Sweating, more commonly known as soldering, is the process of joining copper pipe together using copper or brass fittings. It's not too difficult a job and the results should provide a leak-proof pipe that lasts a lifetime. Bear in mind that sweating copper pipe to brass or bronze fittings is a little trickier than sweating copper pipe to copper fittings.
Step 1 - Preparation
This is the most important step throughout the sweating process. If the copper pipe you intend to sweat is a water pipe, you must drain the line and ensure that it is completely free of water before soldering. Shut the water main off and leave all the faucets in your house open.
Next, you must clean the pipe and fittings as any debris could hamper the quality of their bond. First, use your dry cloth to remove any dirt. Gently sand the pipe and fittings with emery cloth. Your main focus should be the inside and ends of the pipe and fittings.
Step 2 - Fluxing and Affixing
Flux comes in liquid or paste form and allows the solder to flow into the joint. If you're sweating a water pipe, make sure to purchase a suitable flux. Using your flux brush, apply a layer of flux to the outside and ends of the pipe and also to the inside of the fittings. Apply enough to cover the joint area but not so much that you get flux dripping off.
Once the flux has been applied, join the fitting to the pipe and make sure that it is fixed in exactly the right position for its desired use.
Step 3 - Heating the Joint
Put on your safety goggles and your heat-resistant work gloves. Using your blow torch, evenly apply heat to the region where the pipe meets the fitting. Hold the flame about an inch from the pipe and move it up and down to a distance of an inch or so from the joint on either side. If you are sweating a copper pipe to a bronze fitting, give extra attention to the fitting as it is thicker and will require more heat to take full effect.
Step 4 - Applying the Solder
After a few seconds of heating the joint, remove the flame and touch each end of the joint with the lead-free solder. Be sure to move the solder around the joint so that all of it can be lined. You should see the solder melt into the joint. If this doesn't appear to be happening, you may need to reheat the joint with the blow torch. Once a drop of solder falls from the joint, stop soldering.
Step 5 - Cleaning the Joint
Wait a few minutes before cleaning the joint as cooling too quickly can make it brittle and consequently break off. Use a cloth dipped and squeezed in a bucket of water to wipe the pipe and fittings of excess flux and debris.
Step 6- Flushing the System
Once the joint is looking clean and shiny, turn your water mains back on and close all the faucets. Allow the water to run for a few minutes. This is to ensure it is free from debris and excess flux prior to domestic use. Pay close attention to any leak points and rectify immediately.