Piping and plumbing fittings
Copper fittings for soldered joints
Assorted pipe fittings: 1.Copper, solder; 2.Iron or brass, threaded; 3.Brass, compression; 4.Brass, transition from compression to solder; 5.Brass, special adaptors
Fittings are used in pipe and plumbing systems to connect straight pipe or tubing sections, to adapt to different sizes or shapes, and for other purposes, such as regulating or measuring fluid flow. The term plumbing is generally used to describe conveyance of water, gas, or liquid waste in ordinary domestic or commercial environments, whereas piping is often used to describe high-performance (e.g. high pressure, high flow, high temperature, hazardous materials) conveyance of fluids in specialized applications. The term tubing is sometimes used for lighter-weight piping, especially types that are flexible enough to be supplied in coiled form.
Fittings (especially uncommon types) require money, time, materials, and tools to install, so they are a non-trivial part of piping and plumbing systems. Valves are technically fittings, but are usually discussed separately.
- 1 Standards
- 2 Materials
- 3 Gaskets
- 4 Gender of fittings
- 5 Common fittings for both piping and plumbing
- 5.1 Elbow
- 5.2 Coupling
- 5.3 Union
- 5.4 Reducer
- 5.5 Olets
- 5.6 Tee
- 5.7 Cross
- 5.8 Cap
- 5.9 Plug
- 5.10 Nipple
- 5.11 Barb
- 5.12 Valves
- 6 Drain-waste-vent (DWV) and related fittings
- 6.1 Sweep elbow
- 6.2 Closet flange
- 6.3 Clean-outs
- 6.4 Trap primers
- 6.5 Combo-tee
- 6.6 Sanitary tee
- 6.7 Double sanitary tee (sanitary cross)
- 6.8 Wye fitting
- 6.9 Double-tapped bushing
- 7 Hydraulic fittings
- 8 Connection types
- 8.1 Fastener
- 8.2 Threaded pipe
- 8.3 Solvent welding
- 8.4 Soldering
- 8.5 Brazing
- 8.6 Welding
- 8.7 Compression fittings
- 8.8 Flare fittings
- 8.9 Flange fittings
- 8.10 Mechanical fittings
- 8.11 Crimped or pressed fittings
- 9 See also
- 10 References
- 11 External links
There are certain standard codes that need to be followed while designing or manufacturing any piping system. Organizations that promulgate piping standards include:
- ASME – The American Society of Mechanical Engineers
- ASTM – American Society for Testing and Materials
- API – American Petroleum Institute
- AWS – American Welding Society
- AWWA – American Water Works Association
- MSS – Manufacturers’ Standardization Society
- ANSI – American National Standards Institute
- NFPA – National Fire Protection Association
- EJMA – Expansion Joint Manufacturers Association
For example pipes need to conform to the dimensional requirements of :
- ASME B36.10M – Welded and Seamless Wrought Steel Pipe
- ASME B36.19M – Stainless Steel Pipe
- ASME B31.3 2008 – Process Piping
The B31.3 code has requirements for piping found in petroleum refineries; chemical, pharmaceutical, textile, paper, semiconductor, and cryogenic plants; and related processing plants and terminals. This code specifies requirements for materials and components, design, fabrication, assembly, erection, examination, inspection, and testing of piping. This Code is applicable to piping for all fluids including: (1) raw, intermediate, and finished chemicals; (2) petroleum products; (3) gas, steam, air and water; (4) fluidized solids; (5) refrigerants; and (6) cryogenic fluids.
The material with which a pipe is manufactured often forms as the basis for choosing any pipe. Materials that are used for manufacturing pipes include:
- Carbon Steel (CS)
- Low Temperature Service Carbon Steel (LTCS)
- Stainless Steel (SS)
- Non-Ferrous Metals (Inconel, Incoloy, Cupro-nickel etc.)
- Non-Metallic (ABS, GRE, PVC, HDPE, tempered glass, etc. )
- Chrome-molybdenum steel (Alloy steel) — Generally used for high temperature service
The bodies of fittings for pipe and tubing are most often of the same base material as the pipe or tubing being connected, for example, copper, steel, polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), or acrylonitrile butadiene styrene (ABS). However, any material that is allowed by the plumbing, health, or building code (as applicable) may be used, but must be compatible with the other materials in the system, the fluids being transported, and the temperatures and pressures inside and outside of the system. For example, brass- or bronze-bodied fittings are common in otherwise copper piping and plumbing systems. Fire hazards, earthquake resistance, and other factors also influence choice of fitting materials.
Gaskets are used for sealing of flange joints. In general, gaskets should not be reused. Various types of gaskets are available depending upon their construction, materials, and features. The following are the type of gaskets commonly used:
- Non-Metallic Gaskets (ASME B 16.21)
- Spiral-Wound Gaskets (ASME B 16.20)
- Ring Joint Gaskets (ASME B 16.20)
Non-Metallic Gaskets are used with flat face or raised face flanges. Spiral-Wound Gaskets are used with raised face flanges. They are available with an inner ring and outer ring, which is also known as the cantering ring. Ring Joint Gaskets are used with Ring Type Joint (RTJ) flanges. They are available in octagonal or oval cross sections.
A very high surface stress is developed between an RTJ gasket and the flange groove when RTJ is bolted up in a flange. This leads to plastic deformation of the gasket. Thus, the hardness of the gasket is kept less than the hardness of the groove to achieve coining i.e bringing two metal surfaces of different hardness so tightly together that the softer surface deforms to match harder surface exactly in shape and finish. Hence RTJ gaskets are recommended for reuse.
Gender of fittings
Piping or tubing are usually (but not always) inserted into fittings to make connections. To avoid confusion, connections are conventionally assigned a gender of male or female, respectively abbreviated as “M” or “F”.
Common fittings for both piping and plumbing
While there are hundreds of specialized fittings manufactured, some common types of fittings are used widely in piping and plumbing systems.
Short radius or regular 45° elbow (copper sweat)
Long radius or sweep 90° elbow (copper sweat)
An elbow is a pipe fitting installed between two lengths of pipe or tubing to allow a change of direction, usually a 90° or 45° angle, though 22.5° elbows are also made. The ends may be machined for butt welding, threaded (usually female), or socketed, etc. When the two ends differ in size, the fitting is called a reducing elbow or reducer elbow.
Elbows are categorized based on various design features as below:
- Long Radius (LR) Elbows – radius is 1.5 times the pipe diameter
- Short Radius (SR) Elbows – radius is 1.0 times the pipe diameter
- 90 Degree Elbow – where change in direction required is 90°
- 45 Degree Elbow – where change in direction required is 45°
A 90 degree elbow is also called a “90 bend” or “90 ell”. It is a fitting which is bent in such a way to produce 90 degree change in the direction of flow in the pipe. It used to change the direction in piping and is also sometimes called a “quarter bend”. A 90 degree elbow attaches readily to plastic, copper, cast iron, steel and lead. It can also attach to rubber with stainless steel clamps. It is available in many materials like silicone, rubber compounds, galvanized steel, etc. The main application of an elbow (90 degree) is to connect hoses to valves, water pressure pumps, and deck drains. These elbows can be made from tough nylon material or NPT thread.
A 45 degree elbow is also called a “45 bend” or “45 ell”. It is commonly used in water supply facilities, food industrial pipeline networks, chemical industrial pipeline networks, electronic industrial pipeline networks, air conditioning facility pipeline, agriculture and garden production transporting system, pipeline network for solar energy facility, etc.
Most elbows are available in short radius or long radius variants. The short radius elbows have a center-to-end distance equal to the Nominal Pipe Size (NPS) in inches, while the long radius is 1.5 times the NPS in inches. Short elbows are widely available, and are typically used in pressurized systems.
Long elbows are typically used in low-pressure gravity-fed systems and other applications where low turbulence and minimum deposition of entrained solids are of concern. They are readily available in acrylonitrile butadiene styrene (ABS plastic), polyvinyl chloride (PVC) for DWV, sewage and central vacuums, chlorinated polyvinyl chloride (CPVC) and copper for 1950s to 1960s houses with copper drains.
Pipe coupling (copper sweat)
A coupling connects two pipes to each other. If the size of the pipe is not the same , the fitting may be called a reducing coupling or reducer, or an adapter. By convention, the term “expander” is not generally used for a coupler that increases pipe size; instead the term “reducer” is used.
A combination pipe union and reducer fitting (brass threaded)
A union is similar to a coupling, except it is designed to allow quick and convenient disconnection of pipes for maintenance or fixture replacement. While a coupling would require either solvent welding, soldering or being able to rotate with all the pipes adjacent as with a threaded coupling, a union provides a simple transition, allowing easy connection or disconnection at any future time. A standard union pipe is made in three parts consisting of a nut, a female end, and a male end. When the female and male ends are joined, the nuts then provide the necessary pressure to seal the joint. Since the mating ends of the union are interchangeable, changing of a valve or other device can be achieved with a minimum loss of time. Pipe unions are essentially a type of flange connector, as discussed further below.
In addition to a standard union, there exist dielectric unions which are used to separate dissimilar metals (such as copper and galvanized steel) to avoid the damaging effects of galvanic corrosion. When two dissimilar metals are in contact with an electrically conductive solution (even tap water is conductive), they will form a battery and generate a voltage by electrolysis. When the two metals are in direct contact with each other, the electric current from one metal to the other will cause a movement of ions from one to the other, dissolving one metal and depositing it on the other. A dielectric union breaks the electric current path with a plastic liner between two halves of the union, thus limiting galvanic corrosion.
Reducer fittings, bronze threaded (left) and copper sweat (right)
Main article: Reducer
A reducer allows for a change in pipe size to meet hydraulic flow requirements of the system, or to adapt to existing piping of a different size. Reducers are usually concentric but eccentric reducers are used when required to maintain the same top- or bottom-of-pipe level.
Whenever branch connections are required in size where reducing tees are not available and/or when the branch connections are of smaller size as compared to header size, olets are generally used. The following are few configurations of olet connections :
- Flanged Olet
- Socket-Weld & Threaded Olet
- Lateral & Elbow Olets
- Nipple Olet
- Butt-Weld Olet
- Swage Nipples
Pipe tee (copper sweat)
A tee is the most common pipe fitting. It is available with all female thread sockets, all solvent weld sockets, or with opposed solvent weld sockets and a side outlet with female threads. It is used to either combine or split a fluid flow. It is a type of pipe fitting which is T-shaped having two outlets, at 90° to the connection to the main line. It is a short piece of pipe with a lateral outlet. A tee is used for connecting pipes of different diameters or for changing the direction of pipe runs. They are made of various materials and available in various sizes and finishes. They are extensively used in pipeline networks to transport two-phase fluid mixtures. They are categorized as:
When the size of the branch is same as header pipes, equal tee is used and when the branch size is less than that of header size, reduced tee will be used. Most common are tees with the same inlet and outlet sizes. Some of the industrial tees are Straight Tee, Reducing Tee, Double Branch Tee, Double Branch Reducing Tee, Conical Tee, Double Branch Conical Tee, Bullhead Tee, Conical Reducing Tee, Double Branch Conical Reducing Tee, Tangential Tee, and Double Branch Tangential Tee.
The above tees are categorised on the basis of their shapes and structure. They can also be classified on the basis of the application they are required to perform.
The three outlet sizes should be named in order (e.g. left, middle, right; measuring 15-22-15).
Cross fittings are also called 4-way fittings. If a branch line passes completely through a tee, the fitting becomes a cross. A cross has one inlet and three outlets, or vice versa. They often have solvent welded socket ends or female threaded ends.
Cross fittings can generate a huge amount of stress on pipe as temperature changes, because they are at the center of four connection points. A tee is more steady than a cross, as a tee behaves like a three-legged stool, while a cross behaves like a four-legged stool. (Geometrically, “any 3 non-colinear points define a plane” thus 3 legs are inherently stable.) Crosses are common in fire sprinkler systems, but not in plumbing, due to their extra cost as compared to using two tees.
Pipe cap (copper sweat)
A type of pipe fitting, usually liquid or gas tight, which covers the end of a pipe. A cap is used like plug, except that the pipe cap screws or attaches on the male thread of a pipe or a nipple. A cap may have a solvent weld socket end or a female threaded end and the other end closed off. If a solvent weld cap is used to provide for a future connection point, several inches of pipe must be left before the cap. This is because when the cap is cut off for the future connection, enough pipe must remain to allow a new fitting to be glued onto it. In plumbing systems that use threads, the cap has female threads. Industrial caps can be round, square, rectangular, U-shaped, I-shaped and have a round hand grip or a flat hand grip.
A plug closes off the end of a pipe. It is similar to a cap but it fits inside the fitting it is mated to. In a threaded iron pipe plumbing system, plugs have male threads. Some of the popular types of plugs are:
- Mechanical pipe plug
- Pneumatic disk pipe plug
- Single size pneumatic all rubber pipe plug
- Multi-size pneumatic pipe plug
- Multi-size flow-through pipe plug
- High pressure pipe plug
A short stub of pipe, usually threaded steel, brass, chlorinated polyvinyl chloride (CPVC) or copper; occasionally just bare copper. A nipple is defined as being a short stub of pipe which has external male pipe threads at each end, for connecting two other fittings. Nipples are commonly used for plumbing and hoses, and second as valves for funnels and pipes.
A plastic elbow fitting with a hose barb at the top, and male pipe threads at the bottom
A barb is used to connect flexible hoses to pipes. A barb clamp fitting has a male-threaded end used to mate with the female-threads. The other end of the fitting has either a single or multiple barbed tube having a tapered stub with ridges which is inserted into the flexible hose to secure it. An adjustable worm driver screw clamp helps to keep the hose from slipping off the barbed tube. Barb fittings can be made of plastic or brass. Brass is used for hot water applications while plastic is used for cold. The barb fitting can be either elbow-shaped or straight.
Valve is equipment designed to stop or regulate flow of any fluid (liquid, gas, condensate, stem, slurry etc.) in its path. Valves are categorized depending on their applications like isolation,throttling and non-return. It is installed in the piping system based on its requirement. Various type of valves are available depending upon the type of construction as follows:
- Gate valve – used for isolation only
- Plug valve – used for isolation only
- Globe valve – used for throttling
- Butterfly valve – used for isolation as well as throttling
- Check valve – used for preventing reverse flow (non-return)
- Diaphragm valve – used for isolation as well as throttling
- Ball valve – used for isolation only
Drain-waste-vent (DWV) and related fittings
Because they operate at low pressure and rely on gravity to move fluids (and often entrained solids), drain-waste-vent systems use fittings designed to be as smooth as possible on their interior surfaces. The fittings may be “belled” or expanded slightly in diameter, or otherwise shaped to accommodate insertion of pipe or tubing, without forming a sharp interior ridge that might catch debris or accumulate buildup of material and cause clogging. The absence of interior snags also makes it much easier to “snake out” or “rod out” a clogged pipe using long flexible tools made for this purpose.
Underground piping systems for landscaping drainage, or disposal of stormwater or groundwater, similarly use gravity flow at low pressure, often with entrained solids. Piping fittings used for these systems bear a strong resemblance to DWV fittings, though often at a larger scale. When high peak flow volumes are involved, the design and construction of these systems are closely inter-related to sewer design.
Fittings for central vacuum systems are very similar to DWV fittings, though usually of thinner and lighter construction, since the weight of the materials conveyed through the system is much less. Vacuum system designs share with DWV designs a concern about eliminating internal ridges, burrs, sharp turns, or other obstructions to smooth flow that might cause build-up of material into pipe blockages.
Hydraulic systems use extremely high fluid pressures to create useful work, such as in the hydraulic actuators for powered machinery such as bulldozers and backhoes. Therefore, hydraulic fittings are designed and rated for much greater pressures than those experienced in general piping systems, and they are generally not compatible for use in general plumbing. Fittings are designed and constructed to resist leakage and sudden explosive failure. More information on hydraulics and their specialized fittings can be found in the hydraulic machinery article.
Much of the work of installing a piping or plumbing system involves making leakproof, reliable connections. Depending on the technology used, basic skills may be required, or specialized skills and professional licensure may be required.
A fastener is a hardware device that mechanically joins or affixes two or more objects together. The following are the type of fasteners commonly used:
- Stud bolt with nut
- Machine bolt with nut
Usually the stud bolts are used with full threading and with two heavy hexagonal nuts.
MIP pipe and FIP elbow fitting (steel threaded)
A threaded pipe is a pipe with a screw thread at one or both ends for assembly. Steel pipe is often joined using threaded connections, where tapered threads (in the US/Canada see National Pipe Thread, in Commonwealth Nations such as the UK, Australia, New Zealand see British standard pipe thread) are cut into the end of the tubing segment, sealant is applied in the form of thread sealing compound or thread seal tape (also known as PTFE or Teflon tape), and it is then threaded into a corresponding threaded fitting using a pipe wrench.
Threaded steel pipe is still widely used in many homes and businesses to convey natural gas or propane fuel, and is a popular choice in fire sprinkler systems due to its high heat resistance. Threaded brass pipe was once used in a similar fashion, and was considered superior to steel for carrying drinking water, but is now effectively obsolete.
Assembling threaded steel pipe takes some skill, plus careful planning to allow lengths of pipe to be screwed together in proper sequence. Most threaded pipe systems require occasional use of pipe union fittings to allow final assembly.
A solvent is applied to PVC, CPVC, ABS, or other plastic piping, to partially dissolve and fuse the adjacent surfaces of piping and fitting. Solvent welding is usually used with a sleeve-type joint, to connect pipe and fittings made of the same (or closely compatible) material.
Unlike regular welding of metals, solvent welding is relatively easy to perform, although care is still needed to produce reliable joints. Solvents typically used for plastics are usually toxic, may be carcinogenic, and may also be flammable, requiring adequate ventilation.
To make a solder connection, a chemical flux is applied to the inner sleeve of a sleeve type joint, and the pipe is inserted. The joint is then heated using a propane torch or MAPP gas torch, solder is applied to the heated joint, and the melted solder is drawn into the joint by capillary action as the flux vaporizes.
Sweating is an alternate term sometimes used to describe soldering of pipe joints.
In situations where many connections must be made in a short period of time (such as plumbing of a new building), solder offers much quicker and much less expensive joinery than compression or flare fittings. A degree of skill is needed to rapidly make large numbers of reliable soldered joints. If flux residues are thoroughly cleaned, soldering can produce a long-lasting connection at low cost. However, the use of open flames for heating joints can present fire and health hazards to occupants of a building being worked on, and requires adequate ventilation.
Brazing is a thermal joining process in which the two pieces of the base metal are joined when a molten brazing filler metal is allowed to be drawn into a capillary gap between them. It is used to join most metals and alloys commonly used in engineering. Brazing filler metals have very high melting points, but always below the melting point of the metals being joined. It is closely related to soldering, but uses harder materials and higher temperatures. Brazing can be used to join pipes, rods, metal pieces or any other shape as long as the pieces fit neatly against each other without leaving large gaps. It is also capable of joining tungsten carbide, ceramics and similar non-metallic materials.
Successfully brazed joints are as strong as the parent metal pieces being joined and can withstand demanding service conditions i.e they are strong and ductile. Well brazed joints have smooth, neat fillets and they offer good electrical conductivity.
Welding of metals differs from soldering and brazing, in that the connection is made without adding a special low-melting-point material (e.g. solder) to complete a joint. Instead, the material of the pipe or tubing is itself partially melted in a carefully controlled manner, and the fitting and piping are directly fused together. Generally this requires that the piping and the fitting be made of the same (or closely compatible) material. Pipe welding is a specialized skill, and is often performed by specially licensed workers who are tested periodically for the quality of their work. For ultra-critical applications, every joint is tested using non-destructive testing methods.
Properly welded and inspected joints are considered to be very reliable, robust, and long-lasting. Proper ventilation is essential to remove dangerous metallic fumes from welding operations. Because of the expensive skilled labor required, welded pipe joints are usually restricted to high-performance applications, such as in shipbuilding, chemical reactors, and nuclear reactors.
Compression connectors on an isolating valve. Red metal is a copper compression ring.
Main article: Compression fitting
Compression fittings consist of a tapered concave conical seat, a hollow barrel-shaped compression ring, and a compression nut which is threaded onto the body of the fitting and tightened to make a leakproof connection. Fittings are typically made of brass or plastic, but stainless steel or other materials may be used.
Compression connections do not typically have the long life that sweat connections offer, but are advantageous in many cases because they are easy to make using basic tools. A disadvantage of compression connections is that they take longer to make than sweated joints, and sometimes require retightening over time to stop leaks.
Flare connection: 1 Screw thread, 2 O-ring, 3 Body, 4 Nut, 5 Seal interface, 6 Support ring (sleeve), 7 Flared tubing.
Flared connectors should not be confused with compression connectors, with which they are generally not interchangeable. Flared connectors lack a compression ring, but do use a threaded nut. A special flaring tool is used to enlarge tubing into a tapered “bellmouth” shape that matches the tapered projecting conical shape of the flare fitting. The flare nut, which has previously been installed over the tubing, is then tightened onto the fitting. Fittings are typically made of brass or plastic, but stainless steel or other materials may be used.
Flare connections are a labor intensive method of making connections, but are quite reliable over the course of many years. Flared fittings are sometimes thought to be more secure against leaks and sudden failures, and are often preferred for safety-critical connections, such as in hydraulic brake systems.
Flange connection, using a gasket
Flanges are generally used when there is a connection to valves, in-line instruments and/or connection to equipment nozzles is required. Flange fittings generally involve pressing two surfaces to be joined tightly together, by means of threaded bolts, wedges, clamps, or other means of applying high compressive forces. Often, a gasket, packing, or an O-ring is installed between the flanges to prevent leakage, but it is sometimes possible to use only a special grease, or nothing at all, if the mating surfaces are precisely formed. Flanges are designed to the following pressure ratings: 150 lb, 300 lb, 400 lb, 600 lb, 900 lb,1500 lb and 2500 lb or 10 Bar, 15Bar, 25Bar, 40Bar, 64Bar, 100Bar and 150Bar. Various types of flanges are available depending upon the type of their constructional features. The following are types of flanges generally used in piping. These flanges are available with different facing like raised face, flat face, ring joint face etc.
- Weld Neck
- Lap Joint
Slip On flanges are slipped over the pipe and then welded from both inside and outside to provide sufficient strength and prevent leakage. This flange is used instead of weld necks by many users because of its lower cost and also the fact that it requires less accuracy when cutting pipe to length.
Blind flanges do not have a bore and are used to shut off a piping system or vassal opening. Its design permits easy access to vassal or piping system for inspection purpose. It can be supplied with or without hubs at the manufacturer’s option.
Weld Neck Flanges are designed to be joined to a piping system by butt welding. They are expensive because of its long neck, but is preferred for high stresses to the pipe, reducing stress applications. The neck, or hub, transmits stress concentration at the base of the flange. The gradual transition of thickness from the base of the hub to the wall thickness at the butt weld provides important reinforcement of the flange. Turbulence and erosion are reduced due to the matching bore size of the pipe and flange.
Socket Flanges are similar to a slip on flanges in outline, but the bore is counter-bored to accept pipe. The diameter of the remaining bore is same as the inside diameter of the pipe. A fillet weld around the hub of the flange attaches the flange to the pipe. An optional interval weld may be applied in high stress applications. Its biggest use is in high pressure system such as hydraulic and steam lines.
Lap Joint flange is again similar to a slip flange, but it has radius at the intersection of the bore and the flange face to accommodate a lap stub end. The face on the stub end forms the gasket face of the flange. Its applications are where sections of piping systems need to be dismantled quickly and easily for inspection or replacement.
Flanged connections tend to be more bulky than other connections, but can perform well in demanding applications, such as large water mains and hydroelectric power systems.
Multiple mechanical sleeve clamps connecting piping
Manufacturers such as Victaulic or Grinnell produce special sleeve clamp fittings that are increasingly replacing classic flanged connections. They typically attach to the end of a pipe segment by using circumferential grooves pressed (or cut, in older designs) around the end of the pipe to be joined. Mechanical connectors are widely used on larger steel pipes, but can also be used with other materials.
The chief advantage of these newer connectors is that they can be installed in the field after cutting the pipe to length, which is much faster than traditional flanged connections, which must be factory-welded or field-welded to pipe segments.
Crimped or pressed fittings
Crimped or pressed connections use special fittings which are permanently attached to tubing with a powered crimper. The special fittings, manufactured with sealant already inside, slide over the tubing to be connected. High pressure is used to deform the fitting and compress the sealant against the inner tubing, creating a leakproof seal.
The advantages of this method are that it should last as long as the tubing, it takes less time to complete than other methods, it is cleaner in both appearance and the materials used to make the connection, and no open flame is used during the connection process. The disadvantages are that the fittings used are harder to find and cost significantly more than sweat type fittings.