What is the difference between coupling, union, and nipple?

It is recommended to check the standards or search for images online; by comparing them, you will understand. Pipe joint coupling: available in internal thread or plug-welded form; it serves a function similar to that of a flange, acting as a fitting for connecting pipes together ； Union fitting: available in internal thread or butt-welded version, three-piece design; both the male and female ends have internal threads. It consists of a sleeve that is screwed together, with the male and female ends being secured by another component to ensure sealing. It is easier to disassemble compared to coupling ； Short nipple: featuring external threads or welding, it can extend into the male and female parts of the coupling/union to achieve a sealed connection.

Pipe fittings include couplings, unions, and nipples. It’s important to distinguish between unions – as the name suggests, their ends are movable and not fixed; they have a sealing ring in between. They can be made either by casting or forging. The methods of connection include socket welding and threaded connections. In the industry, pipe fittings are also referred to as pipe clamps, which can also be produced by casting or forging; they come in threaded and socket-welded versions as well. Generally, these fittings have a short shape and exist in concentric or eccentric types, with the concentric type being more commonly used. A nipple, simply put, is something with external threads; it can be single-ended or double-ended, and it may be of standard type or hexagonal design. Usually, their diameter remains constant

Wow, let me pick some flaws. . . ;P The union also has a hard-sealed version, one without a ring, right? Coupling – I’ve really never seen one that’s biased. . .

(1) Coupling: It is commonly used between two pipes to connect them. When two straight pipes are connected, it is called a coupling. When one pipe is connected vertically to another, the connection point is referred to as a half coupling. Threaded or plug-welded type. (2) Union fitting: It is mounted on a sleeve; by tightening it, the male and female parts are secured together with another component to ensure sealing. Easy to disassemble ； (3) Short nipple: in the form of threads or plug welding, equivalent to a short tube. Yue Jincai’s book „Pressure Pipeline Technology“ and Song Keké’s book „Examples of Pressure Pipeline Design Projects“ cover this topic

Pipe joint coupling: This refers to pipe clamps, which are a commonly used accessory in the connection of industrial pipes. It is a short tube used to connect two pipes, also known as an external connector. Forged pipe collars are made by heating steel ingots or bars and forging them into shape, followed by threading them on a lathe. Based on the type of connection, they can be divided into socket-type couplings and threaded couplings; further, they can be classified into single-socket couplings, double-socket couplings, single-threaded couplings, and double-threaded couplings. The socket-and-spigot coupling uses a socket-and-spigot design, which reduces the cost of pipe joints; it is extremely convenient for installation, use, and maintenance, and also offers high leak prevention capabilities. Due to its ease of use, it is widely applied in civil buildings, industry, agriculture, and other fields. The main manufacturing standards are generally GB/T14383, ASME B16.11, and BS 3799. Union fitting: also known as a swivel joint, it is a commonly used pipe connection element that facilitates easy installation and removal. It mainly consists of three parts: a nut, a knurl, and a flat joint. Pipe fittings forged from round steel or steel ingots and then machined. Its connection methods include socket welding and threaded connection. Socket welding involves inserting the steel pipe into a socket and then welding it, which is why it is called a \"socket joint.\" Threaded connection involves screwing the steel pipe into a threaded hole to achieve connection; there is also a type of connection that uses external threads. Therefore, it is called a \"threaded union,\" with the main manufacturing standard being MSS SP-83. Flexible joints are widely used for connecting pipes of different diameters, and they are also commonly used to connect instruments, valves to pipes. It is mainly suitable for industries and fields such as petrochemicals, pharmaceuticals and healthcare, electricity, aerospace, military industry, firefighting, metallurgy, shipbuilding, gas, nuclear power, and environmental protection, where high pressure resistance and precise dimensions are required. Short nipple: It is generally divided into short tubes, reduced-diameter short nipples, and threaded short nipples. Threaded splices are a commonly used fitting in industrial pipeline connections, and they are divided into single-threaded splices (single wire) and double-threaded splices (double wire). The threads comply with the American standard ASME B16.11 and the Chinese standard GB/T14626; NPT and RC threads are commonly used. For the production drawings, see: Single-End Threaded Spool – Drawing No. HGS04-04-01-1 ； Double-ended threaded spool - Part number HGS04-04-02-1. Reduction splices are commonly found in MSS SP-95 concentric reduction splices; eccentric reduction splices are also known as \"telescoping tubes\".