Difference between nipple, coupling and union

What is a Pipe Coupling

Pipe Coupling is a short tube, also called an outer joint; it is a commonly used accessory for industrial pipe connections. The forged coupling is formed by heating and forging with a steel ingot or a round bar, and then machined on the lathe to make the thread. The main manufacturing standards are ASME B16.11, BS 3799, and GB/T14383.

How to buy pipe couplings How to buy pipe nipples How to buy pipe unions
Types of Couplings Types of pipe nipples Types of pipe unions
What is a Pipe Nipple What is a Pipe Union Difference between nipple, coupling and union

Salient Features:
Some important features of couplings are as follows:

  • Couplings come in all standard pipe sizes and are available for almost all types of pipe.
  • Available in several finishes.
  • Mostly cylindrical in design.
  • Couplings compensate for axial, lateral and angular shaft misalignment.
  • Couplings operate in quiet and smooth way.
  • There is a great degree of torsional stiffness.
  • There is the right angular transmission of angular motion and torque.
  • Usually long life.
  • Easy mounting and dismounting.
  • Low lateral stiffness etc.

Materials Used:
Pipe couplings are made of various materials and the buyers should always consider the material used for making them. Some of the materials used for making couplings are:

  • Brass
  • Aluminum
  • Cast Iron
  • Stainless Steel
  • Copper
  • Bronze etc.
Designs on couplings:
Couplings are available in various shapes and forms. The various designs available on couplings can be as follows:
  • Grid type
  • Gear type
  • Disc type
  • Rubber/Elastomer element type
  • Fluid Couplings

Areas of application for couplings:
Besides being used as an important pipe fitting, couplings are also used in the following:

  • Machine tools
  • Assembly machinery
  • Industrial robots
  • Automated plants
  • Printing machinery
  • Servo drives
  • Robotic axes
  • Manipulators
  • CNC milling / grinding
  • Linear actuators
  • Packaging machinery
  • Woodworking machinery
  • Textile machinery
  • Printing machinery
  • Metal cutting machinery etc.

How to buy pipe couplings?

There is a long list of evaluation factors that affect the type of coupling best suited for an application. It is not necessary that all couplings will have all the features. The factors to be considered are as follows:

  • Design Adaptability
  • Alignment Capabilities
  • Axial Freedom
  • Backlash
  • Chemical Resistance
  • Damping Capacity
  • Ease of Installation
  • Fail Safe or Fusible Link
  • Field Repairable
  • High Speed Capacity
  • Inherent Balance
  • Maintenance Required
  • Number of Component Parts
  • Reciprocating Drivers and Loads
  • Temperature Sensitivity
  • Torque Capacity to Diameter
  • Torque Overload Capacity
  • Torsional Stiffness

Types of Couplings:

Couplings are an integral part of pipe fittings and are of various types like:

  1. Rigid couplings: Rigid couplings are used to connect rotating members such as shafts. They are compact, economical components for the timing, joining or aligning of shafts and provide transmission of torque and motion. They are used at lower speeds, particularly where zero backlash is desired. These type of couplings do not allow for angular or parallel misalignment. Rigid couplings are also not intended for use as a critical part of a drive line or as a substitute for flexible or universal joints. They are also not meant for other power transmission devices. They are basically used for aligned shafts only. They are the most cost-effective coupling option suitable for all rigid shaft connections.
  2. Flexible coupling: Flexible couplings are used to connect two shafts, end-to-end in the same line, for two main purposes. The first purpose is to transmit power that is torque from one shaft to another, thereby causing both to rotate in unison, at the same RPM. The second purpose is to compensate for small amounts of misalignment and random movement between the two shafts.

What is a Pipe Nipple

pipe nipple is a length of straight pipe with male threads on both ends. It is one of the most popular category of pipe fittings. It is a connector or a coupling threaded on both ends. Pipe nipples are used to allow plumbing to be connected to a water heater or other plumbing. They are used to fit straight end hose or pipe. A combination of pipe nipples are recommended for low-pressure discharge and suction service for various compatible liquids and not for compressible products like air, nitrogen or steam.

Nipples can be divided into single head and double head; it can also be divided into ordinary and hex nipples, both generally of equal diameter. It adopts either external thread or plug-in welding to reach the male/female head of the coupling/union, matching the seal. 
Nipples can also be divided into short tube, reducing nipple and threaded short nipple. Threaded short nipple is either single head threaded or double head threaded, commonly used in industrial pipe connections. The main thread standards are the American standard ASME B16.11 and the national standard GB/T14626. Among all, NPT (National-American Pipe Thread) RC threads (Conical Threaded, Female) enjoy great popularity in the market.

The working pressure of pipe nipples will vary with the size and construction of the pipe, the type and number of clamps used, clamp placement, proper installation of clamps, temperature and product being conveyed. Pipe nipples are available in the widest variety of wall thicknesses and materials in the industry.

Finishes on pipe nipples:Materials used:
Various materials are used to make pipe nipples such as:
  • Brass
  • Aluminum
  • Stainless steel
  • Iron
  • Copper
  • PVC
  • Carbon steel
  • Cast Iron etc.

Pipe nipple fabrication:

  • Threaded nipples
  • Grooved nipples
  • Bended nipples
  • Barbed nipples
  • Seamless nipples
  • Black coating
  • Electro galvanized
  • Hot-dipped galvanized finishes
  • Copper plating etc.

How to buy pipe nipples?

What should buyers look for in the bulk purchase of pipe nipples?
Tube selection

  • Material, thickness
  • Diameter

General technical specifications

  • Pressures
  • Safety coefficients
  • Temperatures
  • Conformity to the standards, Certifications
  • Standard, Double duty, Extra duty, Extra double duty

End Connections

  • Threads
  • Beveled Ends
  • Square Cut Ends
  • Grooved
  • Bended
  • Barbed
  • Seamless

Types of pipe nipples:

  • Barrel nipple: This is a type of a short tubular with a taper thread outside at each end and which is un-threaded in the middle.
  • Weld nipple: Weld nipple is used as another method of connecting tube fittings. These kind of nipples are suitable for use under extreme conditions of vibration, pressure surges and changes of temperature.
  • Swage nipple: The basic purpose of a swage nipple is to bringing the flow of fluids from one pipe size to another. These are available with plain, beveled or threaded ends.
  • Hexagon nipple: Hexagon nipples are available in a variety of threads, materials and lengths.

Pipe nipples: End finishes:

pipe nipples2 - Difference between nipple, coupling and union

Tapered pipe thread

pipe nipple3 - Difference between nipple, coupling and union

Straight pipe thread

pipe nipple4 - Difference between nipple, coupling and union

Roller Cut

pipe nipple5 - Difference between nipple, coupling and union

Reamed and chamfered

pipe nipple6 - Difference between nipple, coupling and union

Square cut

pipe nipple7 - Difference between nipple, coupling and union


Applications of pipe nipples:
Pipe nipples are used as pipe fittings in a wide variety of industrial applications like:

  • Chemical processing industries
  • Petrochemical
  • Pharmaceutical
  • Food & beverage
  • Pulp & paper
  • Shipbuilding / marine
  • Waste incineration
  • Machine building
  • Architectural
  • Semiconductor etc.

What is a Pipe Union

Pipe Union is a type of fitting equipment designed in such a way to unite two pipes which can be detached without causing any deformation to the pipes. Any kind of small diameter piping connections requiring a positive seal and easy assembly as well as disassembly are made with the help of pipe union. In other words, the pipe unions can disjoint two pipes very easily. They are widely demanded in the pipe fitting market.

The union is widely used to connect pipes of different calibers, and is also widely used for connection of instruments, valves and pipes. It is mainly used in those sectors and fields that require high pressure and precision, such as petrochemical, medical and health, electric power, aerospace, military, fire, metallurgy, shipbuilding, gas, nuclear power, and environmental protection.

Materials used:

  • Stainless steel
  • Cast iron
  • Aluminum
  • Nickel
  • Copper
  • Brass
  • Bronze
  • Alloy
  • Plastic
  • Rubber etc.

How to buy pipe unions?

Important features that buyers should look for:

  • Type
  • Standard
  • Material
  • Size
  • Durability
  • Easy to install
  • Corrosion resistance

Three parts of pipe union:

  • A nut
  • A female end
  • A male end

With the joining of the female and male ends, the nuts are used to provide the necessary pressure to seal the joint.
pipe union2 - Difference between nipple, coupling and unionThe parts of the pipe unions are normally locked together by at least one radial screw or nut with sized cross section. When severe pulling stress is applied onto the pipe union from the outside, the locking screw breaks and removes the two parts of the union, which in turn separates together with the pipes to which they are attached. Under normal conditions elastically stressed sealing objects ensure maintenance of watertightness between the union parts.

Types of pipe unions:
There are two basic types of pipe unions:

  • Ground Joint Union
  • Flange Union

The difference between the two is that the former consists of three pieces while the latter two pieces.

pipe union3 - Difference between nipple, coupling and unionApplications of pipe unions:
Pipe unions are used in various municipal and industrial applications like as follows:

  • Fire protection
  • Process piping system
  • Water and wastewater etc.

Advantages of pipe union:
There are various advantages of pipe unions like:

  • To provide a leak-proof disconnection point in any piping system.
  • Used for inserting metering and regulating devices into any plumbing application.
  • Can connect piping system to vessels.
  • Can join two pipes of different size together.
  • Can easily remove the join between two pipes.
  • Easy to install.
  • Economical.

Difference between nipple, coupling and union

Pipe coupling is a kind of commonly used fittings in industrial pipeline connection. It is a short pipe, also known as an external joint, used to connect two pipes. Forged pipe coupling is formed by heating and forging ingot or round bar, and then processing thread on lathe. According to the nozzle type, it can be divided into socket coupling and threaded coupling. It can also be subdivided into half coupling, full coupling, half thread coupling and full thread coupling. The socket coupling adopts the socket structure, which reduces the cost of the pipe joint, makes the installation, use and maintenance very convenient, and also has a very high leak-proof ability. Because of its convenient use, it is widely used in civil construction, industry, agriculture and other fields. The main manufacturing standards are generally GB/T 14383, ASME B16.11 and BS 3799.
Pipe union is a common pipe connection which can be easily installed and disassembled. It mainly consists of nuts, heads and joints. Pipeline connectors machined after forging of round steel or ingot. Its connection form is divided into socket welding and threaded connection. Socket welding is to insert steel pipe into socket for welding. Therefore, it is called “socket union”. Thread connection is to screw steel pipe into the screw hole for connection, and also has the form of external thread connection. Therefore, it is called “threaded union” and the main manufacturing standard is MSS SP-83. Unions (optional) are widely used to connect pipes with different calibers, as well as instruments, valves and pipes. Mainly applicable to petrochemical industry, medical and health, power, aerospace, military industry, fire protection, metallurgy, shipbuilding, gas, nuclear power, environmental protection and other departments and fields requiring high pressure and precision size.
Pipe nipple, generally divided into concentric swaged nipple, eccentric swaged nipple, straight hexagonai nipple, reducing hexagonai mippie, half nipple TOE, fu11 nipple TBE. Thread nipples are commonly used in industrial pipeline connection. They are divided into half nipple TOE, fu11 nipple TBE.
Thread conforms to ASME B16.11 and GB/T14626, and NPT and RC threads are mostly used. 

Source: Network Arrangement – China Pipe Fittings Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@steeljrv.com

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