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.

The ANSI/AWWA C150/A21.50 procedure used for calculating truck loads on buried Ductile Iron pipe, which is based on the teachings of Spangler and others, employs the same methods used in ANSI A21.1, the older design standard for Cast Iron pipe. The approach for calculating truck loading is adequate at any depth of cover. However, depths of cover less than 2.5 feet are generally not recommended under roads and highways due to the possibility of high dynamic loading. When 2.5 feet or more of cover cannot be provided, the procedure in ANSI/AWWA C150/A21.50 can still be applied. However, if impact factors higher than 1.5, which is incorporated in the standard, are anticipated, then such impact factors should be employed. Further, in those shallow covers, maintenance of the road surface over the pipe may be more of a concern than serviceability of the pipe.

We apply Fusion-Bonded Epoxy (FBE) coatings to ductile iron fittings in accordance with ANSI/AWWA C116/A21.16 (American National Standard for Protective Fusion-Bonded Epoxy Coatings for the Interior and Exterior Surfaces of Ductile-Iron and Gray-Iron Fittings for Water Supply Service). In AWWA C153 (the standard for Ductile Iron Compact Fittings), FBE is covered under section 4.3.4 (Fusion-bonded epoxy coating), which states "Fusion-bonded epoxy coatings shall be in accordance with ANSI/AWWA C116/A21.16 and shall be applied to interior and exterior surfaces."

The last revision of AWWA C110 (Ductile-Iron and Gray-Iron Fittings) was issued shortly prior to AWWA C116, so references to AWWA 116 (FBE) are not currently in AWWA C110. Wording regarding FBE similar to that currently in AWWA C153 has been requested for addition to AWWA C110 the next time it is revised in the year 2003.

No. FBE fittings are coated in accordance with ANSI/AWWA C116/A21.16 (American National Standard for Protective Fusion-Bonded Epoxy Coatings for the Interior and Exterior Surfaces of Ductile-Iron and Gray-Iron Fittings for Water Supply Service). AWWA C550 is the standard for protective epoxy interior coating of valves and hydrants. While the standards are not the same, we do use the same Fusion-Bonded Epoxy for valves and hydrants, and also use similar application processes. On valves, the FBE is normally applied using a fluidized bed process, whereas the FBE on fittings may be applied utilizing a fluidized bed process or an electrostatic spray process. The observed difference in appearance between valves and fittings probably relates to the different application methods used to apply the FBE. The electrostatic spray process tends to produce an “orange peel” texture on the surface.

Ductile Iron push-on and mechanical joints are covered in ANSI/AWWA C111/A21.11 "Rubber-Gasket Joints for Ductile-Iron Pressure Pipe and Fittings." Section 4.2.2 of that standard states: "The mechanical and push-on joints shall have the same pressure rating as the pipe or fitting of which they are a part." In other words, if the pipe is rated for 150 psi working pressure plus 100 psi surge (250 psi), so is the joint. If the pipe is rated for 350 psi working pressure plus 100 psi surge (450 psi), so is the joint.

This is not to say that Ductile Iron pipe and push-on and mechanical joints cannot be rated above 350 psi working pressure plus 100 psi surge (450 psi). Footnotes under Table 7 in ANSI/AWWA C151/A21.51 "Ductile-Iron Pipe, Centrifugally Cast, for Water" state: "Ductile Iron pipe for working pressures higher than 350 psi is available." There are numerous Ductile Iron pipelines operating at working pressures well in excess of 350 psi throughout the United States. Additionally, Ductile Iron’s push-on joints have been proven effective in actual tests and/or service with at least 1,000 psi internal pressure, 430 psi external pressure, and 14 psi negative air pressure with no leakage or infiltration.

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.

No. It's always a good practice to use the lubricant furnished by the manufacturer. Our lubricant is formulated to be nontoxic, does not support bacterial growth, has no deteriorating effects on the gasket material, and is water soluble so it readily flushes away prior to acceptance testing of the pipeline. It doesn't impart any taste or odor to the water in the pipeline, and meets the requirements of AWWA/ANSI C111/A21.11.

Because it is water soluble, it's sometimes difficult to maintain lubrication on wet surfaces such as a wet trench or stream crossing. In these conditions, it's advisable to apply the lubricant liberally – as much as three times as much as would normally be used.

We do not recommend the use of spray-on lubricants.

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. 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.