The Proportional Hazards Modeling of Water Main Failure Data Incorporating the Time-dependent Effects of Covariates

Proportional hazards models (PHMs) for the times between consecutive pipe breaks were constructed using case study water main break data. The 150 mm individual cast iron pipes in the case study water distribution system were categorized into seven groups according to the past break history to construct a distinct PHM for each group. During the modeling process the assumption of the proportional hazards of covariates was examined to include the time-dependent effects of covariates on the failure hazard in the models. By analyzing the baseline hazard rates, the hazards of the third through the seventh break were found to follow a form similar to a bath-tub. The estimated regression coefficients and the hazard ratios of the selected covariates were used to analyze the variations in the factors and their effects, including the time-dependent effects on the pipe failures. The changes in the relative hazards of the covariates were also analyzed according to the number of breaks. The constructed PHMs were verified by analyzing the deviance residuals of each model.     

Estimating the Timing of the Economical Replacement of Water Mains Based on the Predicted Pipe Break Times Using the Proportional Hazards Models

Deteriorated water mains fail frequently causing service disruption and other inconvenience to the customers. Therefore, the utilities must conduct repair, rehabilitation and/or replacement in a timely manner to satisfy the needs of the customers. To succeed in this process the utilities must also consider the economics of the water main maintenance. The proposed methodology presents not only a method for the optimal maintenance but also a practical way of conducting it by providing the economical time period of maintenance. A method is also presented for analyzing the accuracy of proportional hazards models (PHMs) in forecasting break times and estimating the timing for economical replacement of water mains. A survival probability criterion for the forecasting of the pipe breaks was determined in order to minimize the prediction errors of the PHMs. Subsequently, the criterion was used to estimate the upper and lower bounds of future break times of a water main using the survival functions derived from the PHMs. Two General Pipe Break Prediction Models (GPBMs) for a pipe were estimated for each of the two series of the recorded and predicted, upper and lower bound break times. The threshold break rate (TBR) was coupled with the two GPBMs for each pipe and solved for time to give the upper and lower bounds of the economical replacement time period.     

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.     

国外城市供水管道最佳更换时间预测的经验与借鉴

采用合理且经济的管网修复和更新策略,减少爆管事故的发生率,提高供水系统安全性,是目前管网运行中亟待解决的问题.通过借鉴美国城市供水管道更换时间预测的相关方法,将爆管发生率预测模型和极限爆管率模型相结合,建立换管时间预测模型,得出了确定最佳换管时间的方法.     

Evaluation of the Reliability of a Water Supply Network from Right-Censored and Left-Truncated Break Data

In this paper, we analyze failure data registered in a water supply network in order to evaluate the pipes failure probability. Only failures in normal operation conditions have been considered, excluding those caused by abnormal events. We consider an observation window from year 2000 until 2005, although the life of some of the water pipes started far in the past. This sampling scheme induces left-truncation into the data set (since failures before 2000 are not considered into the sample information) and right-censoring (for pipes that fail after 2005). We used an extended version of the Nelson–Aalen estimator, modified in order to accommodate left-truncation besides right-censoring (LTRC). Influencing factors on water pipes survival are identified. By the use of a semiparametric model based on the Cox proportional hazards model, also adapted to manage left-truncated and right-censored data, the effect of each factor over the failure risk of a pipe section has been estimated.     

Pipe Break Rate Assessment While Considering Physical and Operational Factors: A Methodology based on Global Positioning System and Data-Driven Techniques

An accurate prediction of pipes failure rate plays a substantial role in the management of Water Distribution Networks (WDNs). In this study, a field study was conducted to register pipes break and relevant causes in the WDN of Yazd City, Iran. In this way, 851 water pipes were incepted and localized by the Global Positioning System (GPS) apparatus. Then, 1033 failure cases were reported in the eight zones of understudy WDN during March-December 2014. Pipes break rate (BR_P) was calculated using the depth of pipe installation (h_P), number of failures (N_P), the pressure of water pipes in operation (P), and age of pipe (A_P). After completing a pipe break database, robust Artificial Intelligence models, namely Multivariate Adaptive Regression Spline (MARS), Gene-Expression Programming (GEP), and M5 Model Tree were employed to extract precise formulation for the pipes break rate estimation. Results of the proposed relationships demonstrated that the MARS model with Coefficient of Correlation (R) of 0.981 and Root Mean Square Error (RMSE) of 0.544 provided more satisfying efficiency than the M5 model (R?=?0.888 and RMSE?=?1.096). Furthermore, statistical results indicated that MARS and GEP models had comparatively at the same accuracy level. Explicit equations by Artificial Intelligence (AI) models were satisfactorily comparable with those obtained by literature review in terms of various conditions: physical, operational, and environmental factors and complexity of AI models. Through a probabilistic framework for the pipes break rate, the results of first-order reliability analysis indicated that the MARS technique had a highly satisfying performance when MARS-extracted-equation was assigned as a limit state function.

     

Modeling of Water Main Failure Rates Using the Log-linear ROCOF and the Power Law Process

This paper presents applications of the log-linear ROCOF and the power law process to model the failure rate and estimate the economically optimal replacement time of the individual pipes in a water distribution system. The performance of the two failure rate models is examined using the maximized log-likelihoods for different modeling approaches in which the method of observing failures differs. The optimal replacement time equations for the two models are developed by applying the methodology of Loganathan et al. (J Water Resour Plan Manage ASCE 128(4):271–279, 2002) for the case in which modified time scales are used. It was found that the log-linear ROCOF showed better performance than the power law process when the ‘failure-time-based’ method is used. Furthermore, the ‘failure-time-based’ method is proved to be superior compared to the ‘failure-number-based’ method for the water mains under study, implying that recording each failure time results in better modeling of the failure rate than observing failure numbers in some time intervals.     

高强钢岔管残余应力测试与研究——以呼和浩特抽水蓄能电站为例

呼和浩特抽水蓄能电站钢岔管首次采用国产790 MPa级B780CF高强钢制造,HD值达到4 140 m·m,是我国目前在建和已建水电工程HD值最大的钢岔管。采用x射线衍射法对钢岔管的焊接残余应力进行测试,测试成果为水道系统充水及钢岔管的长期安全稳定运行提供了技术分析和检验依据,同时也可以为工程应用及国内外同类型电站钢岔管的制造、安装有一定的指导和借鉴意义。     

PCCP管在河南省南水北调中线配套工程中的运用

随着我国对水资源的调整和分配,长距离引调水工程逐年增多。我国引进了大量的新型管材和新的生产工艺,为供水工程管材的选择提供了更多的余地。PCCP是近几年在供水工程中采用较多的新兴管材,本文以PCCP管材在河南省南水北调中线配套工程中的应用为例,从PCCP管材的结构组成、受力特性、设计成果以及施工安装技术要求等方面详细介绍其特点,为同类工程应用该种管材提供参考。     

引水隧洞压力钢管安装及洞内运输

随着我国水利、水电建设的快速发展,技术逐渐的成熟,引水隧洞压力钢管大力应用于水利、水电建设中。但是引水隧洞压力钢管大部分都是在洞内埋设,由于现在吊装的方法不完善,安装现场的场地、环境也不能满足施工的需要,影响施工安全的因素也很多,怎样顺利实现压力钢管的运输以及安装,需采取一些安全可靠、科学、合理的施工方法。本文较为详细地介绍了九甸峡水利枢纽压力钢管洞内安装及运输情况,重点介绍了斜管段钢管运输方式,并阐述了洞内运输的安全措施。     

基于层次分析法的长距离输水工程管材适应性评价

大口径长距离输水管道是当前水资源调配的主要手段,在保证水质、管材及线路选择、施工灵活性等方面相对于渠道输水有着较大优势.长输管道工程中管材的选择对工程的运行安全和工程造价至关重要.本文详细分析了钢管、预应力钢筒混凝土管等管材特点,基于层次分析法理论(AHP),建立了长距离输水工程管材适应性评价指标体系,以新疆某长距离输...     

三峡工程右岸电站压力钢管凑合节的整体安装

在凑合节整体安装理论研究成果指导下,经强化对凑合节相邻管口制造周长差、安装合拢口形态及中心相对差的控制,实行凑合节个性化设计,在钢管伸缩节室、上弯段与上斜直段接口、钢管与蜗壳接合部等3个因施工组织关系或工艺关系形成的合拢口实现了凑合节整体安装。实践证明,凑合节整体安装质量优良。     

玻璃钢夹砂管在坪上应急引水工程的应用

山西省坪上应急引水工程采用耐腐蚀性能好、水力性能优的玻璃纤维增强热固性树脂夹砂管作为输水管,由于该输水管的特点,在管道设计时要注意管径、工作压力、刚度、接口、坡降的确定。玻璃纤维增强热固性树脂夹砂管管路系统是一种复合材料的柔性系统,良好的安装施工是其安全运行的根本保证,因此在管道施工时要注意基础处理、管道安装及管道回填,工程竣工验收要按照《埋地给水排水玻璃纤维增强热固性树脂夹砂管管道工程施工及验收规程》执行,以确保工程施工质量。     

阀门结构在复杂引水管道中引起的自激振动

本文应用数值模拟方法，研究了因阀门密封失效，在串联管路，分支管路中产生自激振动的最大水压力，压力脉动的主频率，管长搭配对振动的影响。研究表明：在不利的管长搭配中，最大水压力能达到三倍静水头。在分支管路中，当分支管中的流量大于某一值时，自激振动就不会产生。     

球墨铸铁管安装工艺

球墨铸铁管广泛应用于城镇供水、排水、输气等工程。具有材料资源丰富、可再生、不污染环境,经济可靠、耐腐蚀、寿命可愈百年。介绍了球墨铸铁管安装工艺、水压试验工艺要求及土方回填工艺要求,具有推广价值。     

冷却管导热性能对混凝土坝后冷的影响分析

预埋冷却管通水冷却是混凝土坝主要的人工温控措施。采用大导热系数的金属管加快了冷却速度,但是成本高,施工费时费力;普通塑料(HDPE)管虽然成本低,但是导热性能差,延长了冷却时间。此文旨在通过分析冷却管的导热性能对混凝土冷却效果的影响,能为开发一种在技术和经济上兼优的冷却管提供参考。     

南水北调中线干线工程渠道逆止阀的施工工艺和质量控制

以南水北调鹤壁段第二施工标段为例,介绍了渠道逆止阀的安装工艺,如遵循＂基础开挖→回填第一层粗砂→埋置集水暗管→回填暗管周边粗砂→铺设保温板→铺设复合土工膜→安装逆止阀＂的施工流程;质量控制方法,如控制逆止阀安装位置、高程、数量等。     

Estimating the Cost and Carbon Impact of a Long Term Water Main Rehabilitation Strategy

Research has shown that some water utilities still have a strong preference for using “tried and true” open cut replacement techniques when rehabilitating water pipes in urban areas. Significant cost savings and reductions in carbon emissions can, however, be realised through the implementation of a strategy that incorporates trenchless rehabilitation techniques. This paper investigates the carbon emissions and financial implications of pipe rehabilitation strategies and analyses policies for three water utilities in Australia over a long-term planning horizon (30 years). When monetized, the carbon emissions from pipe rehabilitation are shown to be 0.1–0.2 % of the total revenue of a utility. However, given that direct and intangible cost reductions can be realised and there is a need to mitigate carbon emissions wherever possible, it is concluded that utilities should develop the capacity to use trenchless techniques in urban areas.     

基于组合权重的模糊物元模型在输水管材选型中的应用

在输调水工程中,管材选型问题具有模糊不相容和多目标性的特点,是工程技术人员面临的技术难题。建立了一种基于变异系数和层次分析法的模糊物元评价方法,分析了影响管材选择的各种指标,构建了管材类型选择的综合评价指标体系;引入了变异系数法修正层次分析法确定指标权重时的主观性,从而确定了评价指标的组合权重,建立了模糊物元评价模型,并利用欧式贴近度结合价值工程原理判断最优管型。在研究过程中,以新疆某引水管线工程的管材选型为例进行评价模型的工程应用,经计算可得最适宜该工程的管材类型为玻璃纤维增强塑料夹砂管(FRPM)。结果表明,利用本模型进行管材选型,可以根据实地工程条件以及管材技术特性,考虑技术、经济、施工、安全等多方面影响因素,选择出适宜本工程条件的最优管型。     

引水钢管焊缝缺陷应力影响特性分析

水电站引水钢管通常采用现场制造焊接,在焊接过程中易形成未焊透缺陷,给压力钢管运行带来不可忽视的危险.本文选取某电厂引水钢管,运用ANSYS有限元模型技术,对含未焊透焊接缺陷的厂房引水钢管进行有限元计算,深入分析未焊透缺陷对引水钢管强度的影响,分析缺陷处受力情况,对引水钢管安全运行具有重要意义.