4.11: Joining Copper Piping

Step-by-Step Technical Guide for Joining Copper Piping in HVAC

     Joining copper piping is a critical skill for HVAC professionals, especially in refrigerant lines, water supply systems, and gas piping. Each joining method—flaring, swaging, soldering, brazing, and compression fittings—requires precision, proper tool use, and adherence to safety procedures. This guide will break down each process into detailed, step-by-step instructions, covering materials, best practices, and potential pitfalls that experts need to avoid.

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1. Flaring Copper Tubing: Creating a Leak-Proof Metal-to-Metal Seal

     Flaring is used in HVAC refrigerant lines and soft copper tubing applications where threaded flare nuts create a leak-free joint without soldering or brazing. It is essential for low-pressure applications, such as mini-split systems and some gas piping installations.

 

Step-by-Step Flaring Procedure

Step 1: Select the Correct Tubing and Flare Fitting

• Use only soft (annealed) copper tubing—hard-drawn copper does not flare properly.
• Ensure flare fittings match the pipe diameter to prevent leaks.
• If working with R-410A refrigerant, use 45-degree flare fittings rated for high pressures.

 

Step 2: Cut and Prepare the Copper Pipe

1. Use a tubing cutter to create a clean, burr-free cut.
2. Deburr the cut edge using a reamer or round file—any rough edges will interfere with the flare seat.
3. Slide the flare nut onto the pipe BEFORE flaring—forgetting this step means cutting and redoing the entire process.

 

Step 3: Clamp the Pipe in the Flaring Tool

1. Insert the pipe into the flaring block so that about 1/8 inch extends beyond the surface.
2. Tighten the clamp securely—if the pipe moves, the flare will be uneven.

 

Step 4: Form the Flare

1. Align the flaring cone with the pipe opening.
2. Slowly tighten the flaring tool, pressing the cone into the pipe.
3. Rotate the tool until the flare is evenly formed—avoid over-tightening, which can thin out the metal.

 

Step 5: Inspect and Test Fit the Flare

• The flare should have a smooth, even 45-degree angle without cracks or rough spots.
• Dry-fit the flare against the fitting—it should seat flat against the flare seat without gaps.
• If the flare does not sit properly, re-cut and repeat the process.

 

Common Mistakes to Avoid:

❌ Skipping the deburring step—rough edges will create leaks.
❌ Using too much force—thin, overworked flares will crack under pressure.
❌ Forgetting the flare nut—this requires cutting and starting over.

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2. Swaging Copper Tubing: Expanding Pipes for Soldered or Brazed Joints

Swaging allows two copper pipes of the same diameter to be joined without a separate coupling by expanding one pipe end to fit over another. This method reduces fittings, improves flow efficiency, and strengthens the joint.

 

Step-by-Step Swaging Procedure

Step 1: Cut and Deburr the Pipe

1. Use a tubing cutter to cut the copper pipe squarely and evenly.
2. Remove burrs with a deburring tool or file—failure to do this causes cracks when expanding.

 

Step 2: Choose the Right Swaging Tool

• Hammer Swage Tool: Requires manual force with a hammer.
• Tube Expander Tool: Uses hydraulic or mechanical expansion for precision.
• Swaging Drill Bits: Used with power drills for speed and efficiency.

 

Step 3: Expand the Pipe

1. Insert the swage bit or expansion tool into the pipe end.
2. Apply even force—either by tapping with a hammer or using a hydraulic expander.
3. Expand only enough for a snug fit over the adjoining pipe.

 

Step 4: Inspect and Fit the Connection

• The swaged pipe should fit snugly over the adjoining pipe without gaps.
• If the pipe walls are too thin after expansion, cut and repeat the process.

 

Common Mistakes to Avoid:

❌ Over-expanding, leading to a loose, weak joint.
❌ Skipping deburring—sharp edges will cause cracking during expansion.
❌ Using hard-drawn copper, which does not swage properly.

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3. Soldering and Brazing Copper Pipes: Permanent Leak-Free Joints

Soldering and brazing use filler metals and heat to create strong, sealed joints. Soldering is used for low-pressure water lines, while brazing is required for HVAC refrigerant lines and high-pressure applications.

 

Step 1: Prepare the Pipe and Fitting

1. Cut the pipe to exact length using a tubing cutter.
2. Deburr the pipe ends to prevent flow restrictions and poor sealing.
3. Clean the mating surfaces using emery cloth or a wire brush.

 

Step 2: Apply Flux (for Soldering Only)

• Apply a thin, even layer of flux to the inside of the fitting and outside of the pipe.
• Flux removes oxidation and promotes filler adhesion.

 

Step 3: Heat and Apply Filler Metal

Soldering (For Water Lines)

1. Use a propane or MAP gas torch and apply heat evenly to the joint.
2. Touch the solder to the joint—if the temperature is correct, the solder will flow evenly into the joint.

 

Brazing (For HVAC Refrigerant Lines)

1. Use an oxy-acetylene torch with a high-temperature brazing tip.
2. Heat the joint to cherry-red temperature before applying silver-based brazing rod.
3. Purge nitrogen through the pipes during brazing to prevent oxidation inside the system.

 

Step 4: Allow to Cool and Inspect the Joint

• Soldered joints should be shiny and smooth.
• Brazed joints should have even filler penetration with no pinholes.

 

Common Mistakes to Avoid:

❌ Overheating the pipe—can weaken the metal.
❌ Not using nitrogen purging, which creates oxide buildup inside refrigerant lines.

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4. Compression Fittings: Quick, Tool-Free Copper Connections

Compression fittings provide a strong mechanical seal without heat or soldering, making them ideal for gas lines, water lines, and temporary installations.

 

Step 1: Cut and Prepare the Pipe

1. Use a tubing cutter to create a clean, square cut.
2. Deburr the pipe so that no sharp edges damage the ferrule.

 

Step 2: Install the Compression Fitting

1. Slide the compression nut onto the pipe before the ferrule.
2. Insert the pipe into the fitting body until it seats fully.
3. Slide the brass ferrule (olive) over the pipe and push it into the fitting body.

 

Step 3: Tighten the Fitting

1. Hand-tighten the compression nut.
2. Use two wrenches to tighten 1 to 1 ½ turns past hand-tight.

 

Common Mistakes to Avoid:

❌ Over-tightening, which crushes the ferrule and damages the pipe.
❌ Not fully inserting the pipe—causes leaks due to improper seating.

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By following these detailed procedures, HVAC professionals can execute reliable, leak-proof copper piping installations while maintaining high system efficiency and safety.