A: Because buried Ductile Iron Pipelines are electrically discontinuous and are essentially grounded for their entire length, overhead AC power lines normally don’t impose corrosion or safety concerns.

A consequence of AC power lines and buried pipelines sharing rights-of-way is that AC voltages and currents can be induced by magnetic induction on the pipelines. The magnitude of the induced voltage and current on the pipeline is a function of a number of variables, including the length of pipeline paralleling the AC power line, the longitudinal resistance of the pipeline, and the resistance of the pipeline coating.

Ductile Iron Pipe is manufactured in nominal 18- and 20-foot lengths and employs a rubber-gasketed jointing system. These rubber-gasketed joints offer electrical resistance that can vary from a fraction of an ohm to several ohms but nevertheless is sufficient for Ductile Iron Pipelines to be considered electrically discontinuous. In effect, the rubber-gasketed joints normally segment the pipe, restricting its electrically continuous length, and prevent magnetic induction from being a problem. Also, in most cases, Ductile Iron Pipelines are installed bare with only a standard 1-mil asphaltic coating and therefore are effectively grounded for their entire length, which further prevents magnetic induction on the pipeline.

In corrosive environments, DIPRA and ductile iron pipe manufacturers recommend using loose polyethylene encasement rather than tight, bonded coatings. This encasement is not watertight—it overlaps at joints without sealing, allowing groundwater to seep in. Because moisture can exist between the wrap and pipe, and can conduct electricity to the soil at overlaps, the electrical resistance of the encasement is lower than that of bonded coatings. This lower resistance allows induced AC currents to safely return to ground, reducing corrosion risk.

During construction of Ductile Iron Pipelines in the vicinity of overhead AC power lines, certain safety precautions should be followed, e.g., “limit of approach” regulations governing construction equipment, grounding straps, chains attached to rubber-tired vehicles to provide a ground, grounding mats, etc., especially if safety concerns are heightened due to the use of joint bonding and dielectric coatings.
(Issue: Fall/Winter 2001)

A: Corrosion is the oxidation-reduction process by which metals are oxidized by oxygen in the presence of moisture. The Arrhenius equations show that reaction rates increase with temperature. The rule of thumb is that the rate of a reaction will double with every 18°F increase in temperature. Another factor is oxygen solubility. As temperature increases, the total solubility of oxygen in water decreases, and the rate of solution of oxygen increases. These lines cross at about 176°F, which is the temperature where corrosion is a maximum (available oxygen to fuel corrosion is at its maximum). For this reason, polyethylene encasement is recommended for any elevated temperature installation. The maximum operating temperature for linear low-density polyethylene is 180°F and 200°F for high-density cross-laminated polyethylene.
(Issue: Fall/Winter 2001)

A: Yes. The use of select, non-corrosive material (such as sand or limestone) for bedding and backfill is referred to as “trench improvement.” It is recognized that trench improvement generally provides good structural support and helps delay the onset of corrosion activity. However, experience has shown that trench improvement does not provide long-term protection to the pipe, particularly in highly aggressive soil environments. Permeation of native soil and moisture into the select backfill over time tends to make the select material take on corrosive properties. Therefore, trench improvement should not be used as the only method of corrosion control. Polyethylene encasement remains the most effective method for corrosion prevention of Ductile Iron Pipe.
(Issue: Spring/Summer 2001)

A: Cement-mortar linings. Cement-mortar linings have been successfully used to protect the interior of iron pipe and fittings since 1922. Cement linings prevent tuberculation by creating a high pH at the pipe wall and ultimately by providing a physical barrier to the water.
(Issue: Fall/Winter 2000)

A: Unless otherwise specified, Ductile Iron Pipe manufactured in accordance with ANSI/AWWA C151/A21.51 is supplied with an asphaltic coating approximately 1-mil thick. This coating, which is applied for aesthetic reasons, is used under normal conditions for both above and below ground applications. Typically, it’s used in aboveground applications such as pump stations, bridge crossings, and pipe on supports installations. For special aboveground conditions, other types of coatings – epoxies, for example – are available. Installations that might require such coatings are corrosive wet wells, chemical environments, etc. Furthermore, some installations require the pipe to be primed for finish paint coats. The type of coating specified by the purchaser might depend on several criteria such as resistance to a given environment, temperature resistance, impact resistance, resistance to sunlight, gloss retention, appearance, compatibility to finish coats, etc.

Although Ductile Iron and carbon steel are both ferrous metals, there are inherent differences between the two that preclude the use of the same surface preparation and application of coatings. Attempts to apply steel surface preparation specifications to Ductile Iron is inappropriate and may result in damage to the pipe surface with subsequent reduced coating effectiveness and life expectancy.
Most coating manufacturers require some type of surface preparation prior to application as a condition of warranty. Since their recommendation for surface preparation will vary depending on the type of paint and the ultimate service environment, the coating manufacturer’s technical data sheet should be consulted each time a special coating is used. Normally, recommendations given on coating manufacturer’s technical data sheets are for carbon steel and might not apply to Ductile Iron Pipe. Therefore, the pipe manufacturer should also be consulted regarding the type of coating, method of application, and type of surface preparation to be used. NAPF 500-03: Surface Preparation Standard.
(Issue: Fall/Winter 2000)

A: Ductile Iron Pipe and fittings are normally furnished with a cement-mortar lining conforming to ANSI/AWWA C104/A21.4. Cement-mortar-lined Ductile Iron Pipe can be used for certain wastewater applications such as non-acid-producing gravity sewers and sanitary sewer force mains that unquestionably flow full.

Microbiologically-induced corrosion, which is sometimes referred to as hydrogen sulfide (H2S) corrosion, can occur in gravity sewers. It occurs when bacteria in the anaerobic slime layer reduces existing sulfates to hydrogen sulfide. The H2S is liberated into the crown area of the pipe above the flow where Thiobacillus bacteria further metabolize the H2S into very low pH sulfuric acid. The sulfuric acid is corrosive to cement-mortar and iron.

This cannot occur in force mains where the pipe is flowing full. H2S cannot be liberated and sulfuric acid will not be produced. For such applications, cement-mortar linings are more than adequate. However, if the force main is acid-producing and air pockets are unavoidable in areas such as high elevations, special linings should be considered in those sections. Contact the DIPRA member companies regarding the most suitable lining.
(Issue: Fall/Winter 1999)

A: Yes. Cement-mortar-lined Ductile Iron Pipe can be used for certain wastewater applications. Ductile Iron pipe and fittings are normally furnished with a cement-mortar lining conforming to ANSI/AWWA C104/A21.4. While originally developed to prevent tuberculation in water mains, cement-mortar lining is also highly suitable for non-septic gravity sewers and sanitary sewer force mains. Long-term testing and experience of cement-mortar-lined iron pipe, both in the field and in the laboratory, have proven its effectiveness for these applications. In addition to the uses mentioned above, cement-mortar-lined Ductile Iron Pipe can also be used for seawater applications. Special linings are often recommended for Ductile Iron Pipe used to transport septic sewage where hydrogen sulfides create a corrosion-related problem. Please contact the DIPRA member companies regarding the most suitable lining for this condition or other special services.
(Issue: Spring/Summer 1999)

A: No. Because buried Ductile Iron Pipelines are electrically discontinuous and are essentially grounded for their entire length, underground electrical cables normally do not impose corrosion or safety concerns for Ductile Iron Pipelines. A consequence of underground electrical cables and buried pipelines sharing the same right-of-way is that AC voltages and currents can be induced on the pipelines by the expansion and contraction of magnetic fields. The magnitude of the induced voltage and current on the pipeline is a function of a number of variables, including the length of pipeline paralleling the underground electrical cable, the longitudinal resistance of the pipeline, and the resistance of the pipeline coating. Ductile Iron Pipe is manufactured in nominal 18- and 20-foot lengths and employs a rubber-gasketed jointing system. These rubber-gasketed joints offer electrical resistance that may vary from a fraction of an ohm to several ohms, but nevertheless is sufficient for Ductile Iron Pipelines to be considered electrically discontinuous. In effect, the rubber-gasketed joints segment the pipe and prevent magnetic induction from being a problem. Also, in most cases, Ductile Iron Pipelines are installed bare and are therefore essentially grounded for their entire length which further prevents magnetic induction on the pipeline. If, for some reason, a bonded-joint Ductile Iron Pipeline parallels an underground or overhead high-voltage AC power line, additional investigation may be warranted depending on the pipe coating (if any), length of parallelism, etc. AC voltages induced on a pipeline pose a shock hazard rather than a corrosion concern. Studies have concluded that AC current may cause corrosion at a rate that is only 1 percent or less than that of a similar electrical quantity of direct current. NACE RP0177-95, “Mitigation of Alternating Current and Lightning Effects on Metallic Structures and Corrosion Control Systems,” considers 15 volts AC open circuit to constitute an anticipated shock hazard.
(Issue: Fall/Winter 1998)

A: The physical properties of Gray and Ductile Iron Pipe do not change with time; therefore, corrosion (both external and internal) is the main factor that can affect the structural integrity of the pipe. Cement-mortar linings and special linings have effectively eliminated concerns with internal corrosion; however, older installations may not have been installed with these linings. The first source of information regarding the in-place condition of a pipeline is its break record. This record can supply information such as the number of breaks per unit length of pipeline, location of problem areas along the pipeline, and the type of failures (corrosion, structural, joint, etc.). A soil survey along the pipeline can determine if the soil is considered corrosive to Gray or Ductile Iron Pipe and can locate areas that may be more corrosive than others. From the soil survey and the break records data, a general assessment of the pipeline may be determined. This information may also help locate problem areas. Visual inspection is another method of assessing the condition of a pipeline. When utilizing this method, excavations are normally made along the pipeline at locations that are believed to be the most corrosive. The pipe is then inspected with a geologist’s hammer, scratch awl, or other tool to identify any graphitization present. If graphitization is present, it is then removed, and pit depths measured. Coupons can also be cut from the pipe and sandblasted to record possible pit depths on both the outside and inside diameters. Pipelines can also be internally inspected by remote control cameras. Non-destructive evaluation (NDE) of Gray and Ductile Iron Pipelines is a developing field offering several options and greater potential in the future.
(Issue: Fall/Winter 1998)

A: Properly designed and installed Ductile Iron Pipe systems could easily have a life expectancy of more than 100 years. Unlike other pipe materials, the physical properties of Ductile Iron Pipe do not change with age. If Ductile Iron Pipe is not subjected to loadings and pressures more than its original capabilities, the only factor that could shorten its life is corrosion. Internal corrosion has been effectively eliminated with the evolution of cement-mortar linings and other special linings. Also, not all soil environments are considered corrosive to iron pipe. This is evidenced by the fact that more than 600 utilities in the United States and Canada have had unprotected Cast Iron pipe that has provided service for 100 years or longer, and more than 25 utilities for more than 150 years. A common procedure used to determine if the soil is aggressive to iron pipe is the 10-point soil evaluation procedure outlined in Appendix A of the ANSI/AWWA C105/A21.5 Standard “Polyethylene Encasement for Ductile Iron Pipe Systems” or “The Design Decision Model” brochure. If the soil tests corrosive to Ductile Iron Pipe, then corrosion protection is warranted. V-Bio polyethylene encasement is the corrosion protection method normally recommended by the Ductile Iron Pipe Research Association and the manufacturers of Ductile Iron Pipe. If the soil is determined non-corrosive when tested in accordance with Appendix A of ANSI/AWWA C105/A21.5, or if it is determined corrosive and the pipe is encased with polyethylene in accordance with the standard, Ductile Iron Pipe could have a life expectancy of more than 100 years. If Ductile Iron Pipe is installed in aggressive environments without protection, its life expectancy would mainly be a function of that environment.
(Issue: Spring/Summer 1998)

A: No. The majority of soils found in North America are not considered corrosive to Ductile or Cast Iron. Therefore, in these soils, corrosion protection of any nature is not required. In soils that are considered corrosive to Ductile or Cast Iron, it has long since been proven that the use of sacrificial metal (i.e., additional wall thickness) for corrosion protection is neither reliable nor cost-effective. Additional sacrificial metal, at best, might increase the service life of the product by a few years, which is hardly any consolation to the user. Appendix A to ANSI/AWWA C105/A21.5 standard details an accepted procedure to determine whether the soil is considered potentially corrosive to Ductile or Cast Iron products. Effective, economical protection of Ductile and Cast Iron products in corrosive-soil environments can be achieved by simply encasing them in polyethylene at the trench in accordance with ANSI/AWWA C105/A21.5. This standard includes an approved method of encasing fittings.
(Issue: Fall/Winter 1997)

A: In general, polyethylene encasement can remain effective at sustained temperatures up to around 180° F. Polyethylene encasement softens around 200° F and melts around 220° F to 230° F. Sustained temperatures above 180° F may eventually cause the polyethylene film to become brittle and crack. Stabilizing antioxidants can be added to the film during manufacturing to increase this temperature. As long as the polyethylene encasement continues to prevent direct contact of the pipe with the corrosive soil, and prevent water transfer, it will remain an effective corrosion control system for Ductile Iron Pipelines.
(Issue: Fall/Winter 1997)

A: Because buried Ductile Iron Pipelines are electrically discontinuous and are essentially grounded for their entire length, overhead AC power lines normally don’t impose corrosion or safety concerns.

A consequence of AC power lines and buried pipelines sharing rights-of-way is that AC voltages and currents can be induced by magnetic induction on the pipelines. The magnitude of the induced voltage and current on the pipeline is a function of a number of variables, including the length of pipeline paralleling the AC power line, the longitudinal resistance of the pipeline, and the resistance of the pipeline coating.

Ductile Iron Pipe is manufactured in nominal 18- and 20-foot lengths and employs a rubber-gasketed jointing system. These rubber-gasketed joints offer electrical resistance that may vary from a fraction of an ohm to several ohms, but nevertheless is sufficient for Ductile Iron Pipelines to be considered electrically discontinuous. In effect, the rubber-gasketed joints segment the pipe and prevent magnetic induction from being a problem. Also, in most cases, Ductile Iron Pipelines are installed bare and are therefore essentially grounded for their entire length, which further prevents magnetic induction on the pipeline.

In corrosive environments, the Ductile Iron Pipe Research Association and the manufacturers of Ductile Iron Pipe recommend encasing the Ductile Iron Pipeline with loose polyethylene encasement rather than a tight, bonded coating. Polyethylene encasement is not designed to be a watertight system. The film is overlapped at pipe joints and not sealed; therefore, typically some ground water will seep beneath the wrap. Due to this normal presence of moisture between the film and pipe, and electrically conductive moisture paths to the adjacent soil at pipe joints where the film is overlapped, the coating resistance of loose polyethylene encasement will typically be less than that of a tight, bonded coating. This condition will allow induced AC current to return to ground.

During construction of Ductile Iron Pipelines in the vicinity of overhead AC power lines, certain safety precautions should be followed, e.g., “limit of approach” regulations governing construction equipment, grounding straps, or chains attached to rubber tired vehicles to provide a ground, etc.
(Issue: Fall/Winter 1994)

A: DIPRA’s concern with controlled density backfill products is their potential to be considered corrosive to Ductile Iron Pipe. Some literature published by the manufacturers of the material states that it is not corrosive because of its high pH and is therefore similar to concrete. However, the material usually contains a high percentage of fly ash and, unlike concrete, it is very porous.

Our laboratory has conducted tests on controlled density backfill products in accordance with Appendix A of the ANSI/AWWA C105/A21.5 Standard. The backfill materials did not test corrosive to Ductile Iron Pipe after allowing them to dry out/hydrate; however, after allowing water to soak into the samples (not re-mixing) the backfill materials tested potentially corrosive. Therefore, if the porosity of the material allows the interface between the backfill material and the pipe to experience the addition of moisture in the field, it could cause the material to be considered corrosive.

Another concern is the possibility that the pipe is not completely encased by the material. This would occur if the pipe were placed in the trench, and controlled density backfill material was then poured around the pipe. In this case, the bottom of the pipe would not be encased in the controlled density backfill. This would also occur at the interface where the controlled density backfill material is terminated. In either event, accelerated pH differential corrosion cells may develop because of backfill material having a pH which would normally be much higher than the native soil.

Another point is the possible presence of cinders in the material. Without question, cinders are corrosive to iron pipe. Therefore, if cinders are encountered or suspected, DIPRA would not recommend use of the material for backfill.

As a result, DIPRA considers controlled density backfill material to be potentially corrosive to Ductile Iron Pipe and recommends polyethylene encasement of the pipe in accordance with ANSI/AWWA C105/A21.5 whenever it is used. Care also should be taken to prevent the pipe from floating.
(Issue: Fall/Winter 1994)

A: No. Although studies have shown that this standard coating added to the annealing oxide layer on the outside surface of Ductile Iron Pipe have a positive impact on corrosion resistance, they should not be relied on to control corrosion in aggressive environments.  Primarily, the purpose of the asphaltic coating that is applied to the outside of Ductile Iron Pipe in accordance with ANSI/AWWA C151/A21.51 is to minimize atmospheric oxidation for aesthetic reasons. If soils are determined to be corrosive when tested in accordance with Appendix A of ANSI/AWWA C105/A21.5 or the Design Decision Model® (“DDM®”) DIPRA and its member companies recommend that corrosion control methods found in the DDM® be specified.  For the most part, this involves the application of polyethylene encasement in accordance with the AWWA C105 standard be installed for corrosion protection.
(Issue: Spring/Summer 1993)

A: The Moody diagram is employed to find the coefficient of friction (f) when using the Darcy-Weisbach formula to calculate energy loss (head loss) resulting from the flow of fluids. While the Darcy-Weisbach formula is widely used in academic circles, the Hazen-Williams formula is almost universally accepted by waterworks engineers in this country because it simplifies problem solution using calculators, tables, nomographs, and graphical charts.

Literature has been published regarding this issue. A.M. Friend, in his paper “Flow of Water in Pipelines,” which was presented at a national ASCE meeting, associated a roughness value (e) of 0.0004-feet to a “C” value of 140 for water flowing at 5 ft/sec in a 24-inch diameter pipe. Others have published roughness values of 0.000005-feet, 0.0001-feet, and “smooth pipe law applies” for centrifugally spun cement-mortar linings. Rather than using laboratory surface measurements or short-term flow test results, the roughness can be back-calculated using the Hazen-Williams “C” coefficient of 140 which has been established by many long-term flow tests of in-service pipelines conducted by DIPRA. However, when (e) is correlated to a Hazen-Williams “C” value, it varies with both the pipe diameter and flow velocity. Generally, (e) increases with increasing pipe diameter when holding velocity constant and decreases with increasing velocity when holding pipe diameter constant.

Back-calculating (e), using a velocity of 2.5 ft/sec and a Hazen-Williams “C” value of 140, yields values that range from approximately 0.0002-feet for 4-inch diameter pipe to 0.0006-feet for 64-inch diameter pipe. The relationship between (e) and pipe diameter is not quite linear and will vary with velocity.

A: The first cement-lined cast-iron (Gray Iron) pipe was installed in the water distribution system of Charleston, South Carolina, in 1922. Since then, many improvements have been made in the production of cement-lined iron pipe. In 1929, ASA Sectional Committee A21 on Cast Iron Pipe issued a tentative standard for cement-mortar linings. This standard was published by AWWA as a tentative standard in 1932. After various revisions and refinements, it was officially adopted by ASA in 1939 under the designation of A21.4 (AWWA C104) “Specifications for Cement-Mortar Lining for Cast Iron Pipe and Fittings.” By the early 1950s, cement-mortar linings were normally supplied with cast iron pipe. Cement-mortar-lined pipes are centrifugally lined at the factory to assure that the best possible quality control is maintained and that a uniform thickness of mortar is distributed throughout the entire length of the pipe.

Most of the cast iron pipe sold for waterworks service before the 1950s was provided with a hot-dip bituminous lining and coating. In those systems where the water was relatively hard and slightly alkaline, bituminous linings were generally satisfactory. Where soft-acid waters were encountered, however, problems occurred – such as the water being red or rusty and/or a gradual reduction in the flow rate through the pipe.  The need for a better pipe lining to combat tuberculation led to experiments and research with cement mortar as a lining material.

Today, such tuberculated Gray Iron pipe mains are readily-cleaned and cement-mortar lined in place. Water mains can be cleaned in place in a water distribution system by flushing or by using hydraulic-jets, fluid-propelled devices (pigging), and metal scrapers. AWWA C602 Standard for “Cement-Mortar Lining of Water Pipelines In Place – 4 in. and Larger” covers cement-mortar lining of pipelines in situ.

A: Normally, the maximum recommended flow velocity for cement-mortar-lined Ductile Iron Pipe is dependent on abrasion. Parameters involved in the abrasion phenomenon include flow velocity; the amount of solid particles; the size, shape, and hardness of the particles; the type of flow (turbulent or laminar); surface roughness and hardness of the lining; and the number of fittings per mile. Although the relative influence of these factors can be reasonably appreciated, there is no known equation able to predict abrasion resistance of different pipe materials in various situations. Inevitably, abrasion will occur at locations of changes in direction before it will occur along the length of a pipe barrel.

The abrasive characteristics of potable water are slight since this type of water contains limited amounts of solids and normally has velocities ranging from 2 to 10 fps. Cement-mortar-lined pipes in drinking water service for more than 77 years show no evidence of internal abrasion. In the absence of long-term laboratory testing, the available literature lists satisfactory performance for cement/cement-mortar linings for potable water with velocities of 20 to 40 fps. However, one has to realize that all installations do not perform the same. Different installations will have different configurations, bend angles, flow characteristics, amount and shape of solids content in the water, etc. Using a velocity of 20 fps and applying a safety factor of 2, remembering that the kinetic energy of a particle is a function of the square of the velocity, will result in a velocity of 14 fps. This should normally be a good conservative maximum design velocity for continuous service for most applications. Please contact DIPRA member companies when velocities greater than 14 fps are anticipated.

Cement-mortar linings’ resistance to abrasion is more important in drainage and sewage pipelines where solid particles are present. In these applications, the size, shape, and hardness of the particles will greatly influence the abrasion rate. Again, cement-mortar lined pipe continues to perform satisfactorily in this type of service.

A: No, you do not need to specify that the pipe be lined. The 1996 revision of ANSI/AWWA C151/A21.51, Section 4.3.2 made the cement-mortar lining the standard lining for Ductile iron pipe. Therefore, unless otherwise specified, pipe ordered in accordance with ANSI/AWWA C151/A21.51 will be supplied with a cement-mortar lining.  It is still good practice to specify that cement-mortar linings be provided in accordance with the latest revision of ANSI/AWWA C104/A21.4, “Cement-Mortar Lining for Ductile-Iron Pipe and Fittings.”

A: There is very limited data on the friction loss of C110 as compared to C153 fittings. Data that is available indicates that they are approximately the same. In general, C110 fittings have a larger bend radius than C153 fittings; however, C153 fittings have a larger inside diameter than C110 fittings. It is believed that for engineering calculations, these two differences can be considered to off-set each other and their friction loss considered the same. Because fittings normally result in a small percentage of the friction loss in a piping system, any error that may exist from this assumption should not affect the design or operation of the system.

A: DIPRA and its predecessor, CIPRA, have long advocated a Hazen-Williams “C” value of 140 for use with cement-mortar lined Cast and Ductile Iron Pipe. This recommendation of a “C” value for design purposes is sound. Over the years, DIPRA has conducted flow tests on cement-mortar lined Cast and Ductile Iron Pipes in operational pipelines — new pipelines as well as those that have been in service for extended periods of time. These field tests have shown a “C” value of 140 to be realistic, and one that is maintained over time — even when transporting aggressive water. For additional information on this and related topics, request the following DIPRA brochures: “Cement-Mortar Linings for Ductile Iron Pipe” and “Hydraulic Analysis of Ductile Iron Pipe.”

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 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 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)

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)

Each of our member companies provide step-by-step guidelines on repairing cement lining.

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. 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 filled, it can be argued that external loads might understandably be transferred to the carrier pipe.

If Ductile iron pipe is pulled through a casing pipe, restrained joints are needed. Refer to our member companies for maximum allowable pulling forces on Ductile iron pipe restrained joints based on pipe size.

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.

A: Yes. Ductile Iron Pipe has been used for both directional drilling and microtunneling installations. 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. Horizontal Directional Drilling methods involve drilling a pilot hole a little larger than the outside diameter of the pipe bell. The Ductile Iron Pipe is then pulled through the hole using flexible restrained joints. Ductile iron pipe joint deflection capability allows the pipe assembly to act as a chain as it is pulled through the hole, releasing stresses at the joints and achieving a tight radius of curvature.

Refer to DIPRA’s technical brochure for more information on design and installation of DIP with HDD.

Also, specially designed and manufactured Ductile Iron Microtunneling Pipe is currently available. When the pipe is pulled into position, restrained joints are utilized.

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)

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)

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)

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. Pipe in diameters 3-inch to 12-inch are automatically considered gauged. 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)

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)

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)

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. Refer to DIPRA’s brochure “Gasket Materials Used for Ductile Iron Pipe in Water and Sewage Service” for more information on gasket selection in contaminated soils. 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)

A: Mechanical joint Ductile Iron Pipe is addressed only through 24-inch diameters in ANSI/AWWA C151/A21.51, “Ductile-Iron Pipe, Centrifugally Cast, For Water.” Mechanical joint pipe sizes 30-inch through 48-inch were eliminated from ANSI/AWWA C151/A21.51 during the 1991 revision process. This was done because of the predominate use of the less labor-intensive and labor-reliant push-on joint. Mechanical joint fittings are available in sizes 3-inch through 48-inch in accordance with ANSI/AWWA C110/A21.10, and ANSI/AWWA C153/A21.53.
(Issue: Spring/Summer 2001)

A: Cement-mortar linings may be furnished in accordance with ANSI/ AWWA C104/A21.4 “Cement-Mortar Linings for Ductile-Iron Pipe and Fittings for Water” with or without a seal coat. Only a few locations in this country have sufficiently aggressive waters to necessitate the use of seal coat. In these few locations, leachates from the uncoated cement lining can cause an undesirable rise in the pH of the water, particularly under low flow or stagnant conditions in small-diameter pipe. For this reason, the seal coat was retained as an optional requirement of the standard.

The purchaser of cement-mortar-lined pipe or fittings for use with water corrosive to cement, such as very soft water, should use the appropriate test to determine whether an uncoated lining will impart objectionable hardness or alkalinity to the water. The procedure outlined in Sec. 5.2.2.2 of ANSI/AWWA C104/A21.4, modified by the substitution of the water with which the pipe is to be used, is recommended.
(Issue: Fall/Winter 2000)

A: The pressure rating of flanged joints may not exceed the rating of the pipe or fitting of which they are a part. The maximum pressure rating of a flanged joint for water service is 250 psi. However, flanged joints in the 24-inch and smaller sizes may be rated for 350 psi with the use of ductile iron only flanges and special gaskets whose rating is supported by performance testing as described in Section 4.5 of ANSI/ AWWA C111/A21.11 Standard. These special gaskets incorporate one or more annular rings molded into the gasket to improve joint performance.
(Issue: Spring/Summer 1999)

A: Yes. The metric units shown in parentheses after the nominal pipe sizes in ANSI/AWWA C105/A21.5 and ANSI/AWWA C600 are “soft conversions,” meaning no physical change. This means that the pipe in question will not be sized differently in a metric project. Metric pipe manufactured to ISO standards (e.g. 150 mm), however, are physically different from those specified in ANSI/AWWA standards, with the exception of 54-, 60-, and 64-inch Ductile Iron Pipe.
(Issue: Fall/Winter 1998)

A: Ductile Iron Pipe is centrifugally cast by pouring molten iron against the inside wall of an externally cooled rotating metal mold. The deLavaud casting process incorporates a metal mold which has a peen pattern on its inside diameter. This peen pattern is transferred to the pipe during the casting process. There are a number of reasons why the mold has this peen pattern. Before casting each piece of pipe, an inoculating dry spray is distributed on the inside of the mold. The peen pattern on the mold acts as an anchor pattern that holds and evenly distributes the inoculant. This inoculant allows the iron to solidify in a slower fashion that increases nodule count, helps refine the grain and nodular size, minimizes carbides, and makes the pipe more easily annealed. The inoculant also acts as a deoxygenizer which ties up the oxygen on the surface of the mold, thereby preventing the formation of pin holes. The peen pattern also helps dispense thermal shock and additionally helps the mold pick up the molten iron by increasing surface friction between the mold and the iron as the mold is rotated. The chill-free dual wet spray casting process involves first spraying a binder on the inside of the mold followed by the inoculating dry spray. Because of the binder, no peen pattern is required to hold and evenly distribute the inoculant.
(Issue: Spring/Summer 1995)

A: Not necessarily. ANSI/AWWA C115/A21.15 “Flanged Ductile Iron Pipe With Ductile Iron or Gray Iron Threaded Flanges” permits the use of either Cast Iron or Ductile Iron flanges on Ductile Iron Pipe unless otherwise specified by the owner. Section III of the Foreword to ANSI/AWWA C115/A21.15 lists “the type of material to be used in the flanges” as one of several options that, if desired, must be specified on the purchase order. ANSI/AWWA C115/A21.15 is a standard, not a specification. Consequently, if Ductile Iron flanges are desired, that option must be so stated in the specifications and on the purchase order. Cast Iron flanges, like Cast Iron pipe, have a long and successful service history. However, DIPRA recommends the use of Ductile Iron flanges on Ductile Iron Pipe because of their superior strength and impact-resistance. For more information, request a copy of DIPRA’s “Product Advisory” from the Fall/Winter 1988 issue of the Ductile Iron Pipe News.
(Issue: Spring/Summer 1994)

A: Yes. All U.S. manufacturers of cement-mortar lined Ductile Iron Pipe with and without seal coat have had their products tested in accordance with NSF Standard 61. These products have been certified and found in compliance with all U.S. EPA Maximum Contaminant Levels (MCL).
(Issue: Spring/Summer 1993)

A: DIPRA has conducted extensive direct tapping tests on Ductile Iron Pipe. Many of these tests targeted the minimum wall thickness allowed by ANSI/AWWA C151/A21.51. The lowest number of full thread engagements in these tests was 1.26, which resulted in no leaks when pressurized to 500 psi. (Full thread engagement takes into account the curvature of the pipe and is always less than effective thread engagement.) Because of the confusion between full thread engagement and effective thread engagement, and nominal wall thickness and minimum wall thickness, it is simpler to relate to the maximum recommended direct tap size than the minimum number of threads. Based on DIPRA’s tests, the maximum recommended direct tap sizes, to ensure a water-tight tap, for 3- through 24-inch Ductile Iron Pipe are shown in the table below.

All classes of Ductile Iron Pipe 24 inches and larger in diameter can be direct tapped for 2-inch corporation stops. The cut-off at 2-inch diameter taps was chosen because most, if not all, tapping machines used to direct tap pressurized mains are limited to a maximum tap size of 2 inches.
(Issue: Fall/Winter 1998)

A: Extensive testing conducted by DIPRA on specially produced 6-inch Ductile Iron Pipe with the minimum wall thickness allowed by the ANSI/AWWA C151/A21.51 Standard, has shown that the minimum available pressure class Ductile Iron Pipe in all sizes can be direct-tapped with confidence for 3/4-inch service connections. Additionally, for 6-inch and larger Ductile Iron Pipe, the minimum available pressure class can also be direct-tapped for 1-inch service connections. In the tests, all taps (3/4- and 1-inch) achieved leak-free connections with internal pressure up to and including 500 psi. The use of two layers of pipe thread sealant tape is recommended on all direct taps made on Ductile Iron Pipe to minimize the torque required to affect a water-tight tap.

A: During pull-out and cantilever tests, such as might be experienced if a backhoe bucket were to grab a service line, the corporation stop — not the Ductile threaded connection — failed. For additional information on this topic, request the following DIPRA literature: “Tapping Tests on Ductile Iron Pipe” and “Direct Tapping Comparison Study: Ductile Iron Pipe vs. Polyvinyl Chloride Pipe.”
(Issue: Fall/Winter 1993)

A: DIPRA has conducted many tapping tests on ductile iron showing ductile has no tapping restrictions other than the size of the taps in order to get the AWWA required minimum tread count. Due to the strength and ductile nature of DIP it can be tapped much closer together and does not require any offsets. The only restriction would be the room required for equipment and future maintenance. https://dipra.org/docs/direct-tapping-350-ductile-iron-pipe

A: You do not need to remove the polyethylene encasement. It is recommended that you wrap two to three layers of polyethylene adhesive tape completely around the pipe to be cover the area where the tapping machine and chain will be mounted and, then tap directly through the tape. Saddles are much the same way tape around the area where the saddle is to be installed however, a hole needs to be cut for the gasket of the saddle to sit directly on the pipe. Please see our tapping brochure and reach out to your local DIPRA Regional Engineer for more information and direction if needed. https://dipra.org/technical-resources/design-steps/planning-and-design/pipe-features/tapping