Search results

The purpose of this paper is to inform facility managers of the type of failure affecting certain pipe types more than others. This is useful in asset management as preventive maintenance can be undertaken for those pipe types that experience high probabilities of failure.

The probability of a specific pipe type failing given the cause of break, age at failure, pipe diameter, and type of soil at the location of the break was found using inventory and main break data from the Honolulu Board of Water Supply (HBWS). Bayes’ theorem was then applied to find the posterior probabilities of failure starting from the prior probabilities of failure.

It was observed that the greatest probabilities of failure involved corrosion, pipes aged between 20‐30 years, 8″ pipes, and pipes in fill material. The pipe types were ranked and scored based on their probability of failing due to break cause, age, diameter, and soil type. Cast iron pipes were shown to have the highest probability of failing. As such, attention should be given to replace segments of cast iron pipes as they reach the end of their service lives.

This study serves to address a major query in asset management at a public utility, that of which pipes should be selected for replacement when they reach the end of their service life. In addition, this study helps to understand the causes of failure for the various types of pipe.

The importance of having reliable water supply at low cost has immense social implications in modern communities. To deliver such service, water pipe assets have to be managed efficiently.

This paper addresses the probability of failure in a straightforward manner that the water utility can easily apply to its own data, both in its design and asset management.

Simulation and analysis of a real main steam line break transient at the Thermal Power Plant Drmno are presented. The main events of the transient were the closure of isolation valves in front of a high pressure turbine, an opening of a by‐pass line, and subsequent pipe break in front of isolation valves. Intensive pressure waves were generated and they propagated through the pipe network of the steam line, causing high fluid dynamic forces on the structure. The transient has been simulated by the computer code TEA‐01, based on the Method Of Characteristics with three characteristic directions. Several main steam line boundary conditions have been modelled and verified. Numerical results are compared with plant data logger records. Simulation has been performed for various scenarios in order to investigate the plant behaviour sensitivity on the boundary conditions. The phenomenology of the pressure waves propagation and the influence of the boundary conditions on these processes are described in detail, as well as fluid dynamic forces during the closure of isolation valves and subsequent pipe break in a section of the steam line in the vicinity of the pipe break.

The purpose of this paper is to analyze conditional failure rates, and prioritize water pipelines for replacement based on their expected failure rate where pipes are grouped based on age and pipe type. Thus, predictions can be made on the expected number of breaks in future years.

The time to failure of a pipe can be characterized by the stochastic properties of the population as a whole, from which the likelihood of component failure is derived. When the corresponding failure rate is plotted against time, a bathtub‐shaped curve results. The bathtub curve assists in determining maintenance schedules depending on the age of the pipe. Failure rates help determine whether the rates are more than an acceptable best practice threshold to signal replacement.

Ductile iron pipes had the highest failure rates, followed by asbestos cement pipes; PVC and concrete cylinder pipes had the lowest failure rates, but because concrete cylinder pipes are very time‐consuming to repair and very expensive to install, only PVC pipes are recommended on the basis of this study. Cast iron pipes fit the bathtub shape; ductile iron and asbestos concrete were somewhat bathtub shaped, though the early phase period was not apparent; the bathtub curve for concrete cylinder was fully inverted; while PVC pipes showed zero probability of failure during the middle period. The shapes of bathtub curves drawn on conditional failure rates were similar to those for the failure rates. The bathtub curves indicate that the general failure performance of pipe materials is somewhat contrary to general principles in manufacturing.

Analysis of failure serves a practical purpose for water utilities to allocate funds for pipe maintenance and prepare a schedule for pipe replacement, so as to provide the best quality services and safe drinking water to users of the utility.

The proper prioritization of water supply pipes for repair and replacement is of great social importance to the public at large, which expends considerable funds to maintain their drinking water supply.

The study of bathtub curves has not been seen before in the analysis of water supply pipes. A unique discovery is that the traditional shape of the bathtub curve is not always applicable for water supply pipes.

The purpose of this paper is to investigate performance times from a quality engineering perspective for response and repair of pipes at a public utility. The objective is to scientifically determine the pipe that offers the most desirable downtime (DT) and time to repair (TTR).

Four types of water supply pipes – concrete cylinder (CC), cast iron (CI), ductile iron (DI), and polyvinyl chloride (PVC) – in prevalent use at the City and County of Honolulu Board of Water Supply were analyzed to determine the pipe type that is most consistently repaired to desired performance specifications. Data for mean downtime (MDT) and mean time to repair (MTTR) were used to evaluate the stability and capability of the repair processes for each pipe type. The analysis was completed through the use of control charts, operating characteristic (OC) curves, and process capability indices.

The results of the analysis indicated that CI pipes were the worst material in terms of DT and TTR. The control charts for MDT for all pipe types, and the MTTR for CI and CC pipes, were found to be out of statistical control, but the control charts for the MTTR of DI and PVC pipes were discovered to be in control. According to the OC curves, in which the hypothesis stated that the average MDT or MTTR was between the specification limits, there was a high tendency in all pipe types to accept the hypothesis when it was true. However, the probability of type I errors was high from operational standards at the USL level. Process capability analyses found that only CC pipes were able to meet performance design specifications; however, repair times are extremely large for CC pipes. Overall, it is recommended that CI pipes be replaced when the opportunity arises.

This investigation serves to address a major query in asset management at the public utility, that of which pipes should be selected during design and procurement from a maintenance perspective. In addition, the study helps to understand the trend of DT and TTR for the various pipes.

Quality water supply is of paramount social importance in modern cities.

A quality engineering approach to asset management for pipe systems at public utilities that serves to add a new dimension to asset performance analysis is adopted.

The purpose of this paper is to develop a systemic approach to evaluate physical condition of water pipeline infrastructure with limited condition assessment data that can help asset managers prioritize capital investments in maintenance projects for urban water pipeline systems.

Spatial pattern analyses are conducted in this research to find the spatial pattern of the service life of pipelines. Based on the spatial relationship, the critical areas where groups of pipelines with short service life are likely to be found were located using spatial statistical analyses. A visualized platform was also developed and used to validate the implementation of the proposed approach with the case study of urban water pipeline infrastructure in a city in the Midwest region of the USA.

The results of the spatial pattern analyses reveal that water pipelines are spatially clustered based on their service life. Further, it was found that on average the pipelines in the center of a city have longer service life while the average expected service life of the pipelines in the marginal areas is shorter. The interpolation method produced raster data with continuous information about the service years of pipelines that are useful for asset maintenance planning.

With the limited data, the proposed approach enables identification of the critical area of water pipelines with the likelihood of shorter service life. This result can be used as a priority rule for a rehabilitation plan and contributes to shifting from a responsive to a preventive approach in underground asset management.

Civil utility projects, both open-trench and trenchless, are subject to risk. These risks have both direct and indirect effect on project cost, schedule, quality and safety. It is therefore critical for the project management team to include risk management as an integral part of their project planning and execution. The purpose of this study is to identify the pipe-bursting construction risks and determine their probability of occurrence and cost impact and provide the appropriate responses to mitigate the identified risks.

This is an exploratory design using an industry-wide questionnaire survey to collect data on the probability of occurrence and impact of risks on cost of pipe-bursting projects. A probability-impact model was used to categorize the risks to determine their criticality and the appropriate risk responses.

The model revealed that majority of the analyzed risks have low impact-low probability of occurrence and high impact-low probability of occurrence. Undocumented repairs to host pipe was the only risk identified as having high probability of occurrence and high impact on cost. The risk responses suggest a combination of risk transfer, reduction and acceptance to be appropriately applied to mitigate the risks. A discussion on the good practices indicates that most pipe-bursting operations can be done safely and successfully if site and project conditions are known before bursting and the appropriate measures are taken to address those conditions.

Although the identified risks may apply to other utility construction methods, the focus of this research is limited to risks that occur during the construction phase of a pipe-bursting construction project.

Risk management is very critical to the success of any construction project. Identification and assessment of risks alone will not serve the purpose of risk management unless meaningful ways to mitigate those risks in a structured way are planned. The probability-impact model for the pipe-bursting construction risks with the mitigation strategies will help owners, engineers and contractors plan for and adequately respond to these risks. Additionally, a logical assessment of the risks will aid in effective decision-making regarding the management of the project.

Extensive literature review indicates that there is no existing literature on the probability of occurrence and impact on cost of risks in pipe-bursting projects. This paper presents the results of a wide-ranging analysis on construction risks in pipe-bursting projects. This is the first analysis incorporating the use of the probability-impact model to determine the criticality of various pipe-bursting construction risks.

Los Angeles, California, is facing record drought conditions. As a result, there is interest in all things related to building and maintaining water capabilities. Leaks in the infrastructure can lead to costly losses of water resources. Accordingly, attention increasingly is being devoted to water leak management. Using data available through the City of Los Angeles’ open data movement, the number of leaks is analyzed in order to study both the impact of temperature and whether the number of leaks is decreasing over time. Three different approaches for modeling the number of leaks, including regression, time series, and neural networks, are compared.

Poor quality in building projects is high and increasing. Poor quality can increase the cost of a building by up to more than 50% and can delay a project by up to 50%. This research investigated the poor quality of building elements/components.

The site operatives were requested to rate the frequency of poor quality in 25 building elements/components. The frequencies of the poor quality were scored on a five-point Likert scale, ranging from least often to extremely often. The survey forms were administered to construction site operatives by hand delivery.

The data revealed that poor quality occurred in more than 80% of the building projects completed. Approximately 40% of the cost of a building project is attributed to poor quality. In total, 70% of the respondents measured the poor quality of building elements as being high and frequent. The size and frequency of poor quality are higher in concrete, plaster, brick, foundations and roof trusses.

The research findings would help to reduce claims, disputes, maintenance costs and waste on sites.

This research provides fresh information on poor quality in building projects and provides a systemic process for anticipating poor quality in building projects. The findings also provide an option to increase maintenance span and a means to reduce claims and disputes in the construction sector.

The data structuring mechanisms provided by the current problem solving environment have been found to satisfy modeling the problem solutions for common decision making processes of a static nature, whereas problems of a complex nature (e.g. resource management and optimization) need an abstract data structuring mechanism capable of emulating real‐life objects (e.g. human managers). This paper explains the concept of developing a new data structure based on a semantic network called SYSTEM MAP and shows how this novel data structure can be used to model expert resource management systems of a particularly hierarchical type.

Deals with the dangers to computer systems from flooding and water‐related hazards which so far appear to have been underestimated, and offers preventive and remedial advice to companies which may find themselves in such a position.