What can go wrong with soldering copper pipe?

Soldering copper pipe is a common task for plumbers and DIYers, but it does come with some risks if not done properly. In this article, we’ll go over some of the main things that can go wrong when soldering copper pipes, and how to avoid them.

Using the Wrong Materials

One of the most common mistakes when soldering copper pipe is using the wrong materials. Here are some things to keep in mind:

• Use only lead-free solder intended for copper plumbing. Traditional lead solder can contaminate potable water lines.
• Make sure to use flux designed for copper soldering. Acid-based fluxes for other metals can corrode copper.
• Use copper-specific sand cloth or emery paper when cleaning and preparing the copper surface.
• Only solder compatible metals – copper to copper or brass to copper. Do not solder copper to galvanized steel.

Using the wrong solder, flux, abrasives, or attempting to join dissimilar metals can all lead to leaks, blockages, and corrosion down the line. Always make sure you have the right soldering products for copper pipe before beginning.

Not Cleaning the Pipe Surface

For the solder to bond properly, it needs to make contact with clean, bare copper. Any oils, dirt, or oxidation present can prevent the joint from sealing properly. Before soldering, you need to thoroughly clean the pipe ends with sand cloth or emery paper. The surface should have a bright, shiny copper finish when you’re done cleaning. It’s also important to clean off any old solder, flux, or grime from existing copper pipe you may be working on. Taking the time to properly clean all joining surfaces is key to leak-free soldering.

Failing to Apply Flux

Flux serves a critical purpose in soldering copper pipe. It helps clean and displace surface oxides while protecting newly cleaned pipe from re-oxidizing. Flux also facilitates heat transfer from the torch to the copper. Skipping flux can lead to cold solder joints and leaks. When soldering copper pipes:

• Apply a small amount of flux paste to end of each pipe.
• Spread the flux evenly over 1-2 inches of each surface.
• Apply a small additional amount of flux to the pipe ends right before soldering.

The flux should sizzle and melt when the torch heat is applied, not burn off immediately. Too little flux can be just as problematic as too much when soldering copper pipe.

Using Too Much Heat

Applying excessive heat to the copper pipe when soldering can lead to a number of problems:

• Burnt flux – Flux needs to liquefy; overheating will cause it to burn off or carbonize.
• Discolored copper – The pipe surface will start to turn brown or blue from overheating.
• Weakened metal – Excess heat can soften the copper and make the joint prone to failure.
• Dripping and flowing solder – If the pipe gets too hot, solder will not wick properly.

To avoid these issues, carefully heat the pipe using a low-intensity torch flame. Gradually increase the heat until the flux liquefies and the surface tension breaks. The copper should never get red hot when soldering pipes. Melting the solder, not the pipe, should be the goal.

Poor Soldering Technique

Applying the torch heat and solder incorrectly can also cause soldering problems, such as:

• Heating too wide an area – Concentrate the torch on a 1-2″ area around the joint.
• Not heating evenly – Heat both sides of the joint uniformly.
• Applying solder too soon – Wait until flux liquefies before applying solder.
• Insufficient solder – Use enough solder to fully fill the joint space.
• Excess solder – Aim for a thin solder layer; too much is unnecessary.
• Disturbing the joint – Don’t move or mess with the pipe until solder has cooled.

It takes practice to master proper copper pipe soldering technique. Pay close attention to the joint as you heat it, and make adjustments as needed to achieve proper solder flow and adhesion.

Making Imperfect Joints

The types of joins made when soldering copper pipes also impact the quality and longevity of the connections:

• End-to-end joints – Pipe ends should come into full contact. Gaps can lead to leaks.
• T-joints – Use fittings to create T-joints; avoid them directly between pipes.
• Elbows – Bend pipes gradually to avoid crimping. Use elbow fittings if needed.
• Uneven bead – Solder should fully fill the joint space evenly all the way around.

Visually inspect each joint as you solder copper pipes. Adjust fittings as needed to get proper alignment and full solder fill at all connection points.

Moving Pipes Before Cooling

Freshly soldered copper pipe joints need time to cool and set completely before being handled or stressed. Moving pipes too soon can disturb the solder bond while it is still setting. This can lead to cracks or weak spots in the joint. Follow these cooling guidelines after soldering copper pipes:

• Don’t move or stress the joint for at least 15 seconds after soldering.
• Allow 1-2 minutes of cooling time for small pipe joints.
• Give larger pipe joints 5 minutes or more to fully set.
• Visually inspect the joint to confirm the solder has hardened before moving the pipe.

Keep the pipes well supported as the solder cools. Rushing the job by handling pipes too soon is asking for trouble down the road.

Not Pressure Testing

The last step after soldering and cooling any copper pipe system is to pressure test it. This involves capping off lines and using a pump to subject the system to greater than normal water pressure. Pressure testing serves to check for leaks and confirm the integrity of all solder joints under duress. Never assume joints are leak-free without pressure testing, especially if the system will be concealed behind walls and ceilings.

Conclusion

While soldering copper pipes relies on simple tools and techniques, it does take some care and know-how to get reliable results. Keeping these common soldering mistakes in mind, along with following good fluxing, heating, filling, and cooling practices, will go a long way to creating durable, leak-free soldered copper pipe joints.