How to Weld Copper Pipe

You can weld, braze, or solder copper pipe. Each method has separate advantages and disadvantages, depending on the type of copper pipe and the pipe you want to weld it to.

Can You Weld Copper?

Copper is relatively easy to weld to copper alloys but requires extra considerations when working with other metals.

The melting point of copper is about 1,984 degrees Fahrenheit. However, it has high thermal conductivity, which results in heat loss from the electrode. 

The thermal conductivity of copper alloys is up to 11 times higher compared to carbon steel. It’s also less fluid compared to iron when melted. 

Copper also has a much higher melting point compared to aluminum. Aluminum has a melting temperature of about 1,220 degrees Fahrenheit. Heating the two metals includes the risk of weakening and overheating the aluminum.

The differences between copper, iron, steel, and aluminum can create challenges when welding. Yet, you can fuse copper with other metals using different types of welding. 

Welding Types Suitable for Copper

Here are the best methods for welding copper and its alloys:

  • MIG welding
  • TIG welding
  • Brazing
  • Soldering

Welding requires extremely high temperatures to liquefy two metals and fuse them with a filler metal. Gas metal arc welding (GMAW), or MIG welding is often used to weld copper. Gas tungsten arc welding (GTAW), or TIG welding, is also a common choice. 

MIG welding and TIG welding allow for highly localized heat, which helps counter heat loss due to copper’s thermal conductivity.

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Brazing and soldering may work better when bonding copper to stainless steel, iron, and aluminum. 

Welding involves melting the base materials. Brazing and soldering involve melting a filler material to create a bond. 

These methods involve less heat and solder that acts as a filler. You can bond copper to metals with dissimilar properties as the solder melts at a lower temperature.

welding copper pipe

How to Braze Copper

Brazing copper is recommended when fusing it with carbon steel and other materials with a much higher melting point. Brazing is also frequently used for repairing and fitting copper plumbing.

Brazing involves a higher temperature compared to soldering, but a lower temperature compared to welding. Brazing occurs at about 800 to 900 degrees Fahrenheit.

Brazing is typically done with a brazing torch but may be completed with an oxyacetylene torch. You’ll need to hold the torch much further away when using an oxyacetylene torch.

Oxyacetylene torches can reach temperatures of 5,500 degrees Fahrenheit. 

Brazing doesn’t involve the use of gas. However, you may want to purge copper pipes with nitrogen when working on plumbing. The high temperatures and exposure to oxygen create byproducts that need to be cleaned when working on water-carrying pipes. 

You’ll also need a filler metal rod and flux. The filler metal is a rod that melts at about 800 degrees Fahrenheit. 

Brazing copper typically requires the following steps:

  • Clean the copper 
  • Apply flux
  • Light your torch
  • Preheat the metal
  • Melt the filler metal

You first need to clean the copper to remove any contaminants. Dirt, oil, and debris get in the way of a quality joint. 

Use sandpaper or an abrasive pad to remove coating and contaminants from the surfaces where the bond will occur. Immediately apply flux after cleaning the copper.

Flux helps the filler metal run freely after it’s heated. Flux isn’t required but helps keep the bond between the two pieces clean and secure. Flux also shields against oxidation, which can create a brittle connection. 

Secure the two pieces that you want to bond and light your torch. Preheat the metal for a minute or two. 

You’ll need to preheat just one piece when working with copper pipes. Preheat one of the pieces, apply flux, and connect it to the other piece.

You can either apply solder paste or use a metal filler rod. Solder paste is a little easier to apply, especially for beginners. 

The solder paste, or filler metal, starts melting as soon as you place it near the preheated area and move the torch closer. It takes just seconds for the solder to melt and flow across the flux.

You may need to repeat this process several times to braze a large area or when brazing a thick copper pipe. Copper cools quickly, requiring you to work in small sections. 

Allow the copper to cool for a minute before reapplying the filler metal. You should also run water through the piping when you finish if you’re working on plumbing. 

How to Solder Copper

Soldering is often used as an alternative to brazing when you want to protect the structural integrity of copper pipes. Brazing uses higher temperatures which weakens the pipes more. 

Soldering is typically done with a soldering iron. Soldering irons are handheld instruments with metal tips that can reach temperatures of 400 to 800 degrees Fahrenheit. 

You can also use a propane torch or an oxyacetylene torch but may need to keep the torch further away to avoid melting the solder too fast.

You need solder and flux for soldering. Flux is applied to the pipelines. 

The solder is metal wire placed between the pipe and the torch or soldering iron. The heat melts the solder, which then flows over the flux. 

You also have the option of using solder paste. Again, solder paste is a little easier to apply.

Use solder with high silver content. Standard solder mostly contains tin or nickel. Both alloys have low melting points. Silver has a higher melting point, which helps you create a stronger joint.

Keep the torch or soldering iron constantly moving when soldering copper. This keeps you from overheating the copper, which weakens the material. 

If you’re soldering copper pipes, thoroughly flush the pipes with water. Water will help remove excess flux and loose solder beads. You can also check for any leaks.

How to Weld Copper

You can weld copper using metal inert gas (MIG) welding or tungsten inert gas (TIG) welding. Both options use a consumable filler metal.

Using a nickel-based filler may help ensure a stronger joint when welding copper to stainless steel or cast iron. Nickel helps dilute iron from the base metal without it cracking.

MIG welding requires the use of a consumable electrode, which is also the filler metal. TIG welding uses a non-consumable tungsten electrode and a separate filler metal rod. 

MIG welding is one of the most common types of welding and is easier for novices compared to TIG welding. TIG welding requires a little more practice but allows for greater precision.

Whether you use MIG welding or TIG welding, it’s important to avoid heating the copper too long. 

Welding torches can reach extremely high temperatures and liquefy copper in seconds. Yet, you need to touch the electrode to the metal to start welding, which means you can’t hold the heat source further away. 

You’ll also want to preheat the copper to decrease the risk of cracking the metal. Work quickly and allow the copper to cool gradually, which is easier if you remember to preheat the copper first. 

Equipment Required

While the equipment needed varies depending on the method you choose, you’ll likely need the following:

  • Torch
  • Solder/filler
  • Flux
  • Sandpaper
  • Brush
  • Pipe cutter/hacksaw

Welding copper requires a torch or a welder, depending on your chosen method. You can also use a propane torch to solder or braze. 

Welding, brazing, and soldering require some form of filler metal. With MIG welding, you need a consumable wire electrode. TIG welding and brazing typically use a filler metal rod you manually hold.

Sandpaper is needed for cleaning the pieces that you want to weld. You need to remove debris before welding, brazing, or soldering. You can also use an emery cloth, scrubby pad, or some abrasive cleaner to remove any dirt, oil, or paint from the copper.

A brush may be needed to apply flux. However, some products may come with an applicator. Using a small piece of wire is also a suitable way to apply flux.

You can cut copper pipes with a hacksaw. However, gripping the pipe in a vice may crush it. Holding it with one hand makes it difficult to get a clean cut. 

A pipe cutter is a preferred tool for cutting pipes. You place the pipe in the cutter and tighten the blade to get a snug fit. You then twist the pipe to cut using the built-in blade. 

welding copper

Conclusion

Welding copper pipe isn’t always the best way to bond it to other pipes. Brazing and soldering often work better as these methods involve less heat, which is helpful when bonding copper with a metal with a higher melting point. 

Brazing and soldering both involve the use of filler metal and flux. The flux prevents oxides from forming and helps direct the filler metal flow as it melts. 

Brazing provides a stronger joint compared to soldering and a higher temperature. Soldering is a little more convenient, as you don’t need to purge the pipes with nitrogen.