Is there a need today for education on proper installation practices of ductile iron pipe, and what practices or mistakes are you seeing in the field that cause installers and users problems?

Since ductile iron pipe was introduced in the early 1960s, AMERICAN has been proactive in educating our customers on its strength, flexibility and impact characteristics.  Shortly after ductile iron pipe hit the market, AMERICAN brought groups of customers to our Birmingham facilities for a plant tour. These customers were shown tensile tests, Charpy impact tests, and ring crushing tests. We even dropped a wrecking ball that weighed several tons onto ductile iron pipe to show that it wouldn’t shatter when mistreated like cast iron pipe did. Today’s ductile iron pipe is even better. But like any engineered material, there are limits to the abuse it can tolerate. It should be shipped, handled, and installed in a workman-like manner and in accordance with the standards for which it is designed if it is to provide the installer with the most economical installation and the user with the long life and dependability he is expecting. ANSI/AWWA C600, AWWA Standard for Installation of Ductile-Iron Water Mains and Their Appurtenances and AWWA M41, Ductile Iron Pipe and Fittings, are excellent instructional resources for anyone involved in the installation of ductile iron pipe, whether a contractor, an engineer, or an owner. These documents and ANSI/AWWA C151/A21.51, American National Standard for Ductile Iron Pipe Centrifugally Cast, for Water, contain virtually all of the instructional information needed for a successful installation.  These two documents contain information about most phases of pipe installation, including handling, trench types, depths of cover, installing, backfilling, and other details, including testing and disinfecting. Of course, AMERICAN also has available extensive literature regarding the installation of our pipe and fittings. To answer the second part of the question:  Yes, there are some mistakes we see in the field that unquestionably should be avoided. Many involve the use of either an improper trench type or a poorly prepared trench. The use of an improper trench type for the size and class of pipe at a required depth can result in damaged lining, excessive bending stress and/or excessive deflection in the pipe wall. ANSI/AWWA C151/A21.51 is very clear concerning this subject, showing pipe thickness and Pressure Class required for various depths of cover and trench types in Table 5 of the standard. The use of an improper trench type seems to happen most often when unanticipated field changes are required. When proper depth for a trench type is exceeded, then either a greater Pressure Class pipe should be used or the trench should be improved to accommodate the extra depth. Improper trench preparation is usually related to the trench bottom rather than to backfilling. One of the major sources of these problems occurs when the installer fails to remove rocks or other debris from the trench bottom. AWWA C600, Paragraph 3.2.5., requires that rock in the bottom and sides of the trench be eliminated for a clearance of at least 6 inches for 24-inch and smaller pipe and at least 9 inches for 30-inch and larger pipe. It further states that after the rock is removed, the trench bottom should be brought back up to grade with a layer of appropriate backfill material which is to be leveled and tamped into place. Rocks under and in direct contact with the pipe can act as stress risers and can cause spalling of cement linings and joint leaks. Even if rock is not involved, poor preparation of the trench bottom can result in uneven support of the pipe. AWWA C600 addresses this in Paragraph 3.2.4, stating that “dimensions of bell-hole depressions for push-on-type joints only need to be large enough to ensure that the pipe is not resting on the bells and is supported by the full length of the pipe barrel.” It continues in Paragraph 3.2.4.1 “...the trench bottom shall be true and even to provide support for the full length of the pipe barrel...” Poorly prepared, uneven trench bottoms can result in uneven settlement, excessive joint deflection, and even joint leakage in extreme cases. This seems to be especially true when pipes are being installed “backward”, i.e., installing bells over spigots rather than spigots into bells. When using this method, the installer should be sure that bell holes are not excessive and that the pipe is properly supported over its entire length, as required by C600. Another mistake we see does not have to do with trenching, but with joint assembly, particularly restrained joints. AMERICAN’s restrained joints for pipe and fittings are rated for 250-350 psi working pressure, depending on the type and size. These structures are designed with large safety factors and have been exhaustively tested to confirm their strength both in straight and deflected alignment. But the one factor that all of our design tests have in common is that joints are properly assembled.  If the joint is not properly assembled with the restraining elements properly positioned, the strength of the joint is compromised, and the probable result is leakage or failure during the hydrostatic pressure test, or subsequently at operating pressure. Once a joint is assembled, a visual examination or a check with a feeler gauge is excellent insurance that the joint is properly assembled and will perform under pressure as designed. Make no mistake about it, because of its inherent ruggedness and conservative design, ductile iron pipe can withstand internal and external loading better than any other pipe material out there. And AMERICAN’s joints complement these benefits to the owner and installer. Correct installation completes the picture to ensure maximum realization of these benefits.

Ben Helton, Technical Director, AMERICAN Cast Iron Pipe Company