Ductile Iron (DI pipe) was first used in the United States as early as the 1950s. Because iron pipe was one of the earliest pipe materials used in modern waterworks and wastewater systems, most early fittings and couplings were designed for Grey Cast and then Ductile iron pipe.
So, connecting “other” piping material to DI pipe is very straightforward on the Ductile side of the fitting. The most important item to consider is on the other material side of the connection.
The following information generally refers to pressure pipe applications starting at three inches in diameter and over. This also refers to connecting pipe in line, not a tap or branch connection.
DI pipe can easily connect to other materials in pressure applications using common fittings and specific fittings or couplings.
Mechanical Joint Fittings
One of the most common connections between DI pipe and other pipe is Mechanical Joint Fittings (MJ). Because DI pipe is manufactured to an industry-standard “Outside Diameter” (OD), all DI pipe will have the same OD for each size, regardless of manufacturer.
Since MJ fittings were originally designed for DI pipe, no special considerations are needed for the DI pipe side of the fitting.
When using MJ fittings on other pipe, if the pipe OD is not a Ductile iron pipe size, use special transition gaskets to make up the difference in pipe ODs.
What About Polyvinyl Chloride (PVC)?
As mentioned above, special transition gaskets are needed when connecting Iron Pipe Size (IPS) PVC pipe, IPS HDPE pipe, or steel pipe. You can find ODs in industry-standard OD charts. The OD reference, if not the actual OD, should also be clearly marked on the new pipe.
When connecting to any PVC pipe, pay close attention to the PVC pipe type and resulting OD before making the connection.
The PVC Pipe Association guide, “Making Sense of Diameter Types for PVC,” is a good reference for the type of pipe and resulting OD you may encounter.
If you use restraint at the fitting, take special care to ensure the correct restrainer is used for the correct pipe material. Using a DI restrainer on PVC pipe may damage the pipe. Using a PVC restrainer on DI pipe may not provide the proper torque needed to restrain the pipe.
High Density Polyethylene (HDPE) Pipe
If connecting High Density Polyethylene HDPE pipe, an MJ adapter or an internal “stiffener” will be required in the “Inside Diameter” (ID) of the HDPE pipe to support the MJ compression connection. Size this stiffener based on the (ID), wall thickness, or DR of the HDPE pipe being used.
Common examples of installations using different pipes in MJ fittings include a connection on a building fire riser or transitioning to and from HDPE for a directional drill. You can also transition from one pipe type to another at an MJ valve, the same way you would with an MJ fitting.
Transition Couplings
Many manufacturers make couplings, clamps, restrainers, fittings, and devices that connect DI pipe to other piping materials or fittings. Most couplings manufactured in the water works industry were originally designed for DI pipe and later used for other materials.
The coupling to be installed must first be the correct nominal pipe size and have the correct “range” for the pipes being connected. The OD of the pipe must be within the “minimum and maximum” OD range for the coupling.
This is true for the ductile iron side as well. The only consideration is to check the DI pipe OD to ensure it is within the correct OD range.
This is especially true if you have a large-diameter pipe or have cut the pipe you are connecting. For cut pipe 14 inches in diameter and larger, use pipe marked as “gauged,” if possible, and make sure any cuts are at least 2 feet from the bell. This should ensure that the pipe OD is within spec.
If possible, check the pipe in the field with an OD tape. You can also “field check” the pipe where you are going to connect the coupling by sliding an MJ gland over the pipe where you are connecting the coupling/fitting. Once done, connect and tighten the coupling/fitting per the manufacturer’s recommendation.
The material on the other side of the coupling, along with the coupling manufacturer's recommendation, will determine the steps needed to connect the other pipe material.
Again, the OD of the other pipe must fit within the min–max range for that side of the coupling. Depending on the material, insert stiffeners may also be required.
If you use restraint for this connection, as mentioned above, you may need different restraint methods on the DI pipe side versus the “other” material side of the coupling.
Connecting to Flanges
Flange adaptors, flange coupling adaptors, EZ Flange, Uni-Flange, and other products can connect a DI pipe to a flange connection.
Again, the coupling or adaptor must be the correct size and range for DI pipe. These devices can come in restrained and non-restrained configurations.
Each manufacturer has specific instructions for assembling and tightening the connection for their coupling, depending on the pipe type used. Please follow the manufacturer’s recommendations for the product and pipe being used.
Inserting DI pipe into a PVC pipe bell (DI Size PVC) or inserting DI OD PVC pipe into a DI pipe bell should technically work when no other means are available.
For this application, adjust the depth markings on the pipe being inserted to accommodate the depth of the bell the “other” pipe is being inserted into.
If there is an issue with the joint after installation, the manufacturers of the two pipes may not be able to help with their materials connecting to each other.
Finally, when restraint is required, one manufacturer’s restraint method may not apply to another manufacturer’s material. For example, a DI restraint gasket may not work on PVC pipe designed for DI pipe.
When connecting DI pipe to existing steel pipe, concrete pressure pipe, AC, or other pipe, you may need to expose the existing pipe to determine its type, size, OD, and, if possible, manufacturer. Many pipe types require custom-made couplings to connect to DI (or any other) pipe.
In some cases, the pipe manufacturer may need to make this adapter. Many coupling manufacturers can make couplings for the exact material you are connecting once you have determined the type, size, and OD you are connecting.
I have listed several companies that manufacture standard and special, custom-made couplings that should suit any application you have. Your local McWane Ductile sales representative or McWane distributor can help you find the best option for connecting DI to other pipe materials. When installing any pipe, refer to the recommendations of both the pipe manufacturer and the coupling/fitting manufacturer.
References
Graphics and references in this article are from: DIPRA, PPI, Uni-Bell, Tyler/Union, Romac, JCM, and Ebaa Iron. Other manufacturers of couplings and connections for different pipes are Smith-Blair, Ford Meter Box, Power-Seal, Robar, Nova-Siria, Hymax, Krausz, and Teekay, among others.
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