Search

Pipelines are considered as a major tool to transport hydrocarbons due to its important role in transporting fluids taking into account the operating conditions. Despite the importance of the elbow which considered as a critical part in the pipelines, the repeated failures and defects became a dangerous and enormously costly issue. In this numerical study, the Fluid-Structure Interaction (FSI) analysis was carried out using Ansys software. This work is divided into four main parts: the first part focused on studying and comparing the effect of bending radius of pipe elbow on the maximum of Von-Mises stress values for each radius with the yield stress of the steel of the pipe. The second part focused on the creation of a semielliptical crack for different locations along the elbow angles to show the critical position compared to the stress intensity factors. In the third part, the semi-elliptical crack angle orientation was studied at the critical position to estimate the critical angle. In the last part, the failure assessment diagram (FAD) was used to show the critical crack depth ratios at a critical position and a critical angle. [ABSTRACT FROM AUTHOR]

Pipe elbows (bends) are considered critical pressurized components in the piping systems and pipelines due to their stress intensification and the effect of bend curvature. They are prone and hence more exposed to different corrosion failure modes than straight pipes. Late detection of such elbow damages can lead to different dangerous and emergency situations which cause environmental disasters, pollution, substantial consumer losses and a serious threat to human life. A comprehensive safety and reliability assessment of pipe elbows, including usage of prediction models, can provide significant increases in the service life of pipelines. It is well known that the limit pressure is an important parameter to assess the piping integrity. In this paper, the integrity assessment of damaged pipeline elbows made of API 5L X52 steel was done within the framework of numerical modeling using the finite element method (FEM) and finite element analysis (FEA). The evaluation of numerically FEM modeled limit pressure in the corroded elbow containing a rectangular parallelepiped-shaped corrosion defect with rounded corners at the intrados section was done and compared to different codes for calculating limit pressure. Moreover, the area with the corrosion defects with different relative defect depth to wall thickness ratios was FEM modeled at the intrados section of the pipe elbow where the highest hoop stress exists. The results showed that the codes for straight pipes could not be applied for the pipe elbows due to the significantly higher error in the obtained limit pressure value compared with numerically FEM obtained results. However, the results for modified codes, adapted for the pipe elbow case using the Goodall formula for calculation of the hoop stress in pipe elbows with defects are pretty consistent with the numerical FEA results. The notch failure assessment diagram (NFAD) was also used for the straight pipe and pipe bends with different corrosion defect depth ratios, while the obtained critical defect depth ratios further highlighted the criticality of pipe elbows as an essential pipeline component. • Integrity of corroded pipe elbow was investigated based on the limit pressure. • A parallelepiped rounded borders corrosion defect was created in the intrados section. • The numerical finite element analyses (FEA) were done to modify the codes. • Two models (modified B31G and DNV RP-F101) agrees well with FEA results. • The notch failure assessment diagram (NFAD) confirms the pipe elbow criticality. [ABSTRACT FROM AUTHOR]

Puffiness formation can occur during process of pipelines component fabrication and transportation or during construction, operation, maintenance and their repair processes. The present paper addresses issues related to pipeline design and associated with the unintended actions due to external loads or ground movements. These may introduce longitudinal strains in the pipeline owing to combinations of curvatures and axial forces. Such scenarios can be tackled with Strain-Based Design approaches. Elaboration on checking the strain capacity of pipelines was achieved via the material testing in which a full-scale test was performed on a pressurized pipe under bending load. Numerical modeling procedures for predicting the structural behavior using certain assumptions are also described in this study. The result in local buckling hereafter referred to as puffiness. Such local damages are associated with large plastic deformations, substantial changes of the pipeline geometry and mechanical properties of its material. • Puffiness on pipe occurs by local buckling resulting mixed loading. • Puffiness is characterized by ondulations and ovalization. • longitudinal strains in the pipeline owing to combinations of curvatures and axial forces. • Such scenarios can be tackled with Strain-Based Design approaches. • ovalization is above the code recommended value and effective stress about two times the critical strain. [ABSTRACT FROM AUTHOR]