INSTALLATION FAQS

Q: What is the purpose of the "testing allowance" in ANSI/AWWA C600?

A: ANSI/AWWA C600 "Installation of Ductile-Iron Water Mains and Their Appurtenances" requires that newly installed Ductile Iron water mains be hydrostatically tested at not less than 1.25 times the working pressure at the highest point along the test section and not less than 1.5 times the working pressure at the lowest point of testing.

After the air has been expelled and the valve or valves segregating the part of the system under test have been closed, pressure is then normally applied with a hand pump, gasoline-powered pump, or fire department pumping equipment for large lines. After the main has been brought up to test pressure, it is held at least two hours and the make-up water measured with a displacement meter or by pumping the water from a vessel of known volume. The make-up water is called the "testing allowance," and the allowable amount is a function of length of pipe tested, nominal diameter of the pipe, and the average test pressure. The hydrostatic pressure test helps to identify damaged or defective pipe, fittings, joints, valves, or hydrants, and also the security of the thrust restraint system.

The "testing allowance" is not a "leakage allowance." Properly installed Ductile Iron pipelines with properly assembled joints are bottle-tight and do not leak. The "testing allowance" is, however, a practical measure used to maintain the pressure, which might actually drop because of factors other than leakage, including trapped air, absorption of water by the cement lining, extension of restrained joints and other small pipe-soil movements, temperature variations during testing, etc.
(Issue: Spring/Summer 2002)

Q: Can cement-mortar linings be repaired in the field?

A: Yes. Section 4.6.2 of ANSI/AWWA C104/A21.4 "Cement-Mortar Lining for Ductile-Iron Pipe and Fittings for Water" addresses repair of defective or damaged areas of linings.

Repair is achieved by first cutting out the defective or damaged lining to the metal so that the edges of the lining not removed are reasonably perpendicular to the pipe wall or slightly undercut. A stiff mortar is then prepared, containing not less than one part of cement to two parts of sand, by volume. This mortar is applied to the cutout area and troweled smooth with adjoining lining. To provide for proper curing of patches by preventing too rapid of a moisture loss from the mortar, the patched area is normally seal-coated immediately after any surface water evaporates, or alternatively the area is kept moist (e.g. with wet rags or burlap over the area or with the ends of the pipe or fitting taped over with plastic film, etc.). Of course, in potable water-related applications, no patch or curing components should be used in the repair that would negatively affect health or water quality.
(Issue: Spring/Summer 2002)

Q: Should restrained joints always be used when installing pressurized Ductile Iron pipe through a casing pipe?

A: No. ANSI/AWWA C600 Standard does not contain this requirement but does provide guidance for casing/carrier pipe installations. Casing pipes should normally be 6- to 8-inches larger than the outside diameter of the Ductile Iron pipe bells. Insulating chocks, skids, or spacers normally should be placed on the Ductile Iron pipe (carrier pipe), or affixed to the casing, to ensure approximate centering of the carrier pipe within the casing pipe. In order to further stabilize the Ductile Iron pipe, normally the area between the casing pipe and the carrier pipe is partially filled with sand or grout. Such installations stabilize the Ductile Iron pipe and minimize any movement, flotation, or "snaking" that might occur within the casing pipe, with other influences outstanding. If the annulus is completely filled, it can be argued that external loads might understandably be transferred to the carrier pipe.

If restrained joints are needed to resist thrust forces on a Ductile Iron pipeline (for example, to anchor unblocked bends immediately outside the casing), and the required restrained length extends into a casing pipe, it would then be necessary to install restrained joint pipe into, and often extending completely through, the casing pipe. In normal buried service, the function of restrained joint pipe is to transfer thrust forces to the soil structure. Therefore, if the annular space between the two pipes is not grouted, the length of restrained pipe inside the casing should not normally be considered as part of the restrained length in a thrust calculation to balance the thrust force. When restrained joint pipe is installed through a casing pipe, and if axial thrust movement is a concern or would represent a problem, the restrained joints should normally be fully extended during installation to minimize "take-up."

Of course, if effectively designed thrust blocks are utilized to restrain thrust forces outside a casing, such thrust forces would not pull axially on joints through a casing pipe.
(Issue: Fall/Winter 2001)

Q: Can Ductile Iron pipe be used for directional drilling and other trenchless applications?

A: Yes. Ductile Iron pipe can, and has been used for both directional drilling and microtunneling installations. Standard (belled) Ductile Iron pipe, manufactured in accordance with ANSI/AWWA C151/A21.51, has been installed by utilities using various pipe pushing methods and directional drilling. The methods involve forming a hole a little larger than the outside diameter of the pipe joint. The Ductile Iron pipe is then pushed or pulled through the hole. When the pipe is pulled into position, restrained joints are utilized. Also, specially designed and manufactured Ductile Iron microtunneling pipe is currently available.
(Issue: Fall/Winter 1999)

Q: Can the spigot of a FASTITE^® push-on joint pipe be used in conjunction with a TYTON^® push-on joint bell and vice versa?

A: Yes. All Ductile Iron pipe marketed in North America is manufactured in accordance with ANSI/AWWA C151/A21.51 "Ductile-Iron Pipe, Centrifugally Cast, For Water." This standard requires factory gauging of the spigot end to ensure that the outside diameter of each spigot end falls within the tolerances stipulated in that standard. Therefore, all Ductile Iron pipe spigot ends are required to meet the same dimensional requirements specified in ANSI/AWWA C151/A21.51.

On the other hand, the FASTITE^® and the TYTON^® push-on joint designs are different. Consequently, the bell sockets are different and the gaskets are not interchangeable. Proper gaskets for both designs are readily available.
(Issue: Fall/Winter 1999)

Q: Does it matter which direction the bells face in reference to the direction of flow?

A: No. The design of the joint types available for Ductile Iron pipe results in a very "clean" interior joint surface, with no significant protrusions into the field of flow. Therefore, the direction of the bells is not functionally related to the direction of flow within the main. It is common practice -- but not mandatory -- to lay pipe with the bells facing the direction in which work is progressing. When the main is being laid up a slope, for example, the pipe is frequently laid with the bells facing uphill for ease of installation.
(Issue: Spring/Summer 1999)

Q: Some specifications call for field tests at 120 percent to 150 percent of the pressure rating of the Ductile Iron pipe. Is this proper?

A: Not necessarily. The appropriate standard for testing Ductile Iron pipe is ANSI/AWWA C600 "Installation of Ductile-Iron Water Mains and Their Appurtenances." Requirements to test beyond the suggestions in C600 may cause unnecessary and expensive over-design of the thrust restraint system or possible failure of the thrust restraint system (or excessive movement) if such high test pressures are not taken into account during the design. Additionally, possible damage might occur to valves and appurtenances that may be rated at lower pressures. For an example, assume a 12-inch Ductile Iron pipeline is to operate at 100 psi working pressure. In accordance with ANSI/AWWA C600, the test pressure should not be less than 150 psi (1.5 times the working pressure) at the point of testing and not less than 125 psi (1.25 times the working pressure) at the highest point along the test section. In addition, C600 states that the test pressure shall not exceed pipe or thrust restraint design pressures. For 12-inch diameter Ductile Iron pipe, the lowest pressure class available is 350 psi. A specification calling for a test pressure of 1.5 times the pressure rating of the Ductile Iron pipe would result in a test pressure of 525 psi. This would require thrust blocks to be larger and restrained joint systems to be longer than required. This could result in an unnecessarily proportional movement of the thrust restraint system, as well.
(Issue: Fall/Winter 1998)

Q: Occasionally I have found that cut pipe may be out-of-round to the degree that the joint will not make up. Is this normal, and if so, how can field rounding be accomplished?

A: The ANSI/AWWA C151/A21.51 manufacturing standard for Ductile Iron pipe requires factory gauging of the spigot end. Accordingly, pipes selected for cutting should be field gauged. An MJ gland inserted over the barrel might serve as a convenient indicator for this purpose. Some pipes, especially in the larger diameters, may be out-of-round to the degree that they will need to be rounded after cutting by jacking or other methods to facilitate making the joint. This is a normal occurrence and does not in any way affect the serviceability of Ductile Iron pipe. Instructions for rounding their products can be obtained from the pipe manufacturers.
(Issue: Fall/Winter 1997)

Q: DIPRA's pipe on supports design recommends a saddle support; however, I have seen many installations with pipe resting on rollers or even on flat surfaces (usually structural members) running perpendicular to the pipe, especially for small diameter pipelines. Is this OK?

A: Cradled supports, following the contour of the pipe, are recommended in order to minimize stress concentrations at the supports. The design is discussed in DIPRA's brochure "Design of Ductile Iron Pipe on Supports." If flat supports are utilized, much higher stress concentrations (in the order of a unit of magnitude or higher) can result. The amount of stress is dependent on pipe size, pipe wall thickness, type of support, distance between supports, location of supports along the pipe length, loading, etc. Formulas addressing these high stress concentrations for cylindrical shells and pipes have been published in technical literature. When applying these formulas to Ductile Iron pipe in aboveground installations, utilizing one support per length of pipe located immediately behind the bell, the resultant stresses normally are not considered critical for small diameters. However, the stress analysis is difficult and the results are rendered uncertain by doubtful boundary conditions; therefore, the ultimate responsibility of such a design rests with the design engineer. Supports should not be placed under spigots adjacent to bells, due to higher developed stresses and possible undesirable effects on joints. Also, flat supports are normally not used for underground installations due to possible high loadings.
(Issue: Spring/Summer 1996)

Q: How do I install Ductile Iron pipe in unstable soils - e.g., pipe on supports, restrained joint systems with anchors on each side of the unstable soil area, etc.?

A: One method of installing Ductile Iron pipe in unstable soils is to install the pipe on piers or pilings above or underground. Because of the flexibility of the joints, Ductile Iron pipe supported at intervals usually requires that at least one support be placed under each length of pipe for stability. For further information, request our brochure, "Design of Ductile Iron Pipe on Supports," and/or contact DIPRA member companies.

Another method is to lay restrained joint pipe through the unstable soil area and anchor the pipeline on both sides outside of said area. The anchoring may be achieved by means of concrete abutments, or by continuing the restrained joint pipe an adequate distance beyond the unstable soil. In such an installation, consideration needs to be given to - among other things - maximum joint deflections, maximum axial force, anchor design, etc. In some cases, the only consideration needed is the use of long-pattern sleeves on firm ground along with allowing the pipeline to settle.
(Issue: Fall/Winter 1994)

Q: What precautions should I take when installing Ductile Iron pipe in an area that is or might be contaminated with hydrocarbons?

A: Unlike some substitute materials, Ductile Iron pipe does not deteriorate and is impermeable when subjected to hydrocarbons. With a Ductile Iron pipe system, only the gasketed joints may be subject to permeation. However, due to the relatively small contact area between the gasket and potable water, permeation through Ductile Iron pipe gasketed joints is not likely to be a significant source of contamination unless the gasket is exposed to neat organic chemicals for long periods of time. This is evidenced in the report titled, "Permeation of Plastic Pipes by Organic Chemicals," by Jenkins of the University of California, Berkeley, and published in the August 1991 issue of Journal AWWA under the title "Contamination of Potable Water by Permeation of Plastic Pipe." The results of an extensive literature search together with a survey of U.S. water utilities revealed in this report that plastic pipe was the major piping material involved in permeation incidents with polybutylene, polyethylene, and polyvinyl chloride accounting for 43, 39, and 15 percent respectfully of all the incidents reported. No incident of permeation of Ductile Iron pipe and only one incident of permeation of gaskets was reported. Some gasket materials resist permeation and degradation from hydrocarbons better than others. While tests on other gasket materials show promise, the results to date indicate that fluorocarbon rubber gaskets are the most resistant to permeation. Gaskets of this material are available for use with Ductile Iron pipelines installed in areas contaminated by or susceptible to contamination by hydrocarbons. Soils contaminated with hydrocarbons should not adversely affect the performance of polyethylene encasement as a corrosion protection means for Ductile Iron pipe. Polyethylene encasement protects the pipe by preventing direct contact with corrosive soil. If this barrier is not violated, the corrosion protection system is not compromised. Although hydrocarbons will permeate the polyethylene they are not considered corrosive to iron pipe.
(Issue: Fall/Winter 1993)