How to select Bellows Expansion Joint

Factors Determining the Selection of Bellows expansion joint

         The selection of expansion joint for a particular application is influenced by six primary considerations:

Temperature 

Pressure

Media 

Size

End Fittings

Motion

Temperature 

        The physical properties of any materials vary with temperature. Limits for operation temperature are affected by the working pressure, the type of media being conveyed and the nature of the application. By careful selection of material, it is possible to provide an expansion joint for a wide range of operating temperatures. The choice of type, metal alloy, end fittings and methods fitting attachment determines the temperature limit. Temperature has a great influence on expansion joint.  

Pressure 

        The normal pressure ratings of an expansion joint are varies according to type, material and size. Specific pressure ratings for each type of an expansion joint are calculated according to the applicable design specification. Under actual working conditions, pressure is affected by many other factors such as temperature, pulsating conditions, bending stresses, shock, vibration and external influences. So the pressure of expansion joint is daedal.

Media 

        The type of media being conveyed is an important consideration in the selection process. An expansion joint is subject to corrosion by both the material flowing through it and the outside environment. For almost all applications, an expansion joint can be selected that is resistant to the intended media. 

Size 

       The size of an expansion joint is specified by the nominal diameter. The existing piping will normally dictate the size of the metal hose for a particular application. However, flow rate, velocity and pressure drop considerations may also influence the selection of the expansion joint. The expansion joint is affected by many factors.

End fittings 

        End fittings are attached by welding, silver brazing, soldering depending on the type of the expansion joint and the alloy. Such end fittings may be male or female pipe threads, unions, flanges, flared tube fittings or other specially designed connectors. The use of an expansion joint is complimented by the extensive range of end fittings that are available.

Motion or Movements Required 

        An expansion joint is generally used in four types of application; primarily thermal expansion and contraction, and in addition to the following:

To correct problems of misalignment.

To provide flexibility in manual handling operations. 

To compensate for regular or constant movement. 

To absorb vibration. 

Temperature Adjustment Factors 

        In general, the strength and therefore the pressure rating of an expansion joint decrease as the temperature increase. Thus, as the operating temperature of an expansion joint increases, the maximum allowable working pressure of the assemble decreases. Elevated service temperatures will decrease these pressure ratings by the factors shown in the following chart. We can clearly see the impact of these factors on expansion joint. What also must be considered is the maximum working temperature of the end fittings, and other components of the expansion joint. 

Hardware & Accessories 

        Hardware is designed to meet specific customer, application, or code requirements and includes components such as shrouds and tie-rods. 

Flow Rates 

         Liners are designed normally to EJMA for flow rates specified by the customer. 

         In all types, careful selection and design of the expansion joint and its installation are important for optimal service life. The flexibility of an expansion joint is determined by its mechanical design and the inherent flexibility of its material.

Benefits Offered by a Metal Bellows Expansion Joint 

Compensate for movements and vibration 

Pressure resistant 

Leak Proof without mechanical seals 

Maintenance Free