Failure Pressure Prediction of Crack in Corrosion Defects in 2D by Using XFEM

2020 ◽  
Author(s):  
Xinfang Zhang ◽  
Allan Okodi ◽  
Leichuan Tan ◽  
Juliana Leung ◽  
Samer Adeeb
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Crack Depth ◽  
Longitudinal Crack ◽  
Mesh Size ◽  
Dynamic Crack Propagation ◽  
Dynamic Crack ◽  
Defect Depth ◽  
Failure Pressure ◽  
Element Method

Abstract Aging pipelines may experience several different types of degradation, such as crack and corrosion, which pose serious concerns for the pipeline integrity. Hybrid flaws such as crack-in-corrosion (CIC), can be challenging to model and understand. For instance, predicting the failure pressure using the finite element method (FEM) is relatively difficult; therefore, the extended finite element method (XFEM) is introduced here. Compared to the conventional FEM, which requires extremely fine meshes and is impractical for modelling dynamic crack propagation, XFEM is computationally efficient as there is no need to update the mesh elements for tracking the crack path. This paper aims to study the applicability of XFEM in predicting the failure pressure of CIC defects in 2D. In particular, mesh size sensitivity and the effects of different CIC parameters on the final failure pressure were examined. ABAQUS v 6.14 was used for this simulation study. For simplicity, only half of the pipe was modelled assuming symmetry around the horizontal plane. A CIC defect was placed at the exterior of the pipe. The corroded area was assumed to be semi-elliptical, and the crack was simulated as a longitudinal crack. In this paper, failure criterion was satisfied when the crack has propagated to the last element. Several models were built in which the length and width of the elements at the crack tip were changed. An optimum mesh size was determined and was applied subsequently in several other models to study the impacts of crack depths, corroded area widths, and corrosion profiles. The results showed that when the total defect depth was fixed at 50% of the wall thickness, the failure pressure decreased with increasing the crack depth, while both corroded area width and corrosion profile only have a secondary effect on the failure pressure. In addition, the failure pressure of a CIC defect was bound between that of a crack-only defect and a corrosion-only defect. When the depth of the crack is higher than 50% of the total defect area, the CIC defect can be treated as a crack only defect with a crack depth equal to the total defect depth.

Failure Pressure Prediction of Cracks in Corrosion Defects Using XFEM

2020 ◽  
Author(s):  
Xinfang Zhang ◽  
Allan Okodi ◽  
Leichuan Tan ◽  
Juliana Leung ◽  
Samer Adeeb
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Extended Finite Element Method ◽  
Crack Depth ◽  
Average Error ◽  
Extended Finite Element ◽  
Defect Depth ◽  
Failure Pressure ◽  
Corrosion Defects ◽  
Element Method

Abstract Coating and cathodic protection degradation can result in the generation of several types of flaws in pipelines. With the increasing number of aging pipelines, such defects can constitute serious concerns for pipeline integrity. When flaws are detected in pipelines, it is extremely important to have an accurate assessment of the associated failure pressure, which would inform the appropriate remediation decision of repairing or replacing the defected pipelines in a timely manner. Cracks-in-corrosion (CIC) represent a class of defect, for which there are no agreed upon method of assessment, with no existing analytical or numerical models to predict their failure pressures. This paper aims to create a set of validated numerical finite element analysis models that are suitable for accurately predicting the failure pressure of 3D cracks-in-corrosion defects using the eXtended Finite Element Method (XFEM) technique. The XFEM for this study was performed using the commercially available software package, ABAQUS Version 6.19. Five burst tests of API 5L X60 specimens with different defect depths (varying from 52% to 66%) that are available in the literature were used to calibrate the XFEM damage parameters (the maximum principal strain and the fracture energy). These parameters were varied until a reasonable match between the numerical results and the experimental measurements was achieved. Symmetry was used to reduce the computation time. A longitudinally oriented CIC defect was placed at the exterior of the pipe. The profile of the corroded area was assumed to be semi-elliptical. The pressure was monotonically increased in the XFEM model until the crack or damage reached the inner surface of the pipe. The results showed that the extended finite element predictions were in good agreement with the experimental data, with an average error of 5.87%, which was less conservative than the reported finite element method predictions with an average error of 17.4%. Six more CIC models with the same pipe dimension but different crack depths were constructed, in order to investigate the relationship between crack depth and the failure pressure. It was found that the failure pressure decreased with increasing crack depth; when the crack depth exceeded 75% of the total defect depth, the CIC defect could be treated as crack-only defects, since the failure pressure for the CIC model approaches that for the crack-only model for ratios of the crack depth to the total defect depth of 0.75 and 1. The versatility of several existing analytical methods (RSTRENG, LPC and CorLAS) in predicting the failure pressure was also discussed. For the corrosion-only defects, the LPC method predicted the closest failure pressure to that obtained using XFEM (3.5% difference). CorLAS method provided accurate results for crack-only defects with 7% difference. The extended finite element method (XFEM) was found to be very effective in predicting the failure pressure. In addition, compared to the traditional Finite Element Method (FEM) which requires extremely fine meshes and is impractical in modelling a moving crack, the XFEM is computationally efficient while providing accurate predictions.

Numerical Analysis of API 5L X42 and X52 Vintage Pipes with Cracks in Corrosion Defects Using Extended Finite Element Method

2021 ◽  
Author(s):  
Xinfang Zhang ◽  
Meng Lin ◽  
Allan Okodi ◽  
Leichuan Tan ◽  
Juliana Leung ◽  
...  
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Extended Finite Element Method ◽  
Pipe Wall ◽  
Crack Depth ◽  
Initial Crack ◽  
Extended Finite Element ◽  
Failure Pressure ◽  
Corrosion Defects ◽  
Element Method

Abstract Cracks and corrosion in pipelines can occur simultaneously, representing a hybrid defect known as cracks in corrosion (CIC), which is often difficult to model using the available assessment codes or methods. As a result, detailed modeling of CIC has not been studied extensively. In this study, the extended finite element method (XFEM) has been applied to predict the failure pressures of CIC defects in API 5L Grade X42 and X52 pipes. The pipes were only subjected to internal pressure and the XFEM models were validated using full-scale burst tests available in the literature. Several CIC models with constant total defect depths (55%, and 60% of wall thickness) were constructed to investigate the effect of the initial crack depth on the failure pressure. The failure criterion was defined when wall penetration occurred due to crack growth, i.e., the instance the crack reached the innermost element of the pipe wall mesh. It was observed that for shorter cracks, the failure pressure decreased with the increase of the initial crack depth. The results indicated that the CIC defect could be treated as crack-only defects when the initial crack depth exceeded 50% of the total defect depth. However, for longer cracks, the initial crack depth was found to have a negligible effect on the failure pressure, implying that the CIC defect could be treated as either a crack or a corrosion utilizing the available assessment methods.

Dynamic crack propagation analysis based on the s-version of the finite element method

2020 ◽  
Vol 366 ◽  
pp. 113091
Author(s):  
Kota Kishi ◽  
Yuuki Takeoka ◽  
Tsutomu Fukui ◽  
Toshiyuki Matsumoto ◽  
Katsuyuki Suzuki ◽  
...  
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Crack Propagation ◽  
Dynamic Crack Propagation ◽  
Dynamic Crack ◽  
The Finite Element Method ◽  
Propagation Analysis ◽  
Element Method

scholarly journals A molecular dynamics/extended finite element method for dynamic crack propagation

2008 ◽  
Vol 30 (4) ◽  
Author(s):  
Pascal Aubertin ◽  
Julien Réthoré ◽  
René De Borst
Keyword(s):  
Finite Element Method ◽  
Molecular Dynamics ◽  
Finite Element ◽  
Extended Finite Element Method ◽  
Coupled Model ◽  
Partition Of Unity ◽  
Dynamic Crack Propagation ◽  
Dynamic Crack ◽  
Extended Finite Element ◽  
Element Method

A multiscale method is presented which couples a molecular dynamics approach for describing fracture at the crack tip with an extended finite element method for discretizing the remainder of the domain. After recalling the basic equations of molecular dynamics and continuum mechanics the discretization is discussed for the continuum subdomain where the partition-of-unity property of finite element shape functions is used, since in this fashion the crack in the wake of its tip is naturally modelled as a traction-free discontinuity. Next, the zonal coupling method between the atomistic and continuum models is described, including an assessment of the energy transfer between both domains for a one-dimensional problem. Finally, a two-dimensional computation is presented of dynamic fracture using the coupled model.

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