Remaining strength of API J55 steel casing pipes damaged by corrosion

Ground movements caused by continuous freezing and thawing of the ground in arctic regions can potentially lead to pipeline failures. There are many factors such as internal pressure, pipeline geometry, pre-crack, corrosion, and pre-existing dents that can expedite the failure processes. There exist several methods to predict the failure in pipelines and study the abovementioned factors and their influences. These methods include experiments, analytical models, finite element method (FEM), and extended finite element method (XFEM). For predicting crack propagation in pipelines, XFEM has recently been proposed by researchers as the most efficient among the available methods. The purpose of our work is to conduct a systematic literature review of the available studies that attempted to use XFEM to predict failure due to crack propagation in pipelines and the effect of the abovementioned factors on failure. Articles are summarized according to the performed experiments, the pipeline material grade, failure material model, the investigated effect of various parameters on failure such as internal pressure or defect size, and methods for results verification. The number of articles in the literature using the XFEM for prediction of failure in pipelines was 23 to the best knowledge of the authors. However, in this systematic literature review, all these articles are categorized and investigated. The reviewed articles in general agree that XFEM simulations compare well with experiments, can accurately predict crack propagation in pipelines, and can be used efficiently to study the effect of various parameters on pipeline crack propagation for a wide range of materials.

Systematic literature review of the application of extended finite element method in failure prediction of pipelines

Anomalies as misalignment, microcrack are inevitable for large diameter high strength steel pipelines. To ensure the strain capacity of mismatched welding joint with misalignments of D 1,422 mm X80 steel pipeline, a comprehensive study via wide plate experiments and finite element model simulations was conducted. The full-scale tensile experiment of a X80 pipe wide plate with weld joint was conducted. Strain distributions on the plate was derived by DIC technic. Trends of CMOD at the precrack in the weld joint with tensile strains monitored. A FE model was established to inverse the wide plate experiment and prove the accuracy of numerical model’s prediction results for crack driving forces. Using the same modeling method, a parametrical 3D numerical simulation model for X80 line pipe with cracks in automatic welding joints was established. The double V-shaped groove type welding joint was precisely considered in the geometric model. Difference of the stress-strain relationships of yielding-to-tensile ratio of the BM, softening rate of the HAZ and strength matching coefficient of WM were considered in the material model. A CTOD extracting program coded was employed. Parametric analysis was performed to investigate the effects of load conditions, strength matching coefficient of WM, yielding-to-tensile ratio of BM and softening rate of HAZ on the strain capacity with a critical fracture toughness adopted in pipeline industry. Based on the derived results, mismatched ratio requirements of D 1,422 mm X80 pipes were listed, which provides guidance for the welding parameter design and safety evaluation of automatic welding joints.

Strain capacity analysis of the mismatched welding joint with misalignments of D 1,422 mm X80 steel pipelines: An experimental and numerical investigation

XGBoost algorithm-based prediction of safety assessment for pipelines

Mechanical damage in form of dents, cracks, gouges, and scratches are common in pipelines. Sometimes, these damages form in proximity of each other and act as one defect in the pipe wall. The combined defects have been found to be more injurious than individual defects. One of the combined defects in pipeline comprises of a crack in a dent, also known as dent-crack defect. This paper discusses the development of finite element models using extended finite element criterion (XFEM) in Abaqus to predict burst pressure of specimens of API X70 pipeline with restrained and unrestrained concentric dent-crack defects. The models are calibrated and validated using results of full-scale burst tests. The effects of crack length, crack depth, dent depth, and denting pressure on burst pressure are investigated. The results show that restrained dent-crack defects with shallow cracks (depth less than 50% wall thickness) inside dents do not affect pipeline operations at maximum allowable operating pressure if crack lengths are less than 200 mm. Releasing restrained dent-cracks when the pressure is at maximum allowable operating pressure can cause propagation of deep cracks (depth of 50% wall thickness or more) longer than 60 mm. However, only very long cracks (200 mm and higher) propagate to burst the pipe. Cracks of depth less than 20% of wall thickness inside dents formed at zero pressure are not propagated by the maximum allowable operating pressure. Dent-crack defects having dents of depth less than 2% outside diameter of pipe behave as plain cracks if the dents are formed at zero denting pressure but are more injurious than plain cracks if the dents are formed in pressurized pipes.

https://www.mdpi.com/2076-3417/10/21/7554/pdf

Crack Propagation and Burst Pressure of Pipeline with Restrained and Unrestrained Concentric Dent-Crack Defects Using Extended Finite Element Method

Crack propagation and burst pressure of longitudinally cracked pipelines using extended finite element method

Burst pressure of pipelines with longitudinal cracks located at the centre of rectangular dents varies with defect size and recent reports indicate that it could be very high for shallow cracks inside shallow dents and for cracks inside restrained dents. However, it is not clear whether cracks located in the flank of dents would have the same impact on burst pressure of pipelines with dent-crack defects. In addition, studies show that the location of maximum strain in circular dents shifts away from the centre towards the flank when dented pipes are pressurised, but the implication on the propagation of longitudinal cracks located in various parts of a dent has not yet been widely investigated. In this paper, models of pipelines with longitudinal cracks inside rectangular dents were created using the Finite Element Methods software Abaqus to analyse crack propagation and predict the associated burst pressure. The in-built Extended Finite Element procedure in Abaqus was used to model crack propagation through the pipe. The models were calibrated and validated using previously published results of burst tests and tests of material properties. The effect of longitudinal cracks in both the flank and centre of the dents on the burst pressure was analysed by varying the crack length, the crack depth, the dent depth, the internal pressure during dent formation and the dent constraint condition. The results show that longitudinal cracks in the flank of rectangular dents are more severe for pipeline integrity than cracks located in the centre of dents. Crack depth and crack location inside the dents are the most influential parameters when assessing dent-crack defects in pipelines. Their effects on burst pressure are magnified by crack length, dent depth and denting pressure.

Effect of location of crack in dent on burst pressure of pipeline with combined dent and crack defects


 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 5 L 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 corrosion utilizing the available assessment methods.

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


 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.

Allan Okodi

Papers

Crack propagation and burst pressure of longitudinally cracked pipelines using extended finite element method

Crack Propagation and Burst Pressure of Pipeline with Restrained and Unrestrained Concentric Dent-Crack Defects Using Extended Finite Element Method

Effect of location of crack in dent on burst pressure of pipeline with combined dent and crack defects

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

Failure Pressure Prediction of Cracks in Corrosion Defects Using XFEM