Frequently Asked Questions (FAQs)

FAQs // Frequently Asked Questions (FAQs)

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.

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.

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.

Yes, Ductile Iron products can be successfully Glass lined. Glass lined pipe and fittings have been specified and utilized as a deterrent to interior build-up and clogging of problematic sludge and scum piping systems in wastewater and sewage treatment facilities for over 40 years. Not only is the excellent non-stick characteristic effective in combating the build-up of grease, sludge, and scum, but has been found to be the only deterrent to Struvite and Vivionite build-up as well.

Direct service taps may be made right through the polyethylene encasement. The preferred method is to apply two of three wraps of adhesive tape completely around the wrapped pipe to cover the area where the tapping machine and chain will be mounted. The corporation stop is installed directly through the tape and wrap. Although this method is effective in eliminating damage to the polyethylene during the tapping operation, the entire circumferential area should be inspected for damage and repaired if needed.

To install the gasket correctly in the groove in the bell, it must be uniformly distributed around the interior of the bell circumference. To do this, the gasket must be looped as it is initially placed in the bell. As a general rule:

4" through 12" gaskets generally require one loop. In cooler weather it may be easier to install the 10" and 12" gaskets using two loops placed at the twelve and six o'clock positions.

14" through 20" gaskets generally require two loops but three may be necessary, placed at the twelve and six o'clock positions.

24" through 36" gaskets generally require four loops, spaced approximately 90° apart. Put the bottom loop in first to prevent debris from being introduced into the joint.

42" and 48" gaskets generally require six loops, spaced equally around the circumference of the bell. Put the bottom loop in first to prevent debris from being introduced into the joint.

54" through 64" gaskets generally require eight loops, spaced equally around the circumference of the bell. Put the bottom loop in first to prevent debris from being introduced into the joint.

In cooler weather, it is usually a good idea to warm the gaskets before trying to install them or store them in a warm environment.

Never lubricate the gasket or gasket groove prior to installation of gasket into the bell.

Potable Water
This is by far the most common application for Ductile Iron Pipe. Because of its reliability and durability, it is the ideal choice for the transmission and distribution of potable water. The value of potable water is rapidly increasing. Water lost between the treatment plant and the customer’s meter is revenue lost. From the aspect of protecting the public health, it is vitally important to protect water quality from treatment to point of use. With the exception of some special linings for sewer service, virtually all of the products marketed by U.S. Pipe & Foundry are approved by the National Sanitation Foundation (NSF) for the conveyance of potable water.

Fire Protection
Historically, the primary purpose for developing a system to distribute water was for fighting fire. The concern for the protection of lives and property was paramount, even above that of providing water for drinking and sanitation. A fire protection system must be absolutely reliable and fully functional at all times. Factory Mutual is an insurance organization with a focus on risk management and the prevention of property loss. In that role, they are particularly interested in fire protection systems, most of which are 12" and smaller. Most of the products 12" and smaller marketed by U.S. Pipe and Foundry are approved by Factory Mutual for use in fire protection systems.

The National Fire Protection Association is a national organization that promulgates codes and standards dedicated to fire safety and prevention. It is common for one such body to recognize and accept standards written by another organization, and to incorporate them into their own. Many of the NFPA Standards for fire protection systems incorporate the same American Water Works Association Standards to which U.S. Pipe and Foundry manufactures its products.

Wastewater
Ductile Iron pipe and fittings are ideally suited for wastewater systems. Wastewater pipelines fall into two categories: gravity sewers and force mains. A leaking sewer line can spread contaminated wastewater to the groundwater system. Infiltration and inflow (I&I) can overburden the wastewater treatment plant, since every gallon flowing to the plant must be treated. Severe I&I also leads to extremely excessive treatment costs. It is important to specify and install a durable piping material with reliable joints. U.S. Pipe’s TYTON JOINT® and TR FLEX® Pipe joints are bottle-tight, preventing both I&I and exfiltration.

In a gravity sewer system, wastewater flows downhill through the force of gravity. Gravity systems generally do not flow full, which can lead to septic sewage transformations that can lead to hydrogen sulfide gas being converted to concentrated sulfuric acid, which is very aggressive toward cement mortar linings and Ductile Iron. In a properly designed and constructed gravity sewer system, there will be adequate slope to provide a self-cleaning velocity (generally accepted as 2 ft/sec.). Under these conditions, a standard cement mortar lining will provide adequate corrosion protection for the pipeline. For less than optimum conditions, PROTECTO 401™, a ceramic epoxy lining, is recommended.

Gravity sewers must often be installed at great depths in order to achieve adequate slope. The inherent strength of Ductile Iron enables it to withstand the external loads imposed by the earth at greater depths. As the gravity sewer increases in depth, it will reach a practical limit. At this point in the project, wastewater is collected at a pumping station. The discharge line from the pump station is then a force main, since the wastewater is pumped under pressure.

A sewer force main operates as a pressure line. It does not have to be installed to a precise grade. For maximum hydraulic efficiency it should flow full at all times. This generally requires air relief valves at all high spots in the pipeline. When the pipe is kept full, there is no opportunity for hydrogen sulfide gas to collect, which virtually eliminates the possibility of septic sewage transformations. A standard cement mortar lining is usually adequate to protect the pipeline. Other linings, such as PROTECTO 401™, are available if the designer so specifies.

Reclaimed Water
A reclaimed water pipeline conveys treated wastewater for beneficial re-use. Only products meeting the requirements for potable water should be specified for reclaimed water, since, ultimately, reclaimed water usually ends up in the potable water supply system.

Digester Gas - Not!
Ductile Iron pipe and fittings are not suitable for digester gas service; thus, U.S. Pipe will not knowingly supply products for such a project. At one time, the ANSI A21.52 and A21.14 standards governed the manufacture of Ductile Iron pipe and fittings (respectively) for gas service. These standards were withdrawn a number of years ago. Ductile Iron pipe for gas service was required to undergo special processing and testing. The equipment needed is no longer available at any U.S. Pipe facilities.

If external corrosion is a concern, the Ductile Iron Pipe Research Association (DIPRA) recommends the use of loose film polyethylene encasement, purchased and installed in accordance with AWWA C105. Polyethylene encasement is the most cost-effective means of mitigating external corrosion under the broadest range of possible conditions.

 The subject of external corrosion on underground metallic pipelines has been written about extensively, with many “experts” extolling the absolute necessity for elaborate corrosion control systems.  While the debate continues, two facts are often overlooked:

  1. Extensive soil surveys conducted by a multitude of agencies throughout the country indicate that only about 10% of the soils in the United States are aggressive toward ductile iron products.
  2. Loose film polyethylene encasement has over 45 years of service history protecting your investment in millions of feet of cast and ductile iron pipe.

Sometimes called "Polywrap," loose film polyethylene is inexpensive, easy to install, does not degrade in service and therefore, requires no maintenance.

You may sometimes encounter corrosive conditions so severe that you should consider methods other than polyethylene encasement. When in doubt, ask your U.S. Pipe Sales Representative to arrange a free consultation with a DIPRA Regional Engineer. DIPRA Regional Engineers are NACE International-certified Corrosion Specialists, and will help you make the right decision for your specific project requirements.

Internal Lining Systems

Holiday Test

Minimum Number of Coats

Minimum Thickness (MILS)

Average Thickness (MILS)

Unlined

-

0

-

-

Asphalt Lining

1

-

1

1

3

Cement Lining with Sealcoat

1

-

1

AWWA C104

-

Cement Lining without Sealcoat

1

-

0

-

-

Double Thick Cement Lining with Sealcoat

1

-

1

AWWA C104

-

Double Thick Cement Lining without Sealcoat

1

 

-

0

-

-

Protecto 401 Ceramin Epoxy Lining

5

2500 volts

1

35

40

Induron® Red Oxide Epoxy Primer

1

-

2

8

10

Tnemec® 140 - 1211 Red Oxide Primer

1

-

2

9

11

Induron® Ruff Stuff 3300 Epoxy

6

low volt wet sponge

2

20

24

 

1 NSF approved for drinking water 
2 Primer coat only applied at factory
3 Standard lining and coating for 4" - 24" fittings and valves
4 Conforming to AWWA C116
5 Sanitary sewer only
6 12" and greater, pipe and fittings

 

Select the link below to see our UL Listings.  For FM listings, email info@uspipe.com.   

UL Listings

 

USP recommends that only flexible joints be buried  i.e. Mechanical Joint, TYTON JOINT® and TR FLEX®.

Yes, any Ductile-Iron plain end pipe sized spigot (be it Ductile-Iron, Cast-Iron, Steel or PVC)  having the same AWWA diameter tolerance of Ductile-Iron, will fit and seal in a TR FLEX® or HP LOK®.

Double thickness cement mortar lining in accordance with ANSI/AWWA C104/A21.4, Section 4.7.2., with seal coat in accordance with section 4.11. The cement in the cement mortar lining shall conform to ASTM C150, Type V. The internal joint areas coming in contact with the seawater, the "wetted areas", should be coated with Induron PE-54 epoxy or they can be wrapped with Denso tape. Denso tape can be purchased through DENSO NORTH AMERICA, INC. in Houston, TX - Phone No. 281-821-3355 or www.densona.com.

Although there are differing opinions on this subject, a conservative maximum velocity for design purposes is 7 fps (feet per second).

The AWWA (American Water Works Association) standard for thickness design of ductile iron pipe is C150. The exercise for calculating the required thickness based on internal pressure includes a 100 psi allowance for surge pressure and a 2:1 safety factor. The surge pressure allowance is based on a 50 psi pressure rise for each foot of extinguished velocity, and the fact that most domestic water systems operate at approximately 2 fps.

Ductile Iron pipe may be rated as high as 350 psi service. A pipeline operating at 7 fps velocity could account for a 350 psi pressure surge (7fps X 50 psi/fps). Adding a potential surge pressure equal to the pressure rating of the pipe encroaches significantly on the safety factor. Exceeding 7 fps velocity could produce potentially damaging surge pressure.

The "service allowance" used in the design of Ductile Iron pipe is a holdover from the old Gray Iron pipe days. During that early period, it was called a "corrosion allowance" to offset any initial corrosion or minor surface imperfections that might occur.

With the advent of Ductile Iron pipe and polyethylene encasement for corrosion control, the corrosion allowance was retained for similar general conservatism but renamed as a service allowance.

The addition of a 0.08-inch service allowance, which is unique to Ductile Iron pipe, ensures that the actual wall thickness will always exceed the design thickness, thereby providing an additional margin of safety and dependability.

The external trench load in ANSI/AWWA C150/A21.50 consists of earth load plus truck load. The earth load on pipe increases as the depth of cover increases; the truck load increases as the depth of cover decreases. Therefore, the maximum depth of cover normally is limited by the earth load and the minimum depth of cover is limited by the truck load. For lower pressure classes of pipe in sizes 14 inches and larger installed in a Type 1 trench, this band of allowable depth of cover is limited, or even non-existent. Also, for higher pressure classes of pipe in sizes 14 inches and greater, it would normally be more economical to specify a better trench and a lower pressure class of pipe than a higher pressure class of pipe and a Type 1 trench. Improved bedding is desirable, particularly in larger pipe sizes, to improve uniformity of axial support under the haunches.

Yes. Both ANSI/AWWA C150/A21.50 and ANSI/AWWA C151/A21.51 state that Ductile Iron pipe is available for water working pressure greater than 350 psi. These standards also list Pressure Class and Special Thickness Class Ductile Iron pipe. The Pressure Class designations (150 psi to 350 psi) in the standards are based on a 2.0 safety factor times the sum of working pressure and 100 psi allowance of surge. This establishes a net thickness to which a service allowance of 0.08-inch and a casting tolerance (which is dependent on the diameter of the pipe) is added. Based on the same design criteria, 6-inch Special Thickness Class 56 Ductile Iron pipe would be rated at 1,726 psi internal working pressure. Special Thickness Classes of Ductile Iron pipe are normally specified only because of high external loads due to deep bury, high dynamic loading, etc.; however, Special Thickness Class Ductile Iron pipe has also been specified and installed in systems with working pressures greater than 1,000 psi. For information and limitations, contact the manufacturers of Ductile Iron pipe.

Appendix A of ANSI/AWWA C151/A21.51, Ductile Iron Pipe, Centrifugally Cast, for Water, contains the minimum metal wall thickness required for 2, 3, and 4 threads for different diameter threaded outlets and different diameter pipe. Information is given for both threads conforming to Standard ANSI/ASME B1.20.1 (a.k.a. National Pipe Thread (NPT), Iron Pipe Thread (IP), or Standard Taper Pipe Thread) and AWWA C800 (a.k.a. Mueller Thread, cc thread, Corp Stop Thread). To assure adequate metal thickness for a particular pipe diameter and Pressure or Thickness Class, it is necessary to subtract the casting tolerance found in the Table in Section 4.4.2 from the Nominal Metal Wall thickness found in Table 1 of ANSI/AWWA C151/A21.51.

Concerning the security of a two engaged threads engagement, the Ductile Iron Pipe Research Association (DIPRA) conducted a study of ¾-inch and 1-inch corporation stops direct tapped into 6" Pressure Class 350 pipe. The tests were conducted on pipe sections with less than nominal metal wall thickness. After multiple corporation stops were installed in each piece of pipe under city line pressure, the installations were observed for leakage through the threads.  The water pressure was then raised to 1,000 psi in an effort to fail the 6" pipe and threaded connection. Leakage was not observed at the threaded connection. These tests were conducted with and without 3-mil thread sealing tape applied to the threads of the corporation stop. The installed corporation stops were then subjected to pull-out and cantilever load tests.  In the pull-out tests, the corporation stop failed at loads in excess of 6,500 pounds of force. The pipe threads were undamaged in each of the three tests. In the cantilever load tests, the corporation stops failed at bending moments in excess of 385 foot-pounds of force. Again the threads in the ductile iron pipe wall were undamaged. 

It can be clearly seen that work crews can direct tap service connections into Pressure Class Ductile Iron pipe under pressure, effecting structurally secure, watertight seals. It is recommended that two layers of 3-mil thread sealant tape be applied to the corporation stop threads to achieve a watertight service connection using a minimal tightening torque.

The results of this study have been published by the Ductile Iron Pipe Research Association under the title Direct Tapping of 6-inch Pressure Class 350 Ductile Iron Pipe and is available through the Web Site http://www.dipra.org.