A reference for pipe selection and design

Pipe forms the mostly invisible backbone of our infrastructure, supporting stormwater, wastewater, potable water, transportation, energy, and utility systems nationwide. Since several types of pipe may be suitable for a specific application, civil engineers often must consider a range of performance claims and specifications relative to construction and site factors, hydraulic characteristics, durability, life cycle costs, and safety, among other details. In addition, recent pipe design and manufacturing advancements in the highly competitive industry may change what you thought you knew about a certain type of pipe.

For these reasons, CE News requested some basic information from the associations representing the major types of pipe as a starting point for engineers in the selection and design process. Information from the six groups responding to our request is presented below:

• National Clay Pipe Institute;
• American Concrete Pipe Association;
• National Corrugated Steel Pipe Association;
• Ductile Iron Pipe Research Association;
• Fiberglass Tank & Pipe Institute; and
• Plastics Pipe Institute.

Additional information about each pipe type is available from each association’s website.


Vitrified clay pipe

A: The two most common misconceptions about VCP are that its joints leak and the pipe bodies are brittle, but much has changed with the pipe material over the years.

Inspection videos of pipe installed prior to 1960 often show infiltration. In the early 1900s, infiltration was considered to be a benefit to a system. The additional water helped to clean and flush the system. When compression joints were developed in the early 1960s, they provided for leak-free systems. Today’s factory-applied, compression joint technology has virtually eliminated infiltration.

Clay pipe, like other materials, can be damaged if mishandled, but the clay pipe manufactured today is made with carefully selected raw materials and modern manufacturing processes that make the pipe body stronger than ever.

Q: What applications and environments particularly favor the use of VCP?

A: VCP is used in gravity sewers. It is ideally suited to the aggressive environment found in most sanitary sewer systems because it is the only pipe that is inherently inert and unaffected by any chemical that might commonly be found in effluents or in the soils around a pipe. Sanitary sewers tend to be the deepest part of a municipality’s installed infrastructure and must have the longest lifecycle available. VCP has demonstrated the durability and reliability necessary to meet that need.

Q: What resources does the National Clay Pipe Institute (NCPI) have available for civil engineers wanting to learn more about specifying and using VCP?

A: The NCPI has all of the tools available to help an engineer understand the properties and practices that should be used when specifying VCP. Manuals, handbooks, a hydraulic calculator, technical papers, and training videos are all available through the association’s website. Also, the NCPI has technical representatives around the country that are available to discuss specific issues. Contact information can be found at www.ncpi.org.

Information contributed by National Clay Pipe Institute, P.O. Box 759, Lake Geneva, WI 53147, 262-248-9094, info@ncpi.org, www.ncpi.org.

Concrete

Q: What are some common misconceptions about reinforced concrete pipe (RCP)?

A: The most common misconceptions by the specifying and engineering communities are the following:

• Some specifiers may not consider using RCP because of the misconception that RCP may not be cost competitive when compared with other available piping products. Designers may overlook the need to consider and compare the total installed cost of piping products. The cost of the pipe, trench widths, bedding and backfill material quantities and quality, and testing required during installation and post-installation phases of the project should all be considered when estimating total installed cost of any piping product.
• Failure to realize that in many installation conditions, the RCP itself can provide as much as 85 percent to 90 percent of the structural capacity of the installation. RCP offers a unique benefit: The finished product is designed, manufactured, and structurally verified to carry the loads to be imposed upon it before it even leaves its plant of origin. Not only is RCP unquestionably structurally capable, it also provides an efficient conduit for stormwater or sanitary sewer flows. Conversely, flexible piping systems only provide a conduit as delivered to the jobsite and depend heavily on their structural component (the bedding and backfill material surrounding the pipe) to be constructed during the installation phase of the project.
• Some engineers may not understand that improvements to production techniques and manufacturing equipment, an improved commitment to quality control, and a close working relationship with gasket manufacturers have led to a much-improved joint performance of RCP installations. RCP manufacturers understand and agree that many storm and sanitary sewer applications require silt-tight or water-tight joints.
• As our infrastructure ages, and more emphasis is being placed upon managing precious assets, many communities are evaluating the condition of their piping systems. As this phenomenon grows, the RCP community is finding that many inspectors do not understand the difference between hairline cracks and structural distress or damage. As an industry, we are trying to educate the inspectors who may be required to evaluate pipe in the installed condition and explain the difference between hairline cracks, design cracks, and cracks that may require remediation.

Q: What applications and environments particularly favor the use of RCP?

A: The most common applications include: storm sewer and highway/roadway culverts, sanitary sewer trunk lines, low-head fluid transmission, and agricultural irrigation lines.

RCP is designed and manufactured to outperform other piping options in any environment that requires a long design life with little or no maintenance, requires the pipe to accommodate large structural loads (live truck/automobile or dead loads from deep fill height conditions), and requires efficient transport of storm runoff or sanitary flow.

Various design strengths (Class I—V) and installation combinations give the engineer or specifier the option of combining high quality backfill with a required lower-strength pipe, or a lower-quality pipe envelope combined with a higher-strength pipe design. This flexibility allows the designer to use the available site materials to best benefit the overall installation cost of the pipe system.

Q: What resources does the American Concrete Pipe Association (ACPA) have available for civil engineers wanting to learn more about specifying and using reinforced concrete pipe?

A: The best resources available are the technical marketing and promotional engineers that are employed by both the ACPA member companies and the ACPA itself. The ACPA currently has six civil engineers on staff; they are all registered professional engineers and have a great deal of experience in the civil engineering design field. Most ACPA member companies also have technical or marketing engineers on staff. These technical professionals are comprised of the brightest engineers in the piping industry.

The ACPA staff and our many member companies are always available to answer questions about RCP products, applications, designs, specifications, or installation. You can call us, or we will come to you; our industry is active in carrying information to the engineering and specifying communities through hundreds of technical "lunch and learn" seminars and many large, multi-target seminars held each year. For information about events in your area, visit the ACPA website at www.concrete-pipe.org.

The website is also a great resource for those who want to do their own research or are looking for design aids. It is filled with informative publications, technical design guidelines, and information about design software packages that are available to the engineering and specifying communities.

Information contributed by American Concrete Pipe Association, 1303 W. Walnut Hill Lane, Suite 305, Irving, TX 75038, 972-506-7216, info@concrete-pipe.org, www.concrete-pipe.org.

Corrugated steel pipe

A: CSP has the perception that it cannot be durable, strong, or hydraulically efficient. However, CSP coatings have been developed during the last few years that provide a service life in excess of 100 years in essentially all culvert and storm sewer environments. Since CSP is a flexible structure and depends on a soil-structure interaction, it can have higher fill heights and greater load capabilities than other drainage materials. Smooth interiors for CSP have been developed to provide hydraulic characteristics comparable with other smooth interior drainage systems. Today, CSP systems can be designed to handle fill heights of more than 100 feet, have a service life in excess of 100 years, and a Manning’s "n" of 0.012.

Q: What applications and environments particularly favor the use of CSP?

A: CSP can be a viable option in today’s short-span bridge replacement. Today’s coatings, long lengths, ease of installation, and hydraulic capacity make CSP a product of choice in bridge replacement. With the relatively light weight of corrugated steel structures, many two-lane bridge replacement applications can be preassembled and installed as a single-piece structure. Bridge closure time can be minimal through preassembly and ease of installation. Bottomless options for fish passage or other natural water course requirements are benefits as well. With spans as long as 80 feet, CSP provides design options that can handle large loads and provide superior economics compared with most other bridge alternatives.

With today’s peak discharge rates becoming increasingly greater, spiral rib and double-wall CSP are becoming the economic option of choice. These products can be furnished with coatings for enhanced durability, long lengths for ease of installation, and any type of fabricated fittings. Through the use of fabricated fittings, such as manholes, tees, and elbows, CSP can be manufactured to fit any site configuration. Under the current National Pollutant Discharge Elimination System requirements for controlled runoff release, underground detention or retention structures using CSP can provide the most site-adaptable storage facility with the lowest cost per cubic foot of storage.

CSP uses prime quality steel that is manufactured under applicable ASTM and AASHTO specifications and uses a minimum of 30 percent recycled material. When engineers or designers are working under the U.S. Green Building Council’s LEED rating system, they will find that CSP drainage, storm sewers, or detention systems provide them maximum points for recycled content design.

Q: What resources does the National Corrugated Steel Pipe Association (NCSPA) have available for civil engineers wanting to learn more about specifying and using CSP?

A: The NCSPA website, www.ncspa.org, is the foremost resource for CSP. This website has technical information on different products and their applications. Manufacturers of CSP are listed and are good sources for product availability, application to specific projects, technical information, and estimated material costs.

Specific design and installation resources are the Handbook of Steel Drainage & Highway Construction Products, which covers culvert, structural plate, and special application design; and Modern Sewer Design, covering design for storm drainage and storm storage systems. Modern Sewer Design is available on the website under the Technical tab. Most manufacturers have the handbooks available to their local designers. The Underground Stormwater Detention Design Program can be downloaded from the NCSPA website. In 2007, the CSP Design Manual will be completed and published. Many other technical bulletins and installation guidelines can be found on the NCSPA website as well.

CSP specifications on materials, manufacturing, testing, design, and installation are available from the American Association of State Highway and Transportation Officials (www.bookstore.transportation.org) and from ASTM (www.astm.org).

Information contributed by National Corrugated Steel Pipe Association, 14070 Proton Road, Suite 100, Dallas, TX 75244, 972-850-1907, info@ncspa.org, www.ncspa.org.

Ductile iron pipe

A: While most know about the tremendous strength of DIP, engineers and utilities are sometimes surprised regarding several aspects of DIP use. For example, while its nominal sizes range from 3- through 64-inch diameters, a properly designed pipeline will have an inside diameter that is greater than nominal and typically greater than the inside diameters of other pipes of the same nominal size. With its standard cement-mortar lining, which gives DIP a Hazen-Williams C factor of 140, the headloss when pumping through DIP is less than it is through other pipe materials—even those that tout C factors in excess of 140.

Other aspects of the use of DIP that may not be readily appreciated are that it can be cut in the field and that the joints provide ample deflection to allow the pipe to be routed with a minimal need for fittings. These features provide field-adaptability, save on installation costs, and simplify designs by eliminating the need for laying schedules that some materials require.

Also, DIP is an environmentally friendly pipe; its raw material is recycled scrap iron and steel and can be recycled itself when its service life is completed.

DIP can be installed using trenchless techniques such as horizontal directional drilling (HDD). It is not unusual for ductile iron utilities to contemplate using a substitute pipe material for short sections of their pipelines because of the need to install a section using HDD. These owners and engineers are then pleased to discover that DIP can be installed using HDD, letting them continue to rely on ductile iron in critical installations such as when crossing rivers, major highways, or environmentally sensitive areas.

Q: What applications and environments particularly favor the use of DIP?

A: DIP is used in water transmission and distribution pipelines, wastewater collection systems, and reclaimed water pipelines. Its strength and dependability are relied upon by thousands of utilities that believe reliable service cannot be discounted. While DIP shines under extreme loading conditions, it is a pipe that is useful in virtually all environments and conditions with proper design. In many soils, the corrosion resistance of as-manufactured ductile iron allows the pipe to provide an impressive service life without supplemental corrosion control. There are more than 600 utilities in North America that have had their cast iron pipe serve for 100 years or longer without supplemental corrosion control, more than 20 of which have enjoyed 150 years of service.

In aggressive environments, an effective, economical corrosion control is available that will provide a minimum service life of 100 years at a cost that affords real value. As explained below, the Design Decision Model was developed for that purpose.

Another attractive aspect of DIP is the fact that the pipe wall itself cannot be permeated by contaminants such as hydrocarbons that may leak into the ground. In such unfortunate exposures, permeation-resistant gaskets are available that will keep undesirable compounds out of the water and wastewater streams.

Q: What resources does the Ductile Iron Pipe Research Association (DIPRA) have available for civil engineers wanting to learn more about specifying and using DIP?

A: DIP is a highly standardized material, especially through the American Water Works Association (AWWA) and ASTM standards. Standards exist for manufacture, pipe wall thickness design, corrosion control, fittings, joints, and installation of DIP. Also available from AWWA is Manual M-41 Ductile-Iron Pipe and Fittings that, combined with the standards, cover almost every aspect of design and installation.

Additionally, DIPRA provides technical service to utilities and consultants. It offers technical expertise through its website, technical brochures, and direct contact with its home office and through its regional engineer program.

Information contributed by Ductile Iron Pipe Research Association, 245 Riverchase Parkway, East, Suite O, Birmingham, AL 35244, 205-402-8702, www.dipra.org.

Fiberglass pipe

A: Some common misconceptions about fiberglass pipe include the perception that design engineers lack knowledge of fiberglass pipe material, there is insufficient history on different fluid transmission applications, and it is more costly and requires special jobsite handling.

Regarding design engineer knowledge, nine out of 10 of ENR’s top 500 design firms are specifying fiberglass pipe for the municipal market. In addition, petroleum engineers have installed more than 100 million linear feet of underground fiberglass pipe and 450,000 underground fiberglass tanks in the United States. The latter applications include vehicle refueling facilities and crude oil production fields.

Fiberglass piping has a more than 40-year history, both worldwide and in the United States. In addition, fiberglass pipe has an 18-year U.S. history specific to the municipal sector, and it is estimated that there has been some 4 million linear feet installed in the United States. In the 1950s, centrifugal cast fiberglass pipe was first used in the crude oil production industry as a solution to sulfur corrosion problems. Also in the 1950s, the development of filament-wound pipe polyester, vinyl ester, and epoxy resins resulted in applications in the chemical industry. And later, in the mid-1960s, fiberglass piping was approved by building officials for municipal water, sewage, industrial, and underground flammable and combustible liquids such as gasoline and fuel oils. As a result, fiberglass piping can be found world wide and across the United States in fire fighting, seawater desalination water plants, power plants, chemical plants, chemical waste disposal, irrigation, and petroleum production/transportation and distribution, as well as in gravity and pressure drinking water and sewage applications.

Regarding misperceptions about cost, there are many factors to be considered when comparing pipe material costs. The total project cost should consider the ease and speed of installation, the capability to use lighter versus heavy jobsite equipment, and other construction factors. Further, cost evaluations should consider various factors, including lifecycle cost; operating cost differences, such as internal friction that affects pump sizing; and future maintenance cost. Thus, when estimating costs for fiberglass pipe, the initial cost of the project recognizes the advantages of its light weight and ease to install, and the total cost over the life of the project accounts for long life and lower operating and maintenance costs.

As for special jobsite handling, fiberglass is lighter than all other equivalent performance materials and up to one-tenth the weight of some equivalent strength pipe materials. Lighter weight permits the use of lower-cost handling equipment, transportation of pipe sections as long as 40 feet, and more pipe per truckload. Longer pipe lengths offer many advantages, including fewer joints, quicker installation time, and lower labor costs. Pipe joints are more susceptible to leaks than the pipe itself, thus fewer joints reduces the likelihood of a leak and testing time.

In summary, the misconceptions on design engineer knowledge, historical experience, high cost, and special jobsite handling have been overcome. As a result, today there are five, large-diameter fiberglass pipe manufacturers for the installation of sewer and water transmission applications in the United States.

Q: What applications and environments particularly favor the use of fiberglass pipe?

A: While fiberglass pipe may be applied universally in virtually any application, it is inherently corrosion resistant, possesses smooth interior/exterior walls, has a high strength-to-weight ratio, is lightweight, and has leak-free joints.
Overall, fiberglass pipe is designed for applications above ground, traditional direct bury, micro-tunneling, and slip-lining. It is available in diameters of 3 inches to 158 inches, in lengths up to 40 feet, and with pressure ratings up to 250 psi. In addition, up to 12-inch-diameter fiberglass reinforced epoxy pipe is produced in pressures up to 3,500 psi for down-hole tubing applications. Fiberglass reinforced epoxy pipe has been tested and approved to meet NSF (Standard No. 61) for the conveyance of potable water.

Fiberglass pipe interior is resistant to corrosion from hydrogen sulfide buildup, which is common inside sewage piping systems, particularly when there is a long residency time. And the fiberglass pipe exterior is resistant to corrosion from all corrosion elements found in soils, including de-ionized water, acids, and caustics.

Fiberglass pipe’s high strength-to-weight ratio and low-coefficient-of-friction smooth walls make it ideally suited for micro-tunneling and slip-lining applications; it will withstand the extreme jacking pressures to achieve long pipe pushes. And the low-coefficient-of-friction exterior walls and low-profile joints reduce the jacking pressures required. Further, the low-coefficient-of-friction interior wall compensates for interior diameter loss when slip-lining existing pipes.

The lightweight pipe with weight-to-strength ratios comparable to other heavier materials enables shipping and handling longer pipe lengths to and on the jobsite. Longer lengths result in cost savings for transportation, handling labor, and the fabrication of fewer joints.

Leak-free joints may be in the form of double bell couplings with full face-ribbed gaskets, double bell couplings with gaskets fitted in machined grooves, integral bell and spigot with one or two gaskets fitted in machined grooves, or gasketed couplings with restraining joints. The elastomeric gaskets are compatible with the contained fluid and surrounding environment. Further, fiberglass materials lend themselves to accurate machined grooves to retain the gasket material. All joints meet ASTM D4161 testing under simulated pressurized in-use conditions, including straight alignment, maximum angular rotation, and differential shear loading.

Q: What resources does the Fiberglass Tank & Pipe Institute (FTPI) have available for civil engineers wanting to learn more about specifying and using fiberglass pipe?

A: There are two handbooks for engineers that address both design and installation of municipal fiberglass pipe. One handbook, AWWA M45 Fiberglass Pipe Design, addresses design and is published by the American Water Works Association. The second handbook and video was cosponsored by the FTPI and addresses fiberglass pipe installation. It contains a Resource Manual for Video #6 and is published by the American Society of Civil Engineers Continuing Education program.

In addition, the FTPI’s website (www.fiberglasstankandpipe.com) links with fiberglass pipe manufacturers that will provide engineers with job lists detailing the projects installed to date and published technical information describing their products. Fiberglass pipe manufacturers also offer guide specifications to aid engineers that may not have had previous experience with their products.

Information contributed by Fiberglass Tank & Pipe Institute, 11150 S. Wilcrest Dr., Suite 101, Houston, TX 77099, 281-568-4100, sullycurra@aol.com, www.fiberglasstankandpipe.com.

Polyethylene pipe

A: Many design engineers and municipal specifiers believe PE pipe is a new construction product, when in fact PE pipe has been used for water and gas distribution and stormwater drainage for nearly a half century. Because the manufacturing process of polyethylene was not invented until 1951, PE pipe is thought not to have a long service life (such as 100 years). Yet research has shown no discernable drop in performance for solid-wall pressure PE pipe made in 1956 that is still under long-term pressure testing. Most recently, Grace Hsuan, Ph.D., of Drexel University, demonstrated a service life for PE drainage pipe in excess of 2,500 years.

There is also the misguided belief that PE pipe systems are more expensive than traditional materials. Yet contractors and design engineers have realized total installed savings from 15 percent to 40 percent compared with other pipe materials. Furthermore, this does not take into account service life, and PE pipe is impervious to corrosion, resistant to nearly all naturally occurring environments, and demonstrates superior abrasion resistance.

Lastly, some believe PE pipe is difficult to join. In reality, there are many different ways to join PE pipe, depending upon type and service. Options include heat fusion, electrofusion, mechanical fittings, and traditional bell and spigot.

Q: What applications and environments particularly favor the use of PE pipe?

A: PE pipe is the material of choice in applications where other pipe materials fail. Highly acidic or alkaline soils and flows do not attack PE pipe; thus, it is routinely specified in these harsh conditions and services. In systems where exfiltration of flow (water, sanitary sewer, and gas), or infiltration of leachate or soils (water and stormwater) is strictly forbidden, PE pipe systems, which have leak-free and water-tight joints, are a most economical choice. In today’s ecologically charged environment, preservation of water resources, protection of aquifers, and overall environmental safety make PE pipe a preferred material.

Although PE pipe is routinely installed using open-cut (trench) methods, the flexibility and monolithic pipe string of fused PE pipe (or long coil lengths of smaller diameters) does not require joint constraints, making it a natural choice for trenchless installation practices, including horizontal directional drilling, sliplining, and pipe bursting. Lastly, the relatively longer lengths of PE pipe (including 20-, 30-, 40-, and 50-foot lengths) compared with traditional pipe materials, lowers installation times and cost. Additionally, the long lengths reduce the number of joints per run of pipe, thereby further lowering potential joint problems.

Because of PE pipe’s versatility, features, and benefits, it is the only material routinely specified and used in every utility service, including natural gas distribution, potable water distribution, sanitary and forced sewer, stormwater management, electrical and communication conduit, hot and cold water plumbing, geothermal heating and cooling, and subsurface drainage. Other applications include oil and gas collection, methane and leachate collection for landfills, radiant heating, and industrial and mining slurries and flows.

Q: What resources does the Plastics Pipe Institute (PPI) have available for civil engineers wanting to learn more about specifying and using PE pipe?

A: For more than 50 years, the PPI, by itself and in conjunction with other national standards organizations and associations, has provided extensive information on applications and uses of PE pipe. Today, its website includes all of its documents available for free download, including model specifications and design guidance. The PPI Handbook of Polyethylene Pipe and the Corrugated Polyethylene Pipe Design Manual are available on the website and can also be downloaded for free. The PPI Handbook of Polyethylene Pipe is also available as a printed hardback book and is available for purchase here.

Other pertinent publications the PPI has contributed to are the American Water Works Association M55 - PE Pipe Design and Installation, the American Gas Association Plastic Pipe Manual, and the Residential PEX Water Supply Plumbing Systems Design Guide.

Information contributed by Plastics Pipe Institute, 105 Decker Ct., Suite 825, Irving, TX 75062, 469-499-1044, info@plasticpipe.org, www.plasticpipe.org.