Pipe Break Research Articles

Optimal pipe replacement strategy based on break rate prediction through genetic programming for water distribution network

Pipe breaks often occur in water distribution networks and result in large water loss and social-economic damage. To reduce the water loss and maintain the conveyance capability of a pipe network, pipes that experienced a severe break history are often necessary to be replaced. However, when to replace a pipe is a difficult problem to the management of water distribution system. This study took part of the water distribution network of Beijing as a case and collected the pipe properties and the pipe breaks data in recent years (2008–2011). A prediction model of pipe beak rate was first developed using genetic programming. Then, an economically optimal pipe replacement model was set up. Finally, the optimal pipe replacement time was determined by the model. The results could help the utility managers to make cost-effective pipe maintenance plans.

Oxidation rate of nuclear-grade graphite NBG-18 in the kinetic regime for VHTR air ingress accident scenarios

One of the most severe accident scenarios anticipated for VHTRs is an air ingress accident caused by a pipe break. Graphite oxidation could be severe under these conditions. In this work, the oxidation rate of NBG-18 nuclear-grade graphite was studied thermogravimetrically for different oxygen concentrations and with temperatures from 873 to 1873K. A semi-empirical Arrhenius rate equation was developed for the temperature range of 873–1023K. The activation energy of NBG-18 was 187kJ/mol and the order of reaction was 1.25. The penetration depth of oxidant was about 3–4mm for NBG-18 oxidized at 973K. Increased porosity and changes in external geometry became more prominent at higher temperatures from about 1173 to 1873K. The surface of oxidized NBG-18 was characterized by SEM, EDS, FTIR and XPS.

Study of Flow Problems and Those of Soil Compaction in an Agricultural Farm

In agricultural land can be observed problems regarding water and soil. The problems of water flow can cause breaks in pipes, and the problems associated with soil because of the passage of vehicles and lead to compaction, engender changes in soil parameter directly affects the infiltration water and fruit yield regression plants. In this paper, we will study numerically the flow in pipes and soil compaction. So, a first part examines the phenomena of demurrage pumps; when starting a pump, the speed of the electric motor rises from zero up to the permanent regime speed. This change in regime influences the flow of the hydraulic installation and forced it to follow the starting dynamic law of the motor. Under the effect of the friction force, due to the fluid viscosity, the transient regime is dumped until reaching the normal operating conditions. In this work, we study this phenomenon and see the influence of the pump startup on the hydraulic behaviour of one dimensional flow throw a cylindrical pipe of linear elastic behaviour. The pipe is connected to constant level reservoir at the downstream end. The problem is governed by a two coupled linear hyperbolic partial differential equations which are the equations of continuity and motion. The mathematical model is solved by the method of characteristics where at the upstream end, that is, at the pump station, the boundary condition is given by the differential equation for speed change of the pump motor. A theoretical relationship is introduced to express the motor torque in terms of the time. At the downstream end the discharging reservoir is assumed to be at a constant level. The computed head and discharge time curves, caused by the starting of the pump, are plotted at some cross sections of the pipe. The results show that the evolution of the hydraulic variables is well influenced by the applied motor torque. In a second part of the numerical study of soil compaction is developed.

Non-Axisymmetric Mass Transfer Phenomenon behind an Orifice in a Curved Swirling Flow

The purpose of this paper is to understand the mechanism of non-axisymmetric wall-thinning that caused a pipe break in the pipeline of the Mihama nuclear power plant in 2004. The wall thinning was caused by the flow accelerated corrosion which affects low carbon steel pipelines. The mass transfer rate measurement of the wall thinning behind an office in a curved swirling flow is carried out in a closed-circuit water tunnel using a benzoic acid dissolution method. The experimental results indicate that the high mass transfer rate is observed on one side of the pipe behind the orifice, which is similar to the observation of the wall-thinning rate in the Mihama case. This result suggests that the influence of the secondary flow in the long elbow combined with the swirling flow can produce the non-axisymmetric mass transfer phenomenon behind the orifice.

Particle Size Effects on Optimal Sizing and Lifetime of Pipelines Transporting Multi-sized Solid-Liquid Mixtures

A life-cycle cost analysis model is developed in this study, to examine the effects of particle size distribution of the solid particles to be transported on the optimal sizing and lifetime of the pipelines used for transportation of solid-liquid mixtures. The method determines the lifetime of the pipe corresponding to the least annual total cost per unit length of the pipe. The optimum diameter is obtained so that the total cost per unit pipe length per unit volume of the transported mixture throughout this lifetime is minimum. The total cost includes manufacturing and repair cost of pipe, cost of pumping power as well as the cost of power required for the crushing of particles from an initial size distribution to a desirable particle size distribution. The repair cost of pipe and cost of pumping power increase as the pipe becomes older due to more frequent pipe breaks and due to the pipe wear that makes wall roughness, and thereby pressure drop, greater. These costs together with the cost of power for crushing must be considered for through life costing of pipelines. Since the transportation of solid-liquid mixtures is maintained by several pumping stations in long pipelines, the spacing between two successive pumping stations must also be determined. The study shows interdependence of parameters such as the lifetime, the optimum diameter, the corresponding spacing for a given pumping power and the particle size distribution of solid particles transported in the pipeline. Furthermore, the method also provides the interrelation between the total length of pipeline when crushing is economical and the different particle size distributions.

Assessment of Flood Risk with Surface Leakage Caused by Water Supply Pipe Break Accident

Assessment of Flood Risk with Surface Leakage Caused by Water Supply Pipe Break Accident

General Model for Water-Distribution Pipe Breaks: Development, Methodology, and Application to a Small City in Quebec, Canada

AbstractTo model water-pipe breaks a generalization is proposed of an approach where a Weibull exponential model was used for simulation. In this study, a generalization of this approach was performed by developing a general model using three or more probability distributions to describe the time of occurrence of a pipe’s failure. The previous two-distribution model constitutes a special case of this new general model. In addition, explanatory variables were incorporated into the proposed model. Finally, from the proposed general model, the Weibull-exponential-exponential (WEE) model was derived to model water-distribution pipe breaks in a small city in Canada.

Thermal–hydraulic and safety analysis for Chinese helium-cooled solid breeder TBM cooling system

The thermal–hydraulic behavior and safety performance of the Chinese helium-cooled solid breeder (CH HCSB) test blanket module (TBM) with helium cooling system (HCS) has been studied using RELAP5/Mod3.4 code. According to accident analysis specification for TBM, two design basis accidents including loss of off-site power and TBM first wall (FW) ex-vessel coolant pipe break are investigated. The influences of different break locations and plasma termination behaviors are analyzed comprehensively. The results show that natural circulation is established in helium cooling circuit and the TBM can be cooled effectively after loss of off-site power. It is much more critical when the pipe break occurs at the downstream side of the circulator compared with that of upstream side of the circulator. In case of a more serious accident that the ex-vessel break extends to the TBM FW, the results reveal that TBM could be cooled down by natural circulation and radiation. In addition, at the beginning of ex-vessel loss of coolant accident (LOCA), large temperature difference between break and intact TBM FW pipes is found. The accidental results finally show that the integrity of the FW can be guaranteed if the plasma is terminated with a 3s delay time by fusion power shutdown system (FPSS) in the case of ex-vessel LOCA.

Phenomenological investigation of loss of coolant accident in a research reactor facility

A systematic approach is proposed for describing the thermal hydraulic phenomena taking place during a loss-of-coolant accident in a research reactor facility. The phenomenological investigation is performed employing the RELAP5/MOD3.3 best estimate code in a parametric analysis of loss of coolant transients in the Greek Research Reactor-1 (GRR-1) facility. The results obtained demonstrate the significance of the pipe break location and severity in the transient evolution and reveal the effect of important safety components such as the flappers. As a means for presenting the wealth of information obtained during event development, a “TH phenomena regime map” (also known as “TH map”) is introduced. It is a graphical tool summarizing the accident progression in a user-friendly manner that could be useful in training and decision making.

A practical decision scheme for the prioritization of water pipe replacement

Most water distribution networks are assemblies of buried elements which makes their diagnosis complex and requires implementing an asset management (AM) policy of actions performed in the short, medium and long terms. To implement such an AM, decision makers must diagnose the condition of the asset by developing specific tools for establishing priorities between assets and plan the actions needed to maintain or improve their condition. This study focuses on two topics. (i) The implementation of a spatiotemporal analysis of the propagation of pipe breaks. This innovative approach inspired by criminality analysis allows focusing on hotspot zones in order to discriminate critical assets. We have designed a new ‘clustering’ criterion that can be used as a prioritization criterion for asset sorting. (ii) The second part addresses the issue of multi-criteria decision making concerning the classification of pipe renewal candidates by comparing two kinds of aggregation method: (i) an unsophisticated approach by using adapted weighted sum methods; and (ii) a sophisticated approach by using the Preference Ranking Organization Method for Enrichment Evaluation (PROMETHEE) and the ‘Elicitation Et Choix Traduisant la REalité’ (ELECTRE III). The underlying reason for comparing these methods is to know whether the unsophisticated methods ensure reliable replacement policy compared to the sophisticated one.

Numerical and experimental analysis of transient wave propagation through perforated plates for application to the simulation of LOCA in PWR

Loss of coolant accident is characterized by a transient rarefaction wave propagating inside the primary loop after pipe break, resulting in fluid loading on internal structures, especially on the baffle surrounding the reactor core. In that case, loading comes from differences in rarefaction wave travel times, whether it propagates through the reactor core or through the by-pass between baffle and core barrel, yielding delays and pressure differences on both sides of baffle plates. Propagation is strongly influenced by geometric obstacles such as holes in baffle reinforcement plates, which cannot be represented in a numerical model of the whole primary loop and has then to be replaced by suitable impedance relations. A methodology to validate and calibrate such impedance models, based on specific experimental results and high-order CFD simulations, is thus proposed. Models are tested and integrated into EUROPLEXUS fast-transient fluid–structure dynamics software.

Conceptual study on air ingress mitigation for VHTRs

An air ingress accident following a postulated pipe break is considered a critical event for a very high temperature gas-cooled reactor (VHTR) safety. Following helium depressurization, it is anticipated that air will enter the core through the break leading to oxidation of the in-core graphite structures. Under extreme circumstances and without mitigation features this accident may lead to exothermic chemical reactions between graphite and oxygen depending on the accident scenario and the design. Under extreme circumstances (beyond design basis), a loss of structural integrity may occur in some core structures and lead to elevated release of radiological inventory for the fuel matrix.This paper discusses various air ingress mitigation concepts applicable for the VHTRs that would prevent core damage even in the most extreme scenarios. The study begins with identifying important factors (or phenomena) associated with the air ingress accident using root-cause analysis. By preventing main causes of the important events identified in the root-cause diagram, the basic air ingress mitigation ideas were conceived and developed.Among them, two concepts were finally evaluated as effective candidates. One concept is to inject helium directly into the lower plenum (direct in-vessel injection); the other concept is to enclose the reactor with a non-pressure boundary with an opening at the bottom (ex-vessel enclosure). Computational fluid dynamics (CFD) methods were used to evaluate these concepts for proof of these principles. Results indicate that both concepts can effectively suppress air ingress. In the first concept, the buoyancy of the injected helium replaces the air in the core and the upper part of lower plenum. This prevents air from moving into the reactor core and shows the most potential for mitigating graphite oxidation within the vessel. In the second concept, air ingress is limited by molecular diffusion through the opening at the enclosure bottom, a very slow process that allows sufficient time for the core to cool. Existing VHTR concepts can be modified to accommodate either of these mitigation concepts.

Modeling of pipe break accident in a district heating system using RELAP5 computer code

Reliability of a district heat supply system is a very important factor. However, accidents are inevitable and they occur due to various reasons, therefore it is necessary to have possibility to evaluate the consequences of possible accidents. This paper demonstrated the capabilities of developed district heating network model (for RELAP5 code) to analyze dynamic processes taking place in the network. A pipe break in a water supply line accident scenario in Kaunas city (Lithuania) heating network is presented in this paper. The results of this case study were used to demonstrate a possibility of the break location identification by pressure decrease propagation in the network.

Management of valves to improve performance reliability of distribution systems

The overall reliability of a distribution system depends largely on valve reliability, location, and adequacy of number as well as the frequency of water main failure. Therefore, valve management is an essential aspect of distribution system management. This article details how a computer application, the Strategic Valve Management Model (SVMM), can be used to identify pipe segments associated with pipe breaks, determine valves to isolate the breaks, and perform analyses of valve management alternatives (including present worth costs) to reduce customer service interruptions. Valve management alternatives include the addition of new valves, improvement of valve reliability by exercising valves, or a combination of the two. A set of simple performance indicators was developed to evaluate the performance of valve isolating systems. This article demonstrates applications of the SVMM to hypothetical and actual water distribution systems.

Exploration of the relationship between water main breaks and temperature covariates

Water utilities (especially in colder climates) often experience an increase in water main breaks in colder seasons. Some observers argue that this increase largely occurs during the period when there are sudden and prolonged changes in water and air temperatures, which typically occur during the late fall to early winter (temperature drop) and late winter to early spring periods (temperature rise). This paper examines the impact of temperature changes on observed pipe breakage rate for three pipe materials, namely, cast iron, ductile iron and galvanised steel. Several water and air temperature-based covariates were tested in conjunction with a non-homogeneous Poisson pipe break model to assess their impact on water main breaks, using data sets from three different water utilities in the USA and Canada. Temperature-based covariates, such as average mean air temperature, maximum air temperature increase and decrease, and how fast the air temperature increase and decrease over a specific period of days, were found to be consistently significant. While the availability of water temperature data (which most utilities do not have) can enhanced the prediction of water main breaks, it appears that air temperature data alone (which most utilities can access) are usually sufficient.

A unified model for strength degradation of oxidized IG-430 graphite column in VHTR

Air-ingress events caused by large pipe breaks are important accidents considered in the safety analysis of Very High-Temperature Reactors (VHTRs). A main safety concern is the possibility of core-collapse following the failure of the graphite support column, which can be oxidized by ingressed air. The strength of the oxidized cylindrical graphite specimens under compressive load was tested using IG-430 graphite, a candidate material for the support structure of VHTR concept. The temperature conditions were 600°C where the reaction rate is limited by the kinetics (Zone 1) and 800°C where the reaction rate is affected by both kinetics and mass transfer rate (Zone 2). The graphite specimens were oxidized up to ∼32% of total burn-off. In this study we suggest a new parameter for the unified strength degradation model. The derived Knudsen relation with corrected burn-off in this study is applicable to predict the strength degradation of a graphite column that oxidized in Zone 1 and Zone 2. The exponent k in the Knudsen relation was empirically obtained as 0.079. The obtained relation is applicable to a maximum corrected burn-off of 22%. The Zone 3 is surface oxidation. The strength degradation of graphite column oxidized in Zone 3 can be evaluated by developing the empirical straight line formula. This combination of the empirical straight line formula and the Knudsen relation in terms of corrected burn-off enables us to predict the strength degradation of a graphite column oxidized in Zones 1, 2 and 3.

Review of rehabilitation strategies for water distribution pipes

Effective rehabilitation strategies for water pipes play a very important role in both sustaining the reliability of water distribution systems and reducing costs. Pipe breakage prediction models provide a platform for effective rehabilitation strategies. The strength of the rehabilitation strategies is just an extension to those predictive models. There are different techniques and methods for modeling pipe breakage based on identifying breakage patterns using statistical or data-driven (mining) techniques. This review addresses those techniques from the perspective of rehabilitation strategy applications. Therefore, the rehabilitation strategies presented in the literature were reviewed according to three criteria: the level of pipe breakage prediction (pipe-group level or individual-pipe level), the phase, according to the bathtub curve, in which the predictive model is applicable and the performance of the system after rehabilitation. The use of artificial neural networks (ANNs) was found superior over statistical techniques for predicting pipe failure rates and consequently in rehabilitation strategies. However, ANNs are relatively less concerned with identifying specific relations between the variables involved. A proposal for the future research of environmentally integrated, optimal, dynamic and proactive rehabilitation and operation strategies is highlighted at the end of the article.

Temporal Variability of Bacterial Diversity in a Chlorinated Drinking Water Distribution System

The present work is the first to examine temporal variability of bacterial diversity in a free-chlorinated drinking water distribution system over multiple years. The authors examined seasonal and monthly bacterial diversity by using three different molecular methods. 16S rRNA gene clone library analysis identified the bacteria in Pittsburgh seasonal water samples, collected in fall 2006, and winter, spring, and summer 2007 and an event sample collected following a major pipe break, as primarily members of the alpha-, beta-, and gammaproteobacteria classes, which agrees with previous studies of smaller numbers of bulk water samples over shorter durations. However, in this study, seasonal shifts in relative populations were observed with decreased alphaproteobacteria and increased betaproteobacteria diversity in the winter sample compared to the other seasonal samples, which may be caused by changes in chlorine dosing. Further, in 11 monthly samples collected at the same location from September 2008 to August 2009, quantitative polymerase chain reaction (qPCR) results indicated that alpha- and betaproteobacteria predominated over the year, except in May and October, when changes in chlorine dosing as a result of temperature shifts may have influenced bacterial diversity. Denaturing gradient gel electrophoresis (DGGE) cluster analyses suggested that the monthly samples cluster seasonally with greater than 85% similarity between March and April, June and July, and December and January. These results demonstrate the consistent presence of alpha-, beta-, and gammaproteobacteria in drinking water distribution systems across seasons during routine operational conditions and suggest that changes in bacterial class distributions may be useful indicators of system disruptions.

Preliminary safety analysis of ex-vessel LOCA for the European HCPB TBM system

Ex-vessel loss of coolant accident caused by a double-ended pipe break of the helium coolant system inside port cell is considered as one of the most critical accident for the European Helium Cooled Pebble Beds Test Blanket Module (HCPB TBM) system. The resulting rapid helium blow-down causes an immediate block of the TBM cooling, which requires a prompt plasma shutdown. Even after the plasma shutdown the temperature can increase over the design limit and the accident sequence can lead up to a break of the TBM box protection after the failure of different protection systems. Thus air ingresses in the vacuum vessel from the damaged TBM system and steam from the surrounding ITER blanket and divertor structures. The evaluation of this sequence is very important for the definition of the correct protection strategy of the system. To consider all these different events a methodology has been developed in KIT combining different codes for a complete analysis of the accident. In particular, this paper shows an application of MELCOR code to model beryllium–steam reaction in a particular accidental sequence for the long term cooling.

一般産業施設の被害(TRANSLOG/J-RAIL共同特別企画)

A huge earthquake of Mw 9.0 hit the Tohoku district of Japan on March 11, 2011. The earthquake, which was named as "the 2011 Great East Japan Earthquake", caused serious damage to industrial facilities. Based on the damage investigations conducted by the JSME, the damage to the mechanical structures were due to the strong ground motion, soil deformation and tsunami. Many kinds of damage caused by strong motion, such as the damage at the base of machines, the failure of pipe supports, buckling of tanks and the failure of hook bolts were commonly observed. Soil deformation caused break of buried pipes and misalignment of gantry crane rails. The tsunami also caused various kinds of damage, such as broken equipment due to collisions with floating objects and damage of tanks due to water pressure. Power system damage caused by electrical short circuiting also occurred. Although the earthquake caused a great deal of damage, seismic measures taken before the earthquake could mitigate damage of some facilities. This paper provides an overview of the damage of industrial facilities caused by the 2011 Great East Japan Earthquake, their typical damage cases, and the effects of the earthquake resisting methods.