Pipe fittings are components used to connect and join sections of pipe or tubing together.  They are used to change the direction of flow, control the flow rate, or to provide a connection between different types of pipes or tubing.  Pipe fittings come in many different types, materials, and sizes, depending on the specific application and requirements.  They can be made of materials such as metal, plastic, or rubber, and can be designed to handle different levels of pressure, temperature, and corrosiveness.  Pipe fittings are essential components of many industrial and commercial applications, such as in the oil and gas industry, water treatment plants, and HVAC systems.  They play a critical role in ensuring the safe and efficient flow of fluids and gases, and are often subject to strict regulations and standards to ensure their performance and durability.

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Pipe Fitting Index

• Pipe Fitting Design Classification
• Pipe Fitting End Connection Design Classification
• Pipe Fitting Datasheets
• Pipe Fitting Standards
• Pipe Fitting Specification, BSI

Pipe Fitting Design Classification

Pipe fittings can be broken down into several categories:

• Branch Connection  -  Branch connections are used when two or more pipes come together.  These can be in the form of a complete fitting, such as a tee or cross.  They can also be in the form of an O’let which is a branch connection that is designed to attach directly to the pipe.  Branch connections are available in buttweld, socket weld, threaded and flanged.
• Cap  -  Weld caps are used to seal the end of the piping.  It might be used when old pipe is being abandoned or with a tee to form a hydraulic elbow. Caps are available in buttweld only.
• Coupling  -  Couplings are used to join two different threaded pieces of pipe.  When a coupling is used, it is important not to over torque the piping, otherwise damage to the coupling or union can occur. Couplings are available for threaded pipe only.
• Elbow  -  These are useful when needing to change direction of flow.  Typical elbow directions are 45, 90 and 180 degrees.  Elbows are available in buttweld, socket weld, threaded and flanged.
• Reducer  -  Reducers are used when the pipe needs to change diameter.  Reducers are available in buttweld, socket weld, threaded and flanged.

Pipe Fitting End Connection Design Classification

There are four different type of connections that are used for fittings:P-Trap where the elbows are connected by flanges and fitting make up

• Buttweld Fitting  -  Probably the most common type of fitting.  They are easily manufactured and are easily installed. Butt weld fittings can be connected directly to each other.  This is called fitting make up.
• Flanged Fitting  -  Flanged fittings are piping components where the flange is an integral component of the fitting.  These are most often used in water treatment applications or lined piping where welding would be destructive to the liner.
• Socket Weld Fitting  -  These fittings have a socket weld connection on each end.  They might be used for smaller diameter piping.  These fittings utilize a single fillet weld to join the piping with the fitting.
• Threaded Fitting  -  Threaded fittings are generally four inches and smaller.  The reason for this size constraint is the pipe end needs to be threaded with a male type connection and die sizes are unobtainable in the larger diameters.

Pipe Fitting Standards

API Standards

• API 671 - Special Purpose Couplings for Pumps - Reciprocation

ASME Standards

• ASME B16.1 - Cast Iron Pipe Flanges and Flanged Fittings
• ASME B16.3 - Malleable Iron Threaded Fittings
• ASME B16.4 - Gray Iron Threaded Fittings
• ASME B16.9 - Factory-Made Wrought Buttwelding Fittings
• ASME B16.11 - Forged Fittings, Socket-Welding and Threaded
• ASME B16.14 - Ferrous Pipe Plugs, Bushings, and Lock nuts With Pipe Threads
• ASME B16.15 - Cast Bronze Threaded Fittings, Class125 and 250
• ASME B16.18 - Cast Copper Alloy Solder Joint Pressure Fittings
• ASME B16.22 - Wrought Copper and Copper Alloy Solder Joint Pressure Fittings
• ASME B16.24 - Cast Copper Alloy Pipe Flanges and Flanged Fittings: Classes 150, 300, 600, 900, 1500, and 2500
• ASME B16.25 - Buttwelding Ends
• ASME B16.26 - Cast Copper Alloy Fittings for Flared Copper Tubes
• ASME B16.39 - MalleableIron Threaded Pipe Unions, Class 150, 250, and 300
• ASME B16.42 - Ductile Iron Pipe Flanges and Flanged Fittings: Classes 150 and 300

ASTM Standards

• ASTM A105 - Specification for Carbon Steel Forgings for Piping Applications
• ASTM A181 - Specification for Carbon Steel Forgings, for General-Purpose Piping
• ASTM A182 - Specification for Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service
• ASTM A193 - Specification for Alloy Steel and Stainless Steel Bolting Materials for High Temperature Service
• ASTM A194 - Specification for Carbon and Alloy Steel Nuts for Bolts for High Pressure and High Temperature Service
• ASTM A234 - Specification for Piping Fittings of Wrought Carbon Steel and Alloy Steel for Moderate and High Temperature Service
• ASTM A350 - Specification for Carbon and Low-Alloy Steel Forgings, Requiring Notch Toughness Testing for Piping Components
• ASTM A403 - Specification for Wrought Austenitic Stainless Steel Piping Fittings
• ASTM A420 - Standard Specification for Piping Fittings of Wrought Carbon Steel and Alloy Steel for Low-Temperature Service
• ASTM A694 - Specification for Carbon and Alloy Steel Forgings for Pipe Flanges, Fittings, Valves, and Parts for High-Pressure Transmission Service
• ASTM B21 - Specification for Naval Brass Rod, Bar, and Shapes
• ASTM B98 - Specification for Copper-Silicon Alloy Rod, Bar and Shapes
• ASTM B150 - Specification for Aluminum Bronze Rod, Bar, and Shapes
• ASTM B160 - Specification for Nickel Rod and Bar
• ASTM B164 - Specification for Nickel-Copper Alloy Rod, Bar, and Wire
• ASTM B166 - Specification for Nickel-Chromium-Iron Alloys (UNS N06600, N06601, N06603, N06690, N06693, N06025, and N06045) and Nickel-Chromium-Cobalt-Molybdenum Alloy (UNS N06617) Rod, Bar, and Wire
• ASTM B247 - Specification for Aluminum and Aluminum-Alloy Die Forgings, Hand Forgings, and Rolled Ring Forgings
• ASTM B361 - Specification for Factory-Made Wrought Aluminum and Aluminum-Alloy Welding Fittings
• ASTM B366 - Specification for Factory-Made Wrought Nickel and Nickel Alloy Fittings
• ASTM B381 - Specification for Titanium and Titanium Alloy Forgings
• ASTM B462 - Specification for Forged or Rolled UNS N06030, UNS N06022, UNS N06035, UNS N06200, UNS N06059, UNS N06686, UNS N08020, UNS N08024, UNS N08026, UNS N08367, UNS N10276, UNS N10665, UNS N10675, UNS N10629, UNS N08031, UNS *N06045, UNS N06025, and UNS R20033 Al
• ASTM B564 - Specification for Nickel Alloy Forgings

AWWA Standards

• AWWA C110 - Ductile-Iron and Gray-Iron Fittings, 3 Inch Through 48 Inch (75 mm Through 1200 mm), for Water and Other Liquids
• AWWA C208 - Dimensions for Fabricated Steel Water Pipe Fittings

ISO Standards

• ISO 5251 - Stainless steel butt-welding fittings
• ISO 5256 - Steel pipes and fittings for buried or submerged pipe lines -- External and internal coating by bitumen or coal tar derived materials

MSS Standards

• MSS SP-43 - Wrought Stainless Steel Butt-Welding Fittings Including Reference to Other Corrosion Resistant Materials
• MSS SP-53 - Quality Standards for Steel Castings and Forgings for Valves, Flanges and Fittings and Other Piping Components - Magnetic Particle
• MSS SP-54 - Quality Standards for Steel Castings and for Valves, Flanges and Fittings and Other Piping Components - Radiographic
• MSS SP-55 - Quality Standards for Steel Castings and for Valves, Flanges and Fittings and Other Piping Components - Visual
• MSS SP-75 - Specifications for High Test Wrought Buttwelding Fittings
• MSS SP-73 - Brazing Joints for Copper and Copper Alloy Pressure Fittings
• MSS SP-83 - Class 3000 Steel Pipe Unions, Socket-Welding and Threaded
• MSS SP-97 - Integrally Reinforced Forged Branch Outlet Fittings — Socket Welding, Threaded, and Buttwelding Ends
• MSS SP-106 - Cast Copper Alloy Flanges and Flanged Fittings Class 125,150, and 300
• MSS SP-119 - Factory-Made Wrought Belled End Socket Welding Fittings

SAE Standards

• SAE J514 - HydraulicTubeFittings

Pipe Fitting Specification, BSI

BS 3799 - Steel Pipe Fittings, Socket and Threaded

Note - Class designations correspond to the maximum cold working pressure of fittings in pounds force per square inch.