How Pipe fitting and Tube fitting Work

pipe fitting

Pipe fitting is an occupation of installing or repairing a piping or tubing systems which convey gases, liquid and solid materials in some cases. This work involves the selection as well as preparation of pipe or tube, and joining it together by different means, and the location and repair of leak inclusive.
The cost of energy alone for small leaks in a facility which is using air at around 100 pounds per square inch gauge with an electric consumption cost of approximately 6 cent/kilowatt per hour can waste around $22000 per annum. The figures are much higher when the work to repair the leaks as well as the resultant downtime is considered as well. The ultimate part is that the intangible which range from environment pollution to on-the-job injuries can come into play whenever the leak is not detected or not attended for a limited amount of time.

Leakage usually occurs at a connection which occurs during construction where there can be a failure in the fittings under stress. However, steps can be strictly followed so as to improve and develop the fluid handling capacity of the system so as to minimize problems which might arise and also enhance the overall performance of the system. Some essential condition includes:

  • The kind of connecting devices which is used in joining process piping throughout the whole system
  • The level of knowledge as well as practical experience of those installing and maintaining the application

Any kind of tube or piping fitting can leak when they are subjected to certain conditions, especially in the event that mechanical vibration occurs. Although there might be an absence of an ideal connection which will provide no leakage but leak free operation under each and every system requires a certain fitting designs as well as technologies which provide a great reliability than other ones. And if this system is installed properly, quality fittings can helps to correct the leakage to a level which is less than 3%.

Designs For Tube fitting

Although pipe fitting has been used traditionally on a widespread basis but tube fittings have been proven to be a reliable connection and has gained their place in the market. They are of various designs and have several benefits which are dependent to a greater degree on the demand of the application.
The compression fitting is the first tube fitting to be developed and is made up of three components which are the body, nut and ferrule. The fitting does not need special tools during the assembly unlike the connections in pipes where thread chasers as well as dies are needed so as to make the threads perfect. In addition to that, the seal can be the line type thereby creating a strong force in an area and also provides a great metal-to-metal seal which is available. However, this kind of connection can withstand a minimal pressure because of the presence of the friction grip which is available in a few materials, and does not function perfectly in a system which has vibration, thermal cycling as well as other dynamic forces.
The flare fitting is composed majorly of three major components, they include the sleeve, nut and the body with a flare or coned end. In some scenario, the sleeve can be used on softer tubing materials as a self-flaring option. Whenever you compare with the original compression fittings, you will observe that the flare fittings have an ability to handle higher pressure as well as broad system parameters, and it is also present in various kinds of material and also has wider seal area that helps to provide an outstanding capability in terms of application maintenance. Special flaring tools are required so as to prepare the tubing before it is being installed. In addition to that, flaring of the tubing can result to stress at the base of the flare or result to axial cracks on thin or brittle tubing. Tube cuttings which are uneven and rotational tube cutters which are not designed properly might create a sealing surface which is not even.
The bite-type of tube fittings does not need any special assembly tools and likewise have ability to retain higher-pressure rating than the main compression design. A nut, body, and ferrule are used for this fittings and it has a sharp leading edge, which bite into the skin of the tubing so as to achieve the holding ability. The second seal is made on a long deep surface which is between the internal body taper and the ferrule.
The bite-type of fitting is usually the single ferrule in design and this will necessitate the nose of the ferrule to handle two different tasks: to provide a sealing element for the coupling body and to bite into the tube so as to hold it, and one or the two functions can be compromised easily by the action. Such separation of functions would help in solving this problem due to the fact that the separation would permit each of the elements to be designed for the specific task which you want it to address.
The mechanical grip-type of fitting are usually of two-ferrule in design and these fitting likewise make use of a live-loaded seal characteristics which relates to the spring action of the ferrules during sealing. The front ferrule will be loaded by the fitting pull-up spring as it seals by coining the surface of the coupling and tubing body. A radial collecting or holding action of the back ferrule holds the tube for a distance just outside the tube holding points of the ferrule nose so as to enhance the vibration resistance.
The break and remake of the fitting after the installation can be achieved successfully without causing any damage either to the fitting components or the tubing. Additionally, some manufacturers provide a gauge so as to ensure a proper as well as sufficient pull-up on the initial installation. The major cause of leakage is as a result of under-tightening of tube fittings in harder materials like stainless steel.

Pipe fitting options

This kind of connection is mostly resistant to both the fatigue as well as vibration is known as a pipe butt-weld fitting. It can easily resist vibration and the fatigue is determined by the strength as well as the integrity of the connection which is made.
However there are some demerit of pipe butt-weld fitting, the welding equipment as well as specialized training required to make the connection can be costly. In addition to that, the amount of time which is required to install a fitting into a system pipe butt-welds fittings into a system is more than what will be required for other fitting installation.
The level of knowledge which is required by the installer should also be taken into consideration. It is crucial to have a thorough training in order to achieve a quality weld connections. The accessibility for the future maintenance of fluid system piping is also reduced, unless those that are in charge of maintenance are prepared so as to carry a hacksaw or torch to cut their way into a system line.
One of the connections which is common and are found in the process of fluid handling systems is screwed pipe fitting connections or vibration and the types varies. National Pipe Thread (NPT) fittings which are on the male as well as female ends also have a tapered ends. The seal which is placed in between the joining metal surface is a crush seal and it occurs on the flank, root and crest of the tapered thread.


People usually use the term tube and pipe interchangeably but the two are different and serve different purposes. Pipes serve as a vessel for the transfer in a large plumbing application. However, tubes are mostly used in structural applications which requires a small diameter and are used in features where precise outside diameter is needed. The appropriate tubing can provide an optimal as well as cost effective performance for your plumbing applications. Both hard and soft materials can be used to make tube, however the usage of the tubes falls into three different categories which include:

    • Electrical sheathing: These are tubes which are designed around electrical appliances or wire so as to protect against abrasion.
    • Structural applications: These are the type of tubes which are designed for use in building as well as structures for mechanical properties.
    • Fluid transport: These kinds of tubes are designed for the transportation of fluids from one place to another.

The first step to take when searching for the appropriate device is to ask the question: What do I need? The fittings are attached to the pipes so as to provide different kinds of functions which range from the extension of length to changes in the direction etc.


Due to the fact that the pipes are not made from a single material, it is to be expected that the same goes for fittings as well as tubing. The use of material for fittings depends on several factors which include the temperature conditions, cost, pressure ratings, etc. However, both fittings as well as tubing components are matched with the material which is used for the piping itself. The material which is commonly used for fittings are plastic and metals, including copper, brass, stainless steel, carbon steel, duplex stainless steel, black iron, polyvinyl chloride, high-density polyethylene etc. For tubing, the selection of material plays an essential role in determining the appropriate kind for your application. Hard metal tubing can be used when pipes need hardness and strength. Copper, steel and aluminum are mostly used for tubing. These materials are mostly used in plumbing and heating application for their corrosion resistant and durability.
The most flexible alternative in plumbing system is soft tubing, however the most commonly used plastics include polypropylene, polyethylene, polyurethane as well as polyvinyl chloride. The soft tubing provides corrosion, strength, resistance and also helps in the reduction of pressure leaks.


It is crucial to have an appropriate size so as to have a successful fitting as well as tube selection. The fitting size is determined by the inner diameter (ID) and outside diameter (OD) of the connections and can be measured in inches or millimeters. The inner diameter measures the size of the empty portion of the cylinder while the outer diameter measures the thickness of the tubing wall.
The size of the tubing is somewhat similar and is measured in millimeter or inches, the outer diameter, inner diameter as well as the wall thickness would determine the dimension for tube sizing, however normal sizes for tubes are based on the outside diameter.
By selecting the appropriate tubing and fitting carefully, your plumbing system will be able to operate at its best performance.


The fitting construction as well as material specification is dependent on application, the best approach in this scenario is to consult the fitting supplier so as to get an optimized component. However, most of the tube fittings correspond to either pneumatic or hydraulic systems. The basic system type is the first step in determining the kind of fittings which is right for the application.
Hydraulic applications: This involves the transfer of liquid fluid like water and other chemical solvents. It is essential for the hydraulic fitting to have seals so as to prevent the leakage of liquid and must be able to resist rust as well as other possible corrosion.
Pneumatic applications: This involves transferring gases and the pneumatic fittings needs to have a tight seals so as to prevent gases from leaking and should be able to resist chemical corrosion.
There are other applications like structural design which is incorporated into tube fittings. Such kinds of fittings must have a strong physical integrity but sealing is not required because they do not carry any fluids.
Types of Fittings
The tube fitting can be differentiated based on their connection type as well as the function which they perform.


The fittings are attached to the tube with the aid of different connection, each with its conveniences as well as benefits.
Bite-type fittings: The bite-type fitting is in the form of a sharp ferrule which bites the tube when it is compressed so as to provide a seal. Bite-type fittings such as standard compressive fittings do not require special tools during the assemblage but provides a stronger as well as connection with higher pressure. They likewise come in various kinds of materials and are perfect for metal to metal connections.

Compression fittings are the type which connects tubes by using a compression on a gasket, ferrule or ring. The compression is achieved by tightening a nut onto the fitting over the ferrule and tubing, compressing and securing the tubing inside. The standard compression fittings do not need any tools to assemble, or make them convenient for a quick, simple installation. However, they do not have the ability to withstand an extreme pressure and do not have a higher flexibility like soldered fittings which make them less functional in systems with vibration, thermal cycling as well as other dynamic forces. Other kinds of fittings include Mechanical grip fittings, flare fittings as well as threaded fittings.

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