Pipe and Fittings

Definitions of Pipe

  • A pipe is any rigid tube like material.
  • Tubing is any pipe that is flexible enough to bend.
  • A nipple is a short pipe under 12 inches in length that is threaded on both ends.
  • A fitting is a connecting device used to join pieces of pipe or to connect pipe to other objects such as fixtures, appliances, or pumps.
  • The size of pipe is generally based on the inside diameter (ID) which is a nominal size, not the actual size.
  • However, the outside diameter (OD) may occasionally be used to measure the size of the pipe.

Steel Pipe Plumbing Systems

Steel pipe is available in three grades: standard (schedule 40), extra strong (schedule 80), and double extra strong (schedule 120).


  • Extra strong (schedule 80) and double extra strong (schedule 120) are used primarily in commercial and industrial settings.
  • All grades of steel pipe have the same outside diameter for a given size which permits pipe threading with the same die; it also allows the use of the same sized pipe fittings for all three pipe grades. The additional wall thickness results in reduced inside diameters.
  • Steel pipe is designated in nominal size called Iron Pipe Size (IPS) or Nominal Pipe Size (NPS) Standards.
    Common sizes found in plumbing are 1/8”, ¼”, 3/8”, ½”, ¾”, 1”, 1 ¼”, 1 ½”, 2”, 2 ½”, 3”, 4”,5”, 6”, etc.

Two types of steel pipe are primarily used in plumbing: black iron and galvanized steel.

  • Black iron pipe is used for gas, steam, and emergency fire systems.
  • Black iron pipe has no coating; therefore it provides little resistance to rust. When used for underground gas lines, black iron pipe comes with a Poly-Vinyl-Chloride (PVC) coating to protect it from corrosion.
  • Before 1970, galvanized pipe was used mainly for water supply and cold water systems. It is still used in combination with other materials because of its strength and ability to support cantilevered weight.
  • Galvanized pipe will meet the minimum pressure requirement of 125 psi when standard (schedule 40) is used.
  • Galvanized pipe not only creates greater friction losses than copper and plastic pipes do, but it also has a greater tendency to scale and thus it reduces flow capacity.
  • Galvanized pipe lasts at least 30 years in most soils.

Connecting steel pipe in plumbing construction requires two types of
fittings: threaded and dielectric fittings

Threaded fittings are tapered threads (NPT – National Pipe Thread) which create an interference fit that should not be used in combination with other threads such as machine or hose threads.

  • Threaded fittings are time consuming to make.
  • Threaded fittings require some type of pipe thread compound such as pipe joint compound or Teflon tape to create a water tight seal.
  • Female threads are made on the inside of a pipe or fitting.
  • Male threads are made on the outside of a pipe or fitting.

Dielectric (non-conducting) fittings (couplings or bushings) are necessary when dissimilar pipes are used in combination with copper pipe or tubing in order to minimize electrolysis which causes corrosion.

Additional Standard Information Regarding Steel Pipe

  • The standard length of steel pipe is 21 feet.
  • Steel pipe is the best material for resisting mechanical or fire damage.
  • Water quality should be considered before selecting pipe materials. Investigate the local plumbing code.
  • Galvanized pipe nipples can be purchased in half-inch increments up to 6 inches and 1-inch increments up to 12 inches.

Steel pipe requires the application of a sealant to ensure a leak proof fit.

  • Pipe thread compound, which commonly contains Teflon, is used on the threads of pipes to prevent leaks.
  • Teflon tape can be used as an alternative to pipe thread compound.

Copper Pipe Plumbing Systems

Copper pipe is available in two types: rigid pipe and flexible tubing. It is used in water supply and Drainage-Waste-Vent (DWV) systems.

Rigid copper pipe is available in four wall thicknesses and is color coded.

  • Thin-walled (type M-red) is usually adequate for home plumbing.
  • Medium-walled (type L-blue) is generally used for re-pipes, repairs, residential service lines when properly sleeved and commercial plumbing.
  • Thick-walled (type K-green) is used on outside work that may be subject to mechanical damage, hospitals, or for underground burial when properly sleeved and under corrosive conditions.
  • Drainage-Waste-Vent (DWV-yellow) may be used in any DWV system. This is the thinnest-walled form of copper pipe.

Additional Information Regarding Rigid Copper Pipe

  • Rigid copper pipe diameter is measured by the nominal ID.
  • The OD is a given nominal size which remains the same for all four weights of pipe.
  • Rigid copper pipe is sold in standard 10 and 20 foot lengths.
  • Rigid copper pipe can be soldered only; it cannot be flared.
  • Rigid copper pipe, although comparatively expensive, is easy to work with in both new installations and modified systems. The savings in labor will generally offset the high cost of materials.
  • Common sizes are ¼, 3/8, ½, 5/8, ¾, 1, 1 ¼, 1 ½, 2, 2 ½, 3, 3 ½, 4, 5, and 6
    Fittings: Copper fittings are either threaded (NPT) or slip (for soldering).

Lead free solder in potable water supply lines is the medium used to join copper pipe and fittings.  The process of joining copper pipe and fittings is known as “sweat” soldering.

  • Solder comes in a variety of types. 50-50 solder is a combination of 50% tin and 50% lead and is suitable for moderate temperature and pressure. If a stronger joint is required, 95-5 solder (which is 95% tin and 5% antimony,) may be used.
  • 50-50 solder is no longer allowed for use in water supply systems because of its lead content. Therefore, check the local plumbing code, and use a lead-free solder such as 95-5 where appropriate.
  • Flux is necessary to remove oxides, promote wetting, and protect surfaces during heating. It. Manual cleaning is required. should not be relied upon to clean the surfaces of copper pipe and fittings.

Flexible copper tubing, unlike rigid copper pipe as described above, is not color coded. However, it is graded according to two types of wall thicknesses and is marked every eighteen inches with its type and manufacturing information.

  • Medium-walled (type L) is used in most homes, principally for gas service lines.
  • Thick-walled (type K) is used in most homes for underground water service lines.
  • There is no thin-walled or DWV type of flexible copper tubing.
  • The chief advantage of flexible copper tubing is its flexibility; it can easily be bent across the knee. However, care must be taken to avoid kinking.
  • Flexible copper tubing is resistant to most corrosion.
  • Fittings: Copper tubing uses either flared fittings or compression fittings.

Plastic Pipe Plumbing Systems

Plastic pipe, similar to copper pipe, is available in two types: rigid pipe and flexible tubing.

Rigid Plastic Pipe

  • Rigid plastic pipe is manufactured out of three different synthetic products: PVC, ABS, and CPVC.
  • PVC (polyvinyl chloride) is used primarily for cold water supply, DWV, and irrigation lines.
  • ABS (acrylonitrile butadrene stryene) is used exclusively for DWV systems.
  • CPVC (chlorinated polyvinyl chloride) is used in hot and cold water supply. Although it costs three to four times more than PVC it normally is used because it withstands heat and maintains its strength. The local plumbing code should be checked prior to CPVC installation.

Plastic rigid pipe is available in many weights:

  • “Schedule” sizes are based on steel pipe dimensions and come commonly in schedule 40, and 80; all weights meet the minimum pressure rating of a closed water system.
  • “Class” sizes are designed for a specific working pressure (ex. Class 200 – 200 psi). Common class sizes are 125, 200, and 315.

Common PVC sizes found in plumbing are ½”, ¾”, 1”, 1 ¼”, 1 ½”, 2”, 2 ½”, 3”, 4”, 5”, 6”, etc.

Additional Information Regarding Rigid Plastic Pipe

  • Rigid plastic pipe is sized according to its nominal ID based on IPS.
  • Rigid plastic pipe is available in standard 20 feet lengths.
  • The OD remains constant while the ID varies according to weight; this allows the use of the same fittings.
  • PVC Primer is a solvent designed to clean and soften PVC pipe and should be used when gluing pipes larger than 1”

Plastic pipes and fittings are joined by a solvent weld joint.

  • Primer is essential for a solvent weld joint in plastic pipe and is used for pipe larger than 1”. Priming cleans the surface, removes glaze, and starts the softening process to make a proper joint. Use the appropriate primer for the type of plastic pipe being used.
  • Solvent glues or cements are available for ABS, PVC, CPVC plastic pipe. Use the appropriate type for the pipe being used. All purpose or universal solvent glues are convenient to use when using more than one type of plastic pipe.
  • Time and temperature play an important role in getting a good seal. Solvents are designated by color (gray or clear), set time (e.g. slow or fast), and body (e.g. light, medium). Lighter body, faster setting glues, are used on small pipes and heavier body, slower setting glues, are used on large pipe. Special glue is available that works well on wet pipe for use in repair of sprinkler systems.

Local codes generally forbid the use of rigid plastic pipe behind or within walls.  Schedule 40 or 80 is recommended for out-of-ground exposed work.

Flexible Plastic Tubing

Flexible plastic tubing is available in only two types of Synthetic Material:

  • PE (polyethylene), commonly used in landscape drip irrigation.
  • PE-RT (raised temperature) used in domestic hot and cold water systems.

Additional Important Information Regarding Flexible Plastic Tubing:

  • The inside diameter of flexible plastic tubing remains constant while the outside diameter varies according to the quality.
  • Flexible PE tubing can be used only for outside cold water systems such as wells or sprinklers.
  • Flexible plastic tubing is connected to itself or steel pipe by using polystyrene fittings and couplings. Stainless steel base clamps are used to secure the slip joints. Solvent is not used. Irrigation applications use low pressure slip on connectors
  • There are several advantages to working with flexible plastic tubing: low material cost, ease and speed to work with, and flexibility.
  • Flexible plastic tubing does not normally corrode; however, it will deteriorate with extended exposure to direct sunlight. If it is not exposed to direct sunlight, flexible plastic tubing has a long life expectancy.
  • Flexible plastic tubing creates less friction loss than metal pipes do.
  • PE tubing is commonly used in agriculture for drip and micro sprinkler lateral (above ground) piping.

Small PE tubing is available in copper tubing sizes for cold water applications. Compression fittings similar to copper tubing are used. Compression fittings specifically designed for use the PE tubing should be used. Common sizes are: ¼”, 3/8”, ½”, 5/8”, ¾” (O.D). Common applications are water supplies for swamp coolers and refrigerators.

Plumbing Fittings and Valves

Plumbing fittings have different shapes which allow rigid straight pipe to change both direction and diameter. Since the names of plumbing fittings derive from either their shape or their function, the names remain the same regardless of the material from which they are made. Fittings are generally divided into two categories: Water Supply or DWV (Drain, Waste and Vent.)

A description of the most common plumbing fittings follows:

  • Elbows are used to change the angle or direction of the pipe run. The most common elbows come in 90 degree and 45 degree turns. The sweep of the fitting describes how fast a transition or change in direction is made. Therefore--especially in DWV fittings--the long sweep fittings are chosen to avoid clogs. 90 degree elbows are generally called ells.
  • On threaded street elbows, one end of the fitting has male threads and the other end has female threads. Street elbows are common in galvanized steel and copper pipe. They are convenient because they do away with the need for a nipple and work well in tight quarters.
  • Tee or T-fittings allow for branch lines. They are shaped like the letter T. DWV tees are known as waste or sanitary Ts. In these fittings the intersection is slightly curved in order to avoid clogs. Gradual bends are best for smooth flow of waste.
  • Couplings are used to join two straight pieces of pipe of the same diameter.
  • Reducers are used to join pipe of different diameters. Galvanized steel reducers are called bell reducers because they look like a bell. All reducers make a gradual transition between different diameters of pipe and therefore they take up considerable space.
  • Bushings are used to make the diameter of a pipe fitting smaller. They differ from reducers in that they make abrupt changes in diameter and take very little space. Two examples of galvanized steel bushings are face bushings, which take the least amount of space, and hex bushings which can be tightened with an adjustable wrench.
  • Unions are used to join pieces of pipe where pipes cannot be turned or when a piece of equipment may have to be removed for maintenance or replacement.
  • Adaptor fittings are used to change the end of a non-threaded pipe to male or female threads as needed. Adaptors are commonly used in copper and plastic plumbing jobs. For example adaptors are used to convert from a PVC glue connection to a threaded connection or from a copper soldered connection to a threaded connection. Male adapters and female adapters are both common.
  • Caps are used to close the end of a dead end pipe.
  • Plugs close an opening on a pipefitting normally used for inspection and cleanout.
  • Nipples are short lengths (under 12") of pipe threaded at both ends.
  • Wyes (pronounced like the letter Y) are used primarily to gain inside access to DWV systems.
  • Valves are devices that control the flow of liquid or gas through or from a pipe. Types of plumbing valves are: compression valves, ball valves, sleeve-cartridge valves, ceramic disc valves and more.

PVC Fittings

PVC fitting come in a wide variety of configurations. They many be glued or threaded or both. Glued fittings are referred to as “slip” fittings. When specifying a PVC fitting the size and type of connection are specified. Some examples are:

  • ¾” x ½” ST Ell – A reducing ell with a ¾” slip x ½” thread
  • ¾” x ¾” x ½” SST Tee – A reducing tee with a threaded outlet
  • ¾” x ½” SS Bushing = A bushing with slip connections.

Copper Tubing Fittings

  • Copper tubing use compression fittings.
  • Fittings are available to adapt from compression to IPS and from compression to soldered fittings.
  • Common fittings include couplings, ells, and tees.

Valves and Hose Bibs - Valves are used to control the flow of water or other fluids in a plumbing system. Common types of valves include the following:

A gate valve is a valve situated between the point of connection and the rest of the plumbing system.

  • It usually remains wide open, but can be shut down in case repairs or additions have to be made to the system.

A gate valve is not designed to be opened and closed on a regular basis. It has a movable wedge that is turned via a handle and spindle to regulate the size of the opening.

Repairs are simple. Remove the handle and packing nut and replace the packing washer. Reassemble and install. Remember to check for leaks. Do not over tighten the packing nut.

A check valve allows the fluid in the pipe to flow in one direction only.

  • Check valves are used in water wells to prevent the backflow of water.
  • There are two basic types: swing or flapper and lift check valves. Both work automatically.

A globe valve is a valve used when frequent adjustment of the flow rate is necessary.

  • It is a compression-type valve with a disk or washer that is compressed into a seat to form a tight seal.
  • Repair is made by replacing the stem washer or disk.

A hose bib is a threaded exterior faucet that allows for the attachment of a garden hose or appliance hose.