A pipe bellows also known as expansion joints are necessary for pipeline systems. Because of high temperature. And to absorb movement and vibration. A typical joint is a bellow of metal. Also, plastic (such as PTFE), fabric, or an elastomer such as rubber is used in pipe bellows. Moreover, pipe joints are made up of convolutions. Additionally, the shape of the convolution designed to withstand the internal pressures of the pipe. But they are flexible enough to accept axial, lateral, and angular deflections.
Expansion joints are also designed for other criteria. For instance noise absorption, anti-vibration, earthquake movement, and building settlement. Pipe bellow joints have to 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 for Fabric Expansion Joints. 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 pipe bellow.
All-metal pipe joints can handle higher temperatures than rubber expansion joints. They reduce stress, vibration, and noise in piping systems by providing a point of flexibility to absorb movement. Joints are usually made of steel. The flanged ends rotate for easy bolt hole alignment during installation. Flanges mate with the same-size flat surface.
Flexible bellows, also known as expansion joints, are flexible elements that absorb movements in the pipe system. These movements they absorb are defined by axial, lateral, angular, and universal movements. The flexible bellows can be designed to absorb one of these movements or to absorb more of these movements in combination.
Axial movement for 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 bellows shorten in length, or extensive where the bellows extend in length. In the majority of applications, the flexible bellows are deemed necessary because of the increasing temperature of the pipe system. In some cases, typically cryogenic and chilled water services, the pipe system contracts in service causing the expansion joint to extend in length. Thermal expansion of the pipe system results in axial compression of the installed expansion joints. 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 is moving perpendicular to the bellow’s longitudinal axis; it is a shearing movement of the bellows with one end offset from the other, usually with the ends of the bellows remaining parallel to each other. A single 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. For larger lateral movement capability, it is usual to utilize a twin bellows arrangement with an intermediate pipe between the bellows. The flexible bellows’ lateral movement 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. 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 its influence on the bellows should always be avoided. 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 bellows and movements
It is important that the designer of flexible bellows is fully informed of all the movements that the expansion joint will encounter. Knowledge of the amount of movement, its direction, and any combination of axial, lateral, and angular movements occurring together is essential for the correct design of the expansion joints.