Last year I had a project that required several small copper pipe connections to be soldered. Having never sweated (don't ask me why they call soldering that) copper pipes before, I read an article or two and then tried it for myself. My first attempts worked out quite well and I've since soldered a few more connections. While I don't profess to be an expert in pipe sweating, I thought I would write a quick Instructable to pass along what I've learned in the hope that some of you may find it useful.
Step 1: Cut Your Pipe
The first step to assembling copper pipe is to cut your pipe to length. The easiest and best way to accomplish this is by using a tubing cutter. I've been using a small close quarters cutter, but there are larger cutters, which operate on the same principle. The operation of all of these cutters is similar. Once the cutter is placed around the pipe, it is tightened until the pipe is clamped between the cutting wheel and the two rollers used to support the pipe. The cutter should be tightened slightly past the point where the cutting wheel first begins to contact the pipe. Be careful not to over tighten as the copper pipe can easily be crushed. After tightening the cutter, it is rotated around the pipe several times until the tension on the cutting wheel begins to be released as a grove is cut into the pipe. By retightening the cutter and continuing to rotate it around the pipe, this grove will continue to deepen until it cuts completely through the pipe. If you've done everything correctly, you will have a neatly cut pipe. It is also good practice to remove the small lip on the inside of the pipe produced by the cutter wheel. While this lip may not pose an immediate problem, it can result in sediment accumulating in the pipe, which could eventually plug the pipe. Some larger tubing cutters have a built in deburring tool or you could use a purpose-build reamer to easily accomplish the same thing.
Step 2: Cleaning the Pipe and Fitting
Prepwork is critical to ensuring a good soldered joint and cleaning of the copper is the first step. I've used several tools and methods for cleaning both the pipe and fitting. One method is to use a wire-based tool, such as the cleaner I use to clean the outside of the pipe in the image above. Small wire bristles inside of this tool scrape away the oxide layer on the outside surface of the pipe until it is nice and shiny. There are also wire tools available to cleaning the insides of fittings.
An alternative method for cleaning the pipe and/or fittings is to use emery cloth. To clean the insides of the fittings I rolled the emery cloth into a small cylinder. By rotating this cylinder inside of the fitting, it was quickly cleaned.
Step 3: Flux It
The second critical preparation step is the application of flux to the joint. Since the solder cannot be applied directly inside the joint, the flux will "pull" the solder into the joint, making a strong, sealed connection between the pipe and fitting. Without flux, the solder can only form a superficial layer at the entrance of the joint and even if it initially does not leak it won't hold up long. I apply a liberal layer of flux to both the inside of the fitting and the outside of the pipe before sliding the two parts together.
Step 4: Heat It
Soldering copper pipe requires a relatively large amount of high intensity heat, which is why a propane torch is typically used to heat the joint. You can't use a soldering iron here. The heat should be applied as evenly as possible around the fitting. The amount of heat needing to be applied will vary, but we'll deal with that in the next step.
Step 5: Solder It
As I heat the joint, every few seconds I will remove the heat and touch the tip of my solder to the joint to see if the metal is hot enough to melt the solder. If it does not melt or only slightly melts, I remove the solder and continue to heat until the solder easily melts onto the copper. Once the solder easily melts onto the joint, I apply enough solder to fill the joint and then re-heat the fitting, which draws the solder into the joint. You'll know you have applied enough solder when there is a silver band the entire way around the joint. When this band is flush with the surface of the pipe, you'll know that solder has been drawn into the joint. If you apply too much solder, a small solder bubble will form on the lower side of the joint. This does not affect the integrity of the joint, but can look a bit messy. Also note that excess solder can flow into the inside of the pipe, which can interfere with flow through the pipe if the quantity of this solder is large.
At this point you have completed your joint and can simply clean away any flux remaining on the joint. However, if you stick with me I'll give you two other tips I've learned.
Step 6: Re-soldering a Joint
If you're new at this you'll most likely need to re-solder a joint at some point. You can easily disassemble a soldered joint by heating the joint and pulling it apart using a pair of pliers. Once you've disassemble the joint, you'll most likely find it impossible to reassemble as the solder will prevent the two parts from sliding together. There are two ways around this. First, you can heat the joint until the solder softens and then reassemble it. While this can sometimes work, it is a bit tricky as you have to reassemble hot parts. A neater method I've found is to sand the outside of the pipe and inside of the fitting with emery cloth, which quickly removes most of the soft solder. With this solder removed, the parts can be re-fluxed, slid together, and re-soldered.
Step 7: Supporting Joints
Fittings with multiple joints (such as a T-fitting) can be tricky to solder together as the heat intended for one joint can easily soften the solder of the adjacent joint. While this isn't necessarily a problem, if the adjacent joint is situated such that gravity will pull it apart, it can easily fall apart. To prevent this from happening, I always position the joint(s) adjacent to the one being soldered in a horizontal position.
Step 8: You're Done
I've found soldering copper to be very rewarding and useful for numerous projects. It really isn't very difficult and it will open up numerous possibilities in your mind of what can be accomplished using this skill. Happy making!
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