Journal of Pipeline Systems Engineering and Practice

To 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.

Plumbing-system designers, who routinely use Hunter’s curve for estimating domestic demand, actually solve complex problems based on the probabilistic approach. Recently, serious questions have arisen about the accuracy of Hunter’s curve. In some instances, using the curve to estimate the water-demand load has given highly inflated results. However, this consistent problem in applying the curve to design should in no way be interpreted as a criticism indicating that Hunter’s basic research and approach are incorrect. Many things have changed since 1940 when Roy B. Hunter’s BMS65 Methods of Estimating Loads in Plumbing Systems, was published as a national standard in the United States. In the context of water conservation, which should be the primary goal in the global water-stressed scenario, designers are giving importance to using low-water-use (demand) fixtures. Merely recommending the use of low-water-flow fixture cannot address the issue of water conservation. Hunter’s curve was based on 1940 high-flow fixtures with a very high confidence level (CL) of 99%. Hunter’s curve needs to be modified in this context. In the present study, to obtain the optimal water demand of the plumbing system, Hunter’s curve has been modified by incorporating low flow rates of modern fixtures, the reduced probability of a modern fixture being on at any moment, and reduced CL in the binomial probability function as used by Hunter. Low-flow fixtures will be meaningful when the demand calculations must also address the issue of water conservation, and in this context, this paper’s modified Hunter’s curve will address optimal design of plumbing systems thereby facilitating the conservative and sustainable use of water.

Concrete sewer pipes encounter corrosion as a predominant form of deterioration that reduces the service life of the pipeline system and increases the costs of maintenance and rehabilitation. Reliability analysis can help pipeline owners and sewer-system managers to predict the service life of the pipes and the time for repair or replacement. To include uncertainties in the reliability analysis, the corrosion process can be considered a stochastic process. This paper presents a stochastic gamma process model to account for temporal variability and uncertainties associated with the corrosion process in concrete sewer pipes that typically increase the probability of failure with the aging of the pipe. The proposed methodology is then applied to a specific concrete sewer system. The key element of the proposed method is the use of the gamma process concept. A gamma process can model the monotonic behavior of the ageing and deteriorating process. The application of the gamma process presented in this paper can potentially contribute to widening the use of stochastic processes for the modeling of structural degradation processes such as wear, fatigue, corrosion, crack, erosion, and creep.

By incorporating the variation of peak soil friction angle ($\varphi$) with mean principal stress (${\sigma }_m$), the effect of pipe diameter ($D$) on the vertical uplift resistance of a long horizontal pipeline embedded in sand has been investigated. The analysis has been performed by using the lower bound finite-element limit analysis in combination with nonlinear optimization. Three well-defined $\varphi$ versus ${\sigma }_m$ curves reported from literature for different sands have been used. It is observed that for a given embedment ratio, with an increase in pipe diameter, the magnitude of the uplift factor ($F_{\gamma }$) reduces quite significantly, which indicates the importance of considering scale effects while designing buried pipe lines. The scale effects have been found to become even more substantial with an increase in the embedment ratio. The analysis compares well with various theoretical results reported from literature. On the other hand, as compared to available centrifuge test results, the present analysis has been found to provide quite a higher magnitude of the uplift resistance when the theoretical prediction is based on peak soil friction angle. However, if the theoretical analysis is performed by using the friction angle that accounts for the progressive shear failure, the difference between the theoretical and centrifuge test results decreases quite significantly.

The total cost of a pumped water supply system includes the capital costs of the pipeline and pumping units, the replacement costs of various components included, and the energy costs related to the system’s operation. The capital cost of pipeline and energy cost are nonlinear functions of the pipe diameter. In addition, the pump characteristics, the replacement costs of components, and the escalating energy costs are of a nonlinear nature. In this paper, a nonlinear optimization model is developed to design a pumping main for required discharge, static head, pump characteristics, and economic parameters. The optimization model minimizes the total annual cost of the pumping main and pump, satisfying the pump characteristic curve equations. The applicability of the developed model is demonstrated with the help of a design example. The optimization model determines the optimal diameter of pumping main with pump efficiency for a required discharge or optimal discharge range with pump efficiency for an available diameter. The optimization model shows the effect of escalating costs of components and energy on the size of pumping main. Further, the model can also be used to determine the optimal operating conditions for a new pumping system or to evaluate an existing pumping system.

Longitudinal dispersion in pipelines leads to changes in the characteristics of contaminants. It is critical to quantify these changes because the contaminants travel through water networks or through chemical reactors. The essential characteristics of longitudinal dispersion in pipes can be described by the longitudinal dispersion coefficient. This paper presents the application of evolutionary gene expression programming (GEP) to develop new empirical formulas for the prediction of longitudinal dispersion coefficients in pipe flow using 220 experimental case studies of the dispersion coefficient with a $\mathsf{R}$ range of 2,000–500,000 spanning transitional and turbulent pipe flow. Gene expression programming is used to develop empirical relations between the longitudinal dispersion coefficient and various control variables, including the Reynolds number, the average velocity, the pipe friction coefficient, and the pipe diameter. Four GEP models are developed, and the weight and importance of each control variable is presented. The prediction uncertainties of all of the developed GEP models are quantified and compared with those of existing models. Finally, a parametric analysis is performed for further verification of the developed GEP models. The results indicate that the proposed relations are simple and can effectively evaluate the longitudinal dispersion coefficients in pipe flow.

This paper presents a methodology for evaluating fitness-for-service (i.e., safety, serviceability, and reliability) of corroded metal pipelines. A model for predicting pipe failure pressure is developed from a series of nonlinear finite-element analyses of metal pipes of different diameters and wall thicknesses with corrosion defects of different sizes and depths. The strength limit state (burst) and service limit states (yield and leakage) both are investigated in the pipe fitness-for-service analyses. Uncertainties associated with in situ measurement of flaw size, pipe geometry, pipe material properties, operating pressures, and corrosion in exposure environments are considered in a time-dependent reliability analysis of pipe performance over a service life of 50 years. Engineering variables that have the most significant impact on the reliability of a corroded pipe are identified through Monte Carlo–based sensitivity studies. Finally, a set of simple reliability-based evaluation tools are presented for assessing pipeline safety. The procedure and the results presented in this paper can be used to support decisions related to continued safe operation of pipes, optimal pipe inspection intervals, and maintenance schedules.

The integer discrete particle swarm algorithm is used as an optimization technique for the design of water distribution networks in order to minimize its total cost. Because the particle swarm is highly sensitive to its parameters and boundary conditions, the available restricted boundary conditions are applied. Also, a new boundary condition called the billiard boundary condition is introduced, which does not depend on the velocity clamping that mainly depends on human assumptions. The performance of the boundary conditions are tested under different populations, and a new initialization method by setting the initial position to one side of boundary solutions that is set to the maximum available diameter. The Newton-Raphson method is used as the hydraulic solver. The technique is applied to the optimal design of both the two-loop water distribution network, which is a well-known benchmark in the literature, and to a large-scale previously investigated two-source pipe network. The results show that the application of the integer discrete particle swarm algorithm with the proposed billiard boundary condition and initialization method in the least-cost design of water distribution networks is more effective when compared to others in reducing the pipe cost and the function evaluation number.