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

Real-time monitoring of fluid properties in tubular systems, such as viscosity, flow rate, and pressure, is essential for industries utilizing the liquid medium. Today such fluid characteristics are studied off-line using laboratory facilities that can provide accurate results. Nonetheless, it is inadequate to match the pace demanded by the industries. Therefore, off-line measurements are slow and ineffective. On the other hand, commercially available real-time monitoring sensors for fluid properties are generally large and bulky, generating considerable pressure reduction and energy loss in tubular systems. Furthermore, they produce significant and persistent damage to the tubular systems during the installation process because of their bulkiness. To address these challenges, industries have realigned their attention on non-destructive testing and noninvasive methodologies installed on the outer tubular surface to avoid flow disturbance and shutting systems for installations. Although, such monitoring sensors showed greater performance in monitoring and inspecting pipe health conditions, they are not effective for monitoring the properties of the fluids. It is limited to flowmeter applications and does not include fluid characteristics such as viscometers. Therefore, developing a convenient real-time integrated sensory system for monitoring different fluid properties in a tubular system is critical. In this dissertation, a fully compliant compact sensory system is designed, developed, examined and optimized for monitoring fluid properties in tubular architectures. The proposed sensor system consists of a physically flexible platform connected to the inner surface of tubes to adopt the different diameters and curvature shapes with unnoticeable flow disruption. Also, it utilizes the microchannel bridge to serve in the macro application inside pipe systems. It has an array of pressure sensors located bellow the microchannel as the primary measurement unit for the device. The dissertation is supported by simulation and modeling for a deeper understanding of the system behavior. In the last stage, the sensory module is integrated with electronics for a fully compliant stand-alone system.

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

Previous research by Rushing et al. (2002) identified key factors contributing to the formation of pinhole leaks in copper plumbing. These factors included high chlorine, pH levels and the presence of aluminum solids. Experiments were conducted to 1) examine the interplay between these constituents, 2) confirm that the water was aggressive enough to eat a hole through a pipe, 3) examine phosphate inhibition, and 4) try to determine the scope of this pitting problem in other distribution systems and on a national level. The first set of experiments clearly defined the controversial trends from earlier work. At certain pH values, the presence of chlorine and aluminum solids does seem to initiate pitting corrosion of copper. Although the problem is most severe at higher pH, it is likely that long-term exposure at lower values such as pH 8 could lead to pitting. There is a concentration effect of aluminum solids at pH 9.0, in that higher concentrations cause an earlier rise in the potential for copper to corrode if sufficient chlorine is present. The second phase of experiments are the first to prove that a potable water containing aluminum, high chlorine residual, and relatively high pH can cause pinholes in copper tube. To our knowledge this is the first time the phenomenon of pinhole leaks has been reproduced in the laboratory as it occurs in the field. It therefore proves that "aggressive water" alone can cause the problem of pitting. The role of flow, pipe orientation and hypothesized surface defects was directly examined as part of this evaluation. Pitting increased with greater water usage and for sections of straight pipe exposed to hydraulic conditions near bends. Copper pipe sections polished to a mirror like finish to remove surface defects were also severely attacked. The role of phosphate in mitigation of copper pitting corrosion was defined in a subsequent experiment using synthesized water. Phosphates did not have an effect at pH 7.7 and were found to reduce electrochemical indications of pitting in the synthetic water at the pH of 8.3. Phosphates had lesser benefits at higher pH even in synthetic water, but overall, even at pHs as high as 10, some benefits from orthophosphate dosing might be anticipated. Effects of orthophosphate on the inhibition of copper pitting corrosion were then applied to treated water from a utility in Washington D.C., whose consumers have experienced an outbreak of pinhole leaks in household copper plumbing. After comparing electrochemical results from synthetic and actual water from the treatment plant, there was evidence of a natural inhibitor to pitting corrosion in WSSC water that is not present in the synthetic water. The higher chloride concentration in the water after ferric chloride was dosed at the treatment plant may have reduced the pitting propensity of the water. The effects of phosphates seemed to reduce the pitting propensity of real water at pH 8.3 although little benefit was seen at pH 9.1. These defined characteristics of copper pitting were then applied in a systematic evaluation of a water utility experiencing pitting corrosion in Roanoke, VA. This case study further supported the hypothesis that high levels of aluminum, chlorine, and pH may be combining to catalyze copper pitting in practice. Recommendations to alter the treatment strategies at these utilities were proposed to help mitigate the pitting corrosion problems in these areas. A national survey then confirmed pitting is occurring at a significant frequency at other large utilities across the U.S. / Master of Science

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[pt] Este trabalho tem por objetivo investigar o efeito de dutos troposféricos nas ligações em visibilidade. O modelo matemático desenvolvido para analisar o problema é baseado na ótica geométrica. Através desta formulação é possível estimar a influência dos parâmetros de uma ligação (distância e altura das antenas) e da estrutura dos dutos no comportamento do sinal recebido. O modelo matemático é aplicado na interpretação das medidas experimentais de um enlace onde os dados meteorológicos disponíveis indicaram uma forte evidência de formação de dutos de superfície na região. A conclusão final mais importante do trabalho é a sugestão do emprego de diversidade em espaço para aumentar a confiabilidade do sistema. / [en] This work deals with the effect of tropospheric ducts in line-of-sight links. The mathematical model used is based on the geometrical optics. Through this formulation it is possible to estimate the influence of link parameters (distance and antenna heigths) and duct structure on the behaviour of the received signal. The mathematical model is applied to explain experimental data from a link where mereorological conditions have shown a strong evidence of surface duct formation. The most important final conclusion is the recommendation to use space diversity as a solution to improve system realiability.

<p> The failure of the Ancaster forcemain was thought to be related to waterhammer effects. The sequence of breakages of the main are reviewed. A series of pressure recordings were made on the forcemain, leading up to and including collapse. The recordings comprise a unique data set.</p> <p> These pressure recordings were digitized and subjected to power spectral analysis. The power spectra pointed out several significant events that were not evident from the pressure record alone.</p> <p> These included the fact that the original break occurred in the forcemain several days prior to its ultimate collapse and discovery on the surface. It was also determined that the break in the pipe was due to the apparent merging of the primary waterhammer wave with an existing but gradually changing lower frequency wave. This second wave was associated with rigid column motion and gradually increased its frequency. The resultant wave carried sufficient energy to cause the ultimate failure of the evidently already damaged forcemain.</p> <p> Power spectral analysis proved useful as a method for analysing waterhammer effects in a forcemain complicated by column separation, leakage and vapour pocket collapse. and may be a useful way of monitoring the performance of longer pipelines.</p> / Thesis / Master of Engineering (MEngr)

<p> The pressure gradients for sphere trains in 1 in. and 2 in. pipes have been measured with water flowing past the stationary spheres at Reynolds numbers (based on pipe diameter) from to 4 - 105 , and sphere/pipe diameter ratios ranging from 0.486 - 0.84. Two dimensionless pressure ratios have been derived so that the experimental results obtained can be generalised to any pipe diameter with the above constraints on Reynolds number and diameter ratio. Drag coefficients have also been calculated from pressure drop measurements for the 0.84 diam. ratio spheres in· 1 in. pipe. These have been compared with McNoun's drag coefficient. </p> <p> The application of the results to predict pressure gradients for sphere trains in any pipe diameter has been illustrated. </p> / Thesis / Master of Engineering (MEngr)

No description available.

No description available.