Journal of Pipeline Systems Engineering and Practice

Abstract

Legacy gas pipelines experience problems as they age. Pipe rehabilitation and replacement using internal pipes or liners is a trenchless renewal approach to address these issue-prone facilities. Here, a set of performance objectives is identified using data from both the field and the literature. First, observations of recorded pipeline incidents of cast/wrought iron gas distribution mains were analyzed to understand the causes of damage in host pipe systems. Natural force damage, including subsidence, frost-related deformation, and other earth movements, was identified as the leading cause of incidents in such systems. An internal-repair pipe would be expected to withstand such events. Secondly, a literature review of the mechanical behavior of rehabilitating internal pipes or liners was performed. Considerable work has been performed to understand how such systems behave under internal hydrostatic pressure, external pressure, surface loads, and external loads reflective of expected earth movements. Under internal pressure, stresses higher than that expected for an unconfined repair pipe or liner can develop at large holes in the host pipe. Studies to understand earth movements in rehabilitated pipelines often apply bending moments or axial loads to repaired specimens with joints or full-circumferential cracks. The literature demonstrated that the behavior of internal pipes or liners at discontinuities in the host pipe is critical for rehabilitated pipeline performance. Most available studies, however, have focused on nonstructural or semistructural repair systems, which may be unsuitable for full rehabilitation of deteriorating gas pipelines over an extended design life. The set of performance objectives described in this paper will help improve the understanding of structural pipe-in-pipe to enable effective design and implementation of trenchless repair systems for existing natural gas pipelines.

Practical Applications

Aging pipes can be repaired with internal rehabilitating pipes. This review provides insight into the causes of problems in gas distribution mains of cast/wrought iron, an important subset of legacy gas pipelines, by analyzing field observation records from between the years 1970 and 2020. Natural force damage was an important driver of damage; common subtypes of natural force damage are related to flexural deformation. Such deformation needs to be addressed by an internal repair pipe. Many researchers have studied the mechanical response of pipes repaired with internal pipes or liners. In these studies, the major loads are reflective of internal pressure, external pressure, surface loads, and soil movements. Interaction between the aging host pipe and internal rehabilitating pipe is an important factor. Performance objectives for internal rehabilitating pipes are outlined in this paper on the basis of field observations and existing work. The systematic identification of performance objectives most critical to these systems is intended to provide a pathway for future development and to qualify new pipe-in-pipe (PIP) system performance over a desired service life.

High-density polyethylene (HDPE) is one of the most commonly used materials for manufacturing pipelines. In this paper, the deformation behavior of HDPE materials under uniaxial tensile stress was investigated by employing uniaxial tensile tests and macroscale/mesoscale morphology analysis. The experimental results indicated that the stress–strain relationship of HDPE is nonlinear, and the ductile fracture characteristics of necking and local failure appear in the sample after the engineering strain reaches 35%. Therefore, for the first time, a hyperelastoplastic constitutive model that describes the elasticity by the Marlow model and combined the isotropic plasticity-ductility damage correction is established, and a corresponding numerical approach is proposed. The simulation scheme was implemented in finite-element software, and the mechanical responses of HDPE under uniaxial tensile and bending loads were predicted. Obtained calculations were relatively consistent with experimental observations. Hence, the proposed model and approach have a good simulation effect on the mechanical properties of HDPE and can be employed for the process prediction of such materials. This study is beneficial to the in-depth understanding of the hyperelastoplasticity and failure mechanism of HDPE and provides ideas for the deformation and failure study of other polymer materials.

In this study, a new mechanical model is proposed to compute earth pressure above a pipeline considering pipe-soil interaction and three-dimensional soil arching effects of cohesive fills, based on the Terzaghi vertical sliding surface theory. In this model, the pipeline was mechanically separated into buried and suspended segments, whose stress distribution and deformation were solved according to the boundary conditions and geometric conditions. Comparisons to both the test data and corresponding finite element codes concretely verify the proposed mechanical model. Then a parametric investigation indicated that the mechanical behavior of the pipe is greatly affected by the size of a subsidence area and the flexural rigidity of the pipe.

The erosion of elbows by particles in shale gas pipelines poses a great threat to the production safety of pipelines. Accurate prediction of the erosion rate is critical to ensuring the safe operation of pipelines. Previous predictions of the erosion rate is based on experiments and numerical simulation. However, because many factors of affecting pipeline erosion lead to strong nonlinearity of the physical scene, these two methods are time-consuming and labor-intensive and have many assumptions. This paper presents a data-driven approach for efficiently predicting erosion rates in shale gas pipelines, which has a high prediction accuracy based on an amount of data without experiments and numerical simulation. The model mixes the adaptive $t$-distribution-based sparrow search algorithm and support vector machine. Through case studies, the following results were obtained: (1) the minimum mean square error (MSE) of the proposed model is less than 10%; (2) compared with the hybrid model without considering the adaptive $t$-distribution, the MSE of the proposed model is reduced by 32%; and (3) the MSE, Theil U statistic 1 (U1), and Theil U statistic 2 (U2) of the proposed model in the test set are 47%, 47%, and 34% lower than the average MSE, Theil U statistic 1 (U1), and Theil U statistic 2 (U2) of benchmark models, respectively. Two cases of multiphase flow and gas–solid conditions showed that the improved hybrid model has higher prediction accuracy than support vector machines with other optimizers and has strong generalization performance. This study may be helpful for pipeline maintenance and repair in practical engineering.

The Pipeline Assessment and Certification Program (PACP) was developed by the National Association of Sewer Service Companies, the industry-accepted protocol for condition rating sewer pipes in the US. The PACP method relies exclusively on visual inspections performed using closed-circuit television (CCTV), where certified operators observe existing structural and operation and maintenance (O&M) defects limitation of the PACP method is that it does not use pipe characteristics, depth, soil type, surface conditions, pipe criticality, and capacity, nor the distribution of structural defects or history of preventative maintenance to determine the condition rating of the sewer pipe segment. Therefore, this research addresses the limitations of the PACP with the development of a new wastewater pipe rating system known as the comprehensive rating (CR) system. The CR evaluation system is based on a commonly used decision-making approach known as the analytical hierarchy process (AHP) to analyze problems and issues. The new CR model incorporates pipe characteristics (age, corrosion, diameter, and shape), external characteristics (depth, soil type, traffic loading, waste type, seismic zone), and hydraulic characteristics (structural score, O&M score, and repair history). The results showed a below-average validity percentage because linear regression assumes a linear relationship between the input and output variables but the relationship between the response and the predictor is not linear.The CR methodology can be improved by increasing the number and variability of experts who evaluate the condition of existing sewer pipes, enhancing geospatial data for locational accuracy, and establishing evaluation standards for inspectors to minimize human error. More research is needed to determine a suitable nonlinear relation that can be used to model data from this new comprehensive rating system.

Corrugated steel pipe (CSP) culverts have been widely used for decades; however, their structural behavior under surface loading may not be correctly captured by design codes based on results from recent experimental studies. To address this, the data from nine full-scale experiments investigating the structural behavior of corrugated steel culverts with different burial depths and surface loading configurations, instrumented with distributed fiber optic strain sensors, were compared with three-dimensional finite-element analyses. Parametric studies were undertaken that included different models for the corrugation properties (i.e., explicit modeling of the corrugated geometry and orthotropic, and isotropic shell), contact between soil and pipes, and the soil properties (soil moduli and elastic and elastoplastic behavior). It was found that the orthotropic model was a good substitute for explicit modeling of the corrugated geometry, which saves computation time and still provides an accurate estimation of the thrusts and moments. The moments in the culvert were found to be sensitive to the distribution of soil moduli, whereas thrusts were not. Based on this investigation, three-dimensional analyses using orthotropic shell models, elastic soil properties with moduli varying with depth, and tie constraints between the soil and the culvert are recommended for future investigations of corrugated steel pipe responses to surface loads.

With the progressive rise in energy demand, the scale of oil and gas pipelines continues to increase. Tunnels have been developed to plan the space reasonably and to reduce pipeline maintenance and repair difficulties. However, for natural gas pipes laid in the tunnel, leakage accidents can cause severe results. Based on the computational fluid dynamics (CFD) theory, the leakage and diffusion characteristics of natural gas in tunnels under various scenarios are analyzed using flame acceleration simulation (FLACS) software. It can be concluded that (1) natural gas leakage in the tunnel can result in the occurrence of self-suffocation, where small-hole leaks pose a greater threat than large-hole leaks, which clearly differs from leaks into open rooms; (2) the larger the leakage diameter, the shorter the tunnel and the higher the chance of self-suffocation happening; (3) the flammable gas mass in a tunnel depends on several factors, including gas leak rate, gas mixing rate, diffusion rate between gas with higher concentrations and gas with much lower concentrations, and the gas diffusion rate as it exits the tunnel; (4) when a leakage hole is in the middle of the tunnel and the leakage direction is upward, there is the greatest danger; and (5) for the same tunnel length, the larger the leakage diameter, the smaller the flammable gas mass. The study presents the characteristics of natural gas diffusion in a tunnel and offers suggestions for leakage accident emergency repair.

Analysis of the properties of diverse pipe materials is a must for delivering the requirements of hydrocarbon pipeline projects. Three of the most commonly used hydrocarbon pipe materials are carbon steel, glass fiber-reinforced plastic (GRP), and glass fiber-reinforced epoxy (GRE). An integrated multicriteria decision-making (MCDM) and lifecycle assessment (LCA) method is utilized to select the most suitable pipe material for hydrocarbon pipeline projects. In this research, the decision-making trial and evaluation laboratory (DEMATEL) analysis is integrated with the analytic network process (ANP) and with LCA. The proposed hybrid decision-making model defines complex causal relationships among different criteria. It can also combine technical, economic, and environmental criteria for pipe material selection in hydrocarbon pipeline projects. Results show that the environmental impacts of carbon steel pipes are higher than other materials in almost every impact category, whereas GRE pipe is the most environmentally friendly of the three alternatives. The subcriterion of global warming potential is significant in the life cycles of all three pipe materials. This innovative model considers a range of relevant technical, economic, and environmental criteria and selects carbon steel pipe as having the highest value among the three alternatives.

Abstract

In this study, the effect of using electric arc furnace (EAF) slag for infrastructure pipes was investigated. By using EAF slags and natural aggregates, normal and high strength concrete mixtures with and without steel fiber were produced for concrete pipes. The physical, mechanical, and permeability properties and fracture behavior of these concrete mixtures were determined. The usability of EAF slags in concrete and reinforced concrete pipes with acidic corrosion risk was investigated by exposing the concrete samples to sulfuric acid attacks. In addition, some concrete samples and concrete pipes were covered with polyurea material. Thus, apart from using EAF aggregates, the effect of a polyurea coating on the resistance of concrete pipes against acid effects and crushing strength were also investigated. When EAF aggregates were used instead of natural aggregates, the mechanical properties and resistance of the concrete against acidic corrosion increased. The polyurea coating on concrete pipes provided a more obvious improvement against acid attack and increased the crush strength of the pipes. As a result, it is possible to produce concrete pipes with a longer service life by using EAF aggregates or polyurea coatings.

Practical Applications

The slag produced as waste in iron and steel plants is one of the major problems for producers. EAF slag can be used in concrete production by substituting natural aggregates. Concrete pipes are widely used in infrastructure sewer applications. However, the chemical environment in the sewage causes physical and chemical deterioration of the concrete. One of the effective ways to protect reinforced concrete structural elements against acid corrosion is coating the inner surface of the concrete pipe with polyurea. This study was aimed to determine the resistance of the reinforced concrete infrastructure pipes against the sulfuric acid attacks when they are produced using EAF slag aggregates or if their inner surfaces are covered with a polyurea material. In addition, the effects of these applications on the mechanical performance of concrete and reinforced concrete pipes were determined by concrete tests in the laboratory and crush strength tests in industrial products. As a result of the study, both the use of EAF aggregates in the production of pipes or the coating of the inner surfaces of the pipes with a polyurea material were found beneficial in terms of both mechanical behavior and resistance to acid effects in infrastructure pipes. However, in the case of the polyurea coating on the inner surfaces of the pipes, the resistance to acid attacks improved more significantly compared to the use of electric arc furnace (EAF) aggregates.

The stability of pressure pipe bends is evaluated by the equilibrium between the thrust force and resistance forces in the current design, and the behavior of pipe bends is not considered. Force–displacement (F–D) relationships, which are used for predicting the displacement of pipe bends, include the performance of pipe joints in the design of pipe bends and shift the design method to a performance-based approach. However, F–D relationships have been proposed only under plane-strain conditions. The behavior of pipe bends cannot be represented in two dimensions. Therefore, in this study, the prediction method of the F–D relationship for buried structures is extended to a three-dimensional condition to improve the design method of pipe bends with thrust restraint. Lateral loading experiments on thrust restraint, using rigid thrust blocks and flexible thrust restraints with geogrids and gravel, were conducted in dry sand to investigate the lateral behavior of rigid and flexible thrust restraints and to obtain F–D curves with different dimensions of thrust restraint. The experimental results revealed that the deformation of the flexible thrust restraint had little effect on the lateral resistance force if proper dimensions of the thrust restraints were determined. Using the experimental results, the F–D relationship was formulated based on a hyperbolic curve. The proposed equations were able to predict the resistance force relatively well at small lateral displacements. In addition to the formulation of the F–D relationship, a new design procedure considering the pipe displacement and performance of pipe joints was developed by combining the proposed F–D prediction method and the joint separation model proposed in previous studies.

In this study, we examine the efficacy of repurposing natural gas (NG) pipelines for transporting hydrogen blends (with NG), ammonia, and ${\mathrm{CO}}_2$ (gaseous and supercritical) from the standpoint of materials compatibility. Some information pertaining to component performance is also included, especially those components critical for pressurization and monitoring of flow. A listing of critical pipeline components and materials was developed, and their compatibilities was assessed for each fluid or gas type based on known compatibilities. Results indicate that pipeline materials should be suitable for gaseous ${\mathrm{CO}}_2$ and anhydrous ammonia, but hydrogen blends greater than 12% may be problematic. Current compressor/regulator stations will not be suitable for use with either supercritical ${\mathrm{CO}}_2$ or ammonia. Important knowledge gaps were identified, including (1) polymer performance with hydrogen/NG blends at low pressures, (2) compressor/regulator station polymers and epoxy coating materials with supercritical ${\mathrm{CO}}_2$, and (3) metal performances of hydrogen/NG blends at low pressures.

The demand to reduce fiber-reinforced polymer (FRP) composite wrap to repair damaged pipes is increasing. However, there is currently no proper execution and evaluation of improving the properties of the infill material, i.e., putty for pipeline repair. Finite-element analysis (FEA) is used to investigate the performance and behavior of composite repair components individually, i.e., pipe, putty incorporating graphene nanoplatelets (GNPs), and composite wrap. A finite-element (FE) model was developed and verified with previous studies with a margin of less than 15% error, followed by finite-element (FE) simulation using different putty properties. The burst capacity of the repaired pipe increased by 1.5%, indicating a nonsignificant contribution of GNPs toward load-bearing capacity. Nevertheless, putty with GNPs minimized a pipe’s sudden rupture and improved the putty’s load-transfer and load-sharing mechanisms by serving as secondary layer protection in the event of composite wrap failure.

In this paper, a numerical model is proposed to simulate the effect of a leak occurring at a pipe junction. The developed model, based on the method of characteristics, considers both hydraulic singularities, the leak and the junction, as superposed boundary conditions located in the same section. Obtained results representing the temporal evolution of pressure signals have allowed for locating the leak through the separation of its effect from that of the junction. For testing purposes, the transient was created by a sudden closure of a downstream valve in a reservoir-two series pipe-valve system. The novel proposed approach has proven its usefulness on locating and sizing the leak through detailed test cases. In sizing the leak, better accuracy is obtained when using the maximum pressure head reached by the incident wave before encountering the leaky junction instead of that of the transmitted wave through the leak. On the other hand, for the localization of the leak, rather than looking for an equivalent characteristic period of the two-pipe system, it was shown that the characteristic period of the pipe connected to the reservoir, once incorporated into the localization formula, leads to precise results with minimal uncertainty. For the piping system, two cases of configuration, viz. expansion and shrinkage (narrowing), were tested. In general, using the proposed approach, the maximum uncertainty values for the sizing and localization of a leak in the junction are 0.1513% and 1.09%, respectively. Additionally, the friction effect on the localization and sizing of the leak at the junction was investigated to conclude that the friction does not significantly affect the precision of the numerically obtained results for the sizing and localization of the leak at the junction.

Design methods for corrugated steel culverts in current design standards consider the circumferential force in culvert walls (i.e., hoop thrust) to be the dominant load-carrying mechanism in these structures. However, recent studies have shown that bending moment, rather than thrust, is often the more dominant response for corrugated steel culverts under shallow burial conditions and vehicle loading. In addition, 2D finite element analyses have historically been unable to effectively capture the effects of discrete surface loads, such as wheel loads, on the response of buried metal culverts. To investigate these issues, the bending moment and thrust responses from an experiment involving an elliptical corrugated steel culvert under shallow burial conditions and simulated vehicle loading are compared with the bending moment and thrust estimates from the Canadian bridge design code and CANDE-2019 (a commonly used public domain finite element software package) and the thrust estimates from the American AASHTO LRFD bridge design code (which does not consider moment directly). The comparisons show that the Canadian code and CANDE-2019 models with a fine mesh and the continuous load scaling elasticity-based method appear to be the most effective for the investigated culvert and loading, while there is a need to modify the American AASHTO LRFD code to consider moment more directly. In addition, the results suggest that, under these conditions, the current approaches for estimating the peak bending moment response are more effective compared with the approaches for estimating the peak thrust response.

Abstract

Fuel theft of oil pipelines is a concern faced by various countries and oil and gas companies due to its impact on the environment and the safety of neighboring communities. Oil pipeline monitoring and inspection with the support of alerts is essential to preventing suspected fuel-theft events and mitigating risks. Monitoring systems trigger alerts, and patrols are sent to confirm the occurrence of illegal tapping. However, various signals can be activated briefly, and the correct prioritization is essential to identifying illegal tapping as quickly as possible. This work aims to use machine-learning techniques to develop a predictive model capable of forecasting the probability of an event resulting in illegal tapping and understanding the factors that influence the occurrence. A Brazilian oil and gas transportation company provided data from a monitoring system supervised from January 2019 to August 2021. Five machine-learning algorithms were used in this study: Logistic Regression, Random Forest, XGBoost, Catboost, and Multilayer Perceptron. The Random Forest obtained the best results in classifying alerts associated (or not) with an illegal tapping, showing accuracy, specificity, and sensitivities of 76.8%, 68.3%, and 100%, respectively. In this problem, specificity implies reducing the sending of patrols to the field in 68.3% of circumstances, and sensitivity means that the model is a good predictor for positive cases. As for the external validation, the model also performed well, with an accuracy and specificity of 61%. The factors that most highly influenced illegal tapping occurrences were the alert duration, previous events in the same area, and events during the night.

Practical Applications

The problem of fuel theft of oil pipelines affects several countries worldwide and is a major concern due to its impact on the environment and the safety of neighboring communities. Oil pipeline surveillance through monitoring systems is important to prevent suspected fuel-theft events and mitigate risks. However, many alerts can be triggered in a brief period, and their correct prioritization is essential to identifying illegal tapping as quickly as possible. This work used machine-learning techniques to develop a predictive model capable of forecasting the probability of an event resulting in illegal tapping. Moreover, it has identified the factors that most influence a fuel-theft occurrence: alert duration, previous events in the same area, and the night period. The developed model can be used to assist companies in prioritizing alerts and improving the efficiency of patrol responses, contributing to combat, and reducing fuel theft.

A method of urban pipeline leakage infrasound signal processing based on spectrum analysis is proposed in order to address the issues of low recognition rate of infrasound signal of urban nonmetallic pipeline leakage and the existence of false signal interference, which results in low accuracy of pipeline leakage location. Firstly, the frequency spectrum of leakage and nonleakage signals is analyzed on the basis of a large number of tests, and the frequency spectrum characteristics and leakage judgment criteria of urban nonmetallic pipeline infrasound leakage signals are summarized. Secondly, the improved complementary ensemble empirical mode decomposition (ICEEMD) method is used to decompose the infrasonic leakage signal into the effective signal component and noise signal component to remove the false signal. Finally, the fine composite multiscale entropy algorithm is used to screen and reconstruct the entropy value of each signal component to extract effective and pure infrasonic leakage signal data. The experimental application demonstrated that the proposed method’s signal-to-noise ratio (SNR) increased from 13 to 25 dB and its average root-mean square error (RMSE) decreased from 24.82% to 3.39%. This significantly increases the accuracy of the identification of infrasound signals of urban nonmetallic pipeline leakage and provides a basis for pipeline leakage location.

The paper analyzes possible approaches to the technical evaluation of the process pipelines according to the diagnostic results using strength calculation based on the finite-element method. Process pipelines have a complex dimensional configuration and a complex stress–strain state, so traditional approaches to technical diagnostics and assessment of the technical condition of main pipelines are not applicable. Qualities of the process pipelines as objects bring relevance to the development of the practical approaches to its numerical modeling and formalization of boundary and loading conditions when using software systems based on the finite-element method. This paper presents the results of experimental studies of the stress–strain state of a number of test benches simulating elements of pipeline structures. Therefore, analytical research is presented that allows recommendations to be formulated for the numerical modeling of the process pipelines. The formulated recommendations allow us to correctly simulate process pipelines when calculating their stress–strain state using the finite-element method to model the conditions of fastening and loading, thereby ensuring high accuracy of the assessment of the technical condition of structures based on the results of their diagnostics.

Work herein is focused on evaluating factors affecting tetrachloroethene (PCE) contaminant ingress into the subsurface concrete pipe embedded in the saturated soil profile and assessing the efficacy of permeable reactive barriers (PRB) in mitigating PCE concentration. A three-dimensional groundwater flow and solute transport numerical model is established using MODFLOW paired with reactive transport (RT3D) software, in which the model is developed using a finite-difference numerical scheme. The analyses parameters are developed from data for a site in Wilson, North Carolina, at which subsurface chlorinated organic solvents from a dry-cleaning facility occurred in the presence of subsurface highway concrete drainage pipe. Modeling results after 10 years of simulation period indicated that the natural attenuation process taking place in the native soils with coefficients of $K_{\mathrm{PCE}}=0.00019{\mathrm{d}}^{-1}$, and $0.0033{\mathrm{d}}^{-1}$ reduced the PCE concentrations breaking through the concrete pipe by 30.7% and 34.1%, respectively. On the other hand, with a greater percent of the soil sorption as manifested by organic carbon content, the PCE concentration breaking through the pipe increased by 137% for the same simulation period as a result of the prolonged presence of PCE concentration within the pipe trench. The hydraulic conductivity of the PRB ($k_{\mathrm{PRB}}$) modestly affects the level of PCE breaking through the pipe, while the increase in thickness of the PRB was found to be the most effective in decreasing the level of PCE ingress into the pipe.

In this study, a methodology to evaluate and predict the vulnerability of the natural gas supply chain is proposed, and both the dynamics and stochasticity of the natural gas supply chain are considered. In the methodology, the evaluation system of the vulnerability is established firstly based on the definition of the vulnerability of the natural gas supply chain, and the evaluation system is composed of 12 evaluation indicators that cover the upstream, midstream, and downstream of the natural gas supply chain. Then, a combination weighting method based on the analytic hierarchy process method and entropy weighting method is employed to determine the weight of each indicator. Finally, the dynamic evaluation and prediction models of the vulnerability of the natural gas supply chain are developed based on the set pair analysis and Markov chain. Furthermore, the methodology is applied to evaluate and predict the vulnerability of the natural gas supply chain in China. According to the evaluation results, the vulnerability level in the year of 2021 is relatively vulnerable, and the natural gas supply chain in China was relatively stable in the last 10 years, but it is developing toward a more vulnerable trend. Moreover, some suggestions to reduce the vulnerability of China’s natural gas supply chain are proposed as well.

Contaminant intrusion in water distribution networks is an important concern and must be identified as soon as possible. Although optimization techniques are widely used for source identification, the performance of these methods decreases with increasing the size of the water network. To overcome this problem, this paper presents a new approach to reduce the search space, based on network topology, as a prior step to applying a search algorithm. In this method, all hydraulically connected nodes to the sensor node (with a positive detection) are identified using graph theory and considered as the new reduced search space in the optimization process. The effectiveness of the proposed method was investigated on three different benchmark water networks with different complexity and sizes. The results showed that the proposed approach can decrease the computational time by 18% to 63% while improving the success rate of contaminant source identification by 14% to 150%.

Cross-winding steel-wire–reinforced thermoplastic pipes (CSWRTPs) have been widely applied in oilfield gathering environments in China because of their excellent physical properties. In this study, the failure mode, short-term burst pressure, and strain for a CSWRTP with an external diameter of 75 mm and a wall thickness of 10 mm under internal pressure are investigated through experimental measurements conducted with a burst test system and simulations completed with ANSYS software. A new three-dimensional finite-element burst failure model of CSWRTPs is proposed. Simulation results are in good agreement with the measurements. An axial ductile crack was found on the tested pipe with an uneven circumferential expansion deformation. The simulated short-term burst pressure is in a good agreement with the measured value (19.7 MPa) with an error of $+8.7\%$. The growth of the strain is initially zero, followed by a linear growth, rapid growth, and a clifflike drop when the crack is generated. The effective plastic strain within the inner polyethylene liner is greater than that within the outer polyethylene sheath, and the effective stress within the inner steel wire is greater than that within the outer steel wire. The ultimate pressure–bearing capacity decreases linearly as the strength of the steel wire decreases. Therefore, reduction of the ultimate pressure–bearing capacity of CSWRTP results from the decrease of steel wire strength from corrosion when applied in oilfield gathering systems. This finite-element analysis method can provide a reference to optimize the structural design of CSWRTP.

With aging and deterioration of underground sewer utilities, there is an urgent need for a framework to track their reliability over expected lifetime to facilitate asset management decisions like inspection, maintenance, or replacement. This study proposes multilevel, multifailure framework model for reliability evaluation of reinforced concrete sewer pipe (RCSP) considering the effect of adverse environmental factors such as chloride and sulfide induced attacks, uncertainties in different properties, seasonal temperature and humidity variations, and cracking effects. Monte-Carlo simulation with Latin hypercube sampling is chosen for stochastic analysis to reduce the computational burdens and enhance the accuracy. The application of this framework is illustrated for a case study of an RCSP that has been in service for more than 35 years. Based on results, it is shown that at serviceability stage, sulfide wall erosion is redundant relative to other serviceability issues; therefore, it cannot be used solely for serviceability evaluation of RCSP, as previously done in the literature. At the ultimate level, the effect of chloride pitting corrosion dominates and expedites failure rate. It is proven that there is a huge potential for reinforcement brittle failure under the effect of pitting corrosion, which can lead to a catastrophic collapse.

In the coming years, gas production in Indonesia is projected to decrease so that the option to abandon a plant and temporary shut down will increase. The 762-mm and 102-km offshore gas pipeline is planned to be shut down for 4 years. Therefore, the comprehensive method from the premothballing, mothballing, and recommissioning stages should be developed. In this study, these methods have been developed and the pipeline can be preserved for 4 years with some remarks where the coating repairs, freespan rectification, and analysis of the sacrificial anode remaining life must be performed before premothballing stage. In the premothballing stage, 4 different pigs are used to clean the pipeline until the deposit released is less than 20 L. In mothballing, the internal pipeline is filled with nitrogen gas to prevent the corrosion. The injection of nitrogen gas will be conducted by the train pig method, where each train pig is pushed by nitrogen gas. The internal pressure of the pipeline must be maintained at 1.1 MPa and should not be less than 0.9 MPa to avoid buckle propagation. Continuous maintenance and monitoring should be conducted on the pipeline. The corrosion coupon monitoring should be performed every six months, pressure and right of way (ROW) monitoring should be carried out every two weeks, and regular monitoring and maintenance reports should be conducted at least once a year. Recommissioning begins with evaluating data and conducting remotely operated vehicle (ROV) inspections. Nitrogen gas displacement is performed using a train pig driven by fresh nitrogen gas on two pigs and the production gas should be streamed to push the third pig. The inline inspection (ILI) must be performed to determine the percentage of actual metal loss. The ILI results can be used to perform remaining life analysis and as requirements for pipeline recertification so that the pipeline can be reoperated.

X-ray weld images are investigated to achieve nondestructive identification of defects in oil and gas pipeline welds. The content mainly includes image filtering and enhancement, weld defect suspected defect region (SDR) segmentation, and defect identification. (1) The x-ray image quality is poor, as shown by a lot of noise and low contrast. Therefore, the mean filtering method is used to filter out the noise, and a nonlinear enhancement using sin function is proposed to improve the contrast between the weld and the background. (2) In the image segmentation, a segmentation method of SDR is proposed. Region of interest (ROI) is first extracted, and then SDRs are segmented using clustering. (3) In defect identification, deep learning networks are used for SDRs. A 6-stage, 10-layer convolutional neural network (CNN) network structure is designed, and the convolutional kernels are set to be $5\times 5$ and $3\times 3$. In the experiments, the proposed method is able to automate the processing of x-ray weld images and improve the processing efficiency. The identification accuracy rate is 98.9%.

Research and engineering practice for the earthquake, landslide, or tunneling response of underground pipelines has focused on large ground deformation (LGD) effects, recognizing that LGD often causes the most serious local damage in buried pipelines. The adjacent soil reaction that develops as the pipe moves, i.e., soil–pipe interaction, is of key importance in the response of underground pipelines subject to LGD. A finite-element elastoplastic model can be used to analyze the soil–pipe interaction, and the model requires a soil modulus to simulate the force versus displacement behavior. In the simulation of soil–pipe interaction, a secant modulus associated with high stress and strain should be used in the finite-element model rather than an initial tangent modulus. This research provides a strain-compatible secant modulus that can be used in a finite-element analysis (FEA) of soil–pipe interaction for lateral, upward, downward, and oblique pipe movements. The favorable comparison between the experimental data and the FEA using the strain-compatible secant modulus implies that the proposed approach is suitable to predict soil–pipe behavior under large ground deformation.