MANUFACTURING FAQS

Q: Why are manufacturers not producing mechanical joint pipe in some sizes?

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)

Q: When should non-sealcoated cement-mortar linings not be used for potable water service?

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)

Q: What is the pressure rating of flanged joints with standard ring or full-faced gaskets, and with specially designed gaskets?

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 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)

Q: If I order metric diameter pipe using the metric equivalent shown in certain tables in ANSI/AWWA C105/A21.5 and ANSI/AWWA C600, will I receive the equivalent English size? For example, if I order 152 mm diameter, will I receive 6-inch diameter Ductile Iron pipe?

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)

Q: Why is there a peen pattern on Ductile Iron pipe?

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)

Q: If I specify Ductile Iron pipe in accordance with ANSI/AWWA C115/A21.15, will the flanges be made of Ductile Iron?

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)

Q: Is Ductile Iron pipe in compliance with the National Sanitation Foundation (NSF) Standard 61, "Drinking Water System Components - Health Effects"?

A: Yes. All U.S. manufacturers of asphaltic seal-coated cement-mortar lined Ductile Iron pipe 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)