Pipeline Girth Welds Research Articles

Study on fracture behaviour of pipeline girth welds based on curved wide plate specimens: Experimental and numerical analysis

Understanding the fracture characteristics and strain capacity of pipelines with girth welds under external loads is crucial for evaluating pipeline safety. The use of curved wide plate (CWP) specimens closely resembling full-scale (FS) pipelines in geometry provides a more realistic representation of crack tip constraint states compared to small-size fracture toughness test specimens in laboratory settings. This study aims to investigate the ductile fracture characteristics of center cracks on the outer surface of girth welds in high-grade steel pipelines under external loads through large-scale CWP tensile tests and advanced numerical simulations. Tensile tests were conducted on CWP specimens using a kiloton tensile testing machine, with double crack opening displacement (COD) gauge monitoring crack mouth opening displacement (CMOD), and high-precision displacement sensors and strain gauges tracking deformation and strains at various positions. The study yielded significant experimental results, and a finite element (FE) model of the CWP was developed using the nonlinear finite element method (FEM) to validate the experimental data against simulation results. The FE model was then used to investigate the influence of material properties on crack propagation resistance and driving force curves. A method for determining the ultimate tensile strain capacity (UTSC) of pipelines based on actual material fracture toughness was proposed. This research contributes valuable experimental data for further exploration of fracture behaviour in large-scale pipeline girth welds and offers insights for safety evaluations of such welds.

Al2O3-MnS Inclusions and Pitting Corrosion in the Weld Heat-Affected Zone

Manganese sulfide inclusions have been identified as a key factor contributing to the degradation of pitting corrosion resistance in both carbon and stainless steels. However, the precise reasons behind the differential reactivity of various sulfides, with some serving as active sites for pitting while others remain inactive, are not yet fully understood. The effect of debonding occurring at the interface between these inclusions and the steel matrix in relation to pitting corrosion has not been extensively investigated. In this study, an examination of a service-exposed pipeline girth weld was conducted. Immersion testing in blowdown water and multiscale characterization techniques investigated the inclusion-matrix interface debonding within the heat-affected zone. Our findings suggest that interfacial debonding is more likely at the Al2O3- MnS cluster interface. This observation offers a rationale for the selective reactivity of sulfides that form clusters with oxides, highlighting the likelihood that only sulfides clustering with oxides act as active pitting initiation sites.

Inhomogeneous Strain Behaviors of the High Strength Pipeline Girth Weld under Longitudinal Loading.

Unforeseen failures in girth welds present a significant challenge for the pipeline industry. This study utilizes 3D Digital Image Correlation (DIC) assisted cross-weld tensile testing to analyze the strain response of high-strength thick-walled pipelines, providing essential insights into the strain migration and fracture mechanisms specific to girth welds. The results reveal that the welding process significantly affects the mechanical distribution within the girth weld. The tested Shielded Metal Arc Welded (SMAW-ed) pipe exhibited undermatched girth welds due to high heat input, while Gas Metal Arc Welding (GMAW) introduced a narrower weld and Heat-Affected Zone (HAZ) with higher hardness than the base metal, indicative of overmatched girth welds. Strain migration, resulting from a combination of metallurgical heterogeneous materials and geometrical reinforcement strengthening, progressed from the softer HAZ to the base metal in the SMAW-ed sample with reinforcement, ultimately leading to fracture in the base metal. In contrast, the GMAW-ed sample shows no strain migration. Reinforcement significantly improves the tensile strength of girth welds and effectively prevents failure in the weld region. Sufficient reinforcement is crucial for minimizing the risk of failure in critical areas such as the weld metal and HAZ, particularly in SMAW-ed pipes.

Influence of welding defects on hydrogen embrittlement sensitivity of girth welds in X80 pipelines

Hydrogen embrittlement poses a considerable threat to girth welds in high-grade steel pipelines. This study investigated the influence of welding defects on the hydrogen embrittlement sensitivity of girth welds in X80 pipelines through slow strain rate tensile (SSRT) testing, scanning electron microscopy, hydrogen permeation test, and finite element analysis. The findings indicated that regardless of the presence of welding defects, the hydrogen embrittlement sensitivity of pipeline girth welds increases with negative current density. Welding defects can lead to a substantial increase in the hydrogen embrittlement sensitivity of girth welds and can shift crack initiation points from the surface areas of SSRT specimens to the locations of the defects. Stress concentration caused by welding defects results in the redistribution and local enrichment of hydrogen under the effect of stress-induced hydrogen diffusion, thereby leading to a considerable increase in hydrogen embrittlement sensitivity.

Effect of pre-strain on microstructure evolution and fracture behavior of undermatching X80 pipeline steel girth weld

This work aims to study the effect of pre-strain on the fracture behavior of X80 pipeline girth weld joint, a comprehensive analysis was conducted on the microstructure and mechanical properties of the girth weld before and after pre-strain treatment. The mechanical properties were evaluated through tensile testing, Charpy impact testing, and digital image correlation (DIC) strain analysis. Furthermore, the microstructure and fracture morphology of the girth weld were observed using optical electron microscopy (OM) and scanning electron microscopy (SEM). The results show that the application of pre-strain treatment leads to dislocation accumulation at the grain boundary of X80 pipeline girth weld, resulting in stress concentration and subsequent formation of damage holes. This process disrupts the continuity of chain M-A island and initiates small cracks at the grain boundary, ultimately causing a significant decrease in impact toughness and impact work from 177 J to about 10 J.

Correction on stress intensity factor of root within pipeline girth weld considering various geometric parameters

The study focuses on the stress intensity correction factor (Mk) for internal surface cracks located at the girth pipe root toe. To assess the impact of various parameters on Mk, three-dimensional finite element models are developed. These models take different types of misalignment, a range of variable-wall-thickness ratios, and initial crack depths into account. The findings reveal that the stress intensity correction factor Mk tends to increase with the rise in misalignment and variable-wall-thickness ratio. Conversely, an increase in the initial crack depth leads to a decrease in Mk. The study demonstrates that the Mk values, when accounting for different geometric factors, are significantly higher than those calculated using BS 7910. This suggests that the BS 7910 standard may provide overly optimistic predictions. As a result, a revised Mk formula is proposed, which generally maintains an error margin of less than 10 %. This modified formula offers a significant enhancement to prevailing codes and standards, furnishing a more dependable benchmark for the assessment of structural integrity in pipeline laying procedures.

Data-driven probabilistic failure assessment curve based on similitude principle

In the study, based on the similarity in crack-tip fields between pipeline structure and standardized single-edge notched tension (SE(T)) test specimen, a methodology using a data-driven machine learning technique is proposed to determine the specific failure assessment curves for full-scale pipeline girth welds. By considering constraint similitude and ductile tearing, the probabilistic failure assessment line obtained from SE(T) resistance curves with a 50% survival rate can provide the most accurate failure assessment, as validated using the experimental full-scale pipeline data in the literature, particularly for the zone dominated by ductile fracture. Moreover, Option 1 (in R6 terminology) fracture assessment curve of British Energy R6 approach, which corresponds to a 15% survival rate, is proven to be overly-conservative.

The effect of pipeline root weld microstructure on crack growth behaviour

The girth weld is the weak link of high-pressure pipeline, which is easy to crack under the combined action of internal and external loads, defect and stress concentration. At present, the safety hazards of high-strength pipeline girth welds are prominent, and it is of great significance to study the failure law of girth welds to ensure the safe operation of pipelines. In this paper, the failure analysis of 6 welded joints with crack defects excavated on site in a gas transmission company was carried out. Through metallographic analysis, scanning electron microscope (SEM) observation and electron backscatter diffraction (EBSD) analysis, the relationship between root welding, weld microstructure and crack generation was analyzed in detail. The influence of grain boundary distribution behavior of weld microstructure on crack propagation path was studied, and the mechanism of welding inclusions on crack propagation and aggregation nucleation was revealed. The results show that the cracks in root welding, hot welding, filling welding and heat affected zone are all transgranular propagation types, and the deflection of crack propagation path may be related to the complex stress state at the welded joint. Local strain concentration often exists in the near crack surface, secondary crack and crack deflection position on the crack propagation path, which indicates that the formation and propagation of root cracks are likely to be related to the deterioration of weld metal properties caused by local strain concentration at the root. The research conclusions have certain reference value for the intrinsic safety design, construction, and integrity operation and maintenance of pipeline girth welds.

CIVA Modelling Module for Zonal Discrimination Method Part 2-System Qualification Aspects

Automatic Ultrasonic Testing (AUT) systems for pipeline girth weld inspections are usually subjected to a qualification process. This process consists of assessment of performance capabilities including detection, sizing, temperature range and repeatability. One of the most demanding qualification programmes is described in DNV ST-F101 Appendix E [1]. With the introduction of the AUT module in the 2023 edition of CIVA simulation software, the incorporation of metamodeling allows users to predict detection reliability via probability of detection (POD) and sizing accuracy of the zonal discrimination method (ZDM) using amplitude apportioning. Part 1 of this project demonstrated the ability of CIVA to simulate the calibration block and strip chart output. In Part 2 we illustrate the techniques that can be used to predict POD and sizing accuracy as might be done in a system qualification. Results compare well to field data.

Fatigue performance of riser quality girth welds: Analysis of TWI and DNV's databases

AbstractIn the fatigue design guidelines which focus on welded joints, when the applied loading is of variable amplitude (variable amplitude loading, VAL), the slope of the S‐N curves at endurances above the slope transition point (STP) changes from m to m + 2 in DNV‐RP‐C203 and BS7608. However, the position of the STP is different in BS7608 and DNV RP C203. This results in different calculated fatigue lives and the difference in calculated fatigue life can be significant. In order to provide better guidance to industry on the approach to use for fatigue analysis of girth welds in pipelines and risers specifically, TWI and DNV carried out a project where the ultimate aim was to provide guidance on a common S‐N curve suitable for calculating the fatigue life of girth welds with focus on the slope change area of the S‐N curves. This was attempted by re‐analyzing TWI's and DNV's databases of girth weld fatigue test results and comparing the outcomes. Although it was not possible to agree on a single STP from the analysis carried out, regression analysis of high endurance results from the databases suggest that an STP between the two current values 1E7 and 5E7 may be plausible. This is supported by fracture mechanics analysis, which suggests that the position of the STP depends on the fatigue Class, and the magnitude of the applied stress ranges.

Full-scale Fatigue and Burst Tests on Notched Pipeline Girth Welds, under Complex Loading Conditions

Full-scale Fatigue and Burst Tests on Notched Pipeline Girth Welds, under Complex Loading Conditions

Addressing the inspection selection challenges of in-service pipeline girth weld using ensemble tree models

Natural gas transportation predominantly utilizes pipelines, and the safety of these systems largely hinges on the integrity of girth welds. However, once pipelines are buried post-construction, pinpointing weld inspection sites becomes complex. Presently, weld risk assessments rely on costly and specialized inspections. Hence, enhancing the accuracy in identifying defective welds and discovering superior inspection techniques is paramount. Our research employed machine learning, specifically an ensemble model of RandomForest and CatBoost, to prioritize weld inspections. After analyzing the West-East Gas Pipeline Girth Weld Dataset and addressing data imbalances using the SMOTE technique, we refined the model parameters. The culminating model yielded an F1-score of 0.815 and an average accuracy of 0.836, outperforming standalone models. Employing the SHAP method improved the model’s transparency, facilitating a more informed decision-making process regarding pipeline inspections. This study underscores the potential of machine learning in elevating oil and gas pipeline safety measures.

Intelligent identification of girth welds defects in pipelines using neural networks with attention modules

Girth weld defects (crack, lack of penetration, lack of fusion, and edge nibbling) can cause pipeline cracking failure accidents. Internal magnetic flux leakage (MFL) detection can successfully identify pipeline defects, while the intelligent identification of MFL signals based on deep learning can promote the accurate determination of pipeline girth weld defects. Although the YOLOv5 model can effectively identify abnormal image objects, it exhibits no attention preference during the feature extraction process, proving insufficient for small objects. This study targeted minor defects in the girth weld of the pipeline and used the Convolutional Block Attention Module (CBAM) to optimize the YOLOv5 network model structure, increasing detection network attention preference toward extracting small-target defect signals. The CBAM+YOLOv5 model improved the detection accuracy of the MFL signal of the girth weld in the pipeline from 89.33% to 98.11% and correctly identified and classified the MFL signal of the pipeline girth weld with 85% confidence, with minor anomalies. The CBAM+YOLOv5 model effectively improved the identification accuracy of the girth weld defect signal in the pipeline, providing technical support for safety grade assessment and excavation verification.

Research on Internal Shape Anomaly Inspection Technology for Pipeline Girth Welds Based on Alternating Excitation Detection.

Abnormal formation of girth weld is a major threat to the safe operation of pipelines, which may lead to serious accidents. Therefore, regular inspection and maintenance of girth weld are essential for accident prevention and energy security. This paper presents a novel method for inspecting abnormal girth weld formation in oil and gas pipelines using alternating excitation detection technology. The method is based on the analysis of the microscopic magnetic variations in the welded area under alternating magnetic fields. An internal inspection probe and electronic system for detecting abnormal girth weld formation were designed and developed. The system's capability to identify misalignment, undercutting, root concavity, and abnormal formation height of girth weld was tested by numerical simulation and experimental study. The results show that the detection system can effectively identify a minimum misalignment of 0.5 mm at a lift-off height of 15 mm. The proposed method offers several advantages, such as rapid response, low cost, non-contact operation, and high sensitivity to surface flaws in ferromagnetic pipelines.

Failure Risk Prediction Model for Girth Welds in High-Strength Steel Pipeline Based on Historical Data and Artificial Neural Network

Pipelines are the most economical and sensible way to transport oil and gas. Long-distance oil and gas pipelines consist of many steel pipes or pipe fittings joined by welded girth welds, so girth welds are an essential part of pipelines. Owing to the limitations of welding conditions and the complexity of controlling weld quality in the field, some defects are inevitably present in girth welds and adjacent weld areas. These defects can lead to pipeline safety problems; therefore, it is necessary to perform failure risk assessment of pipeline girth welds. In this study, an artificial neural network model was proposed to predict the failure risk of pipeline girth welds with defects. Firstly, many pipeline girth weld failure cases, pipeline excavation, and inspection data were collected and analyzed to determine the main factors influencing girth weld failure. Secondly, a spatial orthogonal optimization method was used to select training samples for the artificial neural network model to ensure that the training sample set could cover the feature space with a minimum number of samples. Thirdly, a prediction model based on BP neural networks was established to predict the failure risk levels. The training dataset/testing dataset was 602/4215, and the prediction accuracy for all risks of girth welds achieved an acceptable level. This study can provide a valuable reference for pipeline operators to prevent pipeline accidents.

Study on Numerical Simulation Method of Fracture Behavior of Pipeline Girth Weld

Abstract The failure accidents in girth weld of pipelines occur frequently due to the combination of internal defects and external loads. However, the research on the fracture behavior of girth weld defects is relatively poor at present. To solve this problem, the cracking behavior and strain evolution law of the inner wall defects of the pipe girth weld are studied in combination with full-scale tests (FST). The constitutive and Gurson-Tvergaard-Needleman damage parameters of the pipe base metal zone, weld zone and heat-affected zone (HAZ) are calibrated through the small punch test (SPT) and single edge notch bending (SENB) test. On this basis, the welded pipe model with inner wall defects is established, and a numerical simulation method for dynamic fracture behavior based on damage mechanics is formed. The numerical simulation method is verified by FST data and theoretical calculation. The results show that the numerical results are consistent with the FST and theoretical calculation in the elastic stage, plastic stage, and fracture stage, and the error is within 10%. The novel numerical simulation method is provided as a means for the fracture behavior research of pipeline girth weld.

A novel method for determining the stress-strain constitutive relationship of high-grade pipeline weld zone material

As a typical welding structure, the girth weld of high-grade pipelines has obvious heterogeneity. Therefore, the axial mechanical properties of girth weld materials cannot be accurately tested, and the safety evaluation of the girth weld of the pipeline is seriously affected. Based on MATLAB-PYTHON-ABAQUS co-simulation, an optimization inversion method of the material stress-strain constitutive relationship in the weld zone of the high-grade pipeline is proposed in this paper. Four groups of uniaxial tensile tests with different notch sizes are carried out, and the load-displacement curves of each specimen are obtained. The true stress-strain constitutive relationship of the weld zone material is obtained by the Bayesian regularization back propagation (BRBP) neural network and the Grey wolf optimizer (GWO). The accuracy of the constitutive relationship is fully verified by the test data, and the relative error is less than 1%. In addition, taking the weld material of the oil and gas pipeline as an example, this paper proposes a universal design method of specimen size with a notch, which is convenient for researchers in different fields to measure the stress-strain constitutive relationship of different materials. The proposed inversion method can provide an accurate stress-strain constitutive relationship for the safety evaluation of girth welds of high-grade pipelines.

Fracture Response of X80 Pipe Girth Welds under Combined Internal Pressure and Bending Moment.

In order to determine the effect of defect size on the pipeline fracture performance of girth welds in oil and gas pipelines, ABAQUS was used to simulate the fracture responses of X80 pipelines with girth weld defects under internal pressure and bending moment conditions based on damage mechanics. In particular, the length and depth of defects were parametrically studied; the defect depth range was 20-80% of the wall thickness, and the circumferential length range of the defects was 5-20% of the pipeline circumference. The results show that, under the combined action of internal pressure and bending moment, the defect depth was more associated with adverse effects than the circumferential length of the defect. The failure load did not linearly decrease as the size of the defect increased, but when the depth of the defect reached a certain value, the failure load suddenly decreased.

Full-Scale Tests of Pipeline Girth Welds Under Complex Cyclic Internal Pressure and Static Bending Loading Conditions

The critical elements of high-pressure hydrocarbon transporting pipelines are often the girth welds, which are subjected to complex loads. The aims of our research and this paper are to introduce our full-scale pipeline fatigue and burst tests applying cyclic internal pressure and superimposed external bending stress on girth welds, furthermore, attracting the importance and the applicability of the investigation results. A unique testing system was built to study the behaviour of pipeline girth welds under simultaneous loads. The tests were evaluated using video camera recordings, internal pressure vs. burst time functions and failure pressure values.

Improvement of fracture assessment method for pipe girth weld based on failure assessment diagram

The increasing demand for oil and gas resources in China has promoted the rapid construction and development of oil and gas pipeline networks. With an increase in the mileage of high-grade pipeline, the intrinsic safety of pipeline girth weld faces serious challenges, and the existing fracture assessment methods have many shortcomings. The failure assessment diagram of the commonly used fracture assessment method in engineering is taken as the research object. Aiming at deficiency that it cannot accurately consider the strength matching characteristics of girth welds. Based on the failure assessment diagram theory and the equivalent stress-strain relationship method, the influence of crack size, pipeline diameter-thickness ratio, and material parameters on the fracture assessment accuracy of the girth weld is studied. The calculation method of optimized limit load and reference stress is established. Moreover, the improved fracture assessment process of pipeline girth weld is proposed, which makes up for the lack of conservative assessment results in traditional methods and improves the accuracy of fracture assessment girth weld under high-stress conditions.