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The objective of this paper is to study the burst capacity of steel strip reinforced flexible pipe (steel strip PSP) with swaging endfitting, in the situation that the burst point is in pipe-endfitting joint area. Experiment was conducted and an analytical model based on thin-wall cylindrical shell theory was proposed. Hoop stress in local coordinate on the innermost reinforcement layer is introduced to predict the burst strength of the pipe, as the hoop stress on this layer in pipe-endfitting joint area increases, the strain on the same layer in the area far away (x→∞) from endfitting is extracted and the corresponding internal pressure can be then obtained. Results of the theoretical model compare well with experimental data. Study shows that Diameter to thickness ratio of pipe (D/t ratio) may affect the SCE in pipe-endfitting joint area. Some useful conclusions are drawn for the design and application of steel strip PSP. [ABSTRACT FROM AUTHOR]

• Investigate burst capacity of pipelines containing pinhole-in-corrosion defects using parametric FEA. • Burst capacity of PIC defect is insensitive to the pinhole diameter but largely affected by the pinhole depth and location. • Bulging effect identified as the underlying mechanism for the pinhole location effect on the burst capacity. This study carries out extensive parametric three-dimensional elasto-plastic finite element analysis to evaluate the burst capacity of oil and gas pipelines containing pinhole-in-corrosion (PIC) defects. The analysis results reveal that the burst capacity of the PIC defect is insensitive to the pinhole diameter but largely affected by the depth of the pinhole and length of the general corrosion. A pinhole located at the centre of the general corrosion is found to have a larger impact on the burst capacity than the same pinhole located near the edge of the general corrosion. The observed size and location effects on the burst capacity are attributed to the bulging deformation of a corroded pipeline under internal pressure. The findings of this study provide the basis for developing a practical, accurate engineering burst capacity model for PIC defects. [ABSTRACT FROM AUTHOR]

This study develops accurate burst capacity models for steel oil and gas pipelines containing dent-gouge damages through the innovative use of a deep learning algorithm, the tabular generative adversarial network (TGAN), and three machine learning (ML) algorithms, the random forest, extra tree and Gaussian process regression. TGAN is employed to expand a limited number (88) of full-scale burst tests of dent-gouged pipe specimens available in the literature by generating synthetic test data. A dataset consisting of 62 real and 438 synthetic test data is then employed to train the three ML models to predict the dent-gouge burst capacity. Based on a validation dataset of 26 real test data, the accuracy of the ML models is shown to be markedly higher than that of a well-known semi-empirical engineering model: coefficients of variation of the test-to-predicted ratios for the ML models are below 15% compared with about 45% for the engineering model. Uncertainty quantification of predictions by the ML models is also carried out. The present study demonstrates the promising potential and effectiveness of combining deep learning algorithms and ML models to improve the integrity assessment practice for oil and gas pipelines. [Display omitted] • Employ TGAN to generate synthetic full-scale burst test data for dent-gouged steel pipes. • Develop RF, ET and GPR models to accurately predict dent-gouge burst capacity using real and synthetic test data. • Carry out uncertainty quantification of the predictions by RF, ET and GPR models. • Demonstrate effectiveness of deep learning and machine learning models in pipeline integrity management practice. [ABSTRACT FROM AUTHOR]

Based on 14 naturally corroded full-scale pipe specimens, the present study investigates to what extent a corrosion depth threshold influences the burst capacity of naturally corroded pipelines predicted using the finite element analysis (FEA) and well-known RSTRENG model. The study also employs FEA and RSTRENG to investigate the accuracy and effectiveness of five representative interaction rules, namely the B31G, B31.4, CSA, DNV and CW rules, for combining individual naturally-occurring corrosion anomalies into clusters. The analysis results indicate that applying a corrosion depth threshold of 10% of the pipe wall thickness (t) (i.e. any corrosion depths < 10%t are ignored) has a negligible impact on the predicted burst capacity. Furthermore, the CSA interaction rule is considered the most effective among the five interaction rules investigated in that it captures the most critical region of a corroded area without resulting in very large corrosion clusters that are time-consuming to identify and analyze.

The present study applies the two-dimensional discrete wavelet transform to analyze naturally occurring corrosion clusters on external surfaces of in-service steel transmission pipelines. The corrosion depths in a cluster are measured by high-resolution laser scans. The Daubechies wavelet with two vanishing moments (DB2) is adopted in the analysis, and the widely used RSTRENG model is employed to compute the burst capacity of pipelines with corrosion clusters. A methodology is proposed to determine level- and sub-band-dependent thresholds such that those wavelet coefficients below the thresholds have a negligible impact on the burst capacity and can be ignored for the reconstruction of the cluster. Statistical analyses of the preserved wavelet coefficients indicate that most of the features in the natural corrosion clusters are circumferential features, but their influence on the burst capacity is less significant than longitudinal features. Features that have large impacts on the burst capacity prediction are approximately 4–16 mm in width and 4–32 mm in length. It is unnecessary to decompose the natural corrosion cluster to a scale greater than 32 mm because the wavelet coefficients at higher levels have a negligible impact on the burst capacity prediction. • Employ 2D discrete wavelet transform to analyze corrosion clusters on steel pipelines. • Propose a model to estimate thresholds for preserving wavelet coefficients at different levels and sub-bands. • Gain insights into the directional features and length scales of corrosion clusters impacting the burst capacity. [ABSTRACT FROM AUTHOR]

• Consider burst capacity models for pipelines containing dent-gouges. • Collect a large database of burst tests of pipe specimens with dent-gouges. • Improve the predictive accuracy of dent-gouge model using Gaussian process regression. • Provide a new perspective on using full-scale test data and GPR to develop fitness-for-service assessment models. The present study proposes an improvement of the well-known European Pipeline Research Group (EPRG) burst capacity model for pipelines containing dent-gouges by adding a correction term to the EPRG model. The Gaussian process regression is employed to quantify the correction term as a function of six non-dimensional input variables based on 190 full-scale dent-gouge burst tests collected from the open literature. The linear prior mean function and squared exponential kernel are considered in the Gaussian process regression, with the corresponding hyper-parameters evaluated using the maximum likelihood method from the training set of the collected full-scale test data. The correction term is shown to result in a marked improvement of the predictive accuracy of the EPRG model based on a comparison of the observed and predicted burst capacities for the test data. By applying the improved EPRG model to the regression set of the test data, the mean and coefficient of variation of the test-to-predicted ratios equal 1.01 and 9.2%, respectively. The analysis also sheds light on the relative importance of the input variables for the correction term. [ABSTRACT FROM AUTHOR]

Oil and gas pipelines have been used all around the world and becoming more crucial in our daily life. These pipelines are subjected to corrosion and one of the most effective ways for repairing them is using composite wrap. Nevertheless, there are still issues and challenges to be overcome for a more effective design of composite repaired pipelines, which could be further investigated. Defect geometries (depth, width and length) on pipelines can affect the burst pressure that can be sustained by the pipelines. Yet, current standards and practices only account for defect depth in determining minimum thickness of composite wrap required in repairing defective pipelines without considering defect width and length. Thus, the aim of this study is to analyze the effect of defect length and width of composite repaired pipe upon its burst capacity using finite element analysis. A finite element model was created and validated followed by parametric study on the effect of combination defect length and width. For parametric study, a total of seven composite repaired pipe models were created and analyzed. Results showed that as the defect dimension of combinations defect geometries increases, the burst pressure of the composite repaired pipe decreases. The burst pressure between the smallest and largest defect is 31.09% which shows a significant difference. In conclusion, defect geometries are proven greatly affect the burst pressure of the composite repaired pipe and the findings can be used for future studies, in particular to refine the design of the composite pipeline repair practice. • Finite element analysis was conducted to evaluate the effect of defect geometries on composite repaired pipe. • About 31% of burst pressure difference was observed for the largest and smallest defect geometries. • This show defect geometries play a significant role in determining burst capacity of composite repaired pipe. • The finding is significant as it can help in the optimization of composite-repair design in the future. [ABSTRACT FROM AUTHOR]

This paper employs a deep learning tool, the tabular generative adversarial network (TGAN), to generate synthetic full-scale burst test data for corroded pipe specimens by capturing the joint probability distribution of five dimensionless random variables characterizing a database of 258 real full-scale burst tests collected from the literature. A simple criterion is proposed to identify outliers contained in the synthetic dataset. Two machine learning models, the random forest and extra tree, are trained using the real and synthetic test data to predict the burst capacity of corroded pipelines for the purpose of tuning the hyper-parameters of TGAN and also validating the credibility of the synthetic data. The generated synthetic data are shown to accurately capture the joint probability distribution of the real test data. This study provides a viable option to effectively generate a large number of high-quality synthetic full-scale test data to facilitate the development of engineering critical assessment models employed in the pipeline integrity management practice. [ABSTRACT FROM AUTHOR]

This paper develops the probabilistic characteristics of the model errors associated with five well-known burst capacity models/methodologies for pipelines containing longitudinally-oriented external surface cracks, namely the Battelle and CorLAS™ models as well as the failure assessment diagram (FAD) methodologies recommended in the BS 7910 (2005), API RP579 (2007) and R6 (Rev 4, Amendment 10). A total of 112 full-scale burst test data for cracked pipes subjected internal pressure only were collected from the literature. The model error for a given burst capacity model is evaluated based on the ratios of the test to predicted burst pressures for the collected data. Analysis results suggest that the CorLAS™ model is the most accurate model among the five models considered and the Battelle, BS 7910, API RP579 and R6 models are in general conservative; furthermore, the API RP579 and R6 models are markedly more accurate than the Battelle and BS 7910 models. The results will facilitate the development of reliability-based structural integrity management of pipelines. [ABSTRACT FROM AUTHOR]

Abstract: The model errors associated with eight well-known burst capacity models for corroded pipelines, namely B31G, B31G Modified, CPS, the CSA model, the DNV model, PCORRC, RSTRENG and SHELL92, are characterized based on a full-scale burst test database that consists of 150 data points collected from the literature for pipe specimens containing single isolated real corrosion defects. The probabilistic characteristics of the model errors, including the mean values, coefficients of variation and probability distributions, for the burst models are obtained by analyzing the ratios between the test and predicted burst pressures corresponding to the test data applicable to the model. For each of the burst models, separate model errors for short and long defects are also evaluated, whereby the short and long defects are separated by the transition normalized defect length that is identified using the weighted average COV approach. [Copyright &y& Elsevier]

Extensive parametric three-dimensional elasto-plastic finite element analyses are carried out to investigate the interaction effect on the burst capacity of oil and gas pipelines containing closely-spaced corrosion defects under combined internal pressure and load-controlled longitudinal compression. The analysis considers two identical, semi-ellipsoidal-shaped corrosion defects aligned circumferentially or longitudinally on the pipeline. The analysis results reveal that the interaction between circumferentially-aligned defects under combined loads is marked: the burst capacity corresponding to the two-defect case can be lower than that corresponding to the single-defect case by as much as 18% as a result of the enhanced bulging of the defect region due to the presence of the longitudinal compression. This is in direct contrast to the observation that the interaction effect is marginal for circumferentially-aligned defects subjected to internal pressure only. On the other hand, the interaction between longitudinally-aligned defects under combined loads is negligible due to the so-called shielding effect; this is again in direct contrast to the observation that the interaction between longitudinally-aligned defects under internal pressure only is marked. The adequacy of four practical interaction rules, which are developed for the loading condition of internal pressure only, for the combined loading condition is also examined. The findings of this study have important practical implications for the integrity assessment of corroded pipelines under combined loads. • Investigate the corrosion defect interaction effects on the pipe burst capacity under combined loads. • Validate the FEA model and failure criterion by full-scale burst tests of 12 pipe specimens. • Explain underlying mechanisms for the defect interaction under combined loads. • Discuss the adequacy of the existing interaction rules for combined loads. [ABSTRACT FROM AUTHOR]

• Characterize corrosions on pipelines as nonhomogeneous non-Gaussian random fields. • Propose an algorithm to simulate nonhomogeneous non-Gaussian corrosion fields. • Employ discrete orthonormal S-transform and iterative spectral correction methodologies. • Use FEA to evaluate burst capacity of pipelines containing simulated corrosion fields. The present study proposes an iterative algorithm to simulate nonhomogeneous non-Gaussian corrosion fields on buried oil and gas pipeline's external surfaces. The algorithm incorporates the concepts of the discrete orthonormal S-transform and the iterative amplitude adjusted Fourier transform algorithm. This results in the space-wavenumber power spectral density function and marginal distribution function of the simulated corrosion field matching, respectively, their corresponding targets that could be determined from the high-resolution corrosion measurement data obtained from naturally corroded pipe segments. The simulation results demonstrate that the use of the proposed algorithm is able to capture the statistical characteristics of naturally occurring corrosion fields on pipelines. Three-dimensional elasto-plastic finite element analyses are carried out to evaluate the burst capacities of pipe segments containing simulated corrosion fields. Combined with finite element analyses, this algorithm can be employed to conduct virtual full-scale burst tests of corroded pipe specimens, which is of great value to the pipeline corrosion management practice. [ABSTRACT FROM AUTHOR]

• An experimental program is developed to assess the RTP behavior under lateral load impact. • Dents are fabricated using a quasi-static indentation procedure to burst the RTP specimens. • Relationships between the lateral load, indentation depth and the burst pressure is extracted. Reinforced Thermoplastic Pipe (RTP) is a flexible composite pipe that currently receives fair acceptance in the oil and gas industry, with high potentials to be used as a replacement to the carbon steel (CS) pipes especially in high corrosive environment. As RTP is relatively new products, their designs and qualifications are governed by the industry practice at present in the absence of comprehensive technical design standards. Most literatures to date are mainly dedicated to the intact RTPs, while the response of the pipe towards various defects have not been fully understood. Quite often, the assessments are made by referring to the design standards of the CS pipes, which are not entirely suitable due to the flexible characteristics of the composite pipe itself. Thus, this paper aims at assessing the performance of a 4″ RTP when exposed to lateral loads from external interferences such as the anchor dropped. Herein, the damaged to the RTP pipe was made in the form of a dent indented by a cylindrical conical nose under the quasi-static indentation procedures carried out experimentally. The damaged or dented pipe was later tested for its burst capacity using a burst testing facility specially fabricated for composite pipes. During the experiments, two types of failure modes were observed, namely single unit and ply-by-ply failures. Outcomes obtained from the experiments were used to describe the relationships between three important parameters, namely lateral load, indentation depth and burst pressure using polynomial regression equations. These simplified equations may be adopted directly in pipeline assessments and operations of RTP pipes exposed to dents. Moreover, outcomes from this paper will be beneficial in qualifying further RTP as a new free-corrosion risk transportation system for the oil and gas industry. [ABSTRACT FROM AUTHOR]

This paper examines the burst capacity of reinforced thermoplastic pipes (RTPs) under the effect of internal pressure. Used the theory of the three-dimensional (3D) thick-walled cylinder, combined the 3D Hashin failure criterion with the theory of the evolution of damage in composite materials, considered the nonlinear stress-strain relationship of materials, and introduced changes in the winding angle caused by deformation to formulate a analytical model for the progressive failure analysis of RTPs. The model was used to examine the failure sequence and burst capacity of the RTPs, and analytical results agree well with the experimental ones. The results show that the ply number of the reinforced layer had a more significant effect on the burst capacity of the RTPs than the winding angle. Their burst capacity first increased and then decreased with increasing winding angle. When the winding angle was ±60°, the burst pressure reached its peak. With an increase in the ply number of the reinforced layers, the burst pressure of the RTPs increased nonlinearly and its rate of growth gradually decreased. Once a certain ply number in the reinforced layer had been reached, interlaminar separation was more likely to occur in the RTPs before they burst. • An analytical model is proposed to predict failure pressure of reinforced thermoplastic pipes (RTPs). • The 3D thick-walled cylinder theory, combined the Hashin failure criterion is introduced to formulate the progressive failure analysis model. • Considered the nonlinear stress-strain relationship of materials, and introduced changes in the winding angle caused by deformation. • The accuracy of burst pressures calculated by the proposed model is verified by hydraulic burst tests. [ABSTRACT FROM AUTHOR]

This study investigates the burst capacities of corroded pipelines using three-dimensional elasto-plastic finite element analyses validated by full-scale burst tests of corroded pipe specimens reported in the literature. The semi-ellipsoidal idealization of naturally-occurring corrosion defects in FEA is found to lead to more accurate predictions of the burst capacity than the rectangular idealization for defects that are less than 70% through the pipe wall thickness. Results of extensive parametric FEA based on the semi-ellipsoidal idealization of the corrosion defects indicate that the burst capacity in general increases as the defect width increases if the defect depth and length remain the same. The defect width effect is marked for deep, relatively short defects, and should therefore be taken into account accordingly in the empirical or semi-empirical burst capacity models. The defect width effect is marginal for long defects with w/l ≤ 1.5. The observed width effects are explained by considering the change in the membrane and bending stresses in the defect region as the defect width increases. • Investigate the burst capacity of corroded pipelines using extensive 3D elasto-plastic FEA. • Compare the rectangular and semi-ellipsoidal idealizations of corrosion defects. • Investigate the effect of the defect width on the burst capacity based on semi-ellipsoidal idealization. • Defect width is found to have a beneficial effect on the burst capacity of corroded pipelines. [ABSTRACT FROM AUTHOR]