Metal Expansion Joints and Metallic Compensators Main Elements
Which elements make up a metal expansion joint or metallic compensator?
An expansion joint or metal compensator is a device that contains one or more bellows and it is mainly used for the absorption of movements in a pipe system or industrial plant. There are many design alternatives, depending on the elements that make up the metal expansion joint or compensator:
The bellows is the flexible element, composed of one or more waves deformed circumferentially under hydraulic and / or mechanical shaping procedures. This is a matter of key importance, since it allows to get homogeneous thicknesses and stress distributions unlike for those bellows deformed under mechanical conditions or with circumferential welds. In fact, in some sectors, such as the nuclear sector at its level 2, mechanically deformed expansion joints or compensators are not accepted. The total movement of the bellows is proportional to the number of waves that make up the expansion joint bellows. The movement capacity responds to parameters such as the thickness, the number of sheets, the height and wave pitch, among others.
Metal bellows detail
The connections are those parts that link the expansion joint to the plant elements. There is a wide range of connections them, but the most common connections at the ends are welding-neck pipes connections, loose flanges or fixed flanges.
Metal expansion joint with loose flanges
The inner sleeve is the inner tube underneath the bellows, being its duty to protect the bellows from turbulence in the fluid, from direct thermal impacts, from abrasive products, etc. In some cases, the inner sleeve is intended as an axial guidance, thus cancelling out the effects of the internal pressure.
Its role is similar to that of the inner sleeve, but from the outside. The duty of the outer sleeve is preventing particles deposition in the gap between the waves of the bellows, rendering it impossible normal operation of the bellows, welding projections during assembly, etc.
It is important to make the difference between the control rods of the expansion joints and compensators, and the so-called “tie rods”, since the function of the control rods is focused on the guidance and restriction of movements of the expansion joint, and in some cases to contribute to an easier pre-stretching of the metal expansion joints or metal compensators.
The main role of the tie rods on an expansion joint is to continuously restrain the pressure thrust during normal operation. The tie rods are usually used in those expansion joints or compensators that work with lateral movement.
Metal expansion joint with tie rods
Joints are used to allow angular movement in one direction (HINGED) or in many directions (GIMBAL). Its use is limited to those metal expansion joints and compensators that work under conditions of angular and / or lateral movement.
There are two types of rings or reinforcement rings; those that are designed with integral form and, therefore, can not be dismantled; and those made in two halves and, therefore, can be dismantled. The reinforcing rings are placed between the different waves of the bellows to withstand the pressure stresses in high pressure expansion joints and metal compensators.
The service life of a metal expansion joint or metallic compensator can be drastically reduced due to corrosion issues. The design and operation conditions can influence meaningfully, in such a way that the bellows may be affected by corrosion issues whilst the surrounding pipes and supports may not, even though they are made of similar materials.
Design, manufacturing and test procedures are a key factor for metal expansion joints manufacturers. In this technical article we explain briefly how are the most important factor to take into account.
Our know-how designing and manufacturing metal expansion joints and metallic compensators since 1978, has shown us that certain breakdowns rest most of the time with the same mistakes or incidences, such as those set out in the following sections.