A pipe bellow, also known as a flexible bellow, is necessary for pipeline systems because of high temperatures. And to absorb movement and vibration. We can make a pipe joint from metal into a metallic bellow, plastic (such as PTFE), fabric, or an elastomer such as rubber joints. Moreover, pipe bellows have convolutions. Additionally, the shape of the convolution helps withstand the internal pressures of the pipe. But they are flexible enough to accept axial, lateral, and angular deflections.
Expansion joints help with other criteria: noise absorption, anti-vibration, earthquake movement, and building settlement. Also, pipe bellow joints should be designed according to rules laid out by EJMA; for fabric expansion joints, there are guidelines and a state-of-the-art description by the quality association. Finally, pipe expansion joints are also known as “compensators,” as they compensate for the thermal movement. Contact Dannenbaum LLC for more information or a quote on a metal bellow.
Flexible bellows, also known as pipe bellows, are flexible elements that absorb movements in the pipe system. These movements absorbed are axial, lateral, angular, and universal movements. The flexible bellows can absorb one of these movements or absorb more of these movements in combination.
Metal pipe joints can handle higher temperatures than rubber joints. As a result, they reduce stress, vibration, and noise in piping systems by providing a point of flexibility to absorb movement.
Flexible joints are usually made of steel. The flanged ends rotate for easy bolt hole alignment during installation.
Axial Movement Pipe Bellows
Axial movement is the movement of the flexible bellows in the direction of the longitudinal axis. This movement can be compressive, where the laminated bellows shorten in length, or extensive, where the bellows extend in length. In most applications, flexible bellows are deemed necessary because of the increasing temperature of the pipe system.
Typically cryogenic and chilled water services, the pipe system contracts in service, causing the expansion joint to extend in length. In addition, thermal expansion of the pipe system results in axial compression of the installed flexible bellow. Therefore, the specifications for flexible bellows should always state the movements as they affect the flexible bellows and not those generated by the pipe system.
Lateral Movement Flexible Bellows
Lateral movement moves perpendicular to the bellow’s longitudinal axis; it is a shearing movement of the flexible bellows with one end offset from the other, usually with the ends of the bellows remaining parallel.
Thus, a single formed metal bellow expansion joint, working with shearing action, can accept a relatively limited amount of lateral movement, especially when the flow characteristics of the system demand that an inner sleeve is necessary.
It is usual for more extensive lateral movement to utilize a twin bellows arrangement with an intermediate pipe between the bellows. The flexible bellows’ lateral action is taken up by an angular rotation of the bellows in opposite directions.
The amount of lateral movement available depends on the rotational movement capacity of each bellows and the distance between them. Thus, increasing the distance between the bellows increases the lateral movement capability of the flexible bellows proportionally.
In particular, pinned units used in 2-pin or 3-pin arrangements can convert pipe growth into the angular rotation and control the expansion from 2 directions and in 2 planes.
It is important not to confuse angular rotation with torsion. Torsion is a twisting rotational movement around the longitudinal axis; it generates undesirable shear forces within the bellows, and anyone should always avoid putting torsion on the bellows. Instead, please refer to the section about torsion.
Such units usually require a lot of flexibility to absorb significant amounts of movements in combination. However, this often leads to a limited pressure-containing capacity due to considerations towards the bellows’ stability.
Important to know about Flexible Metallic Bellows and Movements
The customer needs to help by telling the designer the properties of the flexible bellow. Knowledge of the amount of movement, direction, and any combination of axial, lateral, and angular movements occurring together is essential for the correct design of the expansion joints.