It would be nice if specifying pipe were as simple as buying a pair of shoes—walk into a store to pick out the style you like and take it home.
Unfortunately, there are a lot more questions to answer in choosing pipe than picking the perfect pair of loafers. What's going to be running through the pipe? In what kind of climate and terrain will it operate? What local codes factor in? What's the budget? Luckily, the pipe industry and associations offer resources to guide you.
The decision-maker in public works pipe installations is usually an engineer within the agency or an outside consultant. This person must look at:
Application: Determine whether the pipe will be used to carry drinking water, transport sewage, drain stormwater, or serve some other purpose.
Cost: Budget constraints—a constant concern for all public works departments—may put one or more types of pipe out of reach, or motivate the specifier to make choices with an emphasis on reducing maintenance and extending pipe life.
Demands: The heaviness of the load placed on a pipe—how much sewage, wastewater, potable water, or other effluent passes through it in a given time period—will affect the installation's needed attributes, including hydraulic capacity.
Environmental conditions: An area's climate, soil conditions, vegetation, population, and other factors all contribute to the external demands placed on installed pipe.
Material: Each type of pipe available offers unique properties and installation requirements that makes it more suitable for some applications than for others. For example, concrete pipe's structural durability makes it more resistant to collapse than other materials, corrugated steel offers flexibility and strength, vitrified clay pipe is corrosion-resistant, high-density polyethylene (HDPE) is lightweight.
Most major utilities are guided by local codes and specifications that require them to choose a specific type or size of pipe for the application. While it may be convenient to have some of the decision already made, sometimes the limitation can be challenging.
“We have construction specifications that dictate type required,” said Chris Holmes, PE., senior engineer with Dayton, Ohio's public works department. “The complete specifications were last reviewed in 1990, and we are now in the process of a rewrite. Minor revisions occur as needed.”
Holmes said crews in his area have installed more than 50,000 linear feet of ductile iron pipe in the past five years, mostly in new construction, but also on miscellaneous replacement projects.
Larry Modlin, director of public works for Boiling Spring Lakes, N.C., said that the installation costs associated with concrete pipe put the material out of his budgetary range. “We use HDPE—NCDOT approved—with couplers in most cases,” he said. “We use some tar-coated, galvanized, corrugated metal on larger-diameter installations due to cost, and the contact with water that is heavy with tannic acids from the pines.” Modlin added that his agency also installs driveway culverts, which usually are galvanized, corrugated steel.
Linings are also an option to consider. If corrosion or abrasion is a concern, as might be the case with wastewater or sewage, one type of pipe might be specified, along with a liner that protects the pipe itself from damage. Naturally, specifying a liner will add to the upfront cost of an installation, but it can extend the life of a pipe, leading to long-term cost savings. Abresist Corp., an Urbana, Ind.-based manufacturer, is just one of the companies that offers such products. Their liners—fused cast basalt and ceramic products—increase a pipe's resistance to corrosive fluids and abrasive slurries.
The pipe industry is supported by a number of associations representing the different types of pipe from which a professional can choose. Most of these associations' members are manufacturers, joined together in the common goal of promoting their type of pipe over others. While each group understandably has a vested interested in its own type of pipe, each offers a wealth of resources for pipe specifiers to rely on when making a balanced, well-informed decision.
For example, the American Concrete Pipe Association (ACPA), like many other groups, runs a Web site containing resources and technical data, including design and specification guidance. The ACPA offers a number of “Buried Facts,” downloadable documents on topics such as culvert inspection, material durability, and least-cost analysis of bids. Most pipe association Web sites, such as the Plastics Pipe Institute site, discuss the use of pipe in different installations.
As public works dollars become increasingly scarce, manufacturers and pipe specifiers alike are working toward finding solutions that enable pipe users to get the most bang for the least number of bucks.
“In the past several years, we have seen a real shift in the industry, as far as owners and engineers accounting for the benefits of a particular product,” said Kimberly Paggioli, P.E., marketing manager for Houston-based HOBAS Pipe USA. “The emphasis is on total life cycle cost, and less on, ‘How cheaply can we get this project built?' With less money going toward infrastructure, and more need as the systems age, agencies are having to make sound investment decisions for the future.”
American Concrete Pipe Association
American Concrete Pressure Pipe Association
Cast Iron Soil Pipe Institute
Ductile Iron Pipe Research Association
National Clay Pipe Institute
National Corrugated Steel Pipe Association
Plastics Pipe Institute