How to CORRECTLY Solder a Copper Pipe




Introduction: How to CORRECTLY Solder a Copper Pipe

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Hi in this article I’ll be thoroughly explaining how to solder copper pipe to get a nice leak-free joint. If you’re unfamiliar with soldering, you’ll be able to solder any diameter pipe after this video with ease and peace of mind.

Step 1:


Alright, so the first things I wanna go thru are the tools and materials you’ll be needing to complete the task. So tool #1 is a torch. You’ll find a good torch at your local hardware store that should cost you between 20$ to 50$ Canadian dollars, Yes there are better models out there for commercial plumbers but if you are a DIYer doing minor work, these will do just fine.

To be able to use your new torch you’ll be needing some fuel. There are 2 varieties of fuels for you to choose from, you’ve got your ordinary “propane” gas which you can either find in the camping ile or in the plumbing section of the store or MAPP gas. The difference between both of these is that MAPP gas burns hotter than propane, which in turn heats up your joint quicker, so it’s up to you to choose which one you want to use.

You'll also need a lighter for your torch, If your torch doesn’t have one built-in, you can use a dedicated striker.

Something else you'll need is some flux. The primary purpose of flux is to prevent oxidation of the base and filler material when soldering.

Finally, you'll need some wire brushes, sandpaper, and solder. The plumbing code specifies to NOT use 50/50 solder as it contains lead, so use 95/5 or any solder that is lead-free.


Preparation is key to having a good leak-free joint. The first step to accomplish this is to clean both parts that’ll be joined together. To clean the pipe, take your sand paper and sand the portion that’ll penetrate the fitting until it resembles this. As you could see, there are no more surface spottings and that’s exactly what we are looking for. Next is the fitting. You’ll wanna use a dedicated size brush for your fitting to get it cleaned, they most often arrive clean from the manufacture but it’s important to get the surface roughed up a bit just so the solder can adhere better.


With both your surfaces now prepped, let’s assemble them, but before you’ll need to apply some flux. Applying the flux is pretty self-explanatory, all that’s needed is enough of it to cover both surfaces that touch just like in the picture.


With your flux now applied it’s time for the actual soldering process which is step 2. Now the goal here is to heat the portion you want your filler material to be pulled into. There’s a term for this and it’s called capillary action. Capillary action is the ability of a liquid (solder in this case) to flow in narrow spaces without the assistance of external forces, meaning it’ll flow upwards which is pretty cool.

It’s imperative to start heating your joint at the bottom FIRST, reason being is if you start heating the top first, your solder will want to flow down due to gravity but won’t have anywhere to go since the bottom of the joint is too cool to melt the solder, so always start from the bottom and work your way up.

So keep heating it up while testing your solder every now and then to see if it gets sucked in. Eventually, your joint will be hot enough to accept your solder so go ahead and run a nice bead all around the joint to ensure full coverage. A good tip here is to always inspect your joint after soldering it, it’ll speak for itself meaning that if you haven’t correctly heated the joint, you should see some voids in the joint. If this happens all you have to do is reapply a bit of flux, heat up the joint and solder the affected area.


As the final step, when you’re sure that your joint is soldered correctly, wait a couple of minutes for it to cool down. Some plumbers will use some flux to clean off the joint while it’s still very hot but doing this will cause a big drop in temperature in a very small amount of time and can fracture the joint causing a leak. Once your solder has solidified, use a rag to wipe off any excess flux that could potentially eat up your pipe in the long run, and you’re done.

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    53 Discussions

    I have been soldering for years and early on it was for hi vacuum applications. I am always concerned about these how to videos, but you did a very good job. Keep on the folks about cleanliness, since that is the key. Bottom up is also a great hint. Again good job.

    1 reply

    Thank you jhowieb, you comment is appreciated!

    Most of us home owners would do more repair work then new copper work. If you are trying to solder on to existing piping make sure that the system is completely drained of water. Failing to do this will not allow the pipe to reach the appropriate temperature and the resulting joint will fail. Very frustrating till you figure out why the solder is not taking.

    1 reply

    Yes, pipe must be free of any water before soldering!


    9 days ago

    This is a nice tutorial. I recently changed all the compression angle stops in my house to screw-thread ones so they would be easily maintained or replaced. This involved cutting the original pipes very close to the wall and soldering on extensions as well as the threaded couplers. I had soldered electronics before but sweating pipes was a new experience. The hardest part was avoiding scorching the wall and vanity cabinet while working in tight claustrophobic spaces. I found many videos that showed doing this out in the open, but very few that showed real-world scenarios like I experienced. Perhaps you could do one of you actually doing a job inside a bathroom vanity.

    I've used standard copper water pipe for compressed air lines (~135 psi) for years with no issues. In North America, you can get a heavier grade (Type L -- usually with blue markings) and the standard grade (Type M -- red markings). There is also even heavier green, Type K tubing that's made for underground use, but that's a waste of money for air lines. I usually end up soldering it with lead-free solder, because that's what I generally have around, but standard tin/lead solder is a little easier to work with. If you are using a piston-type compressor, which vibrates when it's running, I'd recommend attaching a flexible line between the compressor and your copper air line plumbing to avoid work-hardening the copper, which makes it brittle and prone to cracking. Rotary compressors operate smoothly enough that this isn't an issue. Depending on the flow I need, I use either 1/2" tubing, or 3/4" tubing. Below is an image of the passive dryer I made for my home workshop...note that there are a small amount of copper and a few solder joints involved...and not even a pinhole leak anywhere to be found... :)


    wow, looks really cool. Not really sure what it's for, but, looks nice.

    It takes the hot, moist air from the compressor pump, cools it, and separates out the water before sending the air to the storage tank. The section of two-inch copper pipe (vertical at bottom left) is filled with copper wool and directs any moisture down to the bottom of the pipe, where an automatic drain valve dumps the water every time the compressor runs. It's completely passive, so no power is needed, and it does a very good job of drying the compressed air (not quite as good as the ones that refrigerate the air, but good enough). You can do something similar using an automotive A/C condenser in the place of my long copper tubing radiator.

    ah, very interesting. I was wondering why all the length but see now it has to do with cooling. I didn't know some systems use refrigeration, but it makes sense. It would spoil your aesthetic but you could use the expelled water to dampen a "swamp" (evaporative) cooler,, around your cooling tubes to increase the refrigeration/cooling effect even more, and in a passive way too. Maybe you could keep the aesthetic by using copper foam ( ) and capillary action to wick up the drained water to cool the bottom tube or two. (no idea if that'd work).

    It's mean't to dry the air so that water doesn't go into your air tools. If air would go into your air tools, they would rust and eventually fail. Every mechanic I know oils their air tools every 2 days or so since they use them a lot and they last a lot longer like this.

    Before we got a rotary compressor with an integrated dryer at work, we were using piston compressors with no dryers. During our humid season, the tanks would get so full of water, if they weren't drained every couple of hours, that water would spray out of the tools' exhaust ports. On a really bad day, you could shoot water out of the lines, like they were water hoses! Oiling tools does help protect them, but reasonably dry air is where you should start. We're in the middle of the humid season right now, and my home-built dryer seems to be doing the job quite well.

    actually, since you built a nice compressed air system... maybe you have some thoughts on what I'm planning to do: I am wondering if I can buy the motors and compressed air tank separately and put them together myself. I know the tank max. pressure should be higher than what the motors do but beyond that isn't it basically just Legos? My problem is that nearly all compressors I've found that are small enough for me sit horizontally (this is about perfect in tank size, flow rate, dB noise, everything except orientation: I need to have the tank vertically and the motors next to it, just no space otherwise. I found a system where I could take it apart and mount the tank vertically but it appears there's some kind of water drain valve that then would not work since it'd be on the side and not the bottom, so I think I'd have to get a tank designed for vertical use.

    You sure can, i've done it on mine. I used a 4 gallon tank with an old electric motor and compressor motor and it works fine. One thing I have heard, is people using "refrigerator compressors" to compress the air, apparently, it's super quite and does the job just fine!

    Thanks for the vote of confidence. I just explored diy refrigerator compressed air systems, very interesting. I might still just buy the commercial one I linked to though and try to separate the motors and tank and try to make some connector pipes or tubes. As far as I can tell the critical bits to keep working would be a pressure relief valve and a water drain at the (new/rotated) bottom of the tank. The picture shows an extra hole on the end of the tank but I'm not sure what it's for or if I can use it to attach a water drain valve to. I hesitate to play around much since maybe I'm defeating some safety design aspect....

    The joints will be fine. Type M has a psi rating of 430 for annealed 1/2" tubing (350 for 3/4", 295 for 1"). Drawn tubing has even higher ratings. For joints you need to use 95-5 tin-antimony. Ratings for 1/4"-1" is 500 psi @ 100 degrees F -- down to 200 psi @ 250 degrees. 50-50 tin-lead 200 psi @ 100 degrees F, down to 85 psi @ 250 degrees.

    Just don't use PVC pipe. Many have done it successfully, and it will easily hold the pressure. The problem is it gets brittle with age and exposure to sunlight, and it SHATTERS when it bursts. So it can send sharp shrapnel over the shop. You can use black iron threaded pipe, just make sure you have a few low spots with caps or valves so you can drain any water accumulation. An air dryer at the compressor is a good idea for any system, and filter types that remove enough moisture for painting aren't expensive for hobby/home shop levels. High air capacity commercial systems are a different story. Northern Tool and Harbor Freight have several that I'd use in a home shop or light duty commercial setting.

    How much pressure are you running? Normal Home plumbing systems run between 40-80PSI, meanwhile compressed air lines run somewhere up to 120-150PSI. I would suggest "brazing" but "soldering" could work also, it all depends that pressure you'll be pumping in the lines.

    I'm just at the planning stage so, no pressure at all yet. :) I guess most of the compressors I've looked at that will fit the tiny space I have go up to about 8bar. A couple to 11 bar but not sure I even need that much pressure. So 116 - 160psi (but very likely the low end of that). I like the aluminum tube systems but am not sure about how they work yet, how expensive all the coupling bits might be compared to just brazing copper.