Can you attach PVC pipe to metal pipe?

It is common in plumbing systems to need to connect plastic pipes, like PVC, to metal pipes, like copper or galvanized steel. PVC stands for polyvinyl chloride, which is a durable, lightweight plastic that is used for drain, waste and vent (DWV) piping. Meanwhile, metal pipes like copper and galvanized steel are often used for water supply lines.

When making these types of connections, you need to use the proper adapters and transition fittings. Simply gluing or solvent welding a PVC pipe directly to a metal pipe is not possible. However, with the right connectors, PVC and metal pipes can be securely attached.

Can You Glue PVC Pipe to Metal Pipe?

No, PVC pipe cannot be glued or solvent welded directly to metal pipe. The glue and solvent cement used for connecting PVC pipe only works on plastic to plastic connections. It will not bond PVC and metal together.

If you try gluing or solvent welding PVC pipe to threaded metal pipe fittings, it may appear to be connected at first. However, the PVC will not truly adhere to the metal. This type of improper connection is very likely to come apart over time due to the materials not bonding.

Can You Use a PVC Adapter to Connect to Metal Pipe?

Yes, there are special PVC adapter fittings made to provide a transition from PVC to metal pipes like copper and galvanized steel. These PVC adapters have one end with solvent weld connections for attaching the PVC pipe. The other end has a threaded female connection for attaching to threaded metal pipe fittings.

Common types of PVC to metal pipe adapter fittings include:

• PVC female adapters – Solvent weld on one end, threaded female connection on the other
• PVC male adapters – Solvent weld on one end, threaded male connection on the other
• PVC unions – Solvent weld connections on both ends with threaded female connection in the middle

By using the proper PVC to metal pipe adapters, a secure connection can be made between the plastic and metal pipes. Be sure to follow the manufacturer’s instructions for proper installation. An appropriate PVC primer and cement must be used to solvent weld the PVC side of the connections. PTFE thread seal tape or pipe thread sealant should be used on the threaded metal connections.

Can You Use a Threaded PVC Fitting to Connect to Metal Pipe?

Threaded PVC fittings are available that allow connecting PVC to metal threaded pipe connections. One side of these fittings has female or male PVC threaded connections. The other side has the corresponding threads to connect to threaded metal pipe fittings.

These threaded PVC fittings provide an alternative to solvent weld PVC adapters when connecting to metal pipes. Threaded connections can make it easier to disassemble or change the piping system in the future. However, solvent welded connections are typically stronger and less prone to leaking.

As with any threaded pipe connections, use PTFE tape or thread sealant when connecting the threaded PVC fittings to metal pipe threads. Take care not to cross thread or overtighten the connections.

How to Attach PVC Pipe to Metal Pipe

Here are some step-by-step instructions for how to properly connect PVC to metal pipe:

Solvent Welded PVC Adapter Fittings

1. Cut the PVC and metal pipes square using a miter saw or pipe cutter. Deburr the pipe ends.
2. Dry fit the connection to determine the correct adapter fitting and ensure proper fit up. Mark the insertion depth on the PVC pipe.
3. On the PVC pipe, use primer and then solvent cement to connect the adapter fitting per the manufacturer’s instructions. Allow time for curing before disturbing the joint.
4. On the metal pipe, connect the appropriate fittings to match up with the adapter. Use PTFE tape or pipe thread sealant on the threads.
5. Line up the adapter and metal pipe fitting. Tighten by hand, then use a wrench to finish tightening per the recommendation for the pipe size.

Threaded PVC Fittings

1. Cut the PVC and metal pipes as needed. Deburr the ends.
2. Dry fit the threaded PVC fitting and metal pipe fitting to check alignment. Ensure sufficient threading engagement will be made.
3. Apply PTFE thread seal tape to the male threads on both the PVC and metal sides.
4. Spin the fittings together by hand. Use a wrench to finish tightening according to the manufacturer’s instructions.
5. An adjustable wrench may be needed to properly tighten the PVC threaded fitting. Take care not to overtighten.

PVC to Metal Pipe Transition Options

There are a few main options when it comes to connecting PVC and metal piping:

PVC Female Adapter to Male Threaded Pipe Fitting

A PVC female adapter can connect to a threaded male pipe fitting on the metal pipe line. PVC female adapters are readily available in a full range of sizes. Apply solvent cement to connect the PVC pipe into the female adapter. Use thread sealant or tape on the male threads before connecting.

PVC Male Adapter to Female Threaded Pipe Fitting

A PVC male adapter can connect into a female threaded pipe fitting on the metal pipe. As with the female adapters, solvent weld the PVC pipe into the male adapter. Then use thread sealant on the male adapter threads before connecting to the female threaded fitting.

PVC Union with Threaded Ends

PVC unions provide a solvent weld connection on both ends of the fitting with a metal threaded connection in the middle. This allows easily joining two sections of PVC pipe while incorporating a threaded end to connect to the metal pipe. PVC unions often offer more flexibility for adjustment compared to standard adapters.

Threaded PVC Fitting to Threaded Metal Fitting

As an alternative to solvent weld adapters, using threaded PVC fittings can simplify connections between PVC and metal pipes. Apply thread seal tape to the male threads on both the PVC and metal pipe ends. Then spin the threaded fittings together for a leak-free connection.

Common Problems When Connecting PVC to Metal Pipe

There are some issues to watch out for when connecting plastic and metal plumbing pipes:

• Using the wrong type of adhesive/cement on PVC connections
• Not properly priming and cementing the connection
• Failing to allow adequate curing time for PVC cement
• Not using thread sealant or tape on threaded connections
• Over tightening threaded joints
• Incorrect alignment of pipe fittings
• Mismatching pipe schedules/pressure ratings
• Not accounting for thermal expansion and contraction

Taking the time to properly prepare pipe ends, use the correct adhesive products, and allow for full curing of cement is crucial for avoiding leaks. It is also important to follow manufacturer’s torque specifications for tightening threaded connections to prevent cracking or splitting.

Thermal Expansion Differences Between PVC and Metal

One important consideration when connecting PVC and metal pipes is accommodating the differences in thermal expansion. PVC and metal expand and contract at different rates as temperatures fluctuate. This is especially critical in hot water plumbing systems.

If PVC and metal pipes are fused together solidly, thermal expansion forces can potentially cause the pipes to bend, buckle, or even crack at the joints. Properly installed flexible joints and couplings must be used to allow for this movement.

Common ways to address thermal expansion when connecting PVC to metal pipe include:

• Use an expansion coupling – Allows linear movement via an internal sleeve
• Incorporate swing joints into the system design
• Use flexible PVC hoses
• Provide sufficient clearance around pipes
• Include offset pipe alignments

Having the right type of flexible connectors is important for dealing with the temperature changes that plumbing systems undergo. Consult manufacturer’s recommendations and applicable plumbing codes.

PVC to Galvanized Pipe Connections

Galvanized steel is a commonly used metal piping material due to its corrosion resistance. Connecting galvanized pipe to PVC typically involves the use of threaded fittings.

Common tips when connecting PVC to galvanized pipe:

• Use galvanized threaded fittings that comply with ASME/ANSI standards for potable water.
• To avoid cross-threading, start threaded connections by hand before using a wrench.
• Account for differences in thermal expansion rates.
• Isolate PVC from direct contact with galvanized steel to avoid corrosion.
• PVC female adapters provide the most secure threaded connection to galvanized pipe.

The longevity of galvanized pipe is extended by avoiding contact with aggressive water conditions. Connecting to PVC pipe helps keep the water flowing through the galvanized portion less corrosive.

PVC to Copper Pipe Connections

Copper is another popular metal piping material used for interior water supply lines. Like galvanized pipe, copper expands and contracts at a different rate compared to PVC. Follow these guidelines for attaching copper pipe to PVC:

• Use brass or bronze threaded fittings with copper to provide stronger connections.
• Avoid high torque levels which can crack PVC threaded fittings.
• Allow for thermal expansion using expansion joints and flexible connectors.
• Take care not to overtighten connections and fracture the PVC.
• Insulate copper pipe where it connects to PVC to minimize galvanic corrosion.

The use of threaded brass fittings combined with proper installation techniques allows copper and PVC piping to be used together successfully. Manage thermal expansion and take measures to slow corrosion.

Cost to Connect PVC to Metal Plumbing Pipe

For do-it-yourselfers, connecting PVC to metal pipe typically costs $5 to $30 in materials depending on the size and number of fittings required. PVC adapters, unions, and couplings cost $2 to $15 each at hardware and home improvement stores. Threaded fittings for the metal pipe add about $5 to $10 per connection.

Hiring a professional plumber to connect PVC to metal pipes will involve labor charges of $45 to $150 per hour plus materials. Simple connections can often be made in 30 minutes to an hour. More complex transitions or full system retrofits require more time. Get an estimate in advance for the specific work required.

In either case, use of quality fittings and proper application of solvent cements and thread sealants is advised. This helps ensure leak-free function and longevity of the system. Taking the time to make watertight PVC to metal transitions upfront saves hassle and money down the road.

Conclusion

Joining PVC and metal pipe is a common need in residential and commercial plumbing systems. While you cannot simply glue or weld PVC pipe directly to metal, using the appropriate fittings allows creating a secure connection.

PVC adapters with solvent weld ends and threaded metal connections are manufactured specifically for this purpose. Alternatively, threaded PVC fittings can be mated with threaded metal pipe fittings. In either case, use the proper cementing and thread sealing procedures to prevent leaks.

Also be sure to account for the differences in thermal expansion between plastic and metal pipes in the system design. With the right materials and installation techniques, PVC and metal plumbing pipes can be attached successfully. This provides the benefits of corrosion resistant PVC pipe combined with the strength of metal supply lines throughout the plumbing system.