All About Pipe
Metal Pipe
Plastic pipe has been become widely-accepted as the standard for DWV lines, but it has yet to capture a significant portion of the pressure pipe market. Copper is clearly the choice of most plumbing contractors to supply residential drinking water. But metal pipe has a number of other uses for which plastic is not suited, such as for steam heat and for natural gas distribution, or in industrial environments where strength and durability are vital.
Metal pressure pipe with a diameter of 2" or larger is usually welded end to end. This is the most economical and leak proof way of joining large diameter piping. The disadvantage of this type of joint is that weld metal may intrude inside of the piping, which could affect flow of some materials. (A backing ring can be inserted in between the joint to prevent this.)
Plastic pipe is not welded in this manner, but always requires fittings to be joined.
Pressure pipe with a diameter of 1 1/2" or less is usually joined by socket welds or threaded joints.
Socket welding has an advantage over threaded connections because it is easier to install and makes a pipe virtually leak proof, which is critical when dangerous fluids or gases are being carried through the line. There is also no chance of weld material entering the bore of the pipe.
Black pipe and galvanized pipe uses threaded joints or welds. Cast iron no hub pipe is not welded, but uses rubber-sleeved couplings with steel band clamps. Joints in copper pipe are made by solder "sweated" around the circumference of the pipe; plastic pipe generally uses solvent cement unless it’s connecting to steel pipe or hoses, when threads are used.
Sink drains often use chrome-plated tubular brass goods including P traps, S traps, J bends, short lengths of pipe, etc, with slip-joint nuts on both ends.
These are not really considered pipe but rather tubular drainage products. These items consist of ells, couplings and tees in 1-1/4" and 1-1/2" size; all with slip joint nuts and washers. Because their finish is fragile, strap wrenches are recommended for installing and removing them undamaged.
Tubular products are not the same size as IPS pipe. Tubular brass is connected to IPS pipe by means of desanco fittings.
