4.10: Joining Methods

 

     Joining pipes securely is important to ensure they work properly and don’t leak. For copper piping, there are several joining methods: flaring and swaging techniques, which expand the pipe for a snug fit, and soldering and brazing, which use heat and filler materials to create a strong bond. Safety protocols are essential when using a torch for soldering. Compression fittings are another option, and they’re quick to install and can be used in various applications. For plastic piping, common joining methods include solvent welding, where primers and adhesives bond the pieces together, as well as threaded fittings and couplings. PEX piping can be joined using crimping or expansion connections, making it flexible and easy to install. After any type of joining, leak testing is essential to check the pipe’s integrity and ensure everything is sealed correctly. In the next sections, we’ll look at these joining methods and why leak testing is so important.

 

Joining Methods

     Joining pipes securely is essential to ensure leak-free operation, efficient flow, and structural stability. Each material has specific joining techniques that rely on thermal or adhesive bonds.

 

Joining Copper Piping

Copper piping has several joining methods, each with specific applications:

• Flaring and Swaging: These techniques involve expanding the end of the copper tube to join with a fitting. Flaring is used for low-pressure refrigerant lines, while swaging joins tubes of similar size.

• Soldering and Brazing: These are common methods where a filler metal (solder or brazing rod) is melted between two copper surfaces. Brazing uses higher temperatures and is typically preferred for high-pressure systems like HVAC refrigerant lines. Safety is paramount, so always wear protective gear and ventilate the area when using a torch.

• Compression Fittings: Compression fittings are useful in plumbing where disassembly may be required. These fittings consist of a brass ferrule and nut that compresses around the pipe, creating a tight seal.

 

Joining Plastic Piping

For plastic pipes, the most common joining methods are:

• Solvent Welding: For PVC and CPVC, solvent welding uses a primer and cement that chemically fuses the plastic. Apply primer to clean the joint, then use cement to bond. This creates a leak-proof connection as the pipe and fitting are welded at the molecular level.

• Threaded Fittings and Couplings: Threaded connections are helpful for areas requiring easy disassembly. Use thread seal tape to ensure a tight, leak-free seal.

• PEX Connections: PEX connections typically use crimp or expansion fittings. Crimping involves sliding a metal ring over the pipe and compressing it with a crimp tool. Expansion connections involve expanding the PEX and fitting, which contracts around the fitting for a strong seal.

After joining pipes, always perform a leak test using air or water pressure to ensure all connections are secure and functioning as expected.

 

Step-by-Step Procedural Guide for Joining Copper and Plastic Piping in HVAC

     Joining pipes correctly is critical to ensuring leak-free operation, proper refrigerant flow, and long-term system integrity. Below is a detailed, procedural guide for each joining method used in copper and plastic piping, focusing on step-by-step techniques, best practices, and common pitfalls that HVAC experts must avoid.

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Joining Copper Piping: Step-by-Step Techniques

1. Flaring Copper Tubing for Refrigerant Lines

     Flaring is commonly used in low-pressure refrigerant lines and gas piping. The goal is to create a cone-shaped expansion at the pipe end that fits tightly against a flared fitting, ensuring a leak-proof, metal-to-metal seal.

 

How to Properly Flare Copper Tubing:

1. Cut the Pipe Cleanly
   • Use a tubing cutter for a straight, burr-free cut.
   • Remove any burrs using a deburring tool or a round file to prevent damage to the flaring tool.
2. Clamp the Pipe in a Flaring Tool
   • Insert the correct-sized pipe into the flaring block so that the tubing extends slightly past the clamp face.
   • Tighten the clamp securely to hold the tubing in place.
3. Apply Lubrication (Optional for Soft Copper)
   • A drop of refrigerant oil on the flaring cone helps create a smoother, more uniform flare.
4. Form the Flare
   • Align the flaring tool’s cone with the tubing opening.
   • Slowly tighten the flaring tool, pressing the cone into the tubing until the flare is smooth and evenly shaped.
5. Inspect the Flare

    

   • Ensure the flare has a 45-degree angle with no cracks or thinning.
   • Dry-fit the flare against the flared fitting—it should sit flush without gaps.

Caution

Common Mistakes to Avoid:
    ❌ Over-tightening the flare, which can thin out the copper and cause leaks.
    ❌ Skipping the deburring step, leading to cracked or uneven flares.
    ❌ Using hard-drawn copper instead of annealed (soft) copper, which won’t flare properly.

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2. Swaging Copper Tubing for Pipe-to-Pipe Joints

     Swaging is used when two copper pipes of the same diameter need to be joined without using a coupling. Instead of flaring outward, one pipe end is expanded to fit over another.

 

How to Swage Copper Tubing Correctly:

1. Secure the Pipe in a Swaging Tool or Expander Tool
   • Insert the correct-sized swaging bit into the pipe end.
   • If using a hammer swage, insert the bit and strike it lightly with a mallet until the pipe expands evenly.
   • If using a hydraulic or drill-powered swage tool, follow the manufacturer’s expansion procedure.
2. Check the Fit
   • The expanded pipe should snugly fit over the other pipe without excessive force.
   • Ensure there are no thin or weak spots.
3. Brazing or Soldering the Swaged Joint
   • Swaged joints must be brazed or soldered for a permanent seal.

 

Caution

Common Mistakes to Avoid:
    ❌ Over-expanding the pipe, leading to a loose or weak connection.
    ❌ Skipping the inspection step, which could allow improper fits that lead to leaks.

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3. Soldering and Brazing Copper Pipes

Soldering is used for low-pressure water lines, while brazing is required for high-pressure refrigerant lines. Both methods use heat and filler metal to create a permanent joint.

 

How to Solder Copper Pipes (Water Lines Only):

1. Cut and Deburr the Pipe
   • Use a tubing cutter for a straight cut.
   • Deburr and clean the edges using a pipe reamer.
2. Clean the Pipe and Fitting
   • Use emery cloth or a pipe cleaning brush to remove oxidation.
   • Apply a thin layer of flux to both the pipe and fitting.
3. Assemble and Heat the Joint
   • Insert the pipe into the fitting fully.
   • Heat the joint with a propane torch until the flux sizzles.
   • Apply lead-free solder to the joint and let capillary action pull it in.
4. Allow to Cool and Wipe Excess Flux

 

How to Braze Copper Pipes (For HVAC Refrigerant Lines):

1. Use an Oxygen-Acetylene Torch with a Brazing Tip
   • Heat the joint evenly until it reaches cherry-red temperature.
   • Apply silver-based brazing rod to the joint and let it flow into the connection.
2. Purge with Nitrogen During Brazing

    

   • This prevents oxide formation inside the pipe, which can contaminate refrigerant systems.

Caution

Common Mistakes to Avoid:
    ❌ Overheating, which can damage pipe integrity.
    ❌ Not using nitrogen purging, leading to blockages from oxidation.

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Joining Plastic Piping: Step-by-Step Techniques

1. Solvent Welding for PVC and CPVC Pipes

1. Clean and Prime the Pipe
   • Use PVC/CPVC cleaner and primer to prepare the joint.
2. Apply Solvent Cement
   • Coat both the pipe and fitting evenly with cement.
3. Insert and Hold the Pipe
   • Push the pipe fully into the fitting with a twisting motion.
   • Hold for at least 10 seconds to prevent pull-out.
4. Let the Joint Cure Before Testing

 

Caution

Common Mistakes:
    ❌ Skipping primer (this weakens the bond).
    ❌ Moving the pipe before the cement sets.

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2. Threaded Fittings for Plastic Pipes

1. Wrap Male Threads with Teflon Tape
   • Wrap clockwise to ensure a tight seal.
2. Tighten by Hand, Then Use Pliers

    

   • Do not over-tighten, as plastic threads can crack.

Caution

Common Mistakes:
    ❌ Over-tightening leads to cracked fittings.

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3. PEX Crimping and Expansion Connections

How to Make a PEX Crimp Connection:

1. Slide the crimp ring over the PEX pipe.
2. Insert the barbed fitting fully.
3. Position the crimp ring 1/8" from the pipe end.
4. Use a PEX crimp tool to compress the ring until fully secured.
5. Check the connection with a go/no-go gauge.

 

How to Make a PEX Expansion Connection:

1. Slide an expansion ring onto the PEX pipe.
2. Use an expansion tool to widen the pipe in even steps.
3. Quickly insert the fitting before the pipe contracts.

 

Caution

Common Mistakes:
    ❌ Not checking the crimp with a go/no-go gauge.
    ❌ Delaying fitting insertion in an expansion joint, leading to a weak seal.

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Final Step: Leak Testing

After joining, always test for leaks before pressurizing the system:

• For Copper Pipes: Use pressurized nitrogen and soap bubbles to detect leaks.
• For Plastic Pipes: Perform a water pressure test before finalizing connections.

💡 Pro Tip: If a PEX crimp connection fails the pressure test, cut the fitting out and redo it—never reuse a crimp ring.

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By following these detailed procedures, HVAC experts can ensure secure, long-lasting, and professional-grade pipe connections, minimizing leaks and maximizing system performance.