Girth Weld Defects Research Articles

Failure Analysis of Girth Weld Cracking in Gas Transmission Pipelines Subjected to Ground Subsidence and Traffic Loads

Girth welds are weak points in pipelines, and failures occur frequently. In a gas transmission pipeline, a girth weld experienced cracking, prompting a failure analysis using experimental methods and finite element analysis (FEA). Experimental results showed that X-ray non-destructive testing (NDT) revealed cracks, porosity, and lack of fusion in the girth weld. However, the hardness and microstructure of the material showed no abnormalities. During operation, the pipeline experienced an increase in soil cover and was subjected to ground subsidence and vehicle loads. Finite element analysis was conducted on the defective girth weld under different conditions, including varying soil cover depths, different levels of subsidence, and varying vehicle loads, to examine the pipeline’s stress response. The results indicated that the combination of soil cover, subsidence, and vehicle loads led to pipeline failure, whereas none of these factors alone was sufficient to cause girth weld failure. To prevent such failures from occurring again, the following measures are recommended: strengthen on-site welding quality control of girth welds, conduct inspections for defects in girth welds of in-service pipelines, and promptly address any defects that exceed acceptable limits.

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.

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.

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.

Hydrogen-Accelerated Fatigue of API X60 Pipeline Steel and Its Weld

In this work, the hydrogen fatigue of pipeline steel X60, its girth welds and weld defects were investigated through in situ fatigue testing. A novel in situ gaseous hydrogen charging fatigue set-up was developed, which involves a sample geometry that mimics a small-scale pipeline with high internal hydrogen gas pressure. The effect of hydrogen was investigated by measuring the crack initiation and growth, using a direct current potential drop (DCPD) set-up, which probes the outer surface of the specimen. The base and weld metal specimens both experienced a reduction in fatigue life in the presence of hydrogen. For the base metal, the reduction in fatigue life manifested solely in the crack growth phase; hydrogen accelerated the crack growth by a factor of 4. The crack growth rate for the weld metal accelerated by a factor of 8. However, in contrast to the base metal, the weld metal also experienced a reduction of 57% in resistance to crack initiation. Macropores (>500 µm in size) on the notch surface reduced the fatigue life by a factor of 11. Varying the pressure from 70 barg to 150 barg of hydrogen caused no difference in the hydrogen fatigue behavior of the weld metal. The fracture path of the base and weld metal transitioned from transgranular and ductile in nature to a mixed-mode transgranular and intergranular quasi-cleavage fracture. Hydrogen accelerated the crack growth by decreasing the roughness- and plasticity-induced crack closure. The worst case scenario for pipelines was found in the case of weld defects. This work therefore highlights the necessity to re-evaluate pipelines for existing defects before they can be reused for hydrogen transport.

Research on magnetic signal of cracks in girth weld of ferromagnetic pipeline

The crack of pipeline girth weld is one of the most common and dangerous defects in girth weld. According to the magnetic dipole theory model, the magnetic signal model of pipeline girth weld cracks is established. By means of numerical simulation, the distribution characteristics of magnetic signals of crack defects in girth welds and the variation rules of magnetic signals of different flaw sizes and lifting heights of girth welds were studied. The simulation results show that the normal component Hy appears zero crossing and changes direction, and the tangential component Hx appears extreme value upward. Finally, the magnetic signal model of crack defects in pipeline girth weld was verified through field engineering test. The actual magnetic induction intensity detected at the flaw of pipeline girth weld was basically consistent with the theoretical calculation results, which verified the accuracy of the model.

Quality Assessment Algorithm of X-Ray Images in Overall Girth Welds Based on Deep Neural Network

Defect recognition and assessment are essential technologies for the safety of pipelines. Recently, deep neural network methods have shown great progress in recognizing pipeline weld defects. However, the current methods cannot achieve online quality assessment for overall girth welds. To solve this problem, this paper proposes a novel quality assessment algorithm for defect recognition and assessment of X-ray girth weld images. First, a two-stage defect classifier based on residual neural network (ResNet) is proposed, which consists of a ResNet18 region classifier and a ResNet50 defect classifier. It can make up for the lack of a single classifier so that the performance and speed of defect recognition can be improved. Second, the feature-extraction calculator is used to extract and calculate the area of the weld defects based on the smallest bounding rectangle method. Third, we propose a quality evaluator based on an improved ensemble learning algorithm and long short-term memory (LSTM), so that the girth welds can be well assessed. Finally, an experiment is conducted using pipeline girth weld X-ray images. The analytic hierarchy process (AHP) method is used to comprehensively assess the level of overall girth-weld defects. The experimental results show that the proposed method is effective in recognizing and evaluating the girth-weld defects of X-ray images. And the accuracy of the quality evaluator can reach 92% for the quality assessment of overall girth welds, compared with manual quality decisions. It effectively achieves online quality assessment for girth welds and has higher evaluation accuracy.

Image Classification Method Based on Improved Deep Convolutional Neural Networks for the Magnetic Flux Leakage (MFL) Signal of Girth Welds in Long-Distance Pipelines

Girth weld defects in long-distance oil and gas pipelines are one of the main causes of pipeline leakage failure and serious accidents. Magnetic flux leakage (MFL) is one of the most widely used inline inspection methods for long-distance pipelines. However, it is impossible to determine the type of girth weld defect via traditional manual analysis due to the complexity of the MFL signal. Therefore, an automatic image classification method based on deep convolutional neural networks was proposed to effectively classify girth weld defects via MFL signals. Firstly, the image data set of girth welds MFL signal was established with the radiographic testing results as labels. Then, the deep convolutional generative adversarial network (DCGAN) data enhancement algorithm was proposed to enhance the data set, and the residual network (ResNet-50) was proposed to address the challenge presented by the automatic classification of the image sets. The data set after data enhancement was randomly selected to train and test the improved residual network (ResNet-50), with the ten validation results exhibiting an accuracy of over 80%. The results indicated that the improved network model displayed a strong generalization ability and robustness and could achieve a more accurate MFL image classification of the pipeline girth welds.

Development of a 16-Channel Broadband Piezoelectric Micro Ultrasonic Transducer Array Probe for Pipeline Butt-Welded Defect Detection.

Butt welding is extensively applied in long-distance oil and gas pipelines, and it is of great significance to conduct non-destructive ultrasonic testing of girth welds in order to avoid leakage and safety accidents during pipeline production and operation. In view of the limitations of large transducer size, single fixed beam angle, low detection resolution and high cost of conventional ultrasonic inspection technologies, a 16-channel piezoelectric micro ultrasonic transducer (PMUT) array probe was developed through theoretical analysis and structural optimization design. After the probe impedance characterization, the experimental results show that the theoretical model can effectively guide the design of the ultrasonic transducer array, offering the maximum operating frequency deviation of less than 5%. The ultrasonic echo performance tests indicate that the average −6 dB bandwidth of the PMUT array probe can be up to 77.9%. In addition, the fabricated PMUT array probe has been used to successfully detect five common internal defects in pipeline girth welds. Due to the multiple micro array elements, flexible handling of each element, large bandwidth and high resolution of defect detection, the designed PMUT array probe can provide a good application potential in structural health monitoring and medical ultrasound imaging fields.

Prediction of Tensile Strain Capacity for X52 Steel Pipeline Materials Using the Extended Finite Element Method

Strain-based design (SBD) plays an important role in pipeline design and assessment of pipelines subjected to geo-hazards. Under such hazards, a pipe can be subjected to substantial plastic strains, leading to tensile failure at locations of girth weld flaws. For SBD, the finite element method (FEM) can be a reliable tool to calculate the tensile strain capacity (TSC) for better design in pipelines. This study aims to investigate the ductile fracture properties for specific vintage pipeline steel (API 5L grade of X52) using the extended finite element method (XFEM). Eight full-scale tests were simulated using the commercial finite element analysis software ABAQUS Version 6.17. Maximum principal strain is used to assess the damage initiation using the cohesive zone model (CZM) when the crack evolution is evaluated by fracture energy release. A proper set of damage parameters for the X52 materials was calibrated based on the ability of the model to reproduce the experimental results. These experimental results included the tensile strain, applied load, endplate rotation, and crack mouth opening displacement (CMOD). This study describes a methodology for validation of the XFEM and the proper damage parameters required to model crack initiation and propagation in X52 grades of pipeline.

Research progress and prospect of key technologies for high-strain line pipe steel and pipes

The development and supporting technologies of high-strain line pipe steel and pipes used for oil and gas pipeline projects in special geological environments (such as earthquake zone, landslide zone, mine goaf and subsidence zone) is one of the international research hotspots, and it is also a major problem that China's major oil and gas pipeline projects have to solve. Focusing on a series of key technical difficulties in the research & development and application of high-strain line pipe steel and pipes, a number of theoretical and technological innovations have been achieved after more than ten years of joint researches. And the main achievements are as follows. First, the method of applying many different parameters (e.g. stress ratio, yield to tensile ratio and uniform elongation (UEL)) to comprehensively characterize and evaluate the deformation behavior of steel pipes is proposed, and a technical index system and standard for the new products of X70HD/X80HD high-strain line pipe steel and pipes are established. Second, a complete set of X70HD/X80HD steel plate manufacturing technology is researched and developed, and the high-strain steel plate with the properties of low yield to tensile ratio, high uniform elongation, high stress ratio and high strength and toughness is worked out. Third, the X70HD/X80HD JCOE and UOE high-strain longitudinal submerged arc welded pipe manufacturing technology is researched and developed, reasonable performance matching between a steel pipe and a welding seam is realized, and the performance deterioration in the process of forming, welding, diameter-expending and thermal coating is solved. Fourth, a full-scale test device of steel pipe internal pressure + bending large deformation is independently developed, and the physical simulation based steel pipe deformation test technology is formed. X70HD/X80HD high-strain line pipe steel and pipes have been applied in the West to East Gas Pipeline, the China–Myanmar Pipeline and other major gas pipeline projects in the large scale, and their application effects are remarkable. To satisfy the new needs of pipeline construction and long-term safe operation under complex geological conditions, some suggestions were put forwarded, such as developing new methods of strain-based pipeline design, and researching and developing or improving the supporting technologies suitable for the higher matching requirements of girth weld, such as welding methods, welding materials, welding processes, and girth weld performance quality and defect control requirements.

Application of MFL on Girth-Weld Defect Detection of Oil and Gas Pipelines

AbstractGlobally, the integrity of girth weld (GW) of oil and gas pipelines has increased as a concern due to failures with high consequences. A primary integrity issue to pipelines considers defec...

Application of USCCD on Girth Weld Defect Detection of Oil Pipelines

Globally, more and more attention has been paid to the integrity of Girth Welds (GW) of oil and gas pipelines due to their failures with high consequences. A primary concern is that defects originate during field construction but over time may be subject to external loads due to earth movement. GW defects in newly built pipelines are also assumed to exist but would be much smaller in size, and more difficult to detect, which motivated the investigation into minimum defect detection capabilities of the inspection technologies. This study presents the evaluation results of UltraScan™ Circumferential Crack-Like Detection (USCCD) technology for oil pipeline GW inspection, based upon the pull test and in field data from Inline Inspection (ILI) of pipeline by PetroChina Pipeline Company (PPC) using GE PII (General Electric Company, Pipeline Integrity Inspection) 32” UltraScan™ CCD Tool. The performance of USCCD is given according to the ILI data, pull test results and dig NDE (Non-Destructive Examination). It can be concluded that crack-like defects with clear edges can be detected during ultrasonic propagation; however, the irregular shape of weld makes the inspection more difficult. It is still a challenge to identify the type of defects, and depth sizing can only be classified not quantified, which would require more excavations. However, this technology is feasible for the alternative technology of GW defect inspection.

Study on FAD curves of steel pipes based on stress-strain curves

The failure assessment diagram (FAD) method is one of the mainstream methods for assessment of defects in steel pipes and girth welds. In this paper, the FAD curves based on Ramberg-Osgood model and tensile test requirements for steel pipelines from X52 to X100 are established with an accuracy of less than 3%. The results show that the generalized FAD curve is more conservative in evaluating high-grade defective pipelines than in evaluating low-grade pipelines. Based on the tensile test data of DIC technology, the FAD evaluation models of the weld, base metal and the HAZ are established, and the critical crack lengths are evaluated respectively combining with CVN impact test data. R6 Option 1 and BS 7910 Option 1 are found to be conservative in the same regional assessment, ranging from 20.83% to 31.09%. This study can provide convenience and reference for defect assessment of pipeline and girth weld.

Acoustic-Emission Procedure for Rejecting Defects in Multiple-Pass Girth Welds

A procedure is proposed for rejecting girth welds based on an analysis of the main parameters of acoustic emission (AE) signals recorded during multiple-pass welding. The accuracy of locating AE signals recorded from defects and their filtering from noise and interference were ensured by the use of a modified tabular method and rejection grid. Normalized coefficients were calculated from the energy and amplitude of localized AE signals and used for in-process assessment of weld quality. Threshold values were determined for the normalized coefficients above which the weld is rejected. Defects in girth welds were identified using this procedure, and the possibility of determining defect hazardousness in real time was demonstrated.

A calculation method for limit load of the gas pipelines with girth weld surface cracks

In this paper, a finite element model with girth weld defects considering crack tip singularity was established in order to facilitate the accurate and rapid safety assessment on girth weld defects of long distance gas Transmission pipeline. Then the J-integral of girth weld cracks in pipes with different defect sizes was calculated, and the influence of weld matching coefficient and material hardening index on J-integral is analyzed. Furthermore, the influence factors of limit load of pipeline with girth weld defects based on J-integral theory are studied. Based on this, the engineering calculation formula which can calculate J-integral and limit load rapidly in the situations with specific matching coefficient and material hardening index was proposed. And the following research results were obtained. First, the engineering calculation formula based on the fitting of finite element calculation results has high accuracy, which can calculate the J-integral of defects in a large geometric range and the limit load of pipelines with girth weld cracks. Second, the J-integral of cracks in pipes with girth weld defects is closely related to defect size, material properties and weld matching coefficient, and the limit load of pipes with defects decreases as the crack size increases and increases as the material hardening index increases. Third, for the X80 pipes with surface cracks at the centerline of the girth weld, the load carrying capacity of the pipes with low-strength matched weld are lower than that with high-strength or equivalent-matched weld. In conclusion, the research results can be used as reference for the safety evaluation and integrity management of in-service gas pipelines.

Reliability Calculation Method for Natural Gas Pipelines with Girth Weld Defects Identified through In-Line Inspection

To introduce a method for reliability analysis of China's large-scale natural gas pipeline system, one should first have a method to calculate the reliability of pipe segments, compressors, valves, and other factors. This article models the rules prescribed in BS7910-2013, a guide to methods for assessing the acceptability of flaws in metallic structures, and combines pipeline reliability assessments from CSA Z662-2015 to present a method (based on the Monte Carlo method) to calculate the failure probability/reliability of long-distance pipelines containing a large number of girth weld defects. The method involves the destruction of plastic material, brittle fracture failure analysis, consideration of the division of units by using pipeline area classes for calculation, and reliability index analysis. The results of a magnetic flux leakage (MFL) in-line inspection (ILI) of a defective girth weld from a section of a pipeline in China are used to demonstrate how to determine the reliability of the entire pipeline.

Pipe Crack Recognition Based on Eddy Current NDT and 2D Impedance Characteristics

Girth weld cracking of long-distance oil and gas pipelines yields substantial harm to pipeline safety and may cause serious accidents. As of today, non-destructive testing has been one of the most common methods for predicting potential faults and ensuring safe operation. Classical pipeline non-destructive testing methods include magnetic flux leakage testing and the use of ultrasonic testing by electromagnetic acoustic transducers. However, they are incapable of identifying the defects in complex surfaces like girth welds. Magnetic flux leakage testing exhibits poor anti-interference abilities and low space resolution. Ultrasonic testing by electromagnetic acoustic transducers suffer from low conversion efficiency and poor signal quality. In order to overcome the disadvantages of conventional pipeline non-destructive testing methods, we propose an embedded eddy current testing system by leveraging image processing and neural networks. Hough transform and the contour extraction technique are employed to extract the characteristic features from the two-dimensional (2D) eddy current impedance image. Experiment results show that the system can effectively identify the girth weld defects, featuring an accuracy of up to 92%. The low power consumption and compactness of the proposed system makes it a great candidate for pipeline inner inspection.

Effect of Type B Steel Sleeve Rehabilitate Girth Weld Defect on the Microstructure and Property of X80 Pipeline

In recent years, accident caused by girth weld defects is relatively common. The failure mode of girth weld is mostly fracture. It is an effective way to avoid the failure accident of girth weld to find the hidden trouble of girth weld and repair it in time before the failure. The type B steel sleeve is an effective method to repair the girth weld defects. However, quite few works have been carried out on the reliability verification and engineering practice of repairing the X80 pipeline girth welds. Therefore, it is necessary to carry out full-size physical test for engineering and obtain the influence law of welding operation on main pipeline performance, with the aim of reliability of repair quality and service after repair. In the present work, the reliability study of repairing with type B steel sleeve on X80 pipe girth weld defects was verified. The results show that the bearing capacity of the type B sleeve can effectively guarantee the safe operation of the pipeline in the case of leakage from the girth weld. But there are obvious influence on the material properties of the outer surface of the main pipe due to the welding heat. Effects from longitudinal weld seam is smaller than effects from fillet weld. Grain roughening occurred in heat affected zone of fillet weld which results in that the hardness of the main pipe under the fillet weld increased and the yield strength was reduced by 5.5%. Surface cracking occurs during bending test. There is a certain service risk and it should be used under more frequent monitoring than usual.

Recent development in low-constraint fracture toughness testing for structural integrity assessment of pipelines

Fracture toughness measurement is an integral part of structural integrity assessment of pipelines. Traditionally, a single-edge-notched bend (SE(B)) specimen with a deep crack is recommended in many existing pipeline structural integrity assessment procedures. Such a test provides high constraint and therefore conservative fracture toughness results. However, for girth welds in service, defects are usually subjected to primarily tensile loading where the constraint is usually much lower than in the three-point bend case. Moreover, there is increasing use of strain-based design of pipelines that allows applied strains above yield. Low-constraint toughness tests represent more realistic loading conditions for girth weld defects, and the corresponding increased toughness can minimize unnecessary conservatism in assessments. In this review, we present recent developments in low-constraint fracture toughness testing, specifically using single-edge-notched tension specimens, SENT or SE(T). We focus our review on the test procedure development and automation, round-robin test results and some common concerns such as the effect of crack tip, crack size monitoring techniques, and testing at low temperatures. Examples are also given of the integration of fracture toughness data from SE(T) tests into structural integrity assessment.