How to Solder Copper Pipe

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Introduction: How to Solder Copper Pipe

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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    55 Comments

    A trick I learned many years ago from my father-in-law who was a pipefitter by trade. I had copper water pipe in a wall and I could not quite get the water to stop dripping. He suggested packing the inside of the pipe with clay to stop the flow. Once complete and the water turned on the clay flushed out. Neat trick.

    I'm a retired Pipefitter, myself. I was one for 38 years & never tried that method as it has a tendency to clog things up in copper tubing. Course, I had used it when our crew of fitters had to make 60" leaded, bell & hub cast iron joint having 30 pound service water running through it.

    My father in law is a retired pipefitter and gave me this tip when I was trying to replace an outdoor water hydrant. I had to cut a hole inside the interior wall and could not completely turn off the water. I had a slow drip. I called him he suggested either bread or mud. I have tried both over the years and have found both work. The bread or mud will flush out after the water is turned on. One just needs to block the flow for a few seconds while soldering.

    On copper tubing, a ball of bread works best.

    Good idea. Thanks for the input.

    The most difficult part is soldering of vertical parts "on the spot" at the lower end, close to a wall for instance. Because you can't see if you filled the joint all around you will have a tendency to put too much solder. Then gravitation seems to have a more significant effect than capillarity, and the result is often a leaking joint...

    That's why in your repair kit you also have a inspection mirror. Using it you can see the backside of the fitting with it. And, instead of growing a third hand to put a flashlight in it, just turn the gas down on your torch so you can see with the light of your gas torch to see the back side or the underside of the sweated fitting.

    I can see that would be problematic. I'm glad I got to practice first on some easier stuff.

    This is an Angels fear to tread topic - brave to publish.

    The technique you are describing is the UK end feed technique - it's where plumbing becomes a craft. Any fool can do solder ring, but getting molten solder to feed completely by capillary action between pipe and fitting is the craft bit.

    Golden rules - clean all the surfaces to be soldered - don't go near sandpaper - use Scotchbrite or similar. Don't go near hacksaws - use a wheel pipe-cutter that automatically chamfers the cut and makes it square.

    Immediately apply flux - this should be lead-free paste for lead -free solder. The flux stops oxidation. Copper oxidises almost immediately and copper oxide won't solder. Using this technique, you can solder the most difficult pipes like chrome-plated and stainless steel.

    Assemble the pipe and fitting, right up to the stop, rotate to spread the flux.

    Now the tricky bit. I use MAPP gas for heat alone. Heat the fitting, away from the ends of the fitting - don't over-heat - you don't want to burn the flux.

    When the flux starts bubbling, test the temperature with lead-free solder wire (not stick, not electronic) and when the solder melts, that's the time to feed the wire right around the joint.

    A well prepared pipe and fitting require very little solder - a top class joint should have a barely visible ring of solder showing. While still molten, check alignment and if there are dollops of solder, wipe off now.

    Allow to cool to warm/hot to the touch - dip in water and clean up with Scotchbrite. The joint should be a thing of beauty.

    Why clean out the flux? - it might be a drinking water pipe.

    The same technique applies to brazed joints, but the temperature and skill steps up a notch.

    Finally, test it - it needs to be gas or water tight at the maximum working temperature - a very wise plumber told me that with cold water, the flux alone will disguise an unsoldered joint, but pressure and heat will soon find it out.

    End-feed is my joint of choice - it looks better, it's cheaper, it's skillful.

    If you want to go the whole hog, try flared joints, the ultimate cheapskate/skilled method - alternatively, there's always compression fittings, or you can just push a length of plastic pipe into a plastic fitting, but both are another story.

    Scotchbrite? Nah!. I always use sandcloth. It's on the order of emory cloth where the abrasive is on a cloth backing. And, it comes in rolls that are 1-1/2 inch wide and in 5 yard & longer rolls. It's a much faster way to clean copper tubing as you can use it like you're buffing your shoes.

    Being drinking water or not doesn't matter as you sure can't clean the inside of the tube with a cloth rag. where some flux may be. You clean the outside because flux has a greasy feel to it. And, it collects dust, hair & what not. You clean the outside just for looks. And, you run hot water through the system to flush the flux and whatever bugs croaked in the tubing while in storage before it is put in a system to be used.

    And, un-like the person said above, if you want to go whole hog, DO NOT USE flare tubing. Because that also brings out a new set of tools, and experience that the average Joe doesn't have. And, flare or compession fittings can get very pricey very fast. Stick with soldered tubing & fittings. Besides usually, flares are used when your working with gas & soft tubing only.