Underground pipelines are used in various process piping systems to transport gasses or fluids and are usually subjected to the effects of external corrosion. Corrosion can be defined as the deterioration of a material due to a reaction with its environment or the destruction of the material by means that are not mechanical (Fontana and Greene, 1967:2). External corrosion, due to the interaction between the pipe and the soil, is generally a slow process and the corrosion rate is influenced by a variety of external factors. Some of these factors include the ambient pH and salinity, the presence of moisture and bacteria, temperature, the electrical potential difference between the pipe and other structures and the implementation of preventative measures (such as cathodic protection and wrapping). Although the external corrosion of underground pipelines is generally a slow process in mild environments, pipe degradation as a result of external corrosion remains one of the prevalent reasons for the failure of underground pipelines. As with many mechanical systems that are prone to fail at one time or the other, the high costs involved with unforeseen failure necessitate some quantitative (or qualitative) indication of the condition of the pipe system. Some of the costs that can be expected as a result of unforeseen pipeline failure are, amongst others: • costs as a result of the failure of dependent systems; • costs as a result of the loss of production; • costs as a result of the loss of product (in distribution networks); • the cost of unscheduled maintenance (logistical costs); • costs as a result of damage to public property; • fines imposed by customers (in distribution networks); • costs related to pollution control, and • the loss of life The single most important parameter associated with the condition of a system is its profitable remaining life. This is the time during which a sub-system contributes to the well-being of a larger system and the organisation. Therefore, it is necessary to determine, with reasonable accuracy, the extent of the remaining life of a system so that managerial decisions (i.e. investments, cash-flow analyses, maintenance task scheduling and replacement programmes), based on this figure, can be made. Done correctly, this can directly lead to a decrease in maintenance costs and subsequently to an increase in profit. The extent of a corrosive attack on the pipeline might be highly localised or might be fairly uniform over the length of the installation. The fact of the matter is that, since the pipe is buried, it is very difficult to quantify the external damage caused by corrosion. A variety of techniques are in use to survey pipelines and detect anomalies. However, for large pipelines, most of these techniques are either inefficient or too expensive. There will always remain some uncertainty regarding the integrity of the pipeline. The work presented in this study is explained with valid generic examples and aims: 1. to provide the reader with sufficient background information so that the need for determining the integrity of a pipeline becomes apparent; 2. to indicate why a reliability-centred approach is necessary (Chapter 1); 3. to explain the basic principles of corrosion and the electrochemical nature of corrosion (Chapter 2); 4. to indicate areas, based on the basic principles of corrosion, where severe corrosion can be expected (Chapters 2 and 7); 5. to provide and elaborate on information regarding pipe surveillance techniques that are currently available (Chapter 3); 6. to establish the criteria for pipeline failure, in the form of a limit state Junction, for pipes that are subjected to near-constant internal pressures (static failure domain) as well as for pipes subjected to varying internal pressures (fatigue domain) (Chapters 5 and 6); 7. to indicate the sensitivity of the fatigue domain solution to changes in the system variables and to indicate that a significant reduction in the system variables does not necessarily reduce the solution accuracy (Chapter 6), and 8. to integrate the above-mentioned into a practical and workable guideline that can be used to determine the remaining life of an underground pipe network (Chapter 7). / Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2002. / Mechanical and Aeronautical Engineering / unrestricted

Leaks in pipe networks cause significant problems for utilities and water users in terms of lost revenue and interrupted service. In many cities the leakage is as high as forty percent. A water audit is carried out to assess system-wide leakage. However, to detect leakage at the level of a pipeline, a physical measurement technique is generally employed. For large cities the distribution piping length amounts to a few thousand miles. Therefore, the physical measurements can become tedious and expensive. In this thesis it is assumed that a spatial distribution of leakage can be estimated at nodes based on a water audit bookkeeping scheme. A mathematical formulation consisting of continuity, energy (headloss), pressure-dependent demands and/or leakage, and flow direction preservation equations are utilized to distribute demand flows and leakage among pipes. The leakage is attributed to the formation of corrosion holes. Based upon the extent of corrosion, the leakage flow arriving at a particular node is apportioned among all pipes that are converging at that node. Therefore, the formulation presented in this thesis captures the two essential elements behind leakage, namely, pressure driven flow distribution and the vulnerability of pipes to corrosion. The proposed formulation allows utilities to be more proactive in identifying leakage prone districts within the water distribution system. An understanding of the pressure-dependent leakage in the system is helpful when performing a water audit and in developing strategies for leak repair programs. Restoring the full capacity of the water distribution system will greatly increase the reliability of the system, thereby benefiting local utilities and water users. / Master of Science

The need for optimal air vessel sizing tools, in protecting large pipe networks from undue transient pressures is well known. Graphical and other heuristic methods reported in literature are limited to sizing the air vessels for simple rising mains. Although attempts have been made to utilize optimization techniques, they have been largely unsuccessful due to their impractical computational requirements. This research work proposes a robust framework for developing surge protection design tools and demonstrates the usefulness of the framework through an example air vessel sizing tool. Efficiency and robustness of the proposed framework are demonstrated by developing a design aid for air vessel sizing for protecting large pipe network systems against excessive high pressures generated by rapid valve closures. The essence of the proposed framework is in identification of key transient response parameters influencing air vessel parameters from seemingly unmanageable transient response data. This parameterization helps in exploiting the similarity between transient responses of small pipe networks and sub-sections of large pipe networks. The framework employs an extensive knowledgebase of transient pressure and flow scenarios defined from several small network models and corresponding optimal air vessel sizes obtained from a genetic algorithm optimizer. A regression model based on an artificial neural network was used on this knowledgebase to identify key parameters influencing air vessel sizes. These key parameters were used as input variables and the corresponding air vessel parameters as output variables to train the neural network model. The trained neural network model was successfully applied for large complex pipe networks to obtain optimal air vessel sizes for transient protection. The neural network model predictions were compared with optimal air vessel parameters to assess the efficacy of the proposed framework. The validity and limitation of the design aid developed and areas in the framework that need further research are also presented. The proposed frame work requires generation of hundreds of optimization data for small and simple network systems which is a daunting task since genetic algorithm-based optimization is computationally expensive. Selection of a numerically efficient and sufficiently accurate transient analysis method for use inside a genetic algorithm based optimization scheme is crucial as any reduction in transient analysis time for a network system would tremendously reduce the computational costs of bi-level genetic algorithm optimization scheme. This research work also demonstrate that the Wave Plan Method is computationally more efficient than the Method of Characteristics for similar accuracies and the resulting savings in computational costs in the transient analysis of pipe networks and subsequently in the genetic algorithm based optimization schemes are significant.

Fluid flow network simulation codes are commonly used as a design and analysis tool for many engineering problems such as gas distribution networks, power plants and heat pumps. Two formulations of conservation of momentum have been widely applied in fluid flow network simulation models namely those based on static pressure and those based on total pressure. The total pressure formulations are convenient in that they eliminate the difficulties associated with the calculation of the convective terms and components such as pipe junctions are treated in a straightforward manner based on total pressure losses. However, the different formulations of total pressure for compressible and incompressible flow require different formulations of the momentum conservation equation, which is inconvenient for implementation in a generic network simulation code. In this thesis a united total pressure formulation is first derived which is valid for all fluids and therefore eliminates the inconvenience of switching between the compressible and incompressible formulations. A non-iterative method for the solution of the non-isothermal discretised equations based on the total pressure formulation is then introduced and consistency is illustrated. The method appears to be very stable for subsonic flows, while rapid steady state convergence is observed. A systematic comparison is also done with traditional static pressure based methods and the similarities and differences between the two formulations are illuminated. The different time scales involved in the simulation of transient flow in fluid networks are problematic when conventional fixed time step methods are used for time-wise integration. The time scales associated with acoustic and kinematic wave phenomena as well as storage effects can differ by orders in magnitude. This thesis also presents a simple adaptive time step algorithm which can be readily used in conjunction with all the commonly used first order methods for fluid flow networks. Two test problems are selected to demonstrate the efficiency and savings obtained with this procedure. The adaptive time step algorithm correctly selects appropriate time steps for all phenomena and significant computational savings are observed for accurate integration. In addition, a procedure is implemented which automatically selects the appropriate integration method. The resulting algorithm is a fully adaptive algorithm which switches between a fully implicit method and a semi-implicit method. Two test problems are once again used to demonstrate the efficiency and savings. The fully adaptive algorithm correctly selects appropriate methods for all phenomena and significant additional computational savings are observed. / Thesis (PhD (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013

Fluid flow network simulation codes are commonly used as a design and analysis tool for many engineering problems such as gas distribution networks, power plants and heat pumps. Two formulations of conservation of momentum have been widely applied in fluid flow network simulation models namely those based on static pressure and those based on total pressure. The total pressure formulations are convenient in that they eliminate the difficulties associated with the calculation of the convective terms and components such as pipe junctions are treated in a straightforward manner based on total pressure losses. However, the different formulations of total pressure for compressible and incompressible flow require different formulations of the momentum conservation equation, which is inconvenient for implementation in a generic network simulation code. In this thesis a united total pressure formulation is first derived which is valid for all fluids and therefore eliminates the inconvenience of switching between the compressible and incompressible formulations. A non-iterative method for the solution of the non-isothermal discretised equations based on the total pressure formulation is then introduced and consistency is illustrated. The method appears to be very stable for subsonic flows, while rapid steady state convergence is observed. A systematic comparison is also done with traditional static pressure based methods and the similarities and differences between the two formulations are illuminated. The different time scales involved in the simulation of transient flow in fluid networks are problematic when conventional fixed time step methods are used for time-wise integration. The time scales associated with acoustic and kinematic wave phenomena as well as storage effects can differ by orders in magnitude. This thesis also presents a simple adaptive time step algorithm which can be readily used in conjunction with all the commonly used first order methods for fluid flow networks. Two test problems are selected to demonstrate the efficiency and savings obtained with this procedure. The adaptive time step algorithm correctly selects appropriate time steps for all phenomena and significant computational savings are observed for accurate integration. In addition, a procedure is implemented which automatically selects the appropriate integration method. The resulting algorithm is a fully adaptive algorithm which switches between a fully implicit method and a semi-implicit method. Two test problems are once again used to demonstrate the efficiency and savings. The fully adaptive algorithm correctly selects appropriate methods for all phenomena and significant additional computational savings are observed. / Thesis (PhD (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013

Flood propagation over urban areas can cause an interaction between the free-surface flow and large underground pipe networks used for storm drainage and sewage, causing outflows and inflows at the bed. The associated waves may collide with each other and the surface waves. In this thesis the shallow water equations are used to model this type of wave interaction over dry or wet beds with bathymetry gradients and friction terms. The proposed shallow water scheme is solved based on finite volume high-resolution Godunov-type methods. The solver is well-balanced and can accurately balance the source terms and flux-gradients for the steady-state solutions. The solver also utilises a new type of Riemann wave speed to provide depth-positive results over nearly dry beds and dry states. Additionally a new type of source term is introduced in the continuity equation to model pipe inflow and outflow conditions at bed connections. For the standard one-dimensional shallow water equations the numerical results are validated with analytical solutions or other reference solutions provided in the literature. This includes the incipient Riemann problems for nearly dry and dry-states, steady flow over a hump in a rectangular channel and the wave propagation problem. Eventually, the generation of dry bed in the middle, over discontinuous topography is considered. Close agreement is achieved between the shallow water scheme and analytical or reference solutions for the above test cases. For the shallow water problems with influx/efflux source terms comparisons are made with STAR-CD, a commercial Navier-Stokes solver for general fluid flow prediction. The shallow water model is first used to simulate vertical flows through finite gaps in the bed. Next, the interaction of the vertical flows with a dam-break flow is considered for both dry and wet beds. An efflux number, En, is defined based on the vertical efflux velocity and the gap length. A parameter study is undertaken to investigate the effect of the one-dimensional approximation of the present model, for a range of non-dimensional efflux numbers. It is found that the shallow flow model gives sensible predictions at all times provided En<0.5, and for long durations for En>0.5. Dam break flow over an underground connecting pipe is also considered for the one-dimensional efflux problems. To solve two-dimensional problems the shallow water scheme uses the dimensional-splitting method which solves each one-dimensional Riemann problem in the x- and y-directions separately. The cross-derivative terms for second-order accuracy are incorporated by solving another Riemann problem in the orthogonal direction. For two-dimensional problems first the dam-break problems are considered over wet and dry beds. Then, flood propagation over complex terrain is demonstrated. Next, efflux discharge is modelled in isolation over a dry bed and then with dam-break interaction, comparing with STAR-CD results. Again very good agreement is shown between the two-dimensional shallow water model and STAR-CD for the efflux numbers of En<0.5. For modelling the inundation problem over an underground pipe network the solver is coupled with the general underground pipe network solver to calculate the efflux discharge as the flood waves pass through the pipe network. For analysing the pipe network with unknown effluxes an additional set of equations is incorporated into the solution of a general pipe network solver. The shallow water solver coupled to an underground pipe network is then used to simulate dam-break interaction with pipe networks with 9 and 25 nodes to demonstrate the versatility of the method.

Os projetos de redes hidráulicas dimensionam a capacidade de vazão e pressão para atender a uma demanda e prever a resistência necessária para garantir a estabilidade da instalação. Os esforços solicitantes não deverão ultrapassar as resistências estruturais, mantendo-se um coeficiente de segurança que garanta a estabilidade, mesmo nos casos de falhas operacionais. Deve-se proceder à simulação hidráulica tanto para o regime permanente quanto para o regime transitório. Na fase operacional haverão situações transitórias ocasionadas por manobras intencionais ou falhas não previstas que provocarão mudanças do regime permanente para o regime transitório, cuja variação de carga é diretamente proporcional à velocidade de propagação da onda ou celeridade e, dependendo da intensidade do transitório hidráulico, haverá a necessidade de instalar dispositivos de proteção de redes. A concepção dos dispositivos de proteção baseia-se na dissipação do fenômeno transitório por meios de descargas, amortecimento em câmaras de ar comprimido e por reservatórios intermediários que absorvem e suprem os picos de pressão e vazão no início da perturbação, de tal forma que a onda de pressão seja controlada. A celeridade, por sua vez, é função das características do meio fluido, do material da tubulação e da geometria. Ao provocar uma mudança na compressibilidade do meio fluido, tem-se redução no coeficiente de compressibilidade volumétrico da mistura fluida que vai ocasionar uma redução na velocidade de propagação da onda ou celeridade, amortecendo o impacto da variação de carga para níveis que possam ser absorvidos pela instalação. Esta dissertação aborda um dispositivo de redução da velocidade de propagação ou celeridade que pode ser usado como proteção de redes hidráulicas ou atenuador de celeridade, que junto com outros dispositivos e associados em série, distribuídos ao longo da tubulação, podem absorver os excessos de pressão e vazão gerados pelos transitórios e manter os esforços solicitantes inferiores à resistência oferecida pela instalação. / The projects of hydraulic networks define the capacity of outflow and pressure to meet a demand and to achieve the necessary resistance to guarantee the installation stability. The applied loading must not exceed structural resistance, there remaining a safety coefficient which guarantees the stability even in case of operational failure. The hydraulic simulation must be performed both for permanent and transitory regime. In the operational phase, there will be transitory situations caused by intentional maneuvers or unpredicted failures which will cause changes from permanent to transitory regime, with changes in load directly proportional to the propagation speed of the wave or celerity and, depending on the intensity of the hydraulic transient, it will be necessary to provide devices for the network protection. The conception of protection devices is based on the transient phenomena dissipation by means of discharges, shock absorption in air compressed chambers and though intermediate reservoirs, which absorb and supply the outflow and pressure peaks in the beginning of the disturbance. This dissertation approaches a device so that the pressure wave is controlled. The celerity, in its turn, is a function of the fluid characteristics, the network material and geometry. Provoking a change in the mean fluid compressibility there is a reduction in the volumetric compressibility coefficient and also in the specific mass of the mixture, which will cause a reduction in the speed of propagation of the wave or celerity, cushioning the impact of the pressure head variation to a level that can be absorbed by the installation. Therefore, the reduction in the speed of propagation or celerity canbe used is as a protection device for hydraulic nets, or celerity attenuation, which together with other devices, associated in series and distributed along the duct may absorb the excess of pressure and outflow generated by the transitory and keep the applied loading inferior to the resistance supplied by the installation.

Os projetos de redes hidráulicas dimensionam a capacidade de vazão e pressão para atender a uma demanda e prever a resistência necessária para garantir a estabilidade da instalação. Os esforços solicitantes não deverão ultrapassar as resistências estruturais, mantendo-se um coeficiente de segurança que garanta a estabilidade, mesmo nos casos de falhas operacionais. Deve-se proceder à simulação hidráulica tanto para o regime permanente quanto para o regime transitório. Na fase operacional haverão situações transitórias ocasionadas por manobras intencionais ou falhas não previstas que provocarão mudanças do regime permanente para o regime transitório, cuja variação de carga é diretamente proporcional à velocidade de propagação da onda ou celeridade e, dependendo da intensidade do transitório hidráulico, haverá a necessidade de instalar dispositivos de proteção de redes. A concepção dos dispositivos de proteção baseia-se na dissipação do fenômeno transitório por meios de descargas, amortecimento em câmaras de ar comprimido e por reservatórios intermediários que absorvem e suprem os picos de pressão e vazão no início da perturbação, de tal forma que a onda de pressão seja controlada. A celeridade, por sua vez, é função das características do meio fluido, do material da tubulação e da geometria. Ao provocar uma mudança na compressibilidade do meio fluido, tem-se redução no coeficiente de compressibilidade volumétrico da mistura fluida que vai ocasionar uma redução na velocidade de propagação da onda ou celeridade, amortecendo o impacto da variação de carga para níveis que possam ser absorvidos pela instalação. Esta dissertação aborda um dispositivo de redução da velocidade de propagação ou celeridade que pode ser usado como proteção de redes hidráulicas ou atenuador de celeridade, que junto com outros dispositivos e associados em série, distribuídos ao longo da tubulação, podem absorver os excessos de pressão e vazão gerados pelos transitórios e manter os esforços solicitantes inferiores à resistência oferecida pela instalação. / The projects of hydraulic networks define the capacity of outflow and pressure to meet a demand and to achieve the necessary resistance to guarantee the installation stability. The applied loading must not exceed structural resistance, there remaining a safety coefficient which guarantees the stability even in case of operational failure. The hydraulic simulation must be performed both for permanent and transitory regime. In the operational phase, there will be transitory situations caused by intentional maneuvers or unpredicted failures which will cause changes from permanent to transitory regime, with changes in load directly proportional to the propagation speed of the wave or celerity and, depending on the intensity of the hydraulic transient, it will be necessary to provide devices for the network protection. The conception of protection devices is based on the transient phenomena dissipation by means of discharges, shock absorption in air compressed chambers and though intermediate reservoirs, which absorb and supply the outflow and pressure peaks in the beginning of the disturbance. This dissertation approaches a device so that the pressure wave is controlled. The celerity, in its turn, is a function of the fluid characteristics, the network material and geometry. Provoking a change in the mean fluid compressibility there is a reduction in the volumetric compressibility coefficient and also in the specific mass of the mixture, which will cause a reduction in the speed of propagation of the wave or celerity, cushioning the impact of the pressure head variation to a level that can be absorbed by the installation. Therefore, the reduction in the speed of propagation or celerity canbe used is as a protection device for hydraulic nets, or celerity attenuation, which together with other devices, associated in series and distributed along the duct may absorb the excess of pressure and outflow generated by the transitory and keep the applied loading inferior to the resistance supplied by the installation.

Solving for energy losses in pipe junctions has been a focus of study for many years. Although pipe junctions and fittings are at times considered "minor losses" in relation to other energy losses in a pipe network, there are cases where disregarding such losses in flow calculations will lead to errors. To facilitate these calculations, energy loss coefficients (K-factors) are commonly used to obtain energy losses for elbows, tees, crosses, valves, and other pipe fittings. When accurate K-factors are used, the flow rate and corresponding energy at any location in a pipe network can be calculated. K-factors are well defined for most pipe junctions and fittings; however, the literature documents no complete listings of K-factors for crosses. This study was commissioned to determine the K-factors for a wide range of flow combinations in a single pipe cross and the results provide information previously unavailable to compute energy losses associated with crosses. To obtain the loss coefficients, experimental data were collected in which the flow distribution in each of the four cross legs was varied to quantify the influence of velocity and flow distribution on head loss. For each data point the appropriate K-factors were calculated, resulting in over one thousand experimental K-factors that can be used in the design and analysis of piping systems containing crosses.

The multi-utility tunnel has received increased attention as an alternative method for the installation of subsurface infrastructure for the distribution of electricity, water, sewage and district heating. In previous research, the multi-utility tunnel (MUT) has been described as a more sustainable technology compared to the conventionally used technique where the cables and pipes are placed with open-cut excavation (OCE), especially when the entire life cycle is taken into account. This thesis aims to contribute to an improved understanding of MUT's sustainability performance in relation to conventional installation using open-cut excavation. This is done by using literature study, interview study and quantitative sustainability assessments to gain an understanding of the current state of knowledge. Furthermore, this thesis also focuses on how knowledge can be deepened with the help of quantitative sustainability assessments and the challenges of conducting this type of assessment. This thesis shows that the state of knowledge regarding MUT's sustainability performance is low and scattered, with a lack of a holistic approach. Direct economic performance has gained the most attention, followed by indirect and social impact, and the environmental impact has so far barely been assessed. The sustainability performance depends to a large extent on the conditions of the specific case, and these should be considered when assessing the technology. Quantitative assessments have the potential to help deepen the knowledge of the sustainability implications of using MUT. The characteristics of MUT have some similarities with other types of physical infrastructure. Similarities are that the systems are long-lived, have project conditions that affect sustainability performance, and impact a broad spectrum of actors. One difference to typical infrastructure systems is that the owner and management structure of MUT is, by design, more complex as several types of utility systems are in use. The characteristics of MUT give some practical considerations that need to be addressed: data availability, including practitioners; detailed data; transparency; and flexibility. This thesis highlights the complexity of assessing MUT´s sustainability performance and advocates that future studies should have a learning-oriented approach so that the knowledge level can collectively and gradually improve over time rather than focusing on decision-oriented studies. / <p><strong>Funding agencies:</strong> Kampradstiftelsen</p>