned factors, comparing results from pure pipe material specimens with specimens with defect in a slightly over-matched weld metal. The effect of weld metal overmatch on the crack driving force has been discussed by several authors, and examples can be found in Kim et al. (2000), Liu et al. (2007), Gioielli et al. (2007), and Motohashi and Hagiwara (2007).