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The pumping cost influence increases as the length and velocity of the line increase.
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    Calculating costsConsider pumping costs associated with the piping options. The proposal with the most long-term value to the owner should be chosen.Accounting for inside diameters and flow coefficients of pipe can lead to quantitative values for life cycle comparison, as shown here.

There are many costs associated with the planning, design, construction, operation, and maintenance of a pipeline. To make the best use of our dwindling public works dollars, all of these costs must be considered. Reports show that the nation's infrastructure continues to deteriorate and often funds are not available to make the necessary investments. In some municipalities, fines pile up and dollars are allocated to Band-Aid solutions rather than treating the root cause.

So, how did we get to this place? Some say traditional thinking and traditional products brought us here. Despite today's access to advanced technologies and superior products, collapses, overflows, and other costly events continue to occur. Money that could be directed toward building new infrastructure gets diverted, sometimes to more visible projects. The solution, or at least part of it, resides in sound investing today in solutions that will last a lifetime and beyond.

In evaluating the operation and maintenance of a forced pipeline for water, sewer, or other effluents, one of the largest recurring costs is electricity. Other major costs in delivering fluids via a pipeline are the purchase and operation of the system's pumps. Because of the differences in various pipe's hydraulic characteristics, a significant pumping cost saving may be achieved when smooth wall products are used in the pipeline.

The flow of the fluids through a pipeline is resisted by friction along the pipe interior. Smoother pipe wall surfaces cause less friction resulting in less head (pressure) loss. This translates into reduced horsepower requirements that can be satisfied by smaller, less expensive pumps with lower initial capital cost. The smaller pumps consume less electricity, creating daily savings. The present value of the future power savings can be determined to permit meaningful comparisons of total life cycle costs.

PIPE CHARACTERISTICS AND HEAD LOSS

In the pressure systems, the Hazen Williams flow factor (C) is often used in computations to calculate head loss due to friction. Various publications list Hazen Williams's friction values for different products.

The soundest economic analysis and comparison of alternatives considers short- and long-term costs. Investment decisions should not be based solely on which material is least expensive to put in the ground today. To evaluate the most economical piping alternative for a force main, both installed cost and pumping costs should be evaluated. As shown in the example calculation, smoother pipes will save pumping power costs compared to rougher materials. As the velocity of the line increases, the costs can become even more significant. In addition, initial capital cost for pumps also will be reduced due to the lower horsepower requirements.

It is important to look beyond the current project and base choices on the most economical decision for the owner, installer, and community for the long run. Many factors contribute to the costs that might not be evaluated in a traditional model. To obtain a true cost comparison, the present value of differential costs incurred throughout the sewer design life must be considered along with the installed cost.

Products with inherent corrosion resistance (long life), leak-free performance, and superior hydraulic characteristics (higher flow capacity) generally will provide the lowest life cycle cost in most sewer applications. Specify the products you truly need and document the cost saving advantages in your evaluation.

— Richard C. Turkopp, P.E., is vice president of engineering, and Kimberly H. Paggioli, P.E., is marketing manager with HOBAS Pipe USA, Houston.