A numerical investigation into the effect of pressure on holes and cracks in water supply pipes

The effect of water pressure in a pipe on the rate of leakage from leak openings in the pipe is one of the main factors influencing leakage that is still not understood sufficiently. In this study, the behaviours of different types of leak openings (round holes and longitudinal and circumferential cracks) on pressurized pipes were investigated for different pipe materials (uPVC, steel, cast iron and asbestos cement) using finite element analysis. Linear elastic behaviour was assumed. The study found that (1) pipe stresses are significantly affected by a leak opening, and can easily exceed the material's yield strength in the vicinity of the opening; (2) round holes show the smallest expansion with pressure, followed by circumferential cracks and then longitudinal cracks; (3) the areas of all leak openings increase linearly with pressure; (4) longitudinal pipe stresses affect the behaviours of round holes and circumferential cracks, but not that of longitudinal cracks; and (5) the effect of pressure on a leak opening increases exponentially with increasing hole diameter or crack length. An equation is proposed for modelling the effect of pressure on individual leaks.     

A new development in locating leaks in sanitary sewers

A new method called focused electrode leak location system (FELL-41) was developed in Europe for identifying potential leaks in sanitary sewers (mainline and service connections at the mainline). The chief advantages of the FELL-41 technology include: (1) identifying leaking joints on mainline during dry weather; (2) prioritising leak repairs by intensity of leaks; (3) determining leaks in service lateral mainline connections; (4) an alternative to air-pressure testing for acceptance of new and rehabilitated sanitary sewers. The FELL-41 method measures electrical current flow between a probe that travels in the pipe and a surface electrode. Pipe defects that allow liquids to flow into or out of the pipe cause a spike in the electrical signal, thereby locating the sources of infiltration or exfiltration. The intensity of the measured current can be correlated to the magnitude of the leaks. The purpose of this paper is to discuss this technology as well as its limitations. The results of the FELL-41 technology will be validated through several case studies.     

Leakage detection in a real distribution network using a SOM

One great challenge for waterworks is effective leakage detection. This paper presents a method based on the self-organising map for leakage detection in a water distribution network. The data used for training and validating the test results consist of vectors of the flow meter readings and knowledge of reported leak locations. The most important factor facilitating the self-organising-map-based modelling of leaks is the developed leak function. The results of the experiments presented show that the model trained on flow data can detect leaks in a defined distribution network area.     

Water pipeline failure detection using distributed relative pressure and temperature measurements and anomaly detection algorithms

This paper presents the validation of a novel leak detection method for water distribution pipelines, although it could be applied to any buried pressurized fluid flow pipe. The detection method is based on a relative pressure sensor attached non-invasively to the outside of the pipe combined with temperature difference measurements between the pipe wall and the soil. Moreover, this paper proposes an anomaly detection algorithm, originally developed for monitoring website traffic data, which differentiates a ‘leak’ event from ‘normal’ pressure change events. It is compared to two more commonly used methods based on a fixed threshold and a moving average. The validation of the new system in a field trial over a 6-month period showed that all the known leaks were identified with 98.45% accuracy, with the anomaly detection algorithm performing best, making this system a real contender for leak detection in pipes.     

Quantification of groundwater infiltration and surface water inflows in urban sewer networks based on a multiple model approach

The management of sewer systems requires information about discharge and variability of typical wastewater sources in urban catchments. Especially the infiltration of groundwater and the inflow of surface water (I/I) are important for making decisions about the rehabilitation and operation of sewer networks. This paper presents a methodology to identify I/I and estimate its quantity. For each flow fraction in sewer networks, an individual model approach is formulated whose parameters are optimised by the method of least squares. This method was applied to estimate the contributions to the wastewater flow in the sewer system of the City of Dresden (Germany), where data availability is good. Absolute flows of I/I and their temporal variations are estimated. Further information on the characteristics of infiltration is gained by clustering and grouping sewer pipes according to the attributes construction year and groundwater influence and relating these resulting classes to infiltration behaviour. Further, it is shown that condition classes based on CCTV-data can be used to estimate the infiltration potential of sewer pipes.     

塑料管道磨损性破坏事故的分析

PE、PVC管材因其优良特性而在流体输送系统中得到广泛应用，但其某些部位易发生破漏事故。介绍了PE输送矿砂系统与PVC输水系统短时间内发生多次漏损的案例，分析了磨损事故的原因，指出流体扰动对管壁的磨损是管道产生破漏的原因，其实质是管道设计的缺陷所致。     

Novel vibration-based technique for detecting water pipeline leakage

Exacerbating the imbalance between demand for freshwater and available water resources is the sub-optimal performance of water distribution systems, which are plagued with leaks that cause significant losses of treated freshwater. This paper presents an approach for leak detection that involves continuous monitoring of the changes in the correlation between surface acceleration measured at discrete locations along the pipeline length. A metric called leak detection index is formulated based on cross-spectral density of measured pipe surface accelerations for detecting the onset and assessing the severity of leaks. The proposed non-invasive approach requires minimal human intervention and works under normal operating conditions of the pipeline system without causing any operational disturbances. The approach is demonstrated on a 76 mm diameter polyvinyl chloride pipeline test system considering varying leak severities. The preliminary results presented in this paper seem promising and lead to several interesting questions that will require further research.     

Constrained Ant Colony Optimisation Algorithm for the layout and size optimisation of sanitary sewer networks

The incremental solution building capability of Ant Colony Optimisation Algorithm (ACOA) is used in this paper for the efficient layout and pipe size optimisation of sanitary sewer network. Layout and pipe size optimisation of sanitary sewer networks requires optimal determination of pipe locations, pipe diameters and pipe slopes leading to a highly constrained mixed-integer nonlinear programming (MINLP) problem presenting a challenge even to the modern heuristic search methods. A constrained version of ACOA equipped with a Tree Growing Algorithm (TGA) is proposed in this paper for the simultaneous layout and pipe size determination of sewer networks. The method is based on the assumption that a base layout including all possible links of the network is available. The TGA algorithm is used in an incremental manner to construct feasible tree-like layouts out of the base layout, while the constrained ACOA is used to optimally determine the cover depths of the constructed layout. Proposed formulation is used to solve three hypothetical test examples of different scales and the results are presented and compared with those produced by a conventional application of ACOA in which an ad-hoc engineering concept is used for layout determination. The results indicate the effectiveness and efficiency of the proposed method to optimally solve the problem of layout and size determination of sewer networks.     

Evaluation of uncertainties in sewer condition assessment

Closed Circuit Television Inspection is used since decades as industry standard for sewer system inspection and structural performance evaluation. In current practice, inspection data are helpful to support asset management decisions. However, the quality and uncertainty of sewer condition assessment is rarely questioned. This article presents a methodology to determine the probability to underestimate, overestimate or accurately estimate the real condition of a pipe using visual inspection. The approach is based on the analysis of double inspections of the same sewer pipes and has been tested using the extensive data-set of the city of Braunschweig in Germany. Results indicate that the probability to inspect correctly a pipe in poor condition is close to 80%. The probability to overestimate the condition of a pipe in bad condition (false negative) is 20% whereas the probability to underestimate the condition of a pipe in good condition (false positive) is 15%. Finally, sewer condition evaluation can be used to assess the general condition of the network with an excellent accuracy probably because the respective effects of false positive and false negative are buffered.     

污水管网的优化设计

对于污水管网的优化设计,采用了图论中树形结构的理论来描述污水管网,提出用三叉树的形式来处理污水管网的网络结构,把管段当作树的节点作为研究对象;利用树的遍历中的后序法(即节点递归算法)进行水力计算,在优化计算时采取了枚举标准管径法来选取管径,可以提高运算速度;在优化程序中寻求造价最低、最优的同时考虑了管道费用和泵站费用.采用Delphi语言编制了污水管网优化程序,并且用天津某一小区的污水管网对此程序进行了实例考核.其优化设计思路可推广到雨水管道.     

Characteristics of combined sewer overflows in Shanghai and selection of drainage systems

The overflow frequencies of combined sewer systems (CSSs) along Suzhou Creek in Shanghai are definitely lower compared with low interception ratio and design expectation. This noteworthy phenomenon was analysed and the results indicate that large sewer storage capacity due to a dense interconnection between sewer systems, flat pipe slope and pump drainage pattern, as well as the spatial–temporal difference of rainfall on a large catchment that is integrated by the connected network, lead to the overflow frequencies of combined sewer overflows (CSOs) along Suzhou Creek that are much less than those of designed and of Japanese counterparts. The drainage hydraulic model was used to simulate the performance of typical CSSs in Shanghai centre area to further explain the phenomenon. Meanwhile, as separate systems have serious illicit connections and are subject to heavy wet weather pollution in Shanghai, separate systems did not show the expected advantage in nonpoint pollution control. Thus, keeping old CSSs in the Shanghai downtown area seems to be of great value with respect to the control of urban non-point pollution.     

Data-mining analysis of in-sewer infiltration patterns: seasonal characteristics of clear water seepage into Brussels main sewers

Parasitic clear water infiltration is known to increase the waste water volumes in most sewerage systems. Amongst others, a problem arising from that is a significant variation of waste water pollutant concentration over time, which complicates the purification process and increases its cost. Capitalizing on new extensive databases, we propose a new method for the identification of clear water infiltration rates based on data-mining and data consolidation of long time data series. Based on a straightforward anthropogenic tracer, together with a simple but rigorous water budget, the infiltrated volumes are quantified day-by-day for the entire zone treated by a major waste water treatment plant. Brussels city is used as an example of the applicability of the method over several years, demonstrating the significant seasonal changes in sewer infiltration rates in the area and the progress achieved so far by structural sewer repair.     

Automated detection of sewer pipe defects in closed-circuit television images using deep learning techniques

Sanitary sewer systems are designed to collect and transport sanitary wastewater and stormwater. Pipe inspection is important in identifying both the type and location of pipe defects to maintain the normal sewer operations. Closed-circuit television (CCTV) has been commonly utilized for sewer pipe inspection. Currently, interpretation of the CCTV images is mostly conducted manually to identify the defect type and location, which is time-consuming, labor-intensive and inaccurate. Conventional computer vision techniques are explored for automated interpretation of CCTV images, but such process requires large amount of image pre-processing and the design of complex feature extractor for certain cases. In this study, an automated approach is developed for detecting sewer pipe defects based on a deep learning technique namely faster region-based convolutional neural network (faster R-CNN). The detection model is trained using 3000 images collected from CCTV inspection videos of sewer pipes. After training, the model is evaluated in terms of detection accuracy and computation cost using mean average precision (mAP), missing rate, detection speed and training time. The proposed approach is demonstrated to be applicable for detecting sewer pipe defects accurately with high accuracy and fast speed. In addition, a new model is constructed and several hyper-parameters are adjusted to study the influential factors of the proposed approach. The experiment results demonstrate that dataset size, initialization network type and training mode, and network hyper-parameters have influence on model performance. Specifically, the increase of dataset size and convolutional layers can improve the model accuracy. The adjustment of hyper-parameters such as filter dimensions or stride values contributes to higher detection accuracy, achieving an mAP of 83%. The study lays the foundation for applying deep learning techniques in sewer pipe defect detection as well as addressing similar issues for construction and facility management.     

An overview of the U.S. Environmental Protection Agency's storm and combined sewer program collection system research

A state-of-the-art and assessment of the USEPA'S Storm and Combined Sewer Program collection system research pertaining to management alternatives for wet- and dry-weather wastewater transport and interception is presented. These include: maintenance; catchbasins; new sewer design; sewer flushing; polymer injection; infiltration/inflow controls including inflow reduction. Insituform, impregnated concrete pipe and trenchless sewer; upstream storage/attenuation; flow routing and in-pipe storage; new types of flow regulators including swirl and helical bend regulator/concentrators, fluidic regulator and Hydrobrake; and a new rubber “duck-bill” tide gate. The emphasis is on optimal use of the existing sewerage system and optimal city-wide cost-effective strategy for the dual purpose of combined sewer drainage and overflow pollution control.     

大比降高速水流排水管水力计算

大比降排水管水流通常为高速水流,其水力设计已经超过排水设计规范范畴。以实际工程为例,指出该类管道不宜按照有压管路或明渠均匀流计算公式进行水力计算,应按照掺气水流计算,这为实际工程设计提供了参考依据。     

基于管道沉积物控制的CSOs污染负荷削减分析

管道沉积物是合流制排水系统溢流(CSOs)污染的重要来源,因此控制沉积物对于削减CSOs污染具有重要意义。在合流制排水系统截流泵站的上游管道中安装穿孔管,给穿孔管提供高压水产生7.5 m/s以上的射流以冲洗管道,同时在截流泵站内设置旋流分离系统来去除冲洗水中的沉积物。对于水层较浅、管径为DN400、管长为40 m、沉积层厚度为3 cm的管道,可使管道流中的SS从冲洗前的75～170 mg/L增加到2 500～3 000 mg/L,且在2～3 min内冲洗干净。旋流分离器对冲洗水中SS的去除率达到55.6%。两周一次的管道例行清洗维护,可使CSOs中污染物降低25%左右,减轻了受纳水体的污染负荷。     

Pipe network leak detection: comparison between statistical and machine learning techniques

ABSTRACT

This paper investigates an inverse analysis technique to find leaks in water networks and compares different solution strategies. Although a number of strategies have been proposed by different authors to identify leaks on a vast selection of pipe networks, limited research has been done to compare strategies and point out their weakness. Three strategies, a Bayesian probabilistic analysis, a support vector machine and, an artificial neural network were combined with the inverse analysis technique on different numerical and experimental networks to point out each strategy’s weakness. Two numerical networks are investigated and one experimental network. It is shown that the Bayesian probabilistic analysis struggles to find unique solutions when a few observations are available, while the support vector machine and the artificial neural network struggle when only flow measurements are available. Additionally it is shown that the artificial neural network struggles to estimate unique solutions for leak size and location.     

采用PVC-U缠绕管非开挖修复排水管道

在沧州北大街道路排水管道修复工程中，采用了PVC-U双平壁缠绕管，该管具有刚度大、壁厚小、内外壁平滑的特点，很适合用于排水管道的非开挖修复。该修复方法具有工期短、造价低、不破坏其他设施等优点，值得推广。     

城市供水管网漏损探讨

就漏损控制这一项复杂的系统工程，详细地介绍了我国城市供水管网的漏损现状，分析了进行漏损控制产生的效益，造成漏损的主要原因及防治措施，提出漏损量的大小是衡量供水管网技术技术和运行的重要指标。