In this forthcoming article, we shall explore the different types of pipe fittings the materials in which they are available, etc in detail. We have also provided a PDF for the same
Introduction to Pipe Fittings
Pipe fittings are used to connect pipe sections with valves, pumps, and other fluid control products to create pipelines. They are commonly associated with metal and plastic pipes for fluid transportation. Different types of fittings exist for various purposes, including those for architectural elements. Fittings can be welded, threaded, mechanically joined, or chemically adhered, depending on the pipe material. Terminology can vary, but in this article, we will focus on rigid pipe fittings and their connection methods, with limited coverage of fittings for flexible tubes or hoses.
Fitting Materials and Manufacturing Processes
Cast and malleable iron
Cast iron pipe fittings come in hubless and bell-and-spigot styles. Hubless designs use elastomeric couplers with stainless steel band clamps to create a seal. Bell-and-spigot fittings employ elastomeric gaskets inside the bell for joint sealing. In the past, cast iron pipes were caulked with lead and fibrous material. Bolted flanges and mechanical compression connections are also used. Ductile iron fittings are becoming more popular due to their improved properties and lower cost. Malleable iron fittings are commonly used for steel and galvanized pipes in plumbing, although large-diameter threaded fittings are less common due to the difficulty of threading.
Steel and steel alloys
Steel pipe fittings are typically formed by extrusion or drawing over a mandrel from the welded or seamless pipe. In smaller sizes, they are threaded to match the ends of the pipe. For larger sizes and higher pressures, they are welded in place using butt-weld or socket-weld methods. Socket-weld fittings, usually forged, are limited to smaller pipe diameters and come in various pressure ratings. While socket fittings are weaker than butt-welded fittings, they are preferred over threaded fittings for high-end applications. However, their use is not suitable for high-pressure food applications due to the need for an expansion gap in the fitting.
Flanges are employed to connect flanged sections of pipe using bolts, allowing for pipeline breakage and replacement of valves. Various styles of flanges are available, classified by pressure and temperature ratings such as lapped, weld neck, socket weld, ring-type joint, screwed, and slip-on. Threaded flanges are suitable for low- to medium-pressure applications, while welded-on flanges can handle higher pressures. Lapped flanges are convenient for frequent disconnections as they enable easy bolt-hole alignment. Blind flanges are used to seal the end of a pipeline while allowing future connections.
Flanges can incorporate different methods of sealing adjoining faces, including O-rings, seal rings, and gaskets. Seal rings provide a tight joint and can withstand higher pressures compared to flat-face gaskets under the same bolt stress.
Three main standards govern pipe flanges. ASME 16.5 defines the commonly used ANSI flange, while ASME B16.47 covers Series A and B for large-diameter applications. Series A flanges are heavier and thicker than Series B. AWWS flanges, defined by ASME B16.1, are specifically for potable-water service at atmospheric temperatures. Additionally, there are industry-standard flanges based on historical practice. Stainless steel flanges are suitable for sanitary applications and can be fitted with quick-connect clamps for easy dismantling. Stainless steel pipe fittings with integral flanges are also available.
For certain applications, metal pipe sections can be joined using pipe couplings and threaded pipe fittings such as end caps or 180-degree elbows.
Non-Ferrous and Concrete
Nonferrous
Aluminum fittings are commonly produced through casting and are available in a wide range of forms, similar to steel fittings. Aluminum threaded fittings like caps or nipples, as well as fittings combining threaded and butt weld connections, are readily accessible. Socket weld options are also available. Welding aluminum fittings typically involves MIG or TIG processes.
- Aluminum pipe is widely used for constructing handrails, and a variety of weldable and slip-on/clamp-on fittings are available for structural applications.
- Red brass fittings, such as brass pipe nipples, are manufactured to correspond with specific pipe diameters, and these fittings are often joined through soldering or brazing methods.
Concrete
Concrete pipe fittings come in various styles suitable for large-scale civil projects like stormwater control. In addition to standard wye connections, specialized fittings include utility hole portals and various vault styles. The fittings are designed with shouldered ends that mate with corresponding counterparts on the receiving pipes. A rubber gasket ensures a leakproof joint.
Plastic, Glass & Vertified Glass
Plastics
Plastic pipe fittings are offered in socket weld (also known as solvent weld) and threaded styles, with socket weld being the most common. Socket weld fittings are designed to be chemically welded in place, ensuring quick and straightforward installation. Plastic pipes are typically dry-fitted and marked, as the solvent used for connection acts rapidly. Couplings are commonly used to join straight lengths of pipe together.
These fittings are available in standard shapes and styles, following the dimensional size ranges of various plastic pipe materials such as PVC, CPVC, PE, PEX, PP, and ABS.
Standard PVC pipe fittings include reducers, elbows, caps, tees, wyes, couplings, unions, and crosses, among others. The majority of PVC pipe or tubing fittings have a circular cross-sectional profile, although square PVC fittings are available for structural applications such as fences, railings, or furniture. However, these alternative profiles are not associated with PVC pipes used for fluid handling purposes. Structural fittings may use other materials, such as galvanized pipe railing fittings.
Other PVC fittings include barbed insert designs, which are pressed into the tubing and secured with band clamps.
CPVC pipe fittings and ABS pipe fittings are typically joined through solvent welding. Conversion adapters for transitioning between different materials, such as CPVC to brass, are readily available.
In certain applications involving plastic pipe, such as sink drains in plumbing, specific fixtures like p-traps may be connected with threaded connections using nylon washers and retaining nuts, allowing for easy disassembly to clear clogs.
Polyethylene pipe fittings, polypropylene pipe fittings, and PVDF pipe fittings are available with threaded or barbed connections, as well as socket weld or fused options. Nylon pipe fittings can be used where an airtight or watertight seal is necessary, and they are compatible with nylon tubing, other types of plastic pipe, or metal pipe.
Glass
Glass pipes and fittings find application in specialized industrial fluid process settings. Borosilicate glass offers several advantages over alternative piping systems. It has high purity, ensuring no contamination of process fluids. The transparency of glass allows for easy inspection of the process, while the smooth surface prevents the buildup of scale or residues on the interior.
Glass tubing and glass profile fittings are commonly used in laboratory applications. Rember that glass lining pipes and glass pipes are two different things so don’t get confused.
Vitrified Clay
Fittings for vitrified clay pipe are available in typical configurations required for sewer installations. Bell-and-spigot coupling is commonly used for these fittings, with an O-ring or gasket used to create a seal at the joint.
Types Of Pipe Fittings
- Piping Elbow: Used to change the direction of flow, with options like 900°, 450°, long radius, and short radius elbows.
- Tee-Connection: Allows branching of pipelines, with variations such as equal tee, reducing tee, and barred tee.
- Reducer: Helps transition between pipes of different sizes, including concentric and eccentric reducers.
- Pipe Unions: Connect two pipes and allow easy disassembly for maintenance or repairs.
- Adapters: Enable connection between pipes with different end types or sizes.
- Olet-Connections: Provide branching options with weldolet, sockolet, elbowlet, thredolet, nipolet, latrolet, sweepolet, and flageolet.
- Piping Valves: Control the flow of fluids, including gate valves, ball valves, check valves, plug valves, needle valves, butterfly valves, globe valves, pinch valves, solenoid valves, and control valves.
- Crosses: Allow pipelines to intersect at right angles, with options like the equal cross and reducing cross.
- Wyes: Used for branching pipelines at a 45° angle.
- Pipe Cap: Closes the end of a pipe to prevent leakage or contamination.
- Nipples: Short lengths of pipe used for connecting fittings or extending pipe lengths.
- Plug: Seals the end of a pipe when no connection is needed.
- Bushing: Connects pipes of different sizes by reducing the diameter of one end.
- Pipe Flanges: Connect pipes, valves, or equipment by bolting them together.
- Expansion Joint: Absorbs thermal expansion or contraction in pipelines to prevent damage.
- Steam Traps: Remove condensate from steam systems while preventing steam loss.
- Long Radius Bend: Provides a gradual change in direction to minimize fluid flow resistance.
- 3-D Bends: Allows pipelines to change direction in three dimensions.
- 5-D Bends: Similar to 3-D bends, but with a larger bending radius.
- Barb: Used for connecting flexible tubing with a serrated end to ensure a secure fit.
- Locknut: Secures fittings in place by tightening against a threaded connection.
- Miter Bend: Enables pipelines to change direction at a precise angle using welded joints.
Pipe Union, also known as Pipe Fitting Union, is a specialized pipe fitting that connects two pipes together and allows for easy detachment without damaging the pipes. They provide a secure seal and facilitate simple assembly and disassembly. Pipe unions are widely used in small-bore piping and plumbing industries. They are made of various materials such as Carbon steel, Stainless steel, Cast iron, Copper, Nickel, Aluminum, Plastic, and Alloys.
A pipe union is made up of a female end, a nut, and a male end. The male end has external threads and the Female end has internal threads. The nut applies pressure and seals the joint. Pipe Adapters are used to connect pipes of different types. They come in different types such as Offset Pipe Adapters, Female Pipe Adapters, and Male Pipe Adapters, Straight Thread Adapters. Pipe adapters are commonly used in plumbing applications and can be made of Steel, Cast iron, polymers, Brass, Aluminum, Bronze, or copper materials.
Pipe Olet Connections are branch connections used to connect smaller pipe branches to larger main pipes. They serve as an alternative to pipe-to-pipe branching and are widely used when reducing tees is not available. Common types of piping olets include Weldolet, Sockolet, and Threadolet. Other olet fittings include Elbolet, Nipolet, Latrolet, Flexolet, Flangolet, Sweepolet, and Coupolet.
A piping Cross is a four-way pipe fitting with one inlet and three outlet connections (or vice versa). They are less commonly used in the oil and gas industries but can be found in fire sprinkler systems. Wye pipe fittings, also known as lateral connections, are used in drainage systems. They have a branch line at a 45-degree angle to ensure smooth water flow with minimal frictional loss and turbulence.
Caps and Plugs are pipe fittings used to seal the ends of pipes, providing tight closure. They are commonly used at dead ends of pipes or for future connections.
Bushings are pipe fittings that connect pipes of different sizes. They reduce the larger pipe size to match the smaller pipe size and occupy less space than unions or couplings.
Long Radius Bends are used in fluid transportation pipelines that require pigging. These pipe fittings have a long radius and smooth direction change, resulting in minimal pressure drop and smooth flow. Common long-radius pipe bends include 3D and 5D Pipe bends.
Barbs are pipe fittings used to connect flexible tubing with pipes. They have a male-threaded end on one side and a single or multi-barbed tube on the other, which is inserted into the flexible tubing.
types of Pipe Fittings based on their purpose
Pipe Fittings for Extending or Terminating Pipe Runs
- Couplings
- Adapters
- Unions
- Caps
- Plugs
Pipe Fittings for Changing Direction of Flow
- Elbow
- Bends
- Tee-Connections
- Crosses
Pipe Fittings for Connecting Two or More Pipes
- Tees
- Crosses
- Side-inlet Elbows
- Wyes
Pipe Fittings for Changing Pipe Sizes
- Reducers
- Bushings
- Couplings
- Reducing Tees
Pipe Fittings for Flow Control
- Valves
Factors to Consider When Selecting Pipe Fittings
Choosing the appropriate pipe fittings requires careful consideration of several factors. Here are some key points to keep in mind:
- Materials of Construction: The material used for pipe fittings must be compatible with temperature and service conditions. The material of the pipe and material fitting should always be the same
- End Connection Types: It is essential to be familiar with the end connection types required before purchasing any pipe fitting.
- Type of Pipe Fitting: These are identified by certain types such as slip or threaded or female and male. The buyer is responsible to select the appropriate ones for his needs.
- Pipe Fitting Size: Prior knowledge of the fitting size is crucial for proper selection. The size of the fitting is generally determined by the outer diameter (OD) or inner diameter (ID) of the connecting pipe.
- Schedule or Thickness: Pipe fittings are available in various thickness ranges, similar to pipes. Therefore, it is important to ensure the compatibility of the fitting’s thickness with the overall system.
- Pressure Rating: Consider the internal pressure requirements when selecting pipe fittings to ensure they can withstand the intended pressure levels.
- Pipe Fitting Standards and Codes: Several codes and standards govern pipe fittings, such as ASTM, ASME, DIN, BSP, MSS, and ISO, among others. It is essential to select the appropriate standard that aligns with the specific design and use requirements.
Application of Pipe Fittings
- Plumbing Systems: Pipe fittings connect pipes and fixtures in residential, commercial, and industrial buildings.
- HVAC Systems: Pipe fittings control airflow and connect ductwork in heating, ventilation, and air conditioning systems.
- Oil and Gas Industry: Pipe fittings are used for connecting pipelines and controlling flow rates in the extraction, refining, and distribution of oil and gas.
- Chemical and Process Industries: Pipe fittings transport fluids and control flow in chemical processing plants and refineries.
- Water Treatment and Wastewater Systems: Pipe fittings distribute and regulate water flow in treatment plants and wastewater facilities.
- Food and Beverage Industry: Pipe fittings process, convey, and store food and beverages in production facilities.
- Pharmaceutical and Biotechnology Industry: Pipe fittings transport fluids in drug manufacturing and bioprocessing facilities.
- Fire Protection Systems: Pipe fittings connect pipes and control the delivery of firefighting agents in fire protection systems.
Pipe Fitting Standards
Here are the ASME Standards
- ASME B16.9
- ASME B16.28
- ASME B16.11
- ASME B16.1
- ASME B16.3
- ASME B16.4
- ASME B16.5
- ASME B16.14
- ASME B16.15
- ASME B16.25
- ASME B16.36
Conclusion
In conclusion, pipe fittings play a crucial role in various industries and applications, facilitating the connection, direction change, and control of fluid flow in pipelines. They are available in a wide range of materials, including metal, plastic, glass, and vitrified clay, each suitable for specific conditions and requirements. The selection of pipe fittings should consider factors such as material compatibility, end connection types, size, pressure rating, and adherence to relevant standards and codes. By understanding the different types of pipe fittings and their applications, stakeholders can make informed decisions to ensure efficient and reliable fluid transportation systems.
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