An Efficient FE-based Probabilistic Model For Ductile Fracture Assessment of Pipelines With Surface Defects

Sandvik, Andreas (Statoil) | Østby, Erling (SINTEF Materials and Chemistry) | Berg, Espen (FMC Technologies) | Thaulow, Christian (Norwegian University of Science and Technology)

OnePetro 

ABSTRACT:

In this paper a probabilistic model for ductile fracture assessment of pipelines is established. A specially designed program based on shell and line-spring elements for fracture mechanics analyses of surface cracked pipes in different loading scenarios, is applied to establish a set of deterministic response/capacity calculations. Variables are pipe and defect geometry, material properties and ductile tearing resistance. The pipes are subjected to a combination to tension and pressure loads. Some of the results are compared with 3D FEM results obtained from Abaqus/Explicit analyses. The deterministic calculations are used to establish so-called response surfaces suitable for reliability calculations. The proposed methodology is illustrated with examples, where the probability of failure is determined using different solution methods. The results illustrate the simplicity, robustness and efficiency of the proposed probabilistic fracture mechanics model.



INTRODUCTION


To ensure safe and cost effective design and operation of structures like pipelines, it is required to have simple and reliable standardized assessment procedures. This is specifically important when the capacity utilization of the pipeline is high, which typically can be the case when using highly ductile pipeline steel materials. Large deformation may occur in different scenarios like pipeline laying or during operations. A pressurized pipe may be subjected to external loads for example in free spans due to irregular seabed topography or lateral/upheaval buckles caused by thermal loads. Modeling of three-dimensional ductile tearing analyses of pipes with defects is challenging and still not common due to complex modeling, lengthy solution time and extensive post-processing. However, 3D models are important to perform in order to investigate the detailed physics of fracture mechanics problems, see e.g. (Sandvik et al. 2007, 2008). This is neither suitable in engineering fracture mechanics assessment nor as a basis in probabilistic models for pipes where numerous analyses are needed.