Improve safety by reducing the impact of external corrosion on pipelines

• Proactive prevention of corrosion defects from growing to a size that ultimately impacts a pipeline’s structural integrity • Continuous assessment to identify & address where corrosion has occurred, is occurring or may occur • Repairing corrosion defects • Correcting the causes of corrosio

Elastic-plastic defect interaction in (a)symmetrical double edge notched tension specimens

Interaction of defects tends to intensify their crack driving force response compared to the situation where these defects act independently. The interaction between multiple defects is addressed in engineering critical assessment standards like BS7910 and ASME B&PV Section XI. Nonetheless, the accuracy of these rules is open to debate since all of them are based on re-characterization procedures which in essence introduce conservativeness. The authors have developed a fully parametric finite element (FE) model able to generate multiple notches in different topologies, in order to investigate their interaction effect. An experimental validation study is conducted to verify the FE model in terms of CTOD response and surface strain distribution. To that end, symmetrically and asymmetrically double edge notched tension specimens are tensile tested and their deformation monitored by means of 3D digital image correlation. In this study the CTOD is opted as a local criterion to evaluate the interaction between notches. These results are compared with an evaluation of strain patterns on a specimen’s surface, as a global interaction evaluation. Through this comparison a deeper understanding is gained to allow us to develop a novel approach to address flaw interaction. Moreover, the validation of the FE model allows future studies of interaction between other defect types (e.g., semi-elliptical, surface breaking) in plate-like geometries

Development and validation of a high constraint modified boundary layer finite element model

When a notched structure is loaded, its behaviour is not only affected by the material properties but also by the geometry (of both the structure and the defect) and loading condition, alternatively termed as constraint condition. Therefore, the relation between the failure behaviour of a small scale fracture mechanics test and a full scale structure needs to be elucidated. In an attempt to understand and describe such relationships, the crack tip stress fields are analysed by means of finite element simulations and compared for several test specimen geometries. A reference for comparison is the crack tip stress field obtained from a high constraint reference geometry, further called a modified boundary layer model. First, this article provides some theoretical background on the modified boundary layer model. Second, the development of a 2D model is outlined in detail, focussing on the mesh design in the vicinity of the crack tip and the applied boundary conditions. Afterwards, an analytical and numerical validation is provided, based on the level of the applied load and, on the other hand, on the magnitude of the crack tip stress fields. Finally, this validated model is used for the comparison of several constraint parameters. This comparison indicates a weak influence of the T-stress on the Q-parameter for positive T-stresses. In contrast, negative T-stresses result in more pronounced negative Q-values

Influence and evaluation of constraint on fracture toughness in pipeline research

Accessing nowadays fossil fuel reserves requires a strain-based design approach. Within such design, the ductile tearing resistance is a key parameter in assessing the defect tolerance. To determine this tearing resistance, full scale (pressurized) tests can be performed. However, such approach would be costly and time consuming. Consequently, effort is made to select appropriate small scale test specimens. Most research has focused so far on the single edge notch bend (SENB) and tensile (SENT) specimen. To evaluate the suitability of these test specimens, the crack tip stress fields can be examined or the resistance curves compared with full scale structures. This paper aims at comparing the trends observed using these techniques. Furthermore, the suitability of the small scale test specimens is evaluated. It is concluded that sufficiently long (length-to-width ratio equal to ten) clamped SENT specimens have the potential to predict the tearing resistance of full scale pipes. In addition, the internal pressure does not significantly affect the fracture toughness. These conclusions are stated by both experimental results and finite element simulations