Pipe fittings are components used for connecting pipes in many different settings, from plumbing to manufacturing. They can be used to connect two or more pipes, extend or terminate a pipe’s direction, or transition between different size pipes. Fitting ends can be male (fits into a pipe), female (fits around a pipe), or both (one male end, one female end). When identifying the appropriate pipe fitting for a specific application, consider the material, shape, and size of the fitting. Also determine how the pipe will be used, the level of pressure it must be able to withstand, and its required durability.
Pipe fittings are available in a variety of materials, including stainless steel, brass, aluminum, plated metals, and plastics. Metals have more durability and can withstand higher pressure than plastics, while plastics are lighter weight and can be more resistant to corrosive liquids and gases than metals.
Pipe fitting shapes vary depending on the application. Among the shapes are elbows (to change flow direction between pipes), caps and plugs (to terminate a pipe), crosses (to connect and branch four pipes), couplers (to connect two pipes going in the same direction), tees and wyes (to connect and branch three pipes), nipples (to connect two pipes, usually with male ends), and flanges (to connect two pipes and can be bolted together).
Pipe size is standardized in North America as Nominal Pipe Size (NPS), but it is not always the actual measured size of the opening. To determine pipe size, measure the inside diameter (ID) of the pipe that will be connected to the female fitting, the outside diameter (OD) to be connected to a male fitting, and then refer to an NPS table. For unthreaded pipe, the measurement corresponds directly. For threaded pipe, round the measurement up to find the correct corresponding pipe size. For example, if a threaded pipe measures 7/8” in ID or OD, round up to the next size which is 1”, which corresponds in an NPS table to a pipe size of 3/4”. For unthreaded pipe, if it measures .84” in ID or OD, this corresponds directly to a pipe size of 1/2”, without rounding up.
The fitting style (how the fitting connects to the pipe) is determined by its use. For example, butt welds can be used when applications require a water-tight seal or the ability to withstand high pressure. Threaded fittings work when quick installation and disassembly are required. Pipe fittings can be connected to pipes by threading, welding, heating, cementing, or bolting.
Schedule is a number used to define the thickness of a pipe wall. The thickness can be critical because it determines how much pressure the pipe and fittings can withstand. The higher the pipe’s schedule, the greater the wall thickness and ability to withstand pressure. Common schedules include 10, 40, 80, and 160.
Maximum working pressure, also called maximum allowable working pressure (MAWP), is the maximum amount of pressure a piece of equipment should experience during operation. For pipe fittings, maximum working pressure refers to how much pressure the walls of the fitting can safely tolerate without failing. MAWP is different that burst pressure, which refers to the point at which the fitting will fail. Class is a standard relating to tolerance, construction, dimensions, and wall thickness, but it is not a direct measurement of maximum working pressure.
Pipe fittings are used in a number of industries with stringent safety and operational regulations. When selecting a pipe fitting, it is important that it meet the specifications for the application. Pipe fittings are manufactured to meet specifications defined by the American Society of Mechanical Engineers (ASME), American National Standards Institute (ANSI), the U.S. government, and many others.