Journal of Pipeline Systems Engineering and Practice

The assessment of reliability levels associated with the design and safety factors (DFs and SFs) is important for modern pipeline engineering to achieve probabilistic design using a conventional deterministic format. To this end, this paper evaluates the probabilities of failure (POFs) for different pipe configurations, corrosion defects, and DF/SFs. Two limit states are considered: the yielding of intact pipes based on Barlow’s equation and the failure of corroded pipes based on the RSTRENG model under internal pressure. The uncertainties of all the important variables are considered, including the RSTRENG model error. The POFs associated with different DF/SFs are calculated and discussed; the safety levels (e.g., safety class) of pipes based on the different DF/SFs are also determined. The DFs commonly used for the yielding of intact pipes are found to be in the highest safety class. The SFs used for corroded pipes based on the RSTRENG model are also found to be in the highest safety class for long corrosion defects but in the lowest safety class for short corrosion defects.

The moisture gathering line of the Puguang Gas Field in China renders it prone to accumulating liquid at certain points due to topographic differences. Under operational conditions of pigging, liquid slug volumes, end drainage rates, and production separator surge volumes increase. Multiphase flow transient simulation software is used to study the P102 gas gathering station pigging process. The purging gas volume was measured to be $650\times {10}^4{\mathrm{m}}^3/\mathrm{day}$ and the purging duration to be $30\min$. The pigging liquid slug has been effectively controlled. When the spherical pig pushing volume reaches $190\times {10}^4{\mathrm{m}}^3/\mathrm{day}$, the terminal liquid slug flow peak has been declined from 2,264 to $\mathrm{1,634}{\mathrm{m}}^3/\mathrm{day}$, and the separator surge volume has been decreased from 49 to $38{\mathrm{m}}^3$. When a proportion integration differentiation (PID) controller is used rather than applying manual control, the emergent drainage time is reduced from 12 to $7\min$. The bypass pigging system has been designed and improved, and the peak of terminal liquid slug flow has been reduced from 1,375 to $637{\mathrm{m}}^3/\mathrm{day}$. The optimal bypass rate ranges from 6% to 8% to guide onsite pigging operations of the moisture gathering line of the Puguang Gas Field.

Continuous functioning of gas distribution networks (GDNs) is important in the aftermath of an earthquake. Liquefaction has been found to cause a majority of the damages to buried pipeline infrastructure during an earthquake. A model for quantifying the seismic reliability of city-level GDNs is presented in this study. The seismic reliability model was used to select optimal rehabilitation alternatives for buried gas pipelines. Cured-in-place lining (CIPL) and replacement of aging pipelines with high-density polyethylene (HDPE) pipelines using the pipe bursting method were considered as rehabilitation alternatives in the study. A synthetic GDN was designed appropriately using the land-use pattern of the peninsular region of Charleston, South Carolina for demonstration purposes, and the 1886 Charleston earthquake was selected as the representative seismic hazard. Serviceability of the GDN was adopted as the basis for the reliability assessment using the Monte Carlo simulation approach, and a computationally efficient gas-flow model was developed to quantify the serviceability. For the selected seismic hazard, the reliability of the GDN in the study area was found to be 16.78%, and it increased to 18.62% after CIPL lining of all the pipelines. Replacement of all aging pipes with HDPE increased the reliability further to 26.94%. The optimization results informed the optimal selection of the rehabilitation alternative for each pipeline to maximize seismic reliability of the GDN at the cheapest possible cost. The proposed seismic reliability assessment approach and its use for rehabilitation planning will aid gas pipeline operators in their capital improvement works.

A pipeline is prone to axial movement, called pipeline walking, under heat-up and cooldown cycles. The build-up of axial force along the pipeline can result in the phenomenon referred to as lateral buckling. Walking and lateral buckling can both influence pipeline movement performance and threaten the safety of pipeline systems. The numerical simulation method is adopted to study the pipeline movement laws under walking and buckling interactions. Walking and buckling interactions are classified into three types for different forms of seabed slopes, and corresponding mitigation methods are proposed. The effects of buckling number, route bend, sleeper spacing, and anchor position on the lateral displacement amplitude, axial displacement, and effective axial force (EAF) of the pipeline are analyzed. Criteria for the mitigation methods are proposed based on parameters such as the pipeline end expansion, buckling failure parameter, maximum anchor force, and minimum compressive EAF. The results show that the anchor position has a great influence on the intertransformation of pipeline buckling and walking. The difference in anchor force can reach 51.1% considering different anchor positions.

In horizontal directional drilling (HDD), accurate determination of the pullback force for pipe installation (pullback) during the design phase is critical to the success of the project. For the calculation of pullback force, a friction coefficient of 0.3 is generally suggested for the lubricated borehole in the design. In this paper, friction coefficients are determined from data collected during running in hole (RIH), i.e., moving the drill assembly toward the cutting face without drilling, for the drilling of the pilot hole and reaming stage. This gives a friction coefficient that is calculated for hole conditions similar to those in the pullback process. The friction coefficient is back-calculated based on the equilibrium of thrust force (${\mu }_F$) and torque (${\mu }_T$), using three models. The main difference among the three models is whether or not the model incorporates the effect of annular pressure at the drill bit and viscosity of drilling fluid in the calculation. Results indicate the friction coefficient obtained based on the equilibrium of thrust force is larger than that for equilibrium of torque. The range of ${\mu }_F$ is between 0.10 and 0.40 and that of ${\mu }_T$ is between 0.05 and 0.2. This paper also compares three different models based on the calculated friction coefficients to identify the effect of annular pressure and viscosity on the calculation. The results indicate that the difference in terms of the calculated friction coefficient between the models is less than 10%. This paper provides an overall idea of the range of the friction coefficient for a clean hole in HDD based on data collected during an HDD project.

Infiltration of groundwater through reinforced concrete pipe (RCP) joints under hydrostatic pressure has been a major costly challenge in municipal sewer network systems. Analysis of an exclusive designwise infiltration test data of RCP joints showed that conventional regression analysis failed to produce reliable predictions. Accordingly, tree-based machine-learning techniques including random forest, extra trees, and gradient boosting classifiers have been deployed in this study to create reliable models. A large designwise data set identifying failure of RCP joints and the effect of key design parameters was collected using a novel experimental program. Due to the resulting unbalanced experimental data set, oversampling techniques including synthetic minority over-sampling technique (SMOTE) and density based synthetic minority over-sampling technique (DBSMOTE) were employed to enhance predictive performance. Gradient boosting coupled with DBSMOTE offered a robust machine-learning model for predicting RCP joint hydrostatic infiltration. The hybrid gradient boosting classification (GBC)-DBSMOTE model achieved superior predictive accuracy in terms of several classification indicators, with promising capability to create RCP joint hydrostatic infiltration performance charts that capture the effects of key design parameters, such as pressure duration and level, pipe size, and gasket sealing. The robust predictive model could produce design charts that aid municipalities in proactively averting sewage system infiltration problems at low cost, instead of the prevailing reactive approach to this problem.

A partial blockage usually results in undesirable consequences for long-distance conduits. In order to study the disturbance of partial blockages on transient responses, a numerical model was developed to simulate a partial blockage based on the traditional method of characteristics (MOC). The transient responses were simulated using the proposed numerical model for the water supply conduit with a partial blockage. Based on the equivalent resistance conditions, the distribution of extreme pressures was compared to reveal the disturbance characteristics of the partial blockage. The simulation results show that the disturbance of the extreme pressure is the strongest around the blockage site, and decreases linearly with the distance to the blockage. Subsequently, a diagnosis model was established to detect the zone and the intension of the partial blockage, based on the distribution of the extreme pressures of the transient responses. The results show that the diagnosis model has good performances, irrespective of locations or intensions, with a maximum error of about 2%. The proposed approach can be properly used to detect the zone and the intension of the partial blockage in a single long-distance conduit.

Budget distribution over water network segments is one of the challenges that face municipalities worldwide. Most water distribution networks (WDNs) are deteriorating, and thus they require urgent rehabilitation, which costs billions of dollars. Therefore, there is a need to develop a prioritization tool for allocating the budget to the inspected components and selecting the most suitable rehabilitation actions. The present research aims to develop a water network performance–based budget allocation (WNPBA) model to allocate budgets based on the performance assessment optimally. The WNPBA model utilizes Weibull distribution to predict the performance for the components, as well as both genetic algorithm (GA) and greedy heuristics (GH) to allocate the available funds optimally. The data required for this research were collected from experts in Montreal’s water services because the developed model was applied to a subnetwork from Montreal. The model’s recommended actions matched the city water services’ actions, utilizing the AQUAMODEX tool by almost 94%. The developed WNPBA has proven to be a promising tool in allocating budget to water networks. Data from a water subnetwork in Montreal were used to demonstrate the proposed model. Therefore, the model is useful for the decision-making process through any water municipality to facilitate the budget allocation process.

Fiber-reinforced polymer composites are used as emerging materials to repair oil and gas transmission pipelines without stopping the flow of fluids inside. These pipelines are subjected to harsh environment conditions such as being buried under soil and being exposed to high humidity, high temperatures, and different chemicals. It is important to predict the useful life of composite repairs in these harsh conditions in order to design better and to have robust repair solutions. This study evaluates mechanical properties, namely tensile strength tensile modulus, flexural strength, flexural modulus, and lap shear strength, of composite laminates when exposed to harsh environmental conditions such as hot-wet [$70°\mathrm{C}/85\%$ relative humidity (RH)] for 0, 2, 4, and $6\mathrm{weeks}$, steam autoclave [121°C and 1,05,000 Pa (1.05 bar)] for 0, 6, and $12\mathrm{h}$, and ultraviolet (UV) ray exposure of type UVA-340 at 50°C for 0 and $2\mathrm{weeks}$. The glass fiber–reinforced polymer (GFRP) composite laminates are prepared by hand layup process and are cut using a water-jet cutting process to avoid machining defects and to keep a good surface finish. The specimens are exposed to these corresponding environmental conditions for different periods of time, and the changes in their mechanical properties are studied. The tensile strength, flexural modulus, and lap shear strength values are compared with unexposed specimens. Decreases in strength and modulus values are observed for exposed specimens. A simple empirical expression is developed to predict the usable lifetime of a composite repair system exposed to such different harsh environmental conditions.

One consideration for pipeline design is the Delta-T. There may be a tendency to assume a conservative value for winter construction, the extreme value being the air temperature. In applying a low restraint temperature in winter, the Delta-T is increased. The consequence of an artificially high Delta-T is that the pipeline may notionally experience high stresses; in extreme cases, mitigation is required to counteract these stresses. In winter, the soil at pipeline depth will usually be unfrozen or slightly frozen. When a pipeline nominally at ambient air temperature is backfilled, the warmer backfill soil will quickly warm the pipeline steel from the air temperature to a more moderate temperature. As a result, the pipeline is unlikely to attain full axial restraint at low air temperatures but instead at more temperate temperatures. In contrast, for pipelines constructed in summer and assumed to be backfilled at warm air temperatures, the resulting Delta-T may be nonconservative, particularly for hot pipelines. This paper presents the test results for several pipelines installed in winter and summer. The pipelines were instrumented with thermistors to monitor pipeline and soil temperatures and strain gauges to monitor pipeline strains during the backfilling process. Guidance is provided as to appropriate tie-in temperatures.

Buried offshore pipes are prone to upheaval and lateral buckling because of the high temperature and pressure of the materials being transported. An attempt has been made in the present study to evaluate uplift and lateral capacity of buried offshore pipes in a soft clay seabed using finite-element software. The numerical model used in the present study has been validated against results available in the literature. Finite-element analyses are carried out to study the upheaval and lateral buckling behavior of pipes for both the no-tension (NT) condition, i.e., when separation occurs between the pipe and soil, and the full-tension (FT) condition, i.e., when the soil beneath the pipe remains attached to the pipe. The variation of both uplift and lateral normalized capacity factors with soil cover depth ratio is presented for different combinations of soil strength and effective weight. Both uplift and lateral capacity factors have been found to increase and reach a constant peak value with increasing depth of soil cover. A transition from global and local failure mechanisms of a pipe is observed when the capacity factors attain their peak values at a limiting soil cover depth. The critical cases for the design of buried offshore pipe in homogeneous clay are established for both NT and FT conditions.

The development of a small wrinkle defect in a buried pipeline can be a challenging issue for pipeline operators to approach. Although extensive research has been conducted to evaluate the integrity of a pipeline showing signs of irregularities such as corrosion, pipe wall buckling, and/or rippling, limited research data or guidelines are available to assess the severity of a small wrinkle defect. If not dealt with appropriately, these small wrinkle defects can lead to further damage of the pipe wall as a result of fatigue damage caused by internal pressure cycling. A research program comprised of a full-scale two-stage experimental test setup was initiated to investigate the postwrinkling behavior of field pipelines undergoing typical pressure fluctuations. This paper presents test procedures describing both the wrinkle defect initiation stage and the subsequent cyclic pressure fatigue test stage, as well as the corresponding observations and results. The results indicate that wrinkle defects that initiate in pipelines that operate at lower pressures or are temporarily shut down are more susceptible to fatigue failure as a result of pressure fluctuations, due to internal cracks initiating at the apex of the wrinkle and propagating outward.

Plumbing planners and architects choose to use the 1940s Hunter curve that articulated domestic demand to solve the complex and multifaceted difficulties they found in the probabilistic process. This curve was designed to predict the water demand for the installation of high-performance streams operating at an almost maximized level of confidence (CL) of 99%. Many everyday things have changed for the better. At the moment, these problems are creating overestimation consequences according to Hunter’s curve. Allowing the use of modern water use appliances does not reflect the consequences of water sustentation. In the background, Hunter’s curve was modified in 2014 for a maximum of 300 fixtures. In the present study, to meet the high and optimum water demand, Hunter’s curve was remodified by up to 1,000 fixtures by incorporating low flow rates in modern flush valves to effectively reduce CLs, leading to significant water savings. The standardization of the fixture units for those operating valves has been established and is done efficiently using the binomial-probability-function for large-scale system operations, i.e., at various flow rates, low CLs, and reduced consumption. In such a case, water savings can be achieved by 80%–95% in relation to Hunter’s original adoption. The redesigned Hunter curves for optimized CLs used in the current paper focus on the excellent performance of plumbing design by improving water use and prevention.

The wastewater generated in the potash mines of the Bages region in Catalonia (Spain) was experimentally tested at the Paterson & Cooke slurry test facility in Cape Town, South Africa, to determine the flow behavior and limit deposition velocity of various brine and brine-slurry mixtures containing a low solids concentration of fine insoluble particles. The tests measured the limit deposition velocity, viscosity, and flow resistance of a range of brine mixtures at different concentrations of solid particles in suspension, and they are presented and discussed in this paper. Tests were conducted on the slurries using both water tests (WT) and saturated brine tests (BT) as the medium for the solid sediment. In order to replicate the possible situations that could occur during their transport in the pipeline, the mixtures were generated with relatively low sediment concentrations, always less than 5% by volume. The test data showed that the limit deposition velocity at equivalent solid concentrations is higher for the WT mixtures than for the BT mixtures due to the differences in the kinematic viscosity of the medium. Finally, the kinematic viscosity obtained for both WT and BT mixtures trends moderately upward as their volume concentration increases, although the viscosity in BT mixtures presents some particularities that are subsequently described.

The arrangement of gas gathering stations (GGS) and central processing facilities (CPF) in the natural gas gathering pipeline network really counts. Their reasonable number and locations can make the pipeline network economically optimal. Although many scholars have studied the layout optimization of the star–star pipeline network, they have only studied their specific constraints, such as processing capacity, and have not proposed a comprehensive mathematical model. Based on the star-shaped pipeline network structure, this paper proposes a star–star gas gathering station and central processing facility location problem (SSCPLP). Considering the constraints such as capacity, number, radius, and their combination, a general mathematical model of the problem is established correspondingly, which can be used to optimize the pipeline network layout and station location under different constraints according to the engineering application environment. Our layout optimization problem is a location-allocation problem of GGSs and the CPF in discrete space and is a kind of nondeterministic polynomial complete (NP-complete) problem, which can be expressed as a mixed-integer linear programming problem and solved by CPLEX. Two random cases and two real-world cases of actual gas gathering fields are analyzed under three different constraints (capacity, number, and radius). The obtained results not only prove the correctness of the proposed model, but also verify that the model can solve the layout optimization of the actual star–star topology under different engineering requirements.

Controlled low-strength material (CLSM) has been widely used for pipe backfilling applications with several advantages, as described in detail in numerous documents. Our previous study indicated that buried pipelines backfilled with CLSM show better performance when subject to seismic wave propagation. In this study, a nonlinear three-dimensional finite-element (FE) model was used to evaluate the seismic performance of buried steel pipe backfilled with CLSM when subject to a reverse-slip fault. The developed FE model results were validated by full-scale experimental data obtained by others from the available literature. After FE model validation, the developed FE model was utilized to evaluate the effect of various FE model parameters on pipe seismic performance, including CLSM trench continuity through the fault plane, CLSM–pipe friction coefficient, backfill material shear strength and Young’s modulus, and pipe diameter-to-thickness ratio. The seismic performance of pipe embedded in CLSM backfills was compared to pipe embedded in soil backfills. Results from these model parametric studies indicated that the pipe with CLSM backfill did not show better seismic performance than soil backfill due to the higher material stiffness. The research findings from the previous study by the authors in conjunction with the findings from this study provide a more complete understanding of pipe seismic performance backfilled with CLSM in seismic-prone areas.

Pipe material and labor costs constitute about 70% of pipeline construction costs. Pipe and labor costs are subject to considerable fluctuations over time. These fluctuations are problematic for cost estimation and bid preparation in pipeline projects, which are mostly large and long-term projects. The accurate prediction of pipe and labor costs is invaluable for cost estimators to prepare accurate bids and manage the cost contingencies. However, the existing literature does not take advantage of the leading indicators of pipeline construction cost time series to accurately forecast cost fluctuations in pipeline projects. The objective of this research is to identify the leading indicators of pipeline construction costs and develop multivariate time series models for forecasting cost fluctuations in pipeline projects. Nineteen potential leading indicators of pipe and labor costs were initially selected based on a comprehensive review of construction cost forecasting literature. The leading indicators were identified from this pool of potential leading indicators based on unit root tests and Granger causality tests. Multivariate time series models were developed based on the results of cointegration tests. Vector error correction (VEC) models were developed for the cointegrated variables, while vector autoregressive (VAR) models were developed for the non-cointegrated variables. Since multivariate time series models include information from the identified leading indicators, multivariate time series models are often expected to deliver more accurate forecasts than univariate time series models. The forecasting accuracies of multivariate time series models were compared with those of univariate time series models based on three common error measures: mean absolute prediction error (MAPE), root-mean-squared error (RMSE), and mean average error (MAE). The results show that multivariate time series models outperform univariate models for forecasting cost fluctuations in pipeline projects. The findings of this research contribute to the state of knowledge by identifying leading indicators of pipe and labor costs and developing multivariate time series models to forecast them. The multivariate time series models with leading indicators are more accurate than univariate models for forecasting cost fluctuations in pipeline projects. It is expected that the proposed multivariate time series forecasting models contribute to the enhancement of the theory and practice of pipeline construction cost forecasting and help cost engineers and investment planners to prepare more accurate bids, cost estimates, and budgets for pipeline projects.

Experiments are conducted to study the uplift behavior of buried pipes in medium dense sand with ground slopings of 0°, 10°, 20°, and varying burial depths. Test results show that the peak uplift resistance reduces with the increasing sloping, and up to 10% reduction is observed for 20° sloping. The displacement of pipe where the peak is mobilized, ${\delta }_p$, also reduces for 20° sloping. The uplift resistance experiences a quicker reduction after reaching the peak due to the ground sloping. The stress level increases on the uphill side and decreases on the downhill side, resulting in lower and higher dilatancy, respectively. Consequently, the angle of slip plane to the vertical direction become smaller on the uphill side and larger on the downhill side. The slip plane extends to the ground and a complete slip mechanism develops at a pipe displacement of $2{\delta }_p$. The postpeak softening behavior of uplift resistance oscillates at an amplitude increasing with the burial depth and decreasing with the sloping, due to the arching effect as soil moving around the pipe periphery.

A structurally spray-applied pipe lining (SAPL) is a trenchless method to inhibit further deterioration and structurally renew deteriorated pipes, culverts, and drainage structures. The primary SAPL materials generally fall into two broad categories of cementitious and polymeric materials. SAPLs can be a key strategy in extending service life and managing the future issues expected from the aging network of gravity pipes and culverts. However, currently no standard design methodology exists for SAPL. Most lining vendors utilize the cured-in-place pipe (CIPP) design methodology as specified in a current standard, and others use various analytical structural design approaches. This paper assessed the existing conditions of 24 culverts renewed with SAPL in the states of Delaware, Florida, Minnesota, New York, North Carolina, Ohio, and Pennsylvania by considering various physical and operational factors. The inspections were focused on large-diameter corrugated metal pipes (CMPs) and reinforced concrete pipes (RCPs) renewed with cementitious and geopolymer SAPLs. This study is part of a broader research project to develop a standard design methodology for this renewal method. Identifying potential problems after installation can be considered during planning and design of SAPL. Therefore, the first objective of this paper is to conduct field data collections and in situ inspections of recent SAPL projects to identify renewal defects and installation issues. The second objective of this paper is to make suggestions for development of proper performance construction specifications to prevent SAPL potential problems. The data collected through the field inspection are used to assess the structural conditions of these projects. The results present a strong need for SAPL performance construction specifications, a standard design methodology, a robust quality control protocol, postinspection requirements, and recommendations for SAPL installation improvements.

Dents and corrosion are two types of defects commonly found on pipelines. Although major efforts have been made to assess the defects of each type, there is a limited understanding of interaction between the two defects in adjacency. In this work, a finite-element (FE) model was developed, enabling assessment of the interaction between a dent and an adjacent corrosion feature and prediction of failure pressure of the pipelines. Results showed that the geometries of the corrosion feature and the dent affected their interaction. As the interaction increased, the failure pressure of the pipelines decreased. A criterion was proposed to determine the critical spacing between the dent and the corrosion feature, below which an interaction between them existed. The dependences of the critical spacing on corrosion depth, corrosion length, and dent depth were determined. For example, the critical spacing between a dent 20 mm in depth and a corrosion feature 100 mm in length and 50% of pipe wall thickness on an X46 steel pipe was 150 mm. When a corrosion feature was sufficiently long (i.e., 200 mm), it dominated determination of the failure pressure, while the dent-corrosion interaction was negligible. When the corrosion feature was relatively short (i.e., 15 mm), the dent became predominant in failure pressure determination.

Long-distance pipelines are prone to suspend due to geological disasters, and large deformation may occur under gravity or other loads. In this study, mechanical behavior of a suspended pipeline caused by ground subsidence was investigated. Effects of suspended length, pipeline diameter, wall thickness, internal pressure, oil weight, and surrounding soil on the suspended pipeline were studied. The results show that the maximum von Mises stress appears on the upper surface of the suspended pipeline’s end. There is a stress concentration on the pipeline’s lower surface, which is in contact with the soil. The von Mises stress increases with the suspended length increases. At the end of the pipeline, the strain on the upper surface is tensile strain, while it on the lower surface is compressive strain. In the middle of the pipeline, the strain on both upper and lower surfaces are tensile strains. The maximum plastic strain only appears on the upper surface of the pipeline end. As the pipeline diameter increases, the von Mises stress and displacement decrease, but the plastic strain increases. For increasing wall thickness, the von Mises stress is approximately constant, but the plastic strain decreases. The von Mises stress of the pipeline increases with increasing of internal pressure and oil weight. When the stratum around the buried pipeline is rock, there is a stress concentration.

Gas pipelines are an integral part of each stage across several industries, including steel, oil, chemical, and pharmaceutics. Deposit of sediments causes blockages in pipelines, which leads to abrupt failure and functional impairment. Failure of gas pipelines due to blockages is a serious threat as it is catastrophic in terms of safety and economic loss. Hence, it is imperative for preventive maintenance to quantitatively monitor the gas pipelines for blockage conditions. Industries will benefit from information regarding the position and extent of blockage in gas pipelines. This paper demonstrates a novel technique that can be used in pipelines to efficiently identify and measure the extent of blockages. The methodology is based on the idea of differential damping rate, i.e., the location with high sediment deposit dampens sound waves at a higher rate than the pipe locations with low deposits. The disturbance created by a point impact on pipelines with deposit and without deposit differs due to the damping effect of the deposit on the vibration. In this methodology, the damping coefficient is measured for various points circumferentially, and then all the values are compared to each other. The technique is validated with an accuracy of 96.5% with the help of physical measurements of sediment level in the test pipe.

Vortex drop shafts are utilized to dissipate and transport the energy of flows in sewerage networks. A vortex drop shaft is composed of three parts: the inlet structure, the vertical shaft, and the dissipation chamber. This study evaluated the performance of the dissipation chamber in terms of flow energy dissipation, the type of outflow (e.g., subcritical and supercritical), and the amount of pressure imposing on the chamber bottom. To improve the performance of the dissipation chamber, four elements—a baffle, a weir, a venturi, and a sump—were implemented. Then the influence of each element on the performance of the dissipation chamber was investigated. The results revealed that such elements dissipated the inflow to the chamber by 90.5%–96.9%. These elements also take part in controlling outflow and decreasing pressure on the chamber bottom. Considering flow energy dissipation, the type of outflow and imposing pressure on the dissipation chamber bottom, appropriate geometric dimensions for the elements inside the dissipation chamber are proposed.

Data scarcity and missing values are a prime challenge in developing a corrosion prediction model. In this paper, eight imputation techniques are explored using the National Bureau of Standards (NBS) corrosion database. The eight imputation techniques are mean, median, linear regression (LR), $K$-nearest neighbor (KNN), iterative robust model-based imputation (IRMI), multiple imputations of incomplete multivariate data (AMELIA), sequential imputation for missing values (IMPSEQ), and principal component analysis (PCA). The utility of imputation techniques is checked by training a neural network (NN) on the data sets imputed by the eight techniques. Among the techniques, KNN and IMPSEQ performed better by achieving a low error and high coefficient of determination ${\mathit{R}}^2$. Results were compared with a baseline accuracy, where the NN model was trained on the original corrosion data set without the missing values. The NN performance increased from the baseline accuracy (81%) when it was trained by KNN (85%) and IMPSEQ (91%) imputed data sets.

Trenching and backfilling of pipelines is a common practice for physical protection. In seismic regions, buried pipelines may be at risk of fault displacement that causes massive lateral pipe movements and jeopardizes pipeline mechanical integrity. The lower stiffness of the remolded backfilling material relative to the native ground has a significant impact on lateral soil resistance against large pipeline displacements that are rarely considered in current design practice. Finding a safe, reliable, and cost-effective trench configuration is a key aspect of design practice that is affected by pipeline–backfill–trench interaction. In this analysis, a probabilistic approach was used to investigate trenching/backfilling effects on the response of buried pipelines to large lateral displacements. A three-dimensional beam-spring model subject to a strike-slip fault was developed and the effect of trenching/backfilling was incorporated using nonlinear springs. Two limit state criteria were set to identify the safe and failure regions. A code was developed using Python programming software to perform iterative analysis by variation of pipe specifications, native and backfill soil properties, trench width, trench depth, and lateral displacements. The first-order reliability method (FORM) was used to estimate the exceedance probability of failure using the identified limit states, and the results were validated against published studies in the literature. The study showed that the trenching/backfilling of pipeline results in lower lateral soil resistance against displaced pipe. In addition, it was observed that the advantage of load reduction could be used to mitigate trench dimensions and reduce construction costs without sacrificing safety and integrity requirements.

To provide cathodic protection (CP) for gas and oil underground pipelines, a direct current (DC) isolator is needed to isolate the main CP converter from the earth around the pipeline. The DC isolator, proposed in this paper, consists of four parts: a second-order low-pass active filter, voltage level shifter, pulse-width-modulation (PWM) controller, and a ground isolator. This converter is designed to accurately provide an isolated near-ground voltage as a control input of the main CP converter in harsh outdoor environments, which is its privilege in comparison with other solutions. The second-order low-pass active filter is designed to filter possible disturbances in the vicinity of the pipeline and reduce the loading effect of the permanent half-cell resistor. The voltage level shifter provides proper voltage range and increases the precision of the main CP converter. The PWM controller is used to provide alternating current (AC) voltage for ground isolator, and the ground isolator provides enough isolation from the dirty ground near the pipeline. Finally, a prototype is implemented and tested to verify the theoretical and simulation results.

This study investigates the developments of a new experimental setup for the detection of air and solid blockage inside pipes. Earlier research utilized a hollow capillary composed of thin plastic material to detect the existence of air inside the pipeline. The experimental setup is even easier for detecting solids. Prior to the experiment, a simulation using the finite element method (FEM) was conducted to investigate the behavior of acoustic pressure in two phases, namely, liquid solid and liquid gas. An ultrasonic sensor circuit consisting of a transmitter, a receiver, and signal conditioning circuits was constructed. For this experiment, an acrylic pipe with a diameter of 110 mm and a thickness of 5 mm was used, while polyvinyl chloride (PVC) pipes were used as the blockage subject. Two scenarios were considered, which are: a PVC with water inside, and a PVC with air inside. Based on the experimental results, the acoustic wave energy was more attenuate as the size of the blockage inside the pipeline increased, and air is a great discontinuity to ultrasonic transmission.

For underground structures at coastal areas, inflow/infiltration ($\mathrm{I}/\mathrm{I}$) control is a critical procedure to guarantee their quality, especially for manholes, which are more likely to have structural problems and $\mathrm{I}/\mathrm{I}$ problems. There are several methods that could address these problems, including spraying, grouting, and in situ lining. In this case study, a combined grouting method is proposed for a deep-buried double-walled manhole rehabilitation project, the Diyar Al Muharraq (DAM) project in Bahrain. This case study involves $\mathrm{I}/\mathrm{I}$ investigation, rehabilitation design, construction management, and evaluation of rehabilitation according to the monitoring data. The 4-step grouting method shows an excellent rehabilitation performance, the monitoring data show that the water level in manholes lowered by 21.35%, and the brine pressure at the bottom of manholes decreased by 78.26%, which means the combined grouting method is effective for manhole rehabilitation at coastal areas.

Analyses presented herein explore transport aspects related to benzene breakthrough into gasketed subsurface concrete pipe embedded in an unsaturated soil profile. A series of three-dimensional numerical analyses were conducted using the T2VOC code. The simulations yielded results on multiphase multicomponent transport providing insights onto the effect of pipe material and gasket conditions, subsurface soil saturated and unsaturated properties, volatilization to the atmosphere, and the thickness of initial contamination at the source on rate and magnitude of the transported mass. Results showed that the use of lower pipe concrete material quality led to increasing mass transport into the pipe by more than 60%. The use of a damaged gasket also allowed for a considerable breakthrough of the contaminant into the pipe with two orders of magnitude higher mass compared to the use of an intact gasket. While the main mechanism of contaminant migration in the vadose zone is vapor diffusion, benzene transport in the aqueous phase was the main phase breaking through the pipe walls, given the initial matric suction of the concrete pipe wall that leads to the near saturation of the pipe walls once water flow commences. The thickness of the nonaqueous phase liquid (NAPL) at source has a relatively secondary effect on the mass transfer into the pipe. Considering coarse-type soil material versus the sandy clay as the native soil where the pipe is located led to an increase in the concentrations in both aqueous and gas phases inside the pipe by a factor of 6 after 1 year.

Det Norske Veritas is a company that gives an available classification guidance, which can provide a systematic methodology to estimate the risk due to dropped objects for the purpose of subsea pipeline projection. Firstly, dropped objects simulator (DROBS), which has been developed based on the motion dynamics of cylindrical objects, can be used to calculate the hit probability within a ring area. These results will be compared with the results from DNV’s simplified methodology. Further, they can also be integrated into DNV’s methodology to calculate the annual failure frequency. It is found that DNV may underestimate the failure frequency if compared with the results from DROBS. Three different shield plans are proposed, with 0–60, 0–80, 0–90 m shielded, respectively, to quantify the differences between both methods. In each shield plan, there will be six cases discussed, three for long/flat-shaped objects and the other three for box/round-shaped objects. Through this comparison case study, it is found that only Shield plan III can meet the design criteria base on the original layout design; however, an optimal layout design with a lower cost is also proposed. Overall, the outcome of this study can help optimize offshore pipeline layout design eventually. DOI: 10.1061/ (ASCE) PS.1949-1204.0000569. © 2021 American Society of Civil Engineers.