 |
 |
|
|
|
|||
|
|||||
|
|
TAPPING FAQS
Q: How many threads of engagement are required for direct tapping Ductile Iron pipe?
Q: How many threads of engagement are required for direct tapping Ductile Iron pipe?
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.
|
(in.) |
|
||||
|
|
|
|
|
|
|
|
|
|||||
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
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)
Q: Can the minimum available pressure class of Ductile Iron pipe be direct-tapped for service connections or do I need to use tapping saddles?
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 effect a water-tight tap. DIPRA has also conducted tapping tests on production 6-inch Class 50 (this pipe is now designated Special Class 50 in ANSI/AWWA C151/A21.51 Standard) Ductile Iron pipe, which has the same nominal wall thickness as the minimum pressure class pipe available, where material strength, among other factors, was examined. 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)