The rules and best practices for cutting and sealing pipe are, for the most part, universal. All pipes, no matter the type — for water or gas lines, must be:
- Cut square
- Cleaned, reamed or de‐burred (with all debris and filings from the cutting and de‐burring removed)
- Returned to original diameter
- Prepared for joining
Copper pipe may be cut using tubing cutters or a saw. Any burrs that remain on the inside of the pipe and outside of the pipe must be removed. Burrs on the inside must be removed to bring the pipe back to the original diameter and to provide a smooth flow of water and prevent turbulence that can cause erosion and corrosion to the copper pipe. The outside burrs must be removed to ensure full insertion of the pipe into the fitting.
The same procedures must be followed if the copper piping is used for gas or air, as the turbulence would hinder the flow and result in an under‐sizing of the BTU availability in a gas system.
When soldering copper pipe that will be used for water, the pipe and fitting must be cleaned of all corrosion and oxidation. Methods and tools for cleaning vary, but the most commonly used are wire brushes, sand cloth (emery cloth), or steel wool. Both the pipe and fitting must be shiny and dry before joining.
The proper amount of flux must be applied to both the pipe and the fitting — using only enough to completely coat both surfaces. The type of solder often called "soft solder" must be the lead‐free type.
On smaller copper pipe (1/2" nominal through 1" nominal), the heat from the torch is applied to the fitting at the bottom of the socket farthest from the where pipe and fitting intersect and the solder is applied. The flux should turn clear before the solder is applied. The proper amount is determined by the size of the joint: 1/2" of solder for a 1/2"N joint, 3/4" of solder for a 3/4"N joint and 1" of solder for a 1"N joint. For copper pipe larger than 1" nominal, the size and method of soldering and applying heat may vary.
Other methods of joining copper pipe in a water distribution system include: push fittings, compression fittings, mechanically pressed fittings, and flare fittings.
The first three are assembled using the manufacturer's directions and recommendations.
The fourth method — flare fittings — require special tools and a great deal of practice when used to join copper pipe. The method used to flare copper is the same for both water and gas, and the pipe is prepared the same as for soldering (minus the flux).
Flare joints are made using soft tubing. If hard copper must be used, as in a straight run that will be exposed, then the end of the pipe must be annealed. Slide the flare nut over the pipe and insert the pipe into the flaring vice/tool following the vice manufacturer's directions. (Practice will ensure you get a consistent flare every time.) Remove the vice and insert the fitting into the flare nut. If the joint has been done correctly, the angle of the flare 45 degrees will match the inside of the nut and the face of the fitting. One of the advantages of this type of joint is that it can be disassembled and reassembled many times without degrading the integrity of the joint. (Note: This type of joint is not permitted in concealed locations.)
If you choose to solder copper pipe that will be used for gas, the pipe must be silver‐soldered using hard solder.
Threaded pipe may be used for both water and gas, and the method of joining is the same. The type of pipe compound must be applicable for water or for gas, and some types may be used for either. The pipe tape used to join water or gas must be listed for that particular use.
It's worth noting that in different parts of the country, there are differing opinions on the use of these methods of joining threaded pipe for each application. Regardless of the view one supports, the proper way to use pipe compound or pipe tape includes a few rules:
- It is never applied to the first thread of the nipple or pipe.
- The number of turns of the tape is determined by the manufacturer.
- Compound is applied only to the male threads.
- When joining threaded pipe, the joint is made by turning the pipe or fitting to hand‐tight and then no more than two turns to line up the fitting or valve. As you continue with the piping, the last part tightened must be backed up so it will not move or rotate. This will help keep downstream fittings lined up. When tightening threaded pipe, it is critical that the joint not be over‐tightened. There are more leaks in threaded joints by over‐tightening than all other reasons combined. Both the pipe and the fitting are tapered. Over‐tightening will stretch the fitting, and it will have to be replaced.
- Use the proper size wrenches for the pipe and fittings. The smallest wrench that will do the job is the better choice. Use an adjustable wrench if the fitting has flats, because a pipe wrench will mar or damage the fitting and might form sharp burrs that could cause injury.
When used for water piping, PEX pipe requires less fittings, which allows for a smoother flow of water. Different manufacturers limit the number of fittings before the pipe size must be increased, and the installer must be mindful of this. The pipe is cut and joined with crimp rings, compression rings, and push fittings.
Polybutylene pipe is cut and joined in the same manner with the same advantages and restrictions.
Polyethylene plastic pipe, when labeled and used for gas, is for outside use only and must be buried. The pipe is buried 18" deep with a tracer wire and backfilled 6 to 8 inches. Caution tape is placed in the ditch at that level with the words CAUTION GAS LINE BELOW printed on the tape. The stand pipe is attached with a push‐type fitting. A special deburring tool is used prior to installing the fitting.
CPVC pipe is often used as an alternative to copper. It uses the same number of fittings and is more cost effective than copper, but CPVC must be treated more carefully than copper and should be examined for stress fractures if dropped. CPVC comes in the same sizes as copper pipe and has the same fittings, (e.g., 90s, tees, adapters). It is cut with a fine‐tooth saw, deburred, primed and joined with a special CPVC glue, rotating the pipe a quarter‐turn when joining. CPVC can be used for both hot and cold‐water lines.
PVC pipe is used for cold water only, normally not as a distribution pipe but often as a service pipe. PVC pipe is cut squarely with a saw or tubing cutters, deburred, cleaned, primed, and glued with PVC glue, rotating the pipe or fitting a quarter‐turn when joining.